Effect of C3a on in vitro cytokine production by splenocytes from C3^–/– mice stimulated with anti-CD3 (A), by splenic T cells from C3^–/– mice stimulated with anti-CD3 and anti-CD28 (B) and by DO11.10 TCR-OVA transgenic T cells that had been differentiated under Th2 or Th1 conditions (C). A single concentration of C3a (10 nM) was used in experiment C. *P < 0.05 (unpaired Student’s t test). Vertical lines and error bars represent mean ± SEM of five experiments in A and B and three experiments in C.