American paddlefish leukocytes demonstrate mammalian‐like cytochemical staining characteristics in lymphoid tissues
American paddlefish Polyodon spathula leukocytes demonstrated cytoplasmic staining patterns very similar to mammalian leukocytes when stained with acid phosphatase, α‐naphthyl butyrate esterase and β‐glucuronidase. American paddlefish monocytes, lymphocytes and granulocytes stained positive for acid phosphatase. Monocytes stained positive for α‐naphthyl butyrate esterase. Lymphocytes that stained positive for α‐naphthyl butyrate esterase were designated type A. Lymphocytes that stained positive with antibodies to the L chain of white sturgeon Acipenser transmontanus immunoglobulin (Ig) were designated type B. Type A and type B lymphocytes stained positive for β‐glucuronidase. All leukocytes observed were negative for Sudan Black B. Monocytes, lymphocytes and granulocytes were present in the renal haematopoietic tissue, spleen, thymus, pericardial myeloid tissue, lamina propria of the spiral valve, and in meningeal myeloid tissue located dorsal to the brain, at the base of the brain and around the notochord. Peyer's patches were present in the gut. Morphological characteristics of leukocytes stained with Wright's and haematoxylin and eosin and appeared very similar to those of other fish species.
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