Selective elution of HLA antigens and β2‐microglobulin from human platelets by chloroquine diphosphate

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Abstract
To determine whether chloroquine can specifically elute HLA antigens and .beta.2-microglobulin (.beta.2-M) from the platelet surface, quantitative immunofluorescence flow cytometry and monoclonal antibodies were used to show that HLA antigens and .beta.2-M were proportionally eluted from the platelet surface without affecting the membrane glycoproteins IIb and IIIa. Second, an autoradiogram of electrophoresed I125-labeled platelets showed that only .beta.2-M but not other I125-labeled membrane proteins could be eluted. Although HLA antigens were poorly labeled by I125 and could not be detected on the autoradiogram, the eluted HLA antigens could be detected by anti-HLA monoclonal antibody and immunoblotting techniques. No loss of plasma membrane integrity was observed by transmission electron microscopy after chloroquine treatment of platelets. The results indicate that chloroquine selectively elutes HLA antigens and their noncovalently associated .beta.2-M without affecting other integral platelet membrane proteins.