Hu Ly-m5: a unique antigen physically associated with HLA molecules.

A new human cell surface antigen (Hu Ly-m5) detected by a murine monoclonal antibody (E4.3) is described. The tissue distribution of the Hu Ly-m5 antigen is similar to the HLA antigens (with which it was initially confused) but it is not present on all bone marrow cells nor the U266 myeloma, and is expressed on the HLA-negative K562 cell line. Nevertheless, the Hu Ly-m5 antigen has some affinity for HLA molecules as the two entities cocap and the Hu Ly-m5 antigen copurifies with the HLA antigens on an anti-beta 2-microglobulin immunoabsorbent column; however, the antigen complexes did not withstand the procedures used for coprecipitation. Despite their similarities, the Hu Ly-m5 and HLA antigens are distinct molecular entities--Hu Ly-m5 consists of two bands of apparent molecular weight 69 and 60 K while HLA is comprised of the 43 and 12 K bands of the HLA heavy chain and beta 2-microglobulin, respectively. The function of the Hu Ly-m5 antigen is unknown, but no involvement in the cytotoxic T-lymphocyte response to influenza virus-infected cells could be demonstrated. The two properties described (apparent molecular weight and physical association with the HLA antigens) suggests that the Hu Ly-m5 antigen may be a viral-encoded protein.