Spontaneous and antibody directed cytotoxicity of double-negative T cells from autoimmune mice

MRL/Mp-lpr/lpr (MRL/lpr) mice develop a syndrome similar to systemic lupus erythematosus in humans. This strain of mice is characterized by the progressive accumulation of CD4-CD8- (double-negative; DN) T cells which express increased levels of cell adhesion molecules such as CD44 and heat stable antigen (HSA). The DN T cells exhibited a higher level of spontaneous cytolytic activity and contained a higher level of serine esterase as compared with T cells of MRL/Mp-+/+ (MRL/+) mice. We also found that mAbs against CD44, Mel-14, CD45R, and HSA could augment the cytolytic activity of DN T cells of MRL/lpr mice. Antibody-mediated augmentation of cytolytic activity of DN T cells was due to conjugate formation in which the Fc portion of mAb bound to the Fc gamma receptor on target cells and the Fab portion of mAb bound to corresponding cell surface antigens on DN T cells. The antibody-mediated augmentation of cytolytic activity was not detected in T cells of MRL/+ mice and lymphokine activated killer (LAK) cells of C57BL/6 mice. In contrast, anti-CD3 mAbs could augment the cytolytic activity of DN T cells, T cells as well as LAK cells. mAbs against LFA-1 and VLA-4 failed to augment the cytolytic activity of three different effector cells. It should be noted that anti-CD3 mAb-mediated cytolytic activity of DN T cells was substantially reduced by anti-LFA-1 mAb. However, CD44, Mel-14, CD45R as well as HSA-mediated cytolytic activity of DN T cells was not inhibited by anti-LFA-1 mAb.(ABSTRACT TRUNCATED AT 250 WORDS)