Mechanisms involved in the inhibition of growth of a human B lymphoma cell line, B104, by anti-MHC class II antibodies.

The mechanisms involved in the inhibition of growth of a human B lymphoma cell line, B104, by anti-MHC class II antibodies (Ab) were compared with those in anti-IgM Ab-induced B104 growth inhibition. Two anti-MHC class II Ab, L227 and 2.06, inhibited the growth of B104 cells, although 2.06, but not L227, needed to be further cross-linked with a goat anti-mouse IgG Ab (GAM) to show the effect. L227 induced an increase in intracellular free Ca²⁺ concentration [Ca²⁺]_i from the intracellular pool and little or no protein tyrosine phosphorylation, phosphatidyl inositol turnover, or expression of Egr-I mRNA, whereas 2.06 plus GAM induced an increase in [Ca²⁺]_i from both the intracellular and, in particular, the extracellular pools. The inhibition of B104 cell growth induced by anti-MHC class II Ab was Ca²⁺ -independent and not inhibited by actinomycin D or cyclosporin A, and cell cycle arrest at the G₂/M interphase was not observed. These features are very different from those observed in B104 cell death induced by anti-IgM Ab. Neither DNA fragmentation nor the morphology of apoptosis was observed. These findings demonstrate that cross-linking of MHC class II molecules transduced the negative signals through intracellular mechanisms different from those present in the cross-linking of surface IgM. [ABSTRACT FROM AUTHOR]