Chloroquine Treatment of Platelets and Lymphocytes

A N UNDERSTANDING of the structure of human platelet membrane antigens is of both biologic’ and clinical7 interest. HLA-A,B antigens’ and those of the ABH system2 are present on platelets. However, adsorption of exogenous soluble HLA-A,B antigens34 and ABH substances5 onto platelets has been demonstrated in vitro. This raises the question of whether these antigens are integral membrane proteins, as has been shown for the HLA-A,B antigens of lymphocytes, ’ on are adsorbed onto the platelet sunface. Nondestructive removal of HLA-A,B antigens from platelets should be feasible if they are indeed adsorbed from plasma. The antimalarial drug, chloroquine, is known to dissociate immune complexes5 and to remove antibody from ned cell surfaces.9 Because unpublished data from our laboratory demonstrated that chloroquine treatment removed passively adsorbed Lewis blood group antigens from red cells, we attempted to similarly dissociate HLA-A,B antigens from platelets.