Cross-linking CD40 primes the PMN oxidase. PMNs were incubated with a mouse monoclonal antibody to human CD40, isotype controls, or buffer for 60 minutes at 4°C, followed by the addition of a buffer control or a goat anti–mouse F(ab′)2 (GAM) to cross-link the CD40 antibody. Activation of the PMN oxidase was accomplished with the addition of 1 μM fMLP, and priming of the fMLP-activated oxidase was calculated as the augmentation of the maximal rate of O2– in response to fMLP in buffer-treated controls. *Significant increase in oxidase activity compared with the buffer-treated controls (P < .05). The only group to significantly prime the fMLP-activated respiratory burst was CD40 + GAM + fMLP, indicating that cross-linking CD40 directly causes priming of the NADPH oxidase. Importantly, incubation of PMNs treated with isotype controls with the F(ab′)2 cross-linkers did not cause priming of the fMLP-activated oxidase (results not shown). This figure is representative of 7 separate experiments using disparate blood donors as the source of the PMNs. Data are presented as mean ± standard error of the mean.
