A: CD40L stimulates neutrophil Mac-1 integrin expression. Peritoneal neutrophils isolated from C57BL6 mice were stimulated with rm-CD40L (100 ng/ml), without or with pretreatment (30 minutes) by 10 μg/ml of anti-mouse CD40 mAb (HM40–3), anti-mouse CD40L mAb (MR1), or hamster IgG (Iso). Stimulation of neutrophils with phorbol 12-myristate 13-acetate (50 ng/ml) was used a positive control. Mac-1 expression was determined by fluorescence-activated cell sorting analysis of CD11b (αM chain of Mac-1). Data shown are mean fluorescence intensity from three separate experiments and expressed as mean ± SD *P < 0.01 versus bar 1; **P < 0.05 versus bar 3. B: CD40L promotes neutrophil firm adhesion to activated surface-adherent platelets. Peritoneal neutrophils isolated from C57BL6 mice were added to surface-adherent platelets. Neutrophil adhesion was stimulated with rm-CD40L (100 ng/ml) without or with pretreatment (30 minutes) by 10 μg/ml of anti-mouse CD11b mAb (M1/70, αM chain of Mac-1), or rat IgG2b (Iso). Stimulation of neutrophils with phorbol 12-myristate 13-acetate (50 ng/ml) was used a positive control. Neutrophil adhesion was measured as described in Materials and Methods. Data shown are mean ± SD from three separate experiments. *P < 0.01 versus bar 1 indicated condition; **P < 0.05 versus bar 3 indicated condition.