The S1126A mutation gives rise to modifications in activation epitopes. (A) The effects of the S1126A-CD11b mutation on expression of the CD18 activation reporter mAb24 were examined. Jβ2.7 cells were incubated with mAb24 (5 μg/mL) in the presence of phorbol ester (100 nM) or 5 mM Mg²⁺/1 mM EGTA, and mAb24 expression was analyzed by flow cytometry. Significant differences (P ≤ .01) in bracketed comparisons are indicated by a single asterisk. (B) As in panel A, except that KIM127 (5 μg/mL) was used instead of mAb24. Significant differences (P ≤ .05) in bracketed comparisons are indicated by a single asterisk. (C) As in panels A and B, except that CBRM1/5 was used, and both PDBu and Mg/EGTA were used during the activation. Error bars represent SD.