EFFECT OF PHYTOHEMAGGLUTININ ON CD45 IN T-CELLS

In this study the effect of PHA activation on the phosphatase activity of CD45 has been investigated in human leukemic T-cell lines. It has been found that in vivo activation of the cells with PHA resulted in 2 -4-fold increase in enzyme activity. Addition of PHA to the postnuclea r supernatant of cell lysates also resulted in elevation of phosphatas e activity. Elevation of enzyme activity resulted from an increase in the amount of antigen in the immunoprecipitates. Elevation of the quan tity was not the result of a de novo protein synthesis since the prese nce of cycloheximide, a protein synthesis inhibitor, did not modulate the effect of PHA. The effect of PHA was specific since ConA, that als o bound to the CD45 molecules, or crosslinking of the antigen by antib ody did not affect CD45. Since direct binding of PHA to CD45 molecules was shown in immunoblotting analysis, we suggest that the effect of P HA is a consequence of a PHA-induced conformational change of CD45 tha t results in up-regulation of the analyzed CD45 epitopes.