Interactions between a novel cell surface glycoprotein and the H‐2K and H‐2D antigens on myeloma tumor cells

Previous studies have shown that when a subline of plasmacytoma LPC‐1 is grown in ascites form, the tumor cells harvested after 10–12 days (“late” cells) are resistant to lysis by cytotoxic T lymphocytes (CTL), apparently because the cell surface H‐2‐encoded molecules are blocked by a trypsin‐sensitive glycoprotein of approximately 160 kdaltons. The glycoprotein (gp 160) is produced, and accumulates on the cell surface, as the growing cells enter the stationary phase. In contrast, LPC‐1 cells harvested from the peritoneal cavity early in the transplantation cycle (ca. 4 days), while in exponential growth (“early” cells), have far less gp 160 and are susceptible to lysis by CTL. It is shown that, compared with early cells, the late LPC‐1 cells are far less effective in adsorbing antibodies to products of the H‐2 K^d and H‐2 D^d alleles, but only slightly less effective in adsorbing antibodies to la antigen, and fully effective in adsorbing antibodies to several antigens not related to H‐2 (e.g. PC.1, gp70, gp100, B220). The differences suggest that gp160 might preferentially block H‐2‐encoded molecules (especially K and D) Gp160 was also detected on another myeloma, MOPC 315 OPEC, a subline of MOPC 315, where it also appeared to block H‐2 molecules but not PC.1. Additional evidence for an interaction between gp160 and H‐2 molecules was obtained when sonicated membrane fragments were used to elicit secondary CTL responses to H‐2 in culture. The response could be elicited by fragments from early but not from late LPC‐1 cells, unless the late cells were treated with subtilisin (to remove gp 160) before sonication.