BOVINE NK AND LAK SUSCEPTIBILITY IS INDEPENDENT OF CLASS-I EXPRESSIONON B-LYMPHOBLASTOID VARIANTS

Numerous tumors express low or no class I molecules, resulting in thei r avoidance of recognition and destruction by different effector cells of the immune system. Using a parent and two MHC class I mutant cell lines, we have tested the role of MHC class I molecules in natural kil ler (NK) cells, lymphokine activated killer (LAK) cells and cytotoxic T lymphocytes (CTLs). Both class I expressing parent cells and class I loss mutants were insensitive to NK cell lysis as assayed, regardless of the amount of class I molecules on the target cell surface. Howeve r, LAK cells demonstrated higher cytolysis on these target cells than NK cells, suggesting different mechanisms of target cell recognition o r different levels of lytic activity by these two effector cell popula tions. Up-regulation of class I expression on the target surface by ga mma interferon (gamma-IFN) had little influence on NK and LAK suscepti bility, indicating there was no correlation between class I expression and bovine NK or LAK cytolysis. However, allogeneic CTLs mediated a l ytic pattern distinct from NK and LAK cells, in which target sensitivi ty to allogeneic CTLs correlated with the amount of class I molecules expressed on the cell surface. Additionally, effector-target cell conj ugation studies demonstrated that target class I expression was not in volved in NK and LAK cells binding to targets. These results demonstra te that NK and LAK cytolysis of these two class I mutant cell lines is independent of the amount of class I molecules expressed on the targe t cell surface.