Independent expression of the two HL‐A antigen polypeptide chains

Abstract

It is now well established that β₂‐microglobulin constitutes one of the two HL‐A antigen subunits. In this study support was obtained for the previous notion that the human lymphoma Daudi does not produce β₂‐microglobulin (β₂m). Papain‐solubilized as well as nonidet P‐40‐solubilized Daudi HL‐A antigens do not contain any β₂m or any detectable structural analogue of this protein. The chemical and physico‐chemical characteristics of highly purified HL‐A antigens derived from Daudi cells are indistinguishable from those of the HL‐A antigen‐carrying polypeptide chain isolated from the P₃HRIK cell line. Like P₃HRIK‐derived HL‐A antigens, the HL‐A antigens derived from Daudi cells are composed of two identical, heavy, alloantigenic polypeptide chains with a molecular weight of about 50000 each, which are held together by disulfide bridge(s). The HL‐A antigens of P₃HRIK cells contain, in contrast to Daudi HL‐A antigens, two molecules of β₂m. Although no evidence was obtained suggesting any β₂m synthesis in Daudi cells it was apparent that these cells express the HL‐A alloantigenic polypeptide chain in amounts similar to those of other cell lines which produce β₂m The present data suggest [1] that β₂m and the alloantigenic HL‐A polypeptide chain are under separate genetic regulation [2], that the cell surface integration of the HL‐A antigen‐carrying polypeptide chain is independent of the presence of β₂m and [3] that β₂m does not constitute a membrane component absolutely necessary to the integrity of the cell membrane.