Flow Cytometric And Electron Microscopic Characterization Of Channel Catfish (Ictalurus punctatus) Macrophages     Natalia Guseva, Joanne Maki, Harry W. Dickerson   Department of Medical Microbiology & Parasitology, College of Veterinary Medicine, University of Georgia, Athens, GA, 30602-7386   Macrophages from adult channel catfish (Ictalurus punctatus) have been isolated following centrifugation of tissue cell suspensions from head kidney, spleen and peritoneal washes through discontinuous Percoll gradients. Incomplete Freund’s adjuvant, purified i-antigen protein (the 55-kDa predominant surface membrane protein of Ichthyophthirius multifiliis, isolate G5) and live organisms were injected intraperitoneally to initiate an inflammatory response and phagocyte stimulation. Preliminary experiments showed the presence of three main cell populations in the macrophage-enriched fractions. The macrophages were identified by flow cytometry using the parameters of cell size and granularity. Sorting and further characterization of these cells by phase and electron microscopy is currently in progress.  The prevalence of each macrophage cell type from the different tissues will be determined.