Background: Smoking influences numbers and function of peripheral blood lymphocytes (PBL) by a process that is badly understood. We conducted this study to evaluate whether the immune impairment of smoking might be related to changes in the expression or functionality of Fas, a cell surface molecule that plays a central role in immune homeostasis and cytotoxic activity.
Methods: PBL from 10 smoking and 10 nonsmoking healthy volunteers were isolated. Flow cytometry was performed to measure the state of activation, Fas expression and apoptosis of PBL. Functionality of Fas was tested by assessing apoptosis after incubation of isolated lymphocytes with agonistic anti-Fas antibodies in four smoking and four nonsmoking individuals.
Results: Smoking was associated with an increase in the percentage of Fas-expressing CD4+ T and B lymphocytes. A decrease in the percentage of activated (CD38+) B cells was observed. In vitro Fas-induced apoptosis did not appear different between smokers and nonsmokers. No differences in the percentages of circulating apoptotic lymphocytes could be demonstrated between smoking and nonsmoking individuals. Conclusion Smoking is associated with increased Fas expression on PBL in general, and on B cells in particular. This might render these cells more susceptible for apoptosis. As Fas is functionally intact this may also explain the reduced percentage of activated (CD38+) B cells found in smoking individuals. The latter may contribute to the reduced humoral immune response observed in smokers.