INDUCTION OF TYROSINE PHOSPHORYLATION DURING ICAM-3 AND LFA-1-MEDIATED INTERCELLULAR-ADHESION, AND ITS REGULATION BY THE CD45 TYROSINE PHOSPHATASE

Intercellular adhesion molecule (ICAM)-3, a recently described counter -receptor for the lymphocyte function-associated antigen (LFA)-1 integ rin, appears to play an important role in the initial phase of immune response. We have previously described the involvement of ICAM-3 in th e regulation of LFA-1/ICAM-1-dependent cell-cell interaction of T lymp hoblasts. In this study, we further investigated the functional role o f ICAM-3 in other leukocyte cell-cell interactions as well as the mole cular mechanisms regulating these processes. We have found that ICAM-3 is also able to mediate LFA-1/ICAM-1-independent cell aggregation of the leukemic JM T cell line and the LFA-1/CD18-deficient HAFSA B cell line. The ICAM-3-induced cell aggregation of JM and HAFSA cells was no t affected by the addition of blocking mAb specific for a number of ce ll adhesion molecules such as CD11a/CD18, ICAM-1 (CD54), CD2, LFA-3 (C D58), very late antigen alpha 4 (CD49d), and very late antigen beta 1 (CD29). Interestingly, some mAb against the leukocyte tyrosine phospha tase CD45 were able to inhibit this interaction. Moreover, they also p revented the aggregation induced on JM T cells by the proaggregatory a nti-LFA-1 alpha NKI-L16 mAb. In addition, inhibitors of tyrosine kinas e activity also abolished ICAM-3 and LFA-l-mediated cell aggregation. The induction of tyrosine phosphorylation through ICAM-3 and LFA-1 ant igens was studied by immunofluorescence, and it was found that tyrosin e-phosphorylated proteins were preferentially located at intercellular boundaries upon the induction of cell aggregation by either anti-ICAM -3 or anti-LFA-1 alpha mAb. Western blot analysis revealed that the en gagement of ICAM-3 or LFA-1 with activating mAb enhanced tyrosine phos phorylation of polypeptides of 125, 70, and 38 kD on JM cells. This ph enomenon was inhibited by preincubation of JM cells with those anti-CD 45 mAb that prevented cell aggregation. Altogether these results indic ate that CD45 tyrosine phosphatase plays a relevant role in the regula tion of both intracellular signaling and cell adhesion induced through ICAM-3 and beta 2 integrins.