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

Type II Grass Carp Reovirus Infects Leukocytes but Not Erythrocytes and Thrombocytes in Grass Carp (Ctenopharyngodon idella)

Grass carp reovirus (GCRV) causes serious losses to the grass carp industry. At present, infectious tissues of GCRV have been studied, but target cells remain unclear. In this study, peripheral blood cells were isolated, cultured, and infected with GCRV. Using quantitative real-time polymerase chain reaction (qRT-PCR), Western Blot, indirect immunofluorescence, flow cytometry, and transmission electron microscopy observation, a model of GCRV infected blood cells in vitro was established. The experimental results showed GCRV could be detectable in leukocytes only, while erythrocytes and thrombocytes could not. The virus particles in leukocytes are wrapped by empty membrane vesicles that resemble phagocytic vesicles. The empty membrane vesicles of leukocytes are different from virus inclusion bodies in C. idella kidney (CIK) cells. Meanwhile, the expression levels of IFN1, IL-1β, Mx2, TNFα were significantly up-regulated in leukocytes, indicating that GCRV could cause the production of the related immune responses. Therefore, GCRV can infect leukocytes in vitro, but not infect erythrocytes and thrombocytes. Leukocytes are target cells in blood cells of GCRV infections. This study lays a theoretical foundation for the study of the GCRV infection mechanism and anti-GCRV immunity.

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.

The immunoglobulin M heavy chain constant region gene of the channel catfish, Ictalurus punctatus: an unusual mRNA splice pattern produces the membrane form of the molecule

The immunoglobulin (IgM) heavy chain constant region gene of the channel catfish, Ictalurus punctatus, has been cloned and characterized. The gene contains four constant region domain-encoding exons (CH1 to CH4) expressed in the secreted form of the immunoglobulin, and two exons encoding the transmembrane (TM) domain utilized in the lymphocyte membrane receptor form of the immunoglobulin. The sequence of a cDNA clone encoding the 3' region of the message for the membrane receptor form of the mu chain indicates that the TM1 exon is spliced directly to the CH3 exon, and not into a site within the CH4 exon, as occurs in the mammals, a shark and an amphibian. This unusual pattern of splicing, which produces a membrane heavy chain that is characteristically smaller than the secreted heavy chain, may be common to all teleost fish.

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.

Isolation of cDNA clones encoding T cell-specific membrane-associated proteins

Of 10 distinct cloned DNA copies of mRNAs expressed in T lymphocytes but not in B lymphocytes and associated with membrane-bound polysomes, one hybridizes to a region of the genome that has rearranged in a T-cell lymphoma and several T-cell hybridomas. These characteristics suggest that it encodes one chain of the elusive antigen receptor on the surface of T lymphocytes.

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.

Separation of lymphocyte subpopulations in carp Cyprinus carpio L. by monoclonal antibodies: immunohistochemical studies

Lymphoid cell populations in various organs of the carp Cyprinus carpio L. were investigated using a series of mouse monoclonal antibodies raised against carp thymocytes and carp serum Ig. Clones have been designated as Ig+T+, Ig+T- or Ig-T+ on the basis of the reactivity with thymocytes and serum Ig in the enzyme-linked immunosorbent assay (ELISA) screening. Their reaction to the lymphoid organs of carp was investigated on cryostat sections and cytocentrifuge slides using immunoperoxidase techniques. IG+T+ clones could be subdivided into those that stained reticular fibres around blood vessels in various organs (R+) and those that did not (R-). The former stained most thymocytes and most peripheral lymphocytes as well as plasma cells whereas the latter did not stain cortical thymocytes and some peripheral lymphocytes. IG+T- clones were negative for thymocytes but positive for plasma cells and a certain population of peripheral lymphocytes. Ig-T+ clones reacted similarly to Ig+T+R- clones. It is concluded that fish lymphoid cell populations can be distinguished based upon differences in cell surface and/or cytoplasmic determinants. The monoclonal antibodies described can be used for further structural analysis of the determinants and for functional separation of T- and B-like cells in the 'lower' vertebrates.

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.

Surface markers of lymphocytes in the snake, Spalerosophis diadema. I. Investigation of lymphocyte surface markers

A specific antiserum was raised in rabbits against thymocytes from snakes, Spalerosophis diadema, and was absorbed repeatedly with snake erythrocytes and kidney cells. In complement-dependent cytotoxicity assays, the absorbed anti-thymocyte serum (ATS) was, at any given dilution, cytotoxic to Sp. diadema thymocytes > peripheral blood lymphocytes (PBL) > spleen cells and could be titrated to a plateau defining a population of about 98% of thymocytes, 80% of PBL and 72% of spleen cells. Antiserum directed against snake immunoglobulins was obtained by injecting rabbits with gamma-globulins separated from snake serum by DEAE-cellulose filtration. the anti-gamma globulin serum was absorbed with snake erythrocytes, and in indirect membrane immunofluorescence stained no thymocytes while reacted with about 15% of PBL and 29% of spleen lymphocytes up to a 1:8 dilution. Fluorescence of positive cells was distributed in spots, patches or caps; cap formation could be inhibited by maintaining the immunofluorescence test at +4 degrees. In each of six separate experiments performed during spring, the percentage of lymphocytes which reacted with anti-snake gamma-globulin serum complemented the percentage of cells recognized by ATS. It was shown, furthermore, that about 3%, 8% and 21% of lymphocytes from thymus, peripheral blood and spleen, respectively, possess a receptor for 2-mercaptoethanol-insensitive antibody-sheep erythrocyte complexes. The results indicate that lymphocyte structural heterogeneity exists in reptiles.

Molecular properties of T-lymphoma immunoglobulin. II. Peptide composition of the heavy chain

In order to obtain structural information and to facilitate studies of the covalent structure of T-cell immunoglobulin, we have performed investigations of the peptide fragments of the heavy chain of this molecule, on a comparative basis, with heavy chains of serum immunoglobulins. T-cell immunoglobulin was isolated from 125I-labelled culture medium of monoclonal continuously cultured T-lymphoma cells by means of immunoadsorbents. Peptides were prepared from the purified 125I-labelled heavy chain by means of cleavage with cyanogen bromide or digestion with trypsin. We then resolved these peptides and compared them with those peptides derived from 131I-labelled murine mu, gamma and alpha chains separately and in mixed label experiments by means of polyacrylamide gel electrophoresis in sodium dodecyl sulfate containing buffers, 2 dimensional peptide mapping and ion exchange chromatography. The profiles of the radiolabelled peptides obtained from the T-lymphoma heavy chains were quite distinct from those of murine gamma chains but indicated a structural similarity to both mu and alpha chains, which share some common peptides. These results are consistent with the antigenic and physicochemical data available and suggest that T-cell immunoglobulin is a new isotype that shows similarities to IgA and IgM, but of which the precise nature of the constant region has yet to be delineated.

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.

Molecular properties of T lymphoma immunoglobulin. I. Serological and general physicochemical properties

Immunoglobulin (Ig) released into the medium by monoclonal continuously cultured murine T lymphoma cells of the lines WEHI-22 and WEHI-7 was isolated by serological precipitation or solid-phase immunoadsorption techniques. The intact immunoglobulin had an electrophoretic mobility on sodium dodecyl-sulphate (SDS) containing polyacrylamide gels comparable to that of IgG (mass 150,000). This mobility was significantly faster than that of '7S' IgM of murine B lymphocyte surfaces. The T lymphoma immunoglobulin consisted of a pair of heavy chains linked by disulphide bonds and light chains non-covalently bound to the heavy chains. The isolated heavy chains migrated slightly faster than the mu chains of MOPC 104E IgM. Some, but not all, antisera directed against mu chains of normal mouse serum IgM bound T lymphoma immunoglobulin apparently via a cross-reaction localized to the Fd fragment. These data indicate that immunoglobulin of T lymphoma cells and, presumably normal T lymphocytes, represents an immunoglobulin isotype which is distinct from those immunoglobulins found on the B cell surface.

Direct demonstration of murine thymus-dependent cell surface endogenous immunoglobin

Antisera raised in mammals to murine immunoglobulin (Ig) do not detect surface Ig on thymus-dependent (T) lymphoma cells as assessed by immunofluorescence analysis. In contrast, chicken antibodies, produced against the (Fab)2 fragment of normal mouse IgG and purified by binding to and elution from IgG-Sepharose 4B, give strong indirect fluorescence with murine T cells and cultured T lymphoma cells. The surface Ig caps, is shed, and reappears, indicating that it is of endogenous origin. Nonlymphoid tumor cells of various myeloid types do not bind this reagent, even though they bear avid Fc receptors. The capacity of chicken antibodies to bind to both bone-marrow-dependent and T cell lymphomas was abolished by adsorption with myeloma-derived kappa chains coupled to Sepharose. The kappa antigenic determinant recognized by the chicken antibodies may thus be different from that seen by mammalian antibodies, and the degree of exposure of Ig on the T lymphoma surface might also affect ease of detectability with these reagents. These data provide direct evidence that T lymphocytes and T lymphoma cells express and synthesize a surface Ig containing determinants that at least 'crossreact with bone-marrow-cell-derived kappa chains.

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.