APC-expressed C3 and DAF influence in vivo T-cell expansion. (Top) Absolute number of splenic GFP Mar T cells (percentage of GFP⁺CD4⁺ cells in the spleen multiplied by the total number of spleen cells) on day 4 after injection of 10 × 10⁶ GFP⁺ Mar T cells into groups of male WT, Daf1^−/−, or C3^−/− or female control recipients (means ± SD of 3 or 4 animals/group). *P < .05. The total numbers of spleen cells in the male Daf1^−/− mice (445 million) were significantly more than in the WT (252 million) or C3^−/− (127 million) mice. (Bottom) Groups of male bone marrow chimeric mice (n = 3/group) were injected with 5 × 10⁶ CFSE-labeled Mar T cells, and total numbers of Mar cells in the spleen were quantified by flow cytometry (CFSE⁺/Vβ6⁺) on day 4. *P < .05 versus WT→WT control, n = 3 or 4 per group.