HLA Class I (Bg) Antigens on Red Cells of SLE Patients: A Serological Study with Polyclonal and Monoclonal Antibodies

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Abstract
The enhanced HLA class I (Bg) on red blood cells (RBC) of many patients with systemic lupus erythematosus has allowed a significant correlation to be made between their HLA-B types and haemagglutination reactivity with lymphocytotoxic anti-HLA-B sera stimulated by pregnancy alone. Therefore the class I expression on these RBC relates to classical, rather than non-classical, class I gene products. Studies of class I expression of RBC by means of monoclonal antibodies (MAb) to epitopes on the heavy polypeptide chain and .beta.2-microglobulin (.beta.2m) have suggested that the complete extracellular structure is present. The specific effect of chloroquine in ''stripping HLA'' from RBC had been assumed to support the concept that HLA class I was adsorbed from plasma. However, from our data, we conclude that HLA class I is an intrinsic membrane component. We suggest that the action of chloroquine is to remove .beta.2m alone, which prevents normal class I expression and also results in conformational changes to the class I heavy chain, but that it is not capable of removing the membrane-bound heavy chain.