Smoking inhibits lung's immune cells.
Epidemiologic studies indicate cigarette smokers are more susceptible than nonsmokers to respiratory infections but not to other infections. Working with rats, scientists have now found a possible biological basis for this. They report that cigarette smoke preferentially depreses the function of immune cells in lymph nodes that lie within the lung tissue, and that only prolonged smoke exposure induces changes in immune cells stored in other parts of the body. They also found that the smoke primarily affects antibody-producing B-lymphocytes rather than other immune cell types, shedding light on the mechanism of immune suppression, says study coauthor Mohan L. Sopori, an immunologist at Lovelace Medical Foundation in Albuquerque, N.M.
Previous animal studies have shown cigarette-induced immune dysfunction, but these did not focus on lung-associated lymph nodes and did not reveal what types of immune cells were primarily affected. Human studies have yielded inconsistent results, probably because these studies haven't looked at the lung-associated lymph nodes, says George M. Shopp, also at lovelace.
Shopp, Sopori and their co-workers exposed rats to cigarette smoke for varying time periods and compared them with two age- and sex-matched control groups. The smoke-exposed rats, strapped in restraint devices, had their noses attached to a chamber fed by a burning cigarette. Some control rats also were restrained but hooked to a smoke-free inhalation chamber. Others were treated normally. After the exposure period, the researchers removed the rats' lymph nodes to measure antibody secretion by B-cells as well as macrophage and T-cell function.
They found that cigarette exposure for 21 weeks or more significantly depressed B-cell function in the lung-associated lymph nodes, while exposure for more than 35 weeks affected immune cells in other lymphoid tissues such as the spleen. The team saw no significant effect on the function of other immune cell types from the lymph nodes or the spleen, they report in the March 1 TOXICOLOGY AND APPLIED PHARMACOLOGY.
Shopp warns that non-immune-related factors--such as the breakdown of lung tissue or emphysema -- also could contribute to smokers' increased susceptibility to respiratory infections.
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|Date:||Apr 22, 1989|
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