Fig 2.

Competition with inactive ACT (iACT) decreases WT ACT-elicited cAMP accumulation in CHO CR3⁺ and K562 CR3⁺ cells but not in the respective control cells. (A) CHO CR3⁺ cells were incubated with WT ACT at the specified concentrations in the continuous presence of 5,000 ng/ml (30 nM) iACT. (B) Same as described for panel A but with CHO control cells. (C) K562 CR3⁺ (squares) and K562 control (circles) cells were incubated with WT ACT at the specified concentrations either without (closed) or with (open) 5,000 ng/ml iACT. (D) K562 CR3⁺ (gray bars) and K562 (black bars) cells were incubated with 100 ng/ml WT ACT in the continuous presence of 5,000 ng/ml iACT. To examine blocking of cAMP generation by a MAb to CD11b, 100 ng/ml of ACT was added to cells after 1 h incubation at 4°C with 20 μg/ml MAb M1/70 to CD11b or 20 μg/ml isotype control antibody. Data presented are the means ± standard errors of duplicate samples in a single experiment which is representative of 3 (CHO) or 2 (K562) individual experiments.