Transcellular biosynthesis in vivo. (a) Zymosan A–induced peritoneal inflammation. LTB₄ production was measured in the peritoneal lavage fluid. Loss of 5-LO expression impairs LTB₄ production in response to zymosan A stimulation (5-LO→5-LO). In contrast, the presence of leukocytes expressing 5-LO, but unable to produce LTB₄ (LTA₄-H→5-LO), results in LTB₄ production. *P < 0.05. WT, wild-type; 5-LO, 5-LO–deficient mice; LTA₄-H, LTA₄-H–deficient mice. The transplanted groups are identified as donor→recipient genotypes. Results are presented as numerical values in Table 1. (b) Acute cutaneous inflammatory responses to AA. Mice received Evans blue dye and indomethacin immediately before topical application of AA. At 1 hour after the treatment, the inflamed tissue was biopsied, weighed, and the serum exudate present in the tissue was determined. The white bars represent the difference in optical densities (Δ OD) between the ear treated with AA and the ear treated with vehicle (acetone) alone. The black bars represent the difference in ear-disc weights (Δ ear weight) between the AA-treated ear and the vehicle-treated ear for each mouse. While loss of 5-LO or LTA₄-H attenuated the inflammatory response to AA, the response was significantly increased in mice in which the reconstituted immune cells express 5-LO, but are unable to produce LTB₄ (LTA₄-H→5LO). This graph combines data from two separate experiments. Statistical significance is indicated only for the transplanted groups for clarity. *P < 0.05. WT, wild-type; 5-LO, 5-LO–deficient mice; LTA₄-H, LTA₄-H–deficient mice. Results are presented as numerical values in Table 1.