Phylogenetic origins of immune recognition: Lymphoid heterogeneity and the hapten/carrier effect in the goldfish, Carassius auratus

These studies were designed to determine whether the cellular response of the goldfish, Carassius auratus, to heterologous erythrocytes is comparable in complexity and shares similar recognition mechanisms with those of mammals. Immunocytoadherence has been used to monitor the anti-horse erythrocyte (HRBC) response. The levels and kinetics of antigen-binding activity in the thymus, head nephros, and spleen were established following a single high (25%) or low (0.0025%) HRBC challenge. Rabbit anti-goldfish IgM was found to inhibit antigen binding of thymocytes, as well as other immunocytes. Hapten-carrier immunization was used to explore lymphoid heterogeneity in this species. The anti-hapten (2, 4, 6-trinitrophenyl) response was found to be specifically enhanced by carrier priming. The helper function of carrier-stimulated cells was short lived and greatest when low-dose carrier priming was used. The proportion of low-dose, carrier-stimulated thymus and head nephros antigen-binding cells was substantially enriched by passage through a nylon-wool column. However, previously carrier-primed and hapten-stimulated secretory antigen-binding cells were depleted by comparable column separation. The results of hapten-carrier immunization in combination with column separation are indicative of lymphoid heterogeneity for this species. They suggest that cell-cell collaboration is a general and essential part of the vertebrate immune response. Antigen-specific recognition of both lymphoid subsets seems likely to be mediated by surface immunoglobulin, since anti-IgM inhibits antigen binding of thymus and head nephros immunocytes.