In vivo and in vitro action of chloroquine on surface markers of human peripheral lymphocytes.

Chloroquine was administered orally to twenty normal individuals and the effect of the drug on surface markers of peripheral bloof lymphocytes was studied. The total number of circulating lymphocytes and leucocytes in the blood did not change significantly after chloroquine administration. However, there was a significant fall in the percentage and number of lymphocytes with erythrocyte (E) and C'3 markers and an increase in cells lacking both these markers. In vitro experiments were carried out to study the mechanism of action of the drug on the expression of the lymphocyte receptors. Lymphocytes treated with chloroquine in vitro failed to show any change in their capacity to bind erythrocytes or erythrocytes coated with Ab and complement. The sera from chloroquine-treated individuals failed to show any factor inhibiting E and EAC rosette formation. The studies indicate that chloroquine may not act directly on the lymphocyte surface markers and cause inhibition of their expression but that it may act in some indirect way affecting one or more of the many factors involved in the normal expression of the markers.