PGD₂ controls the clearance of peritoneal resident lymphocytes. In response to inflammatory stimuli, lymphocytes in the peritoneum disappear between 6 and 24 hours. (A-E) However, lymphocyte numbers in hPGD₂S knockout mice at 6 hours (■) were found to be equivalent to that present in the naive cavity of wild-type mice (□), suggesting a role for either PGD₂ and/or 15d-PGJ₂ in the initial clearance of lymphocytes. (F) Adding back BW245C (DP1 receptor agonist) to hPGD₂S knockout mice caused a reduction in B cells. Attempts made to identify the fate of CD3 cells generated inconclusive results, with data suggesting that they may die locally by programmed cell death (data not included). n = 8 animals per group. *P ≤ .05 as determined by Bonferroni t test, with data expressed as means plus or minus SEM.