Fish lymphocytes differ in the expression of surface immunoglobulin

Evidence for the existence of an IL-2-like lymphocyte growth promoting factor in a bony fish, Cyprinus carpio

Activity promoting the growth of carp T-like cells has been found in supernatants of mitogen (PHA)- and alloantigen (MLR)-stimulated carp leukocyte cultures. Activity level in culture supernatants was elevated by phorbol myristate acetate. Proliferation of carp T-like lymphoblasts was also promoted in the presence of Il-2-containing supernatants of mammalian origin. The significance of these findings is discussed.

Heterogeneity of mitogen-responsive lymphocytes in carp (Cyprinus carpio)

Peripheral blood leukocytes (PBL) of carp respond in vitro to a variety of phytomitogens, shown to be T-cell specific or B-cell specific in mammalian systems. Some basic differences have been observed in the proliferative response of carp PBL to PHA (phytohemagglutinin), ConA ( concanvalin A) and LPS (lipopolysaccharide): (1) The response to PHA and ConA was found to be highly dependent upon the continuous presence of mitogen in the medium, in contrast to LPS, where after the initial stimulation, cells could continue to proliferate for several days without mitogen. (2) Lymphoblasts grown in long term culture with either PHA or Con A could be transferred into medium containing the other mitogen without impairing cell proliferation, but cell growth was reduced to background level following transfer into LPS-containing medium. LPS grown cells continue to proliferate independently of the mitogen content of the medium. (3) Co-stimulation with LPS+PHA or LPS+ConA results in a synergistic response, while co-stimulation with PHA+ConA results in inhibition of DNA synthesis. (4) Several morphological differences have been observed between cells proliferating in the presence of PHA and those proliferating in the presence of LPS. It is suggested that while the PHA and ConA responsive cells may belong to the same lymphocyte subpopulation, they are distinct from the LPS-responsive subpopulation.

Distinctive subpopulations of catfish serum antibody and immunoglobulin

High molecular weight antibodies and immunoglobulin of the channel catfish were found to be composed of heterogeneous mixtures of covalent subpopulations. Although these proteins appeared tetrameric in physiological buffers (mol. wt approximately 700,000), molecular weight estimates in the presence of the detergent sodium dodecyl sulfate indicated that they dissociated into eight distinct subpopulations. Each dissociative subpopulation was found to be stable under the conditions of electrophoretic analysis, and furthermore each was apparently composed of equimolar H and L chains. Based upon relative mobilities it seems probable that the catfish antibody was composed of various combinations of covalent linkages between covalently-linked H-L chain pairs, i.e. 8, 7, 6, 5, 4, 3, 2 and 1. Further studies suggest the presence of size heterogeneity in catfish light chains. Whether or not this distinction represents isotypic L chain differences is not yet known but these findings coupled with the complex architecture of the physiological tetramer suggest an unusual and previously unappreciated level of complexity present in fish antibody.

Lymphocyte heterogeneity in the trout, Salmo gairdneri, defined with monoclonal antibodies to IgM

A monoclonal antibody to trout serum IgM was tested by immunofluorescence analysis with lymphocytes from thymus, spleen and head kidney. By visual examination, the antibody reacted with only a subpopulation of lymphocytes. The mean values +/- SE for positive cells were 5.2 +/- 2.3% in the thymus, 30.3 +/- 7.9% in the spleen and 12.4 +/- 3.0% in the head kidney. Flow cytofluorometric analysis revealed evidence of heterogeneity by size among the membrane IgM-positive cells of the head kidney and spleen. Depletion of head kidney cells positive for surface IgM by an immune affinity adherence technique of panning, using monoclonal anti-IgM, significantly reduced the mitogenic response to lipopolysaccharide but not to concanavalin A. It is suggested that this information supports the existence of distinct subpopulations of fish lymphocytes that may be homologous in certain respects to mammalian T and B type cells.