Independent expression of the two HL‐A antigen polypeptide chains

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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.