Differential cytochemical staining characteristics of channel catfish leukocytes identify cell populations in lymphoid organs

This is one of the first characterizations of channel catfish (Ictalurus punctatus) leukocytes by enzyme cytochemistry. Leukocytes demonstrated cytoplasmic staining patterns very similar to mammalian leukocytes when stained with acid phosphatase, α-naphthyl butyrate esterase, β-glucuronidase, α-naphthyl acetate esterase, Sudan Black B and anti-immunoglobulin specific immunohistochemistry. Lymphocytes, monocytes, macrophages, neutrophils, and surface immunoglobulin positive (surface Ig+) cells were present in channel catfish renal hematopoietic tissue and spleen and demonstrated distinctive cytoplasmic foci staining patterns, cytoplasmic blushing or cell membrane staining. Monocytes, macrophages, lymphocytes and surface Ig+ cells were present in the thymus. Thymic and splenic cellular organization appeared very similar to these same mammalian tissues. In the thymus, acid phosphatase positive cells were distributed throughout the parenchyma, while α-naphthyl butyrate esterase and β-glucuronidase positive cells were concentrated in the cortex and the medulla, respectively. Surface immunoglobulin positive cells occurred in the cortex. In the spleen, acid phosphatase positive cells were scattered throughout the parenchyma, while α-naphthyl butyrate esterase positive cells were scattered throughout the parenchyma and adjacent to splenic arterioles. β-glucuronidase and surface immunoglobulin positive cells were restricted to immediately adjacent to splenic arterioles. Sudan Black B positive cells were scattered throughout the parenchyma, while α-naphthyl acetate esterase positive cells occurred adjacent to peri-arteriole lymphoid sheaths and appear very similar to mammalian metallophils.