Antigenic cross-reactions among immunoglobulin of diverse vertebrates (elasmobranchs to man) detected using xenoantisera

Cell markers and determinants in fish immunology

Despite the impressive increase in the cloning and expression of genes encoding fish immunoregulatory molecules, the knowledge on "in vivo" and "in vitro" functional immunology of the corresponding peptide products is still at an initial stage. This is partly due to the lacking of specific markers for immunoregulatory peptides, that represent an indispensible tool to dissect immune reactions and to trace the fate of cellular events downstream of the activation. In this review we summarise the available information on functional immune activities of some teleost species and discuss the obtained data in an evolutionary and applied context.

The antibody repertoire in evolution: chance, selection, and continuity

All jawed vertebrates contain the genetic elements essential for the function of the adaptive/combinatorial immune response, have diverse sets of natural antibodies resulting from segmental gene recombination, express comparable functional repertoires and can produce specific antibodies following appropriate immunization. Profound variability occurs in the third hypervariable (CDR3) segments of light and heavy chains even within antibodies of the same ostensible specificity. Germline VH and VL elements, as well as the joining (J) segments are highly conserved among the distinct vertebrate species. Conservation is particularly noted among the VH3-like sequences of all jawed vertebrates in the FR2 and FR3 segments, as well as in the FGXGT(R or K)L J-segment characteristic of light chains and TCRs and the WGXGT(uncharged)VT JH segments. Human VH3-53 and Vlambda6 family orthologs may be present over the entire range of vertebrates. Models of the three-dimensional structures of shark VH/VL combining sites indicate similarity in framework structure and comparable CDR usage to those of man. Although carcharhine shark VH regions show greater than 50% identity to the human VH germline prototype, searches of lower deuterostome and invertebrate databases fail to detect molecules with significant relatedness. Overall, antibodies of jawed vertebrates show tremendous individual diversity, but are constructed incorporating design features that arose with the evolutionary emergence of the jawed vertebrates and have been conserved through at least 450 million years of evolutionary time.

Immunoglobulin genetics of Ornithorhynchus anatinus (platypus) and Tachyglossus aculeatus (short-beaked echidna)

In this paper, we review data on the monotreme immune system focusing on the characterisation of lymphoid tissue and of antibody responses, as well the recent cloning of immunoglobulin genes. It is now known that monotremes utilise immunoglobulin isotypes that are structurally identical to those found in marsupials and eutherians, but which differ to those found in birds and reptiles. Monotremes utilise IgM, IgG, IgA and IgE. They do not use IgY. Their IgG and IgA constant regions contain three domains plus a hinge region. Preliminary analysis of monotreme heavy chain variable region diversity suggests that the platypus primarily uses a single VH clan, while the short-beaked echidna utilises at least 4 distinct VH families which segregate into all three mammalian VH clans. Phylogenetic analysis of the immunoglobulin heavy chain constant region gene sequences provides strong support for the Theria hypothesis. The constant region of IgM has proven to be a useful marker for estimating the time of divergence of mammalian lineages.

Development of an immunoassay to measure the humoral immune response of hybrid striped bass Morone chrysops x M. saxatilis

Hybrid striped bass (HSB) were immunized with bovine serum albumin (BSA) and the specific anti-BSA immunoglobulin (Ig) was affinity purified from the resulting serum by means of an agarose gel-BSA column. The native Ig had an apparent molecular size of 893 KDD, by size exclusion chromatography, and when examined by polyacrylamide gel electrophoresis (PAGE) under denaturing conditions, resolved to heavy (H) and light (L) chains of 76 and 27 KDD, respectively. Affinity purified native HSB Ig was used to immunize a goat which produced specific anti-HSB Ig antibody (Ab). Purified native HSB Ig was also used to produce two murine monoclonal antibodies (mAbs) with specific affinities for H and L chain moieties of the HSB Ig molecule. Both polyclonal and monoclonal antibodies could be used individually in an indirect enzyme-linked immunosorbent assay (ELISA) to measure specific anti-BSA Ig in HSB serum. These antibodies could also be used in combination to measure total Ig in a capture ELISA format. Using both assays, the kinetics of the humoral immune response of HSB was measured for 98 days following two injections of BSA.

Isolation and partial characterisation of immunoglobulin from southern bluefin tuna Thunnus maccoyii Castelnau

Specific and total serum immunoglobulins were extracted by immunoaffinity, mannan-binding protein and Protein A affinity chromatography from southern bluefin tuna (Thunnus maccoyii Castelnau) immunised with rabbit IgG, and from non-immunised southern bluefin tuna. SDS-PAGE in 10% reducing gels revealed two heavy chains with molecular weights of approximately 74.6 +/- 1.3 kDa and 71.2 +/- 0.9 kDa, and two light chains with molecular weights of approximately 29 +/- 1.2 kDa and 28 +/- 1.0 kDa. Under non-reducing, but denaturing, conditions in 4% and 5% SDS-PAGE gels, a high molecular weight and a low molecular weight fraction were demonstrated. By gel filtration using Sephacryl HR 300 a molecular weight of 845 kDa, consistent with a tetramer, was obtained for the high molecular weight fraction, and a molecular weight of 168 kDa, consistent with a monomer, was obtained for the low molecular weight fraction. The extinction coefficient at A280 for the purified immunoglobulin (Ig) was determined to be 1.24. Tuna a-rabbit IgG Ig was reactive with all non-reduced mammalian IgG antigens tested, suggesting that common conformational antigenic determinants were recognised.

Isolation and sequence of a cDNA coding for the heavy chain constant region of IgG from the Australian brushtail possum, Trichosurus vulpecula

A brushtail possum (Trichosurus vulpecula) mesenteric lymph node cDNA library was screened with a South American short-tailed opossum (Monodlelphis domestica) immunoglobulin gamma heavy chain constant region (Cgamma) probe, resulting in the isolation of a 1518 nucleotide cDNA clone. The sequence corresponds to exons 1-3 of Cgamma. The Australian marsupial (T. vulpeculla) sequence is 70% identical at the amino acid level with the American marsupial (M. domestica) sequence, but less similar to the eutherian mammals (45-50%). These data provide the opportunity to compare the evolution of IgG between orders of marsupials separated by at least 75 million years and confirm the appearance of IgG prior to the metatherian/eutherian divergence.

Primordial emergence of the recombination activating gene 1 (RAG1): sequence of the complete shark gene indicates homology to microbial integrases

The rearrangement of antibody and T-cell receptor gene segments is indispensable to the vertebrate immune response. All extant jawed vertebrates can rearrange these gene segments. This ability is conferred by the recombination activating genes I and II (RAG I and RAG II). To elucidate their origin and function, the cDNA encoding RAG I from a member of the most ancient class of extant gnathostomes, the Carcharhine sharks, was characterized. Homology domains identified within shark RAG I prompted sequence comparison analyses that suggested similarity of the RAG I and II genes, respectively, to the integrase family genes and integration host factor genes of the bacterial site-specific recombination system. Thus, the apparent explosive evolution (or "big bang") of the ancestral immune system may have been initiated by a transfer of microbial site-specific recombinases.

Humoral immune response in a marsupial Monodelphis domestica: anti-isotypic and anti-idiotypic responses detected by species-specific monoclonal anti-immunoglobulin reagents

We examined the humoral immune response of the laboratory opossum (Monodelphis domestica) as a model marsupial species. To evaluate antibody responses, IgM and IgG preparations were purified from the sera of naïve Monodelphis. These two immunoglobulin (Ig) preparations were used to generate specific murine monoclonal antibodies for use in ELISA-based serology. Individual Monodelphis were then immunized with a multideterminant protein antigen, a murine monoclonal antibody (Mab) IgG preparation designated Pab 405. In contrast with the primary IgM response of eutherian mammals, the primary response of Monodelphis to mouse IgG involved both IgG and IgM. The specificity of this anti-mouse IgG response appeared isotypic in nature, specifically, the immune sera recognized Ig determinants common to both Pab 405 and a control IgG Mab. Further, to evaluate the antibody responses to mouse IgG, immune sera were adsorbed against a control IgG Mab to remove the anti-isotypic reactivity. The adsorbed Monodelphis sera recognized idiotope specificities expressed on Pab 405. Based on an inhibition ELISA, the anti-idiotype (anti-Id) response recognized an idiotope on Pab 405 associated with its antigen combining site. These results demonstrate that Monodelphis respond to a multideterminant protein antigen such as murine IgG, similarly but not identically to eutherian mammals, and can serve as a useful marsupial model for additional comparative immunological studies.

Recognition molecules and immunoglobulin domains in invertebrates

We have used specific antibody probes to conserved antigenic motifs to identify and characterize immunoglobulin-related molecules in tunicates and a C-type lectin found in lamprey that is related to molecules found in tunicates and mammals. The tunicate immunoglobulin cross-reactive molecule (mu CRM) reacts with antibodies raised to shark IgM heavy chains. Intact tunicate mu CRM is a monomer of Ig light-chain-sized subunits and is oligoclonal by IEF. That this molecule is related to Ig is indicated both by immunochemical data and by peptide sequence homologies. The lamprey lectin is a large polymer (> 500,000 kDa) of 35-kDa and 60-kDa subunits. It appears to be related to C-type lectins as shown by peptide sequence homology and the requirement of Ca2+ for activity. Related molecules appear to be present in tunicates and mammals as shown by cross-reactivity of antibodies in Western blots with single bands from hemolymph and T-cell extracts.

Development of an immune system

Minimally, an immune response is an induced cellular and/or humoral defense mechanism specific for the challenging agent. The system is a cognitive one inasmuch as a second stimulus with the same antigen can specifically induce either an enhanced response (memory) or diminished response (tolerance). The cells responsible for the initial antigen-specific recognition in higher vertebrates are clonally restricted T and B lymphocytes. Accessory cells are necessary for the processing and presentation of antigen, and physiologic mediators (cytokines) are essential for proliferation, interaction, and regulation of the system. Although it now appears that the recombination mechanisms essential for the anticipatory immune response occurred late in the deuterostome stream leading to vertebrates, molecules required for cell adhesion and regulation are widely spread in phylogeny. Their emergence must have preceded the divergence between ancestral protostomes and deuterostomes. Genetic mechanisms underlying the generation of diversity in the light and heavy chains of antibodies of mammals may be quite distinct in primitive vertebrates, particularly elasmobranchs, the ancestors of which diverged from those of mammals more than 400 million years ago. Despite this, clonal selection of antigen receptors of lymphocytes is most probably universal within the vertebrates. There is no need to force induced recognition in protostomes (e.g. insects) or lower deuterostomes (e.g. echinoderms) into mammalian models of immunity.

Cell surface recognition and the immunoglobulin superfamily

Immunoglobulins serve as humoral recognition and effector molecules and as antigen-specific cell surface receptors on B and T cells. These molecules are constructed according to a characteristic domain pattern. Variable and constant domains diverged from one another early in vertebrate evolution, and they are joined by a "switch peptide" specified by the joining gene segments. Peptides specified by J-gene segments are strongly conserved in evolution in comparison among Ig light chains and T-cell receptors. Molecules less strongly related to Ig domains have been assembled into an Ig "superfamily" where the identities to classical IgC or V domains are < or = 20%. Among these are cell surface adhesion molecules, receptors for cytokines, and Fc receptors. Moreover, MHC antigens have an Ig-like membrane-proximal domain significantly related to IgC regions. We will analyze putative evolutionary relationships among canonical Igs and members of the Ig superfamily using highly conserved sequences from light and heavy chains of primitive vertebrates (e.g., the sandbar shark) as prototypes to ascertain similarities between Ig-related molecules of vertebrates and invertebrates.

Shared antigenic determinants of immunoglobulins in phylogeny and in comparison with T-cell receptors

1. Immunoglobulins are a complex multigene family of proteins specified by genes encoding variable (V), sometimes diversity (D), joining (J), and constant (C) domains. 2. Cross-reactions involving conformational determinants related to the VHa system of rabbits occur on heavy chains of vertebrate species ranging from elasmobranchs to man. 3. Serological markers characteristic of mu chains, the heavy chain of the IgM macroglobulins, occur on homologous heavy chains of species representing all vertebrate classes. 4. Serological markers characteristic of gamma type heavy chains, the major isotype in man, are restricted to the mammals, but are found on representatives of even the most primitive mammals, the egg-laying monotremes. 5. Variable region markers characteristic of lambda light chains are shared by light chains of shark and man. 6. Certain idiotypic markers defined by combining site V region sequences are broadly distributed in evolution. 7. Use of synthetic peptides as antigens and in epitope mapping show that amino acid sequences from the third framework region of the variable domain are broadly shared among light chain in phylogeny and between light chains and T-cell receptor beta chains. 8. The "switch peptides" linking the V and C domains of light chains and T-cell receptors, specified by the C-terminal portion of the J segment and the N-terminus of the constant region, are exposed in the three-dimensional structure of immunoglobulin or Tcrs, show striking homology, and form broadly shared antigenic determinants characteristic of immunoglobulins. 9. Although the multigene nature of the immunoglobulins and the complexity of antigenic determinants expressed by these large proteins renders comparison among molecules difficult, serum immunoglobulins and the closely related T-cell receptors express numerous shared determinants defined on the basis of amino acid sequence homology and three-dimensional conformations.

Antibody production in sharks and humans: a role for natural antibodies

Although gene segments specifying Igs of all vertebrates show clear homology, their arrangements differ markedly, thereby suggesting that the mechanisms for the generation of diversity and for the regulation of gene expression may be quite distinct. In the sandbar shark, light chain gene segments are distributed as apparently independent clusters consisting of V, J, and C elements that require rearrangement for expression. The usual distance between V and C in the clusters is 3 kb but larger clusters occur. The V, J, and C elements are clearly homologous to those of human lambda chains. Shark Igs resemble mammalian IgM in structure and gene similarity. IgM may comprise as much as 50% of serum proteins in the shark. By contrast, IgM in humans comprises less than 5%. Human autoantibodies usually are IgM. These show little dependence on thymic function for expression and tend to increase with age. We have carried out a study of the capacity of Igs of unimmunized sharks and people (normals and patients suffering from autoimmune diseases) to react against a panel of antigens, including those usually considered autoantibodies, such as thyroglobulin and single-stranded DNA. Sharks and humans possess IgM antibodies that react with thyroglobulin and ssDNA. Affinity-purified natural shark antibodies to thyroglobulin or ssDNA constitute small fractions of total IgM. They illustrate extensive cross-reactivity comparable to that shown by polyspecific IgM autoantibodies produced by human B cells (CD5+) that appear early in ontogeny.