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Abstract

Here we investigated the role of cellular phosphatases in activation of homotypic aggregation in leukocytes by adding the phosphatase inhibitors okadaic acid (OA) and calyculin A (CA) to cultures of the human monocytic U937 cell line and the human T-lymphocytic Jurkat cell line. We found that OA produces a 120-fold increase of homotypic aggregation with Jurkat cells and a 200-fold increase with U937 cells. Calyculin A increased aggregation of Jurkat cells 10-fold and U937 cells 88-fold. Monoclonal antibodies to LFA-1 completely inhibited the OA and CA induced aggregation in both cell lines, whereas the monoclonal antibody to ICAM-1 only inhibited U937 cell aggregation. These data suggest that phosphatase activity is important in the regulation of ICAM-1 and LFA-1 mediated homotypic aggregation in leukocytes.