Time course of cytokine induction by costimulatory receptors. Human CD4+ T cells were stimulated by α-CD3/B7-2 (A) and α-CD3/B7-H2 (B) respectively and harvested after different time points. Cytokine mRNA level were determined using real-time RT-PCR. Levels were normalized to β-actin and unstimulated cells were set to 1. Each point and bar represents mean ± s.e.mean of duplicates measurements of one donor. Similar results were obtained from three independent donors.