An adhesion-promoting anti-rat CD18 monoclonal antibody differentially alters thymocyte responses to various mitogens.

Leukocyte function-associated antigen (LFA)-1 represents one of the major lymphocyte adhesion molecules being capable of both strengthening cell-cell contacts and cooperating with other relevant surface molecules in signal transduction. We have studied the effects of an adhesion-promoting anti-CD18 monoclonal antibody (mAb) (NG2B12) on thymocyte proliferation induced by various mitogens. As we have recently described, the adhesion-promoting function of this mAb strictly depends upon the activation of several intracellular protein kinases and phosphatases. In the present work we have found that NG2B12 inhibits concanavalin (Con) A-induced thymocyte proliferation suppressing IL-2 production by these cells. Conversely, this mAb enhances proliferative responses of thymocytes to phytohemagglutinin (PHA) and interleukin (IL)2 alone or in combination with the phorbol ester PMA. The effects of this mAb were compared with those of another anti-rat CD18 mAb which potently blocks the LFA-1/Intercellular adhesion molecules (ICAMs) interactions.