Immunoglobulin determinants on the surface of lymphoid cells of carps

Functional aspects of fish lymphocytes

After almost 40 years of studies in comparative immunology, some light has been shed on the evolutive immunobiology of vertebrates, and experimental evidences have shown that acquired immunity, defined by somatic recombination of antigen-binding molecules and memory, is an achievement as ancient as jawless vertebrates. However, the molecular processes generating antigen receptors evolved independently between jawless and jawed fishes, and produced lymphocytic cells with similar functions but employing different sets of genes. In recent years, data have been provided describing some in vitro and in vivo functional responses of fish lymphocytes. After a long gap, the number of specific markers for fish lymphocytes is increasing, thus allowing a first characterisation of lymphocyte subsets. Overall, in the near future it will be possible to open a new chapter in fish immunology and investigate functional immunity of lymphocyte responses by combining the extensive knowledge on immune gene products with markers for molecules and cells. The present review summarizes current knowledge on functional features of fish lymphocytes.

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, WCI12) produced against carp serum Ig. Immunochemical results showed that both WCI4 and WCI12 react with a protein determinant on the heavy chain of Ig (relative molecular mass approximately 70,000). Immunofluorescence microscopic and flow cytometric analyses of lymphoid cells suggest three distinct subpopulations of B cells and plasma cells: WCI4+12- cells, WCI4-12+ cells, and WCI4+12+ cells. WCI4-12+ and WCI4+12+ anti-DNP antibody-secreting cells were also demonstrated with the ELISPOT assay in pronephros and spleen cell suspensions from primary immunised carp. Affinity chromatography of carp serum and sequential immunoprecipitation of 125I-labelled peripheral blood leucocyte (PBL) membrane proteins only indicated the presence of two antigenically different Ig molecules, i.e., WCI4-12+ and WCI4+12+ molecules. WCI4+12- molecules could not be detected by affinity chromatography or immunoprecipitation. During ontogeny, a shift in percentages of WCI4+12- and WCI4-12+ cells was found in the spleen and the 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 decreased during ontogeny. On the other hand, the percentages of WCI4-12+ cells increased during development, and these cells became the major population of B cells from 13 weeks onward. The proportion of WCI4+12+ cells remained almost constant during ontogeny. The distribution of B cell subpopulations in blood was more or less stable at all ages. The functional significance of Ig heterogeneity in fish and in particular carp is discussed.

Applications of monoclonal antibodies in aquaculture

Monoclonal antibodies (MAbs) currently are being applied to the study of fish immunology and fish infectious diseases. MAbs to fish immunoglobulins (Igs) have helped isolate fish Igs, identify heavy and light chain variants in fish Ig, study the ontogeny of B lymphocytes, and improve techniques for the measurement of fish Ig and specific antibodies (Abs). MAbs have been obtained against several leucocyte surface antigens and are being used as markers for different subsets of fish leukocytes: neutrophils, non-specific cytotoxic cells and cells responsible for the mixed leucocyte reaction. The sensitivity and specificity of many immunoassays for identifying fish pathogens have been improved by the use of MAbs. Further improvement of these tests is currently being attempted by the use of MAbs together with the polymerase chain reaction (PCR). Epizootiological studies of fish diseases are beginning to emerge from the use of these reagents and techniques. In the near future these new methods should detect low levels of pathogens in adult carriers and perhaps in eggs, thus helping to prevent the dissemination of fish diseases. MAbs to fish pathogens are also being used for passive immunization studies as well as for conformational probes in the development of genetically engineered vaccines.

Characterization of axolotl heavy and light immunoglobulin chains by monoclonal antibodies

Axolotl specific antibodies to 2,4-dinitrophenyl (DNP) were purified by affinity chromatography from the sera of animals immunized with 2,4,6-trinitrophenylated sheep red blood cells (TNP-SRBC). The purified anti-TNP/DNP antibodies, when analyzed by SDS-PAGE, were constituted of high molecular weight molecules, which in reducing conditions, were separated into heavy 72-88 kD and light 27-30 kD polypeptides. The axolotl heavy antibody chains strongly bound Concanavalin-A and migrate faster in SDS-PAGE after endoglycosidase-F (Endo-F) treatment. Using the same techniques, no carbohydrate components were detected onto light chains. Monoclonal antibodies (MAbs) were obtained against these purified axolotl immunoglobulins (Ig) and their specificities were studied by immunoblotting. MAbs 33.45.1 and 33.101.2 respectively recognized heavy and light chains determinants of the Ig molecule. These determinants were resistant to Endo-F digestion, suggesting that the two MAbs were not directed to polypeptide-associated N-linked high mannose or complex oligosaccharides. MAbs 33.45.1 and 33.101.2 were compared to 11.5.2, an anti-axolotl thymocytes MAb which was reactive for both axolotl leucocytes and soluble Ig. MAb 11.5.2 reacted in immunoblotting against several high molecular weight axolotl serum proteins, including heavy Ig chains. Light chains were not recognized. However, 11.5.2 did not further recognize Endo-F treated Ig, suggesting its specificity for a carbohydrate determinant of the heavy chain, and link to a large diversity of soluble or membrane glycoproteins.

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.

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.

Ontogeny and distribution of cells in B lineage in the American leopard frog, Rana pipiens

Two-color immunofluorescence techniques were used in order to trace the development and distribution of cells expressing immunoglobulin in Rana pipiens. Evidence is provided which suggests that (i) embryo-larval urogenital tissues are sites of generation of cells in B lineage, (ii) during ontogeny, there is a sequential expression of immunoglobulin isotypes on B cell surfaces, (iii) larvae are able to produce the full range of immunoglobulin clases found in adults, and (iv) at least two subpopulations of lymphocytes exist in Rana pipiens, sIg+ and sIg-; thymocytes and presumably peripheral T cells lack conventional surface immunoglobulin. Some ontogenetic and phylogenetic implications are discussed.

Rainbow trout lymphoid organs: cellular effects of corticosteroids and anti-thymocyte serum

Cellular populations were studied in lymphoid organs of rainbow trout. Kidney appeared to be the most important organ by the number of cells harvested. A high percentage of peroxidase positive cells was measured in kidney, spleen and blood. The use of cortisone and rabbit anti-thymocyte serum showed differences in ratio of sensitive cells from different organs. In fish treated with steroids, cell depletion was verified in each organ but histologic lesions were observed only in thymus. Rabbit anti-thymocyte serum was cytotoxic for the quasi-totality of thymocytes while it destroyed only a part of kidney, spleen and blood cells. No correlations could be made between steroid sensitive cells and anti-thymocyte serum sensitive cells.

Fish lymphocytes differ in the expression of surface immunoglobulin

Catfish peripheral blood and splenic lymphocytes were assayed for surface immunoglobulin using fifteen different mouse hybridoma antibodies to catfish immunoglobulin (Ig). These studied showed that this battery of monoclonal antibodies did not detect significant amounts of Ig on all lymphocytes. Unlike polyclonal antisera which demonstrated nearly 100% surface Ig+ cells, the monoclonal antibodies detected approximately 40% surface Ig+ cells. Furthermore, the percentage of Ig+ cells reactive with two of these monoclonals, tentatively shown to react with two different types of catfish light chains, was found to be nearly additive when the two antibodies were mixed. Thus it seems that fish lymphocytes, like their mammalian counterparts, have two different populations of lymphocytes; one which contains abundant surface Ig and one which does not. Whether these two types of cells represent the fish equivalents of B and T cells remains to be determined.

Visualization of a guinea pig T lymphocyte surface component cross-reactive with immunoglobulin

Thymus-derived lymphocytes (T cells) show exquisite specificity in recognition of antigens, but the nature of the cell surface receptor is controversial. Although antigen recognition mediated by immunoglobulin variable (V) regions remains the minimal hypothesis, it has been extremely difficult to definitely establish the presence of immunoglobulins on these cells. Chicken antibodies, produced against the (Fab')2fragment of mouse immunoglobulin G (IgG) and purified by binding to and elution from IgG-Sepharose 4B, bind to an endogenously synthesized surface component of guinea pig T cells. The binding occurred via a cross-reaction with murine k chain and a heavy chain determinant localized in the Fd region, and was visualized by immunofluorescence and immunoelectronmicroscopy using both transmission and scanning techniques. These data provide direct evidence for the presence of a surface component related to immunoglobulin on T lymphocytes.

Evolution of the lymphoid system. II. Evidence for immunoglobulin determinants on all rainbow trout lymphocytes and demonstration of mixed leukocyte reaction

Indirect fluorescent antibody analyses utilizing antiserum specific for rainbow trout serum immunoglobulin (Ig) demonstrated that essentially all rainbow trout lymphocytes from thymus, spleen, anterior kidney and peripheral blood possess either Ig determinants or structures which cross-react with those determinants found on serum Ig. Peripheral blood leukocytes from rainbow trout were found to be caple of participating in a mixed leukocyte reaction. This observation is discussed in terms of the evolution of T cell function.

Lymphocyte surface immunoglobulins: detection, characterization, and occurrence in disease of the lymphoid system

Surface immunoglobulins (Igs) of lymphocytes are of considerable interest because these molecules probably function as receptors for antigen, and knowledge of their molecular properties should provide information on the mechanisms of immune differentiation. The density and types of surface Ig on a cell provide markers useful in indicating the class of a lymphocyte and its stage of maturity. Moreover, knowledge of the specificities of the surface Ig of neoplastic lymphocytes might suggest the nature of agents involved in the generation of the disease. Two broad classes of lymphocytes, bone marrow-derived lymphocytes (B cells) active in antibody secretion, and thymus-derived lymphocytes (T cells) which mediate cellular immune reactions, and their subpopulations must be considered with reference to the nature, origin, and function of their surface immunoglobulin. This article analyzes direct and indirect methods for the demonstration of surface Igs and describes certain physicochemical properties of isolated surface Ig molecules. Roles of these surface molecules in recognition of antigen, initiation of all differentiation, and cooperation among lymphocytes and accessory cells are discussed.

Phylogenetic origins of immune recognition: lymphocyte surface immunoglobulins in the goldfish, Carassius auratus

Membrane immunoglobulin (Ig) of splenocytes and thymocytes of the goldfish, Carassius auratus, was demonstrated by indirect fluorescent-antibody techniques. Observations on shedding and resynthesis indicated that the thymocyte Ig was endogenously produced. The lymphocyte surface proteins were radioiodinated using the lactoperoxidase-catalyzed reaction, and the labeled Ig molecules were isolated by specific precipitation and analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The IgM-like membrane Igs of splenocytes and thymocytes were shown to differ in their ease of solubilization with nonionic detergent, and in the sodium dodecyl sulfate/electrophoretic mobility of their heavy chains. The significance of these observations for the evolution of T-cell recognition is discussed.

Evolutionary and developmental aspects of T-cell recognition

Studies relating to the nature of the antigen-specific T-cell receptor are reviewed in the light of present knowledge of phylogenetic and ontogenetic development. It is suggested that this evidence supports the concept that immunoglobulin (Ig) is the T-cell receptor, and that the following conclusions may be tentatively drawn.

Surface immunoglobulins on the lymphocytes of the skate Raja naevus

Living lymphocytes of the Elasmobranch fish, Raja naevus, have been examined for surface immunoglobulin (Ig) by treatment with a fluorescent anti-Ig system. Large numbers of Ig-positive cells (60-80%) were found in peripheral blood, spleen and thymus. Following modulation of the surface Ig with anti-Ig, resynthesis occurred, showing that the surface Ig is a product of the individual lymphocytes rather than material passively absorbed from the serum. Formation of caps was independent of temperature, occurring as readily at 4 degrees C as at 20 degrees C, a finding which presumably reflects the environmental conditions normally experienced by the skate. The presence of Ig-bearing lymphocytes in the adult skate thymus suggests a similarity to the amphibian larval thymus, which may be a primary lymphoid organ for the production of both T and B lymphocyte analogues.