Elicitation of macrophages from the peritoneal cavity of channel catfish

Four chemicals were evaluated for elicitation of macrophages in peritoneal cavities of 250–300‐g healthy channel catfish Ictalurus punctatus. Cellular exudates were collected at 3, 5, 7, 10, 14, and 20 d following intraperitoneal injections with squalene, Freund's incomplete adjuvant (FIA), goat serum, thioglycollate, or as a control, phosphate‐buffered saline. Injection with either squalene or FIA induced significantly greater (P ⩽ 0.0001) macrophage recruitment than the other chemicals. The effectiveness of squalene and FIA was compared further by macrophage collection daily for 7 d. Squalene and FIA elicited similarly high macrophage responses (P ⩽ 0.0450), the highest being 3.43 × 10⁶ macrophages/mL (SE, 2.4 × 10⁶) at 99% purity at day 2 and 2.1 × 10⁶ macrophages/mL (SE, 0.7 × 10⁶) at day 14 at 80% purity, respectively. In both experiments, the time after injection was not statistically significant, nor was there an interaction between time and chemicals. The occurrence of cells other than macrophages decreased with time to yield macrophage recoveries of 47–99% for squalene and 30–80% for FIA. Two subsets of macrophages were observed by means of flow cytometry. As demonstrated by chemiluminescence, the squalene‐elicited cells produced high‐energy oxygen compounds important to the phagocytic process.