B-CELL AND IMMUNOGLOBULIN HETEROGENEITY IN CARP (CYPRINUS-CARPIO L) -AN IMMUNO(CYTO)CHEMICAL STUDY

B cell and immunoglobulin (Ig) heterogeneity was demonstrated in carp, Cyprinus carpio L., using two monoclonal antibodies (MAbs; WC14, WCI1 2) produced against carp serum Ig. Immunochemical results showed that both WCI4 and WCI12 react with a protein determinant on the heavy chai n of Ig (relative molecular mass similar to 70,000). Immunofluorescenc e microscopic and flow cytometric analyses of lymphoid cells suggest t hree distinct subpopulations of B cells and plasma cells: WCI4(+)12(-) cells, WCI4(-)12(+) cells, and WCI4(+)12(+) cells. WCI4(-)12(+) and W CI4(+)12(+) anti-DNP antibody-secreting cells were also demonstrated w ith the ELISPOT assay in pronephros and spleen cell suspensions from p rimary immunised carp. Affinity chromatography of carp serum and seque ntial immunoprecipitation of I-125-labelled peripheral blood leucocyte (PBL) membrane proteins only indicated the presence of two antigenica lly different Ig molecules, i.e., WCI4(-)12(+) and WCI4(+)12(+) molecu les. WCI4(+)12(-) molecules could not be detected by affinity chromato graphy or immunoprecipitation. During ontogeny, a shift in percentages of WCI4(+)12(-) and WCI4(-)12(+) cells was found in the spleen and th e pronephros. In these organs, WCI4(+)12(-) cells formed the majority of B cells at 2 weeks of age, but the percentages of this cell type de creased during ontogeny. On the other hand, the percentages of WCI4(-) 12(+) cells increased during development, and these cells became the m ajor population of B cells from 13 weeks onward. The proportion of WCI 4(+)12(+) cells remained almost constant during ontogeny. The distribu tion of B cell subpopulations in blood was more or less stable at all ages. The functional significance of Ig heterogeneity in fish and in p articular carp is discussed.