Inflammation, Vol. 16, No. 5, 1992 GRANULOCYTE TURNOVER IN THE FELINE INTESTINE HOLGER ARNDT,1 PAUL KUBES,I MATTHEW B. GRISHAM, 1 ENRIQUE GONZALEZ,: and D. NEIL GRANGER 1 tl3'epartment of Physiology and Biophysics 2Department of Pathology Lc.uisiana State University Medical Center Shreveport, Louisiana 71130 Abstract--The objective of this study was to determine the turnover rate of the extra- vascular pool of granu]ocytes in different regions of the feline gastrointestinal tract. Leukocyte emigration from the vasculature was prevented over a 48-h period by repeated intravenous injections of a monoclonat antibody (MAb IB4) directed against the leukocyte adhesion glycoprotein complex CDll/CD18. Tissue-associated mye- loperoxidase (MPO) activity was used to monitor the total tissue granulocyte pool at 0.5, 12, 24, and 48 I1 after MAb IB4 administration. The mucosal layer of the duodenum, jejunum, ileum, and colon exhibited different kinetics of granulocyte clearance, with average life-spans (t 89ranging between 6.9 (colon) and 10.4 h (duo- denum). Granulocyte clearance rates of 0.5 • 10 6 and 2.4 • 10 6 cells/h/g tissue were estimated (from measured values of t~ and tissue granulocyte pool) for the small bowel and colonic mncosae, respectively. The submucosal layer of the intestine exhibited a biphasic reduction in tissue MPO activity following immunoneutralization of CDll/CD18, with an initial t I < 0.5 h followed by a t89 of 36-60 h. The initial rapid decline in tissue MPO suggests that a significant fraction of grauulocytes in the submucosa is localized in a readily exchangeable pool (e.g., marginated cells within the vasculature). The results of thisstudy indicate that the average life-span of resident granulocytes varies significantly between different regions of the gastrointestinal tract, with the intestinal mucosa exhibiting a t I comparable to that previously reported for circulating feline neutraphils ( - 8 h). INTRODUCTION Once formed in bone raarrow, granulocytes enter the vascular compartment, where they become part of the total blood granulocyte pool (TBGP). The cir- culating granulocyte pod, which is determined from the blood volume and blood granulocyte count, comprises about 50% and 30% of the TBGP in humans and 549 0360-3997/92/1000-0549506.50/0 9 1992 Plenum Publishing Corporation