Human autoimmune diseases: Progress in clinical laboratory tests.

Severe derangements of the human immune system and its associated network can cause more than 40 autoimmune diseases in 5% to 10% of the general population. These diseases injure various organs and tissues of the endocrine, neuromuscular, hematopoietic, cardiopulmonary, gastrointestinal, and dermatologic systems. [1,2] Because of complex interactions among multiple genetic, immunologic, and environmental factors, these autoimmune diseases are heterogeneous in both etiology and the associated clinical and histopathologic manifestations. [3,4]

In industrialized societies, autoimmune diseases are serious medical problems because of their chronic and disabling effects. For example, the end-stage renal failure caused by type-1 insulin dependent diabetes mellitus (IDDM) costs the US Medicare program over $2 billion per year for renal dialysis. [5] Similarly, providing medical care to children with IDDM costs the Australian government $1.5 million per year. [6] Therapy for autoimmune diseases continues to advance, thus increasing the demand for clinical laboratory testing that can help diagnose and monitor treatments and progress. [1,6,7]

This article covers the current concepts in autoimmunity and autoimmune diseases, and advances in related clinical laboratory tests. Additional information is provided on the types of available testing modalities, the use and interpretation of clinical laboratory tests to diagnose and evaluate autoimmune diseases, and future challenges in this area for the clinical laboratory.

Autoimmunity vs. autoimmune diseases

Normally, each person's immune system can distinguish "self' from "non-self," and can respond to any invading foreign molecule without producing adverse reactions against self or host antigens. [1,6] However, many pathways and alterations of the control mechanisms for self-recognition can initiate an autoimmune response, which has been broadly defined as a failure of an organism to recognize its own healthy tissue as self. An autoimmune response can be either humoral (eg, circulating autoantibodies) or cellular (eg, delayed hypersensitivity).

Current thinking is that autoimmunity can explain "normal" regulatory physiologic mechanisms such as aging, physiologic clearance of dead cells and their components, and response to viral and microbial infections. However, autoimmunity can also induce immunologic injury to the host and is the primary cause of diseases such as autoimmune thyroiditis and systemic lupus erythematosus (SLE). In certain other diseases, such as ulcerative colitis, the immunologic response is notably secondary to the initial tissue injury. The term "autoimmune disease" has generally been assigned to those conditions in which an autoimmune mechanism or injury has contributed to the pathogenesis of disease. Thus, the concept of autoimmunity may explain "normal" physiologic and immune regulatory mechanisms in a wide range of clinical states but may also explain the pathogenesis of a number of diseases with an immune mechanism of injury.

Principal factors in autoimmune diseases

Autoimmunity begins with an abnormal interaction of T- and B-cells with autoantigens, but no single theory or mechanism can explain all features of autoimmune disease. [8] The multifactorial etiology of autoimmune diseases is frequently associated with genetic and viral factors that influence immune system regulation. The exact mechanisms of this relationship are unclear, but it is likely that the immune response genes, lymphocytic surface antigens, and possible receptors for specific viruses are often involved in multiple mechanisms or pathways.

Genetic factors. Individual susceptibility to autoimmune diseases is also polygenic, and no single genetic abnormality can produce a specific autoimmune disease. Most of these conditions are not inherited in a simple Mendelian segregation. In monozygotic twin pairs, concordance for diseases is much less than 100% and varies from [less than] 5% for multiple sclerosis to 30% for IDDM. [9] Even with a proven susceptible genotype, not all individuals will develop autoimmunity.

The association between many autoimmune diseases and human leukocyte antigens (HLAs) is well documented, [1,2,10] and is especially striking in cases of ankylosing spondylitis, in which patients possess HLA-B27 antigens in as many as 90% of cases. However, the association does not imply that the disease is caused directly by possession of the HLA-B27 antigen. Certain autoimmune diseases, particularly the organ-specific disorders, such as idiopathic Addison's disease, Grave's disease, IDDM, chronic active hepatitis, and Sjogren's syndrome, occur more frequently in individuals who have the HLA-B8 antigen.

Sex and hormonal factors. Although predominance in men is seen in diseases associated with major histocompatibility complex (MHC) class I such as ankylosing spondylitis and Reiter's syndrome, [2] autoinunune diseases affect women more frequently than men, with female-to-male ratios [greater than] 5:1 reported for scleroderma, SLE, Sjogren's syndrome, Hashimoto's thyroiditis, and primary biliary cirrhosis.11 Sex hormone levels could explain the predominance of autoimmunity in women, and if so, the peak age incidence for autoimmune diseases should occur when sex hormone levels are highest. For black women, the peak incidence of SLE at 2 5-34 years of age is consistent with the previous expectation. [12] However, this association is not observed in:

* Rheumatoid arthritis (RA). The incidence of the disease continues to rise with age into the eighth decade of life. Some investigators believe that the risk pattern for RA is consistent with decreased levels of serum adrenal anabolic steroids. [13] They have observed a substantially lower mean serum level of dihydroepiandrosterone sulfate but not of cortisol among younger premenopausal women before onset of RA. [13]

* Hasbimoto's thyroditis. The peak incidence occurs in the postmenopausal years at ages 50 to 59. [14]

Environmental factors. Environmental issues such as trauma, infec tion, or chemical agents can cause transient autoimmune responses. However, for individuals with genetic susceptibility, environmental chemicals or biologic agents can trigger "pathologic" autoimmune responses and clinical disease.' Infections are also important initiators of autoimmune responses, but the context of the infection is very important, because it will not always induce autoimmunity even in the genetically susceptible host. Only direct analysis of patients and their environment can reveal the pathogenic mechanism of postinfectious autoimmunity. [15] Infectious agents can activate self-reactive and inflammatory disease in acute, chronic, or latent infection. In addition, drugs and toxins can initiate autoimmune disease, such as the drug procainamide, which can induce SLE. [2]

Classification of autoimmune diseases

Traditional classification of autoimmime diseases includes both organ-specific and systemic conditions, but susceptibility to many autoimmune diseases is also strongly influenced by genes encoded in the MHC, particularly the class I (HLA-A, B, B) and class II (Ia, HLA-D MHC molecules." [1,2,6]

Traditional classification: Organspecific and systemic conditions. In organ-specific diseases, the common target organs include the thyroid, adrenals, stomach, and pancreas. The systemic autoimmune diseases include SLE and various systemic rheumatic diseases. There is considerable overlap, and Roitt proposed the concept of a spectrum of autoimmune diseases. [16] For example, thyroid autoantibodies occur with high frequency in patients with pernicious anemia who have stomach autoimmunity.

At the other end of the spectrum, the cluster of rheumatologic diseases also shows significant overlap. For example, features of RA may be associated with the clinical picture of SLE, while SLE immune complexes are deposited systemically in the kidneys, joints, and skin, creating symptoms that would often be associated with rheumatoid arthritis.

HC class I and II. MHC class-I autoimmune diseases can be categorized as:

* HLA-B27-related spondyloarthropathies, including: ankylosing spondylitis, Reiter's syndrome, and reactive artliropathy

* Psoriasis vulgris associated with HLA-B12, B16, and B17.

As mentioned previously, the A'IHC class I-associated diseases predominate in males; this is noted especially in ankylosing spondylitis and Reiter's syndrome. The MHC class II-associated diseases are essentially the 2 main groups described previously: organ-specific and systemic autoimmune diseases. Generally, MHC class II-associated autoimmune diseases predominate in women; this is noted especially in SLE and hyperthyroidism.

Final effector mechanisms. The predominant final effector mechanism of immunologic tissue injury can also be used to classify autoimmune diseases.17"8 These mechanisms include antibodies, immune complexes, and Tcclls (see Table 1).

Organ/system involvement. This classification is probably the most commanly used and practical and includes endocrine organ-specific autoimmune diseases (see Table 2), systemic autoimmune diseases (eg, SLE and other systemic rheumatic diseases) (see Table 3), [19-23] autoimmune diseases grouped by primary organ-system involvement (see Table 4), [1,24,25] and other autoimmune diseases (see Table 3,).

Examples of organ-specific autoimmune diseases

Examples of organ-specific autoimmune diseases include IDDM; Hashimoto's thyroiditis; pernicious anemia with chronic atrophic gastritis; primary adrenal gland atrophy (Addison's disease); MS; pemphigoid skin disorders; and Graves' disease, which is a multi-system disorder characterized by diffuse thyroid gland hyperplasia, myopathy, and exophthalmos. Before clinical onset, organ-specific autoimmune diseases frequently show familiar clustering with a history of viral infection. The autoantibodies detected react with cellular and tissue antigens of the affected organs, but autoantibody titers do not always correlate with disease duration or severity.

IDDM is now regarded as a chronic autoimmune disease that may possibly be initiated by viral infection and molecular mimicry. This cross-reactive mimicry occurs when a viral antigen shares an amino acid sequence with a host's pancreatic islet beta cell antigens. If the virus infects the host and antibodies are formed against the virus, islet beta cells are destroyed by the cross-reactive antibodies and effector lymphocytes.

Patients with IDDM have several types of autoantibodies; the more commonly tested are anti-insulin (IAA), antiglutamic acid decarboxylase (GAD), and anti-islet cell antigen 2 (IA-2), directed against a phosphatasetype transmembrane 37-kD islet beta cell antigen (ICA512) necessary for endocrine signaling. [26,27] These autoantibodies are detected in patients before onset of clinical hyperglycemia, which means that islet beta cell destruction most likely exists for years in a preclinical disease phase. In fact, hyper-glycemia and ketosis may actually reflect late-stage disease when [greater than] 80% of pancreatic islet beta cells have already been destroyed. [26-28]

Recent studies have shown that the presence of a number of different autoantibodies is an important disease predictor. [28] The 5-year risks for developing diabetes for asymptomatic individuals with family history of IDDM are 15%, 44%, and 100% if 1 type, 2 types, and all 3 types of antibodies are detected, respectively. Therefore, a nonautoimmune cause must be considered in patients who develop new-onset diabetes but are negative for all 3 types of autoantibodies. [28]

Many patients (70-80%) with Hashimoto's lymphocytic thyroiditis have high titers ([greater than] 1:1000) of anti-thyroglobulin antibodies, and high titers of this antibody are found in 40% of patients with Graves' disease. Low titers ([less than] 1:80) of antithyroglobulin antibodies can be detected in 25-40% of patients with pemicious anemia and thyroid carcinoma. Other less sensitive but more specific disease-associated autoantibodies are directed against colloid antigens, cytoplasmic microsomes, and thyroperoxidase. A good autoantibody screening test is immunofluorescence using patient sera and primate thyroid tissue as a test substrate. [29] Enzyme immunoassay methods can detect thyroglobulin and thyroperoxidase autoantibodies.

Many patients (80-90%) with pernicious anemia and chronic atrophic gastritis have antibodies against a lipoprotein cytoplasmic component of parietal cells and also receptor blocking antibodies against intrinsic factors. The gastric mucosa biopsy shows lymphocytic infiltrates with loss of parietal and chief cells. Gastric acid production is decreased, with impaired absorption of vitamin B12 in the distal ileum. Patients with idiopathic Addison's disease have autoantibodies to adrenal cortical cell cytoplasm, but these autoantibodies can be infrequently detected in other autoimmune endocrine disorders without clinical adrenal disease. As many as 40% of patients with idiopathic Addison's disease may exhibit polyglandular endocrine syndromes in which immunologic tissue injuries occur in the thyroid, parathyroid, ovary, pancreas, and skin. [30]

Pemphigus vulgaris is an autoimmune skin disease characterized by acantholytic skin lesions with autoantibodies directed against desmoglen, plakoglobins, and cadherin polypeptides of desmosomes and other cell-cell adhesion molecules. The antibody titers correlate with disease severity. [31] Moreover, when injected into neonatal mice, these autoantibodies can directly cause the loss of epidermal cell adhesion with formation of acantholytic blisters. [32]

Examples of systemic autoimmune disease

Examples of diseases in this group include SLE (and its subsets, drug-induced lupus), Sjogren's syndrome, scleroderma, polymyositis (PM), mixed corrective tissue disease (MCTD), and RA. Most of the systemic autoimmune diseases are characterized by generalized dysregulation of the immune system with polyclonal B-cell and T-cell activation and increased immunoglobulin synthesis by B cells. Most of the immunoglobulins are autoantibodies targeting nuclear and intracellular constituents, forming circulating immunecomplexes that cause tissue damage at their sites of deposition. These immune complex-mediated lesions can be acute and fatal when they involve the kidney, brain, or heart but fortunately are only debilitating rather than life threatening when they involve the musculoskeletal system, gastrointestinal tract, lung, and skin.

The common autoantibodies are antinuclear antibodies (ANAs) with various nuclear, nucleolar, or cytoplasmic staining patterns on HEp-2 cell substrate. By molecular analysis, the associated targeted autoantigens are peptides essential for DNA/RNA synthesis, repair, splicing, and transcription. This poly-specificity of autoantibodies is characteristic of SLE. Moreover, by determining the immunologic/antigenic specificity of a patient's ANAs and the mean antibody titers, distinct "ANA profiles" can be generated to help classify the different types of systemic autoimmune diseases. [19-23]

Profile of autoantibodies in various systemic rheumatic diseases. Certain distinct profiles of autoantibodies produced against nuclear and cytoplasmic antigens are seen in different systemic rheumatic diseases. The important characteristics include the presence or absence of certain antibody specificities. [19-23]

* Multiple ANAs are frequently seen in SLE and generally include high levels of autoantibodies to DNA.

* High titers of anti-Smith (Sm) antibodies are generally very diagnostic of SLE, and very low titers have been seen in other systemic rheumatic diseases.

* In drug-induced SLE, the ANAs seen are generally restricted to antihistone autoantibodies. In spontaneous SLE, usually 3 or more ANAs are present.

* In mixed connective tissue disease (MCTD), the ANA is restricted to nuclear ribonucleoprotein (UIRNP) or nuclear RNP antibodies.

* In several of the systemic rheumatic diseases, antibodies against UI-RNP are present with varying frequencies.

* Sera from patients with Sjogren's syndrome (SS) is characterized primarily by the presence of antibodies to SS-A/Ro and SS-B/La.

* The clinical profile for patients with scleroderma contains antibodies against Scl-70, centromere/kinetochore antigen and nucleolar antigens.

* RF anti-Ra33, anti-keratin, antibody against RA-associated nuclear antigen (RANA), antifilaggrin and anti-citrulline antibodies are present in rheumatoid arthritis. [33]

* Autoantibodies to Jo-1 (histidal tRNA synthetase) are detected in the sera of patients with polymyositis/dermatomyositis.

Interpretation of autoantibody levels in autoimmune diseases

Interpretation of test results should be made in association with the patient's medical history and clinical disease states and with a clear understanding of the technical limitations of test systems utilized. In general, the autoantibody level is high in patients with autoimmune disorders and low in apparently healthy persons. However, a low or absent titer of autoantibody does not rule out the possibility of an autoimmune disorder. For example, at the height of severe thyroiditis, the gland itself may absorb and remove circulating antibody. In addition, thyroglobulin may be released into the circulation during the acute stage and neutralize circulating autoantibody. Therefore, the level or titer of a given antibody must be interpreted in relation to the stage or treatment of a particular disease. In contrast, serum antibody levels in pemphigus correlate with disease severity and course. [1,24]

Autoantibodies in healthy individuals. Results from an Australian study of 2,830 healthy individuals for the presence of 13 autoimmune antibodies indicated that 22% of the population displayed one or more autoantibodies. Most interestingly, several of these antibodies, including ANA, thyroid microsomal, and smooth muscle antibodies, persisted 6 years or longer, and parietal cell antibody was detected in 75.3% of individuals. [34,35]

For people older than 40 years of age, the incidence of positive indirect immunofluorescence microscopy for ANA (IFM-ANA) results gradually increases with age in the healthy population, and low positive titers of IFM-ANA can be significant for patients older than 40 years of age, particularly in women. [34-36] Conversely, negative IFM-ANA results will help rule out the diagnosis of SLE unless the patient is being treated with steroids or immunosuppressive drugs.

Autoantibodies and autoimmune diseases in the elderly. There is no definite evidence of a parallel increase in autoimmune disease with age. [37] Most autoimmune diseases are characterized by an onset in youth or early middle age, while only a few begin after age 50 years. In contrast, the incidence of certain autoantibodies increases with advancing age. Of subjects older than 60 years, 50% demonstrated low titers of one or more autoantibodies. For example, the incidence of antinuclear, antiparietal cell, and antithyroid antibodies increased in older women. [34,35] Conversely, the incidence of smooth-muscle antibody and RF was similar in male and female subjects [34,35] and correlates with post-viral infections and history of chronic infections, respectively.

Laboratory testing for autoimmune disease Diagnostic versus evaluative testing. Clinical laboratory tests can be categorized as diagnostic or evaluative. [38,39] To be useful, a diagnostic test must be highly sensitive and specific and provide reproducible results over time. The test for antibody to acetylcholine receptor (AchR) in myasthenia gravis is a example of a good diagnostic test. The current radiolabeled test is sensitive, and positive results confirm the diagnosis of myasthenia gravis while negative results help rule it out.

Evaluative tests are used to determine indices of change in disease activity over time. [40] Because the value and accuracy of an evaluative test are determined by how well it monitors change in disease activity, the results from the new test should be compared with those from an accepted gold standard measurement of that activity. An example of a useful evaluative test would be serum levels of C-reactive protein measured during the acute-phase inflammatory period of rheumatic fever or RA. Results for this test parallel the inflammatory activity during the course of the disease. [41]

Reference ranges and cut-off values for laboratory tests. Each clinical laboratory must establish a normal range for its laboratory tests. The assignment of these cut-off values will determine the proportion of false-positive and false-negative results. [42] For example, does the normal range include 95%, 97.5%, or 99% of the healthy population? Are age-related reference ranges assigned for certain autoantibodies? For many clinical laboratory tests, the cut-off values are designed to include only 95% of the healthy population, allowing a 5% false-positive rate. Thus, if someone without the specific disease has 1 test performed, the chance of an abnormal result is 5%. When multiple tests are performed and the cut-off is 95% of the healthy population, the likelihood of obtaining a false-positive result rises dramatically with the number of tests performed. For example, if 5 tests are performed, the likelihood of 1 abnormal result is 22%. [43] Therefore, if multiple tests have been performed, abnormal results m ust be interpreted with caution.

When establishing normal reference ranges for autoantibody tests, cut-off values should include 97.5% or 99% of healthy individuals, and the test should include some form of quantitation because healthy individuals may have low levels of natural and/or other autoantibodies.

Special laboratory tests to evaluate autoimmune diseases. Physicians select more specialized tests based on patient history and results from routine clinical laboratory tests. The test selection is a critically important factor for determining the positive predictive value of autoantibody tests.

The most widely ordered type of clinical laboratory tests in autoimmune diseases involve detection of circulating antibodies. When patients present with clinical symptoms of systemic autoimmune diseases during the initial evaluation, other laboratory tests that can be helpful include IFM-ANA, RF, cryoglobulins, and circulating immune complexes. Serum immunoglobulin and complement levels may not always correlate with disease activity or severity of tissue damage. [44]

Cellular immune tests are complex and, at the present time, are not as practical as serologic tests. When considering a specific autoimmune disorder, tissue biopsy allows direct histologic and immunohistochemical examination of an affected organ. Biopsy is used most often in autoimmune diseases that involve the kidney or skin to evaluate the tissue injury and determine the immunopathologic mechanism, using techniques such as immunofluorescent localization of immunoglobulin and complement components in the basement membrane of the skin, glomerular basement membrane, or blood vessels.

Methods for detecting autoantibodies. The commonly used immunologic detection tests are listed in Table 5. Immunofluorescence microscopy (IFM), enzyme-labeled antibody, and radioimmunoassay methods involve primary antigen-antibody binding reactions and, because of high sensitivity, are preferred for detecting tissue-bound and circulating antibodies and antigens. These methods may be 1,000 times more sensitive than counterimmunoelectrophoresis (CIE) and immunodiffusion (ID) tests that require precipitin reactions between antibodies and tissue/cell extracts.

Immunoblot assays can further identify polyspecific autoantibodies directed against a variety of multiple soluble and insoluble autoantigens. Immuno-diffusion and immunoprecipitin, CIE, and immunoblot methods may be used to confirm positive IFM-ANA screening results and to define the characteristics of targeted antigens. [45] The tests that involve secondary antigen-anti-body preparations, such as complement fixation, agglutination, and precipitation in agar gel, are not as sensitive as immunofluorescence, EIAs, or radio-immunoassay, but may be technically more suitable for specific identification of certain autoantibodies.

Generally, the highly sensitive tests used to exclude disease have low diagnostic specificity while less sensitive assays may offer greater diagnostic specificity. For example, the chance of having SLE is [less than] 0.14% for patients with a negative IFM-ANA result. [46,47] However, positive IFM-ANA can be seen in 25% to 50% of patients with chronic inflammatory disorders and RA as well as 5% to 10% of healthy individuals. [45] Similarly, the highly sensitive ELISA test for anti-Sm, initially assayed by immunodiffusion and considered diagnostic of SLE, is often positive in low titers in 23%, 25%, and 9% of patients with RA, scleroderma, and polymyositis, respectively. Of 59 healthy individuals, 2% had low titers of anti-Sm by ELISA. [45,48]

IFM test for ANA. Currently, the HEp-2 culture cell is the recommended substrate for IFM-ANA screening, and this test is so highly sensitive that negative results tend to rule out the diagnosis of SLE. [46] However, more definitive secondary tests are important to confirm and further identify the immunologic/antigenic specificity of the positive ANA screening test seen on HEp-2 culture cells.

Most laboratories have noted that if the IFM-ANA test results are negative or the endpoint titer is [less than] 160, the follow-up secondary tests yield positive results in fewer than 5% of cases.49 Additional testing for disease-specific autoantibodies is indicated if the ANA titer is [greater than or equal to]1/160. However, if a strong cytoplasmic staining of HEp-2 cells is noted at lower titers, specific tests should then be considered for certain cytoplasmic autoantibodies, such as Jo-l and RNP. [1]

E/A tests for autoantibodies against nuclear antigens. More recently, several commercial sources have produced EIA kits that rely on natural and recombinant antigens to simultaneously screen for a panel of autoantibodies against nuclear antigens. [50,51] These ETA antinuclear antibody tests claim to detect autoantibodies responsible for homogeneous, speckled, peripheral, centromere, and nucleolar immunofluorescent patterns, as well as detecting specific autoantibodies to SS-A, SS-B, Sm, RNP, Scl-70/DNA-topoisomerase I, histone, and (ds)DNA. These EIA kits are promoted as alternative methods for both screening and detection of "total" ANA, to be used as a replacement for the IFM-ANA test.

While such EIA-ANA tests are less labor intensive and can be used to screen and detect a panel of common specific autoantibodies usually observed in the systemic rheumatic diseases, they are not 100% sensitive when compared with IFM-ANA. Also, the ETA-ANA tests may not detect certain ANAs with atypical and classic immunofluorescent patterns. Results from a comprehensive comparative analysis of these commercial EIA-ANA kits indicate that the titers and patterns of EIA screen-positive sera should be confirmed with IFANA on HEp-2 cells. [51] Thus, reports for negative EIA antinuclear screening tests should state that autoantibodies against specific antigens in the test (eg, SS-A, SS-B, Sm, RNP, Scl-70/DNA-topoisomerase I, histone, dsDNA) were not detected. This clarification will help alert clinicians that a negative EIA anti-nuclear test result is not the equivalent of "negative for all nuclear antibodies."

Consensus study to evaluate tests for ANA

The best studies to evaluate the different methods of detecting autoantibodies against nuclear intracellular antigens were reported by a European Consensus Study Group formed in 1988. [52,53] This Group has conducted 4 annual workshops from 1988 to 1992; the 1988 and 1989 consensus workshops were conducted to define inter-laboratory concordance when detecting autoantibody specificities in rheumatic diseases. Using various methodologies, 28 laboratories participated in the study. [52,53] The objectives of the consensus study initiated in 1989 were to

* define the interlaboratory consensus for detecting autoantibodies and specificities,

* test whether discrepancies were due to the methodology used, and

* develop recommendations for improved quality of test results with improved sensitivity and specificity.

This consensus group has recommended that clinical laboratories should:

* compare positive-specificity anti-bodies in clinical samples against a standard reference serum of known specificity,

* use 2 independent assays to assign antibody specificity in a serum, and

* use some form of validation and quality assurance for commercial testing kits and to evaluate laboratory performance.

Future challenges in laboratory tests for autoimmune diseases

Trends in healthcare continue to emphasize preventive medicine with integration of molecular medicine, information, and computer technology. Future tends will also emphasize predictive tests to screen for data that will identify important population phenotypes that indicate risk factors. [54,55] The application of such predictive tests will be used to identify patient genes that are risks for various specific diseases such as diabetes and autoimmune diseases.

Currently, autoimmune diseases are usually diagnosed at a late stage in their development, and immunointervention is used only when all other treatments have failed. In the future, genetic tests and immunologic markers will be able to predict such diseases before their onset. Such early identification of at-risk patients will allow intervention with autoantigen-specific therapy. Experimental models of spontaneous autoimmune disease show that, at these early stages, the autoimmune response is much more sensitive to immunointervention than in the late stages, when immunosuppression is applied to human diseases. [56] It is also obvious that such early intervention prevents the occurrence of the irreversible lesions that characterize advanced autoimmune diseases. [56,57]

Discovery of new and important clinical laboratory tests that allow prediction and early diagnosis of autoimmune diseases are now being reported, and the most spectacular progress has been achieved in tests for IDDM, in which islet beta cell autoantibodies can be found several years before the onset of clinical disease (as defined by insulin requirement). The quality of prediction is sufficient to enable recognition of future diabetics with a reliability that approaches [greater than] 80%. Various therapies are being studied that would intervene and prevent the onset of IDDM tissue damage mediated by a cellular immune reaction against pancreatic islet beta cells.

Summary

Autoimmunity may explain the pathogenesis of many diseases with an immune mechanism of injury but also can explain "normal" physiologic and immune regulatory mechanisms in a wide range of clinical states, including aging, physiological clearance of dead cells, and response to viral and microbial infections.

The principal factors involved in the etiology of autoimmune diseases are genetic predispositions, hormone levels, sex, and environmental factors that influence the immune system with a resulting abnormal interaction of T cells and B cells with autoantigens.

Clinical evaluation is important in the management of autoimmune diseases, and the laboratory still plays an important role in the evaluation of autoimmune diseases. Laboratory test results help diagnose autoimmune diseases, monitor disease course, predict disease outcome, assess the need for and response to therapy, and gain insight into disease etiology or pathogenesis.

When developing immunologic tests, the clinical laboratory should clearly state the type of immunologic procedure performed, define the reference range when including the cut-off values and indicate what percent of the normal population is included in the reference range.

Future challenges for the clinical laboratory will be to develop predictive tests to screen data identifies important population phenotypes which represent risk factors. The predictive tests will identify patients who are at risk for various autoimmune diseases. The focus of healthcare will be geared toward early intervention to prevent the onset of the specific autoimmune disease such as IDDM.

Dr. Robert Nakamura is Chairman Emeritus and Senior Consultant in the Department of Pathology, Scripps Clinic, La Jolla, CA.

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Classification of autoimmune diseases by final effector mechanisms

Antibody mediated

* Goodpasture's syndrome (with glomerulonephritis caused by basement embrane autoantibodies)

* Antireceptor autoantibodies Hyperthyroidism (Grave's disease) Myasthenia gravis (acetylcholine receptor)

Immune-complex mediated

* SLE

* Polyarteritis nodosa

* immune complex glomerulonephritis

T-cell mediated

* Insulin dependent diabetes meilitus (IDDM)

* Autoimmune chronic hepatitis

* Multiple sclerosis