Ontogeny of channel catfish lymphoid organs

Previously, we showed that catfish could not mount a detectable antibody re sponse after bacterial exposure until 21 days post-hatch (ph). In order to evaluate the changes associated with the development of a functional humora l response, we evaluated the temporal and spatial distribution of immune ce ll populations in developing catfish. Cells functioning in nonspecific immu nity were present in the renal hematopoietic tissue (rht) and thymus at hat ch and in the spleen by day 3 ph. Immunoglobulin (Ig) positive lymphocytes were first detected on day 7, 10, and 14 in the rht, thymus and spleen, res pectively. Mature thymocytes were first detected on day 10 ph. Distinct thy mic regionalization and splenic lymphoid tissue organization were not obser ved until day 21 ph. We suggest that the reason for a lack of antibody prod uction until day 21 ph is the poor organization of secondary lymphoid tissu e until that age. (C) 2001 Elsevier Science B.V. All rights reserved.