Figure 8.

Simplified model of the possible role of COX-1, COX-2, PGs, and PG receptors during T-cell development. COX-1–dependent PGE₂ synthesis is required for an efficient transition of thymocytes from DN to DP. In this model, an autocrine effect of PGE₂ acting on the EP2 receptor of immature thymocytes is hypothesized. However, we cannot exclude an effect of COX-1 in stromal cells. COX-2–dependent PG production positively affects the DN population, and it is also required for CD4 SP formation. We hypothesize a paracrine effect of PGE₂ formed by stromal cell COX-2 acting on thymocyte EP1 receptors in positive selection. It is also possible that COX-2–dependent PG production may also act on the stromal cells in an autocrine fashion.