In vitro lymphocyte reactivity and T-cell levels in chronic cigarette smokers.

Peripheral blood total leucocyte, lymphocyte and thymus-dependent lymphocyte (T cell) levels and in vitro lymphocyte reactivity (LR) to phytohaemagglutinin (PHA) were determined in 153 chronic cigarette smokers and 115 non-smokers ranging in age from 20 to 78 years. Total leucocyte, lymphocyte and T-cell levels were significantly elevated in smokers. There was no correlation with age. LR to PHA was significantly higher in smokers less than 40 years of age or in those with a 20 pack-year or less history of cigarette consumption. Older smokers or those with a history of heavier cigarette consumption did not differ from normals. The results contrast with previous demonstrations of suppression of immune reactivity after exposure to tobacco products. The possible effects of the apparent stimulation of the lymphoid system by chromic cigarette consumption is considered.