NOVEL ANTI-RAT CD18 MONOCLONAL-ANTIBODY TRIGGERS LYMPHOCYTE HOMOTYPICAGGREGATION AND GRANULOCYTE ADHESION TO PLASTIC - DIFFERENT INTRACELLULAR SIGNALING PATHWAYS IN RESTING VERSUS ACTIVATED THYMOCYTES

We have raised a monoclonal antibody (mAb), NG2B12, directed against r at CD18, capable of inducing lymphocyte homotypic adhesion and granulo cyte adherence to plastic. NG2B12-induced aggregation is temperature s ensitive and requires metabolic energy, an intact cytoskeleton and the presence of Mg2+, but is independent of protein synthesis. Ca2+ is no t only dispensable but exerts a suppressive effect on the NG2B12-induc ed adhesion. The adhesion is readily observed in thymocytes and concan avalin A blasts of thymocytes and splenocytes but is very weak in rest ing spleen and lymph node cells. NG2B12 also enhances phorbol 12-myris tate 13-acetate (PMA)-induced aggregation in an additive fashion. The NG2B12-induced homotypic adhesion is mediated by LFA-1. mAb against IC AM-1 completely inhibited the induced adhesion of activated cells but inhibited only partially and in a time-dependent manner the adhesion o f resting thymocytes. The activation of protein phosphatases 1 and 2A (as assessed by the use of okadaic acid) is necessary for the NG2B12-i nduced adhesion of both resting and activated thymocytes. In contrast, H-7 (an inhibitor of protein kinase C and A), substantially suppresse d the adhesion of resting thymocytes, whereas W-7 (an inhibitor of cal modulin-dependent protein kinase) inhibited the adhesion of activated thymocytes. NG2B12 induces both adherence to plastic and homotypic agg regation of granulocytes; the events being blocked by anti-CD18 (WT.3) and anti-CD11b/CD11c (OX-42) mAb, augmented by okadaic acid and not m odified by H-7 and W-7. Additionally, we have demonstrated that NG2B12 and PMA employ distinct intracellular signaling pathways in inducing adhesion of both thymocytes and granulocytes.