Independent expression of the two HL-A antigen polypeptide chains.

It is now well established that beta2-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 beta2-microglobulin (beta2m). Papain-solubilized as well as Nonidet P-40-solubilized Daudi HL-A antigens do not contain any beta2m 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 50 000 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 beta2m. Although no evidence was obtained suggesting any beta2m 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 beta2m. The present data suggest [1] that beta2m 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 beta2m and [3] that beta2m does not constitute a membrane component absolutely necessary to the integrity of the cell membrane.