Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/1997
Publication Date: N/A
Citation: Interpretive Summary: Information on disease-fighting cells of the immune system of channel catfish is lacking. White cells that have the capacity to kill bacterial pathogens, call a macrophage, are very difficult to collect from the blood of catfish. We devised a method to collect almost pure populations of these white cells from the body cavity of catfish. Squalene or shark oil injected into their cavity was found to cause accumulation of these white cells that could be collected by washing the cavity. We believe that development of this method will allow the characterization of bacteria-fighting cells from channel catfish.
Technical Abstract: Four chemicals were evaluated for elicitation and collection of macrophages from peritoneal cavities of 250 - 300 g healthy channel catfish, Ictalurus punctatus. Peritoneal exudates were collected at 3, 5, 7, 10, 14, and 20 d following intraperitoneal injections (0.5 mL) with squalene, Freund's incomplete adjuvant (FIA), goat serum, fluid thioglycollate, or control phosphate buffered saline (PBS). Cellular exudates were collected through a three-way valve 1 to 2 min after the IP-introduction of cold PBS and gentle massage of the abdominal region to dislodge macrophages. Total cell counts were done, and smears of cells were differentially stained by non-specific esterase for macrophages and Wright-Giemsa stains. Injection with either squalene or FIA induced significantly greater (P < 0.0001) recruitment of macrophages than the other chemicals. Squalene and FIA elicited similarly high macrophage responses (P < 0.0450), the highest being 3.43 x 10**6 macrophages/mL (SE 2.4 x 10**6) at 99% purity at day 2, and 2.1 x 10**6 macrophages/mL (SE 0.7 x 10**6 at day 14 at 80% purity, respectively. The occurrence of cells other than macrophages, particularly erythrocytes, decreased with time to yield macrophage recoveries of 47-99% for squalene and 30-78% for FIA. We found two distinct subsets of macrophages using flow cytometry.