CD100-bound PTP activity is due to association of CD100 with CD45 PTP in Eskol cells.

Cell lysates were CD45-immunodepleted through the use of 4 cycles of depletion with O509 mAb. Negative control depletions consisted of SHP-1 immunodepletions (see “Materials and Methods”). Experiments of CD22 immunodepletion were done in parallel. Then, depleted lysates were immunoprecipitated with BJ45 (anti-CD45), BD16 (anti-CD100), or an anti–CD22 mAb, and the immunoprecipitates were assayed for PTP activity. Immunoprecipitates from undepleted lysates were also assayed to determine the basal levels of PTP activity. Negative control values of PTP activity were obtained by using depleted and undepleted lysates that were immunoprecipitated with an anti–CD101 mAb (BB27); this procedure was based on the observation that this cell surface molecule was not expressed on Eskol cells. All procedures are detailed in “Materials and Methods.”