Histological enzyme and flow cytometric analysis of channel catfish intestinal tract immune cells

Channel catfish, Ictalurus punctatus, gastrointestinal tract leukocytes were characterized using flow cytometry, histochemistry, and enzyme staining techniques. Cells obtained from the lamina propria by collagenase digestion were found to be primarily neutrophils, with fewer than 6% B lymphocytes as determined by flow cytometry. Histochemical and enzyme stains were used to determine leukocyte distribution in gastrointestinal tract tissue. Macrophages and T lymphocytes were observed throughout the gastrointestinal tract. As in flow cytometry studies, few B lymphocytes and many neutrophils were observed in the channel catfish gastrointestinal tract. Since cells involved in specific immunity appear to be limited in gastrointestinal tract tissue of channel catfish, we speculate that catfish may rely more heavily on a highly developed innate response for intestinal mucosal immunity than other teleost species studied.