A) U937 cells were treated for the indicated times with 452 mAb (1.0 μg/mL) or control IgG (1.0 μg/mL). Lysates were immunoprecipitated with biotinylated anti-CD13 mAbs. Samples were resolved on SDS-PAGE gels and analyzed by Western blotting using anti-phosphotyrosine and CD13 antibodies. Quantitative data combine 3 separate experiments. B) Time course of CD13 crosslinking-induced adhesion of U937 monocytes. Calcein labeled U937 monocytes were treated with activating 452 mAb for 30 min and after washing, allowed to adhere to human CD13 expressing C33A monolayer cells for indicated periods of time, lysed and calcein fluorescence read at 485/530 nm and expressed as relative fluorescence unit (RFU). *; p<0.05, ***; p<0.001, ns; not significant. C) Peritoneal lavage cells collected from mice with thioglycollate induced peritonitis at day 2 or 4, were lysed and immunoprecipitated with biotinylated anti-pTyr antibody and probed with the anti-mouse CD13 antibody, SL13. D) Peritoneal lavage cells were collected from thioglycollate treated (48h) or untreated controls (resident immune cells) and probed for mCD13 by western blot analysis. n=3 mice for TG treated, resident cells were pooled from 3 mice.