Serial Llama Immunization with Various SARS-CoV-2 RBD Variants Induces Broad Spectrum Virus-Neutralizing Nanobodies

The emergence of SARS-CoV-2 mutant variants has posed a significant challenge to both the prevention and treatment of COVID-19 with anti-coronaviral neutralizing antibodies. The latest viral variants demonstrate pronounced resistance to the vast majority of human monoclonal antibodies raised against the ancestral Wuhan variant. Less is known about the susceptibility of the evolved virus to camelid nanobodies developed at the start of the pandemic. In this study, we compared nanobody repertoires raised in the same llama after immunization with Wuhan's RBD variant and after subsequent serial immunization with a variety of RBD variants, including that of SARS-CoV-1. We show that initial immunization induced highly potent nanobodies, which efficiently protected Syrian hamsters from infection with the ancestral Wuhan virus. These nanobodies, however, mostly lacked the activity against SARS-CoV-2 omicron-pseudotyped viruses. In contrast, serial immunization with different RBD variants resulted in the generation of nanobodies demonstrating a higher degree of somatic mutagenesis and a broad range of neutralization. Four nanobodies recognizing distinct epitopes were shown to potently neutralize a spectrum of omicron variants, including those of the XBB sublineage. Our data show that nanobodies broadly neutralizing SARS-CoV-2 variants may be readily induced by a serial variant RBD immunization.

The Search for Single-Domain Antibodies Interacting with the Receptor-Binding Domain of SARS-CoV-2 Surface Protein

We performed a search for nanoantibodies that specifically interact with the receptor-binding domain (RBD) of the SARS-CoV-2 surface protein. The specificity of single-domain antibodies from the blood sera of a llama immunized with RBD of SARS-CoV-2 surface protein S (variant B.1.1.7 (Alpha)) was analyzed by ELISA. Recombinant trimers of the SARS-CoV-2 spike protein were used as antigens. In this work, a set of single-domain antibodies was obtained that specifically bind to the RBD of the SARS-CoV-2 virus.

Isolation of a panel of ultra-potent human antibodies neutralizing SARS-CoV-2 and viral variants of concern

In the absence of virus-targeting small-molecule drugs approved for the treatment and prevention of COVID-19, broadening the repertoire of potent SARS-CoV-2-neutralizing antibodies represents an important area of research in response to the ongoing pandemic. Systematic analysis of such antibodies and their combinations can be particularly instrumental for identification of candidates that may prove resistant to the emerging viral escape variants. Here, we isolated a panel of 23 RBD-specific human monoclonal antibodies from the B cells of convalescent patients. A surprisingly large proportion of such antibodies displayed potent virus-neutralizing activity both in vitro and in vivo. Four of the isolated nAbs can be categorized as ultrapotent with an apparent IC100 below 16 ng/mL. We show that individual nAbs as well as dual combinations thereof retain activity against currently circulating SARS-CoV-2 variants of concern (such as B.1.1.7, B.1.351, B.1.617, and C.37), as well as against other viral variants. When used as a prophylactics or therapeutics, these nAbs could potently suppress viral replication and prevent lung pathology in SARS-CoV-2-infected hamsters. Our data contribute to the rational development of oligoclonal therapeutic nAb cocktails mitigating the risk of SARS-CoV-2 escape.

Diversity of Immunoglobulin Light Chain Genes in Non-Teleost Ray-Finned Fish Uncovers IgL Subdivision into Five Ancient Isotypes

The aim of this study was to fill important gaps in the evolutionary history of immunoglobulins by examining the structure and diversity of IgL genes in non-teleost ray-finned fish. First, based on the bioinformatic analysis of recent transcriptomic and genomic resources, we experimentally characterized the IgL genes in the chondrostean fish, Acipenser ruthenus (sterlet). We show that this species has three loci encoding IgL kappa-like chains with a translocon-type gene organization and a single VJC cluster, encoding homogeneous lambda-like light chain. In addition, sterlet possesses sigma-like VL and J-CL genes, which are transcribed separately and both encode protein products with cleavable leader peptides. The Acipenseriformes IgL dataset was extended by the sequences mined in the databases of species belonging to other non-teleost lineages of ray-finned fish: Holostei and Polypteriformes. Inclusion of these new data into phylogenetic analysis showed a clear subdivision of IgL chains into five groups. The isotype described previously as the teleostean IgL lambda turned out to be a kappa and lambda chain paralog that emerged before the radiation of ray-finned fish. We designate this isotype as lambda-2. The phylogeny also showed that sigma-2 IgL chains initially regarded as specific for cartilaginous fish are present in holosteans, polypterids, and even in turtles. We conclude that there were five ancient IgL isotypes, which evolved differentially in various lineages of jawed vertebrates.

[Impact of neutron radiation on the viability of tumor cells cultured in the presence of boron-10 isotope]

OBJECTIVE

To investigate the impact of a neutron beam formed with the accelerator-based epithermal neutron source designed at the G.I. Budker Institute of Nuclear Physics (INP) on the viability of human and animal tumor cells cultured in the presence of boron-10 isotope.

MATERIAL AND METHODS

Human U251 and T98G glioma cells and Chinese hamster CHO-K1 and V-79 cells were incubated at various concentrations in the culture medium containing 10B-enriched L-boronophenylalanine. The cells were irradiated with a neuron beam using the accelerator-based epithermal neuron source. A clonogenic assay was used to evaluate the viability of the irradiated cells. The absorbed doses obtained from elastic scattering of fast neutrons by substance nuclei and the doses obtained from boron neutron capture were calculated using the NMS code. The absorbed doses of gamma-radiation were measured with a mixed radiation dosimeter.

RESULTS

The viability of boron-containing and intact human U251 and T98G cell lines and Chinese hamster CHO-K1 and V-79 cells was analyzed after neutron beam radiation. Irradiation of all four cell lines were cultured in the presence of 10B was shown to reduce their colony-forming capacity compared with the control. Elevated boron levels in the culture medium resulted in a significant decrease in the proportion of survived cells. Radiation had the most pronounced impact on the proliferative capacity of the human U251 glioma cell lines.

CONCLUSION

The cultures of human tumor cells and mammalian cells demonstrated that the neutron beam formed with the accelerator-based epithermal neutron source designed at the INP, was effective in reducing the viability of tumor cells in the presence of 10B.

Peptide-MHC multimer-based monitoring of CD8 T-cells in HIV-1 infection and AIDS vaccine development

The use of MHC multimers allows precise and direct detecting and analyzing of antigen-specific T-cell populations and provides new opportunities to characterize T-cell responses in humans and animals. MHC-multimers enable us to enumerate specific T-cells targeting to viral, tumor and vaccine antigens with exceptional sensitivity and specificity. In the field of HIV/SIV immunology, this technique provides valuable information about the frequencies of HIV- and SIV-specific CD8(+) cytotoxic T lymphocytes (CTLs) in different tissues and sites of infection, AIDS progression, and pathogenesis. Peptide-MHC multimer technology remains a very sensitive tool in detecting virus-specific T -cells for evaluation of the immunogenicity of vaccines against HIV-1 in preclinical trials. Moreover, it helps to understand how immune responses are formed following vaccination in the dynamics from priming point until T-cell memory is matured. Here we review a diversity of peptide-MHC class I multimer applications for fundamental immunological studies in different aspects of HIV/SIV infection and vaccine development.

[Expression of human B-cell specific receptor FCRL1 in normal individuals and in patients with autoimmune diseases]

The comparative analysis of expression level of FCRL1 gene encoding human B-cell surface receptor in healthy individuals and patients with autoimmune diseases was carried out. For the expression estimation we used results of DNA dot-hybridization on the membranes, containing cDNA samples from subpopulations of blood cells of patients with autoimmune diseases. The quantitative estimation of hybridization signals showed that expression level of FCRL1 gene in peripheral blood B-lymphocytes was significantly higher in patients with a multiple sclerosis, lupus anticoagulans, Takayasu's arteritis and also in von Willebrand disease than in healthy individuals. FCRL1-specific monoclonal and polyclonal antibodies were raised. They were proven to detect FCRL1 in Western blotting, immunohistochemistry and flow cytometry. It was found that FCRL1 is expressed on the surface of CD19+ mature B-cells. In tonsil FCRL1-positive cells were located in crypt area: in mantle zone of secondary lymphoid follicles and among cells of lymphoepithelium. FCRL1-positive cells were also found in B-cell follicles of the spleen.

Differential expression of FCRLA in naïve and activated mouse B cells

FCRLA is an intracellular B cell protein that belongs to the FcR-like family. Using newly generated FCRLA-specific antibodies, we studied the constitutive expression pattern of mouse FCRLA and monitored changes during an immune response and following in vitro B cell activation. All B cell subpopulations examined expressed FCRLA. However, the level of FCRLA expression is determined by the stage of B cell differentiation. Low expression of FCRLA is characteristic of naïve follicular and marginal zone B cells. High expression was detected in a small fraction of activated B cells scattered along migratory pathways in the lymphoid tissues. FCRLA-bright cells could be subdivided into two subpopulations, with high and low/undetectable level of intracellular immunoglobulins, which phenotypically resemble either plasma or memory B cells. High expression of FCRLA in subset(s) of terminally differentiated B-cells suggests that, being an ER protein, FCRLA may participate in the regulation of immunoglobulin assembly and secretion.

[MHC-multimers and their application in studies of antiviral immune response]

Application of main histocompatibility complex tetrames (MHC-tetramers) for antigen specific T-cells detection and analysis coupled with flow cytometry opened new opportunities for T-cell response analysis. MHC-multimers allow the detection of T-cells against viral, cancer and vaccine antigens with exceptional sensitivity and specificity. This approach has become the "gold standard" for quantative analysis of T-cell immune response. Certain aspects of analysis using MHC-tetramer are examined, and importance of this approach in T-cell response efficacy evaluation in anti-HIV vaccine trials as well as in HIV positive patients are discussed.

FCRLA is a resident endoplasmic reticulum protein that associates with intracellular Igs, IgM, IgG and IgA

Fc receptor-like A (FCRLA) is an unusual member of the extended Fc receptor family. FCRLA has homology to receptors for the Fc portion of Ig (FCR) and to other FCRL proteins. However, unlike these other family representatives, which are typically transmembrane receptors with extracellular ligand-binding domains, FCRLA has no predicted transmembrane domain or N-linked glycosylation sites and is an intracellular protein. We show by confocal microscopy and biochemical assays that FCRLA is a soluble resident endoplasmic reticulum (ER) protein, but it does not possess the amino acid sequence KDEL as an ER retention motif in its C-terminus. Using a series of deletion mutants, we found that its ER retention is most likely mediated by the amino terminal partial Ig-like domain. We have identified ER-localized Ig as the FCRLA ligand. FCRLA is unique among the large family of Fc receptors, in that it is capable of associating with multiple Ig isotypes, IgM, IgG and IgA. Among hemopoietic cells, FCRLA expression is restricted to the B lineage and is most abundant in germinal center B lymphocytes. The studies reported here demonstrate that FCRLA is more broadly expressed among human B lineage cells than originally reported; it is found at significant levels in resting blood B cells and at varying levels in all B-cell subsets in tonsil.

The amphibians Xenopus laevis and Silurana tropicalis possess a family of activating KIR-related Immunoglobulin-like receptors

In this study, we searched the amphibian species Xenopus laevis and Silurana (Xenopus) tropicalis for the presence of genes homologous to mammalian KIRs and avian CHIRs (KRIR family). By experimental and computational procedures, we identified four related ILR (Ig-like Receptors) genes in S. tropicalis and three in X. laevis. ILRs encode type I transmembrane receptors with 3-4 Ig-like extracellular domains. All predicted ILR proteins appear to be activating receptors. ILRs have a broad expression pattern, the gene transcripts were found in both lymphoid and non-lymphoid tissues. Phylogenetic analysis shows that the amphibian KRIR family receptors evolved independently from their mammalian and avian counterparts. The only conserved structural element of tetrapod KRIRs is the NxxR motif-containing transmembrane domain that facilitates association with FcRgamma subunit. Our findings suggest that if KRIRs of various vertebrates have any common function at all, such a function is activating rather than inhibitory.

The Xenopus FcR family demonstrates continually high diversification of paired receptors in vertebrate evolution

BACKGROUND

Recent studies have revealed an unexpected diversity of domain architecture among FcR-like receptors that presumably fulfill regulatory functions in the immune system. Different species of mammals, as well as chicken and catfish have been found to possess strikingly different sets of these receptors. To better understand the evolutionary history of paired receptors, we extended the study of FcR-like genes in amphibian representatives Xenopus tropicalis and Xenopus laevis.

RESULTS

The diploid genome of X. tropicalis contains at least 75 genes encoding paired FcR-related receptors designated XFLs. The allotetraploid X. laevis displays many similar genes primarily expressed in lymphoid tissues. Up to 35 domain architectures generated by combinatorial joining of six Ig-domain subtypes and two subtypes of the transmembrane regions were found in XFLs. None of these variants are shared by FcR-related proteins from other studied species. Putative activating XFLs associate with the FcRgamma subunit, and their transmembrane domains are highly similar to those of activating mammalian KIR-related receptors. This argues in favor of a common origin for the FcR and the KIR families. Phylogenetic analysis shows that the entire repertoires of the Xenopus and mammalian FcR-related proteins have emerged after the amphibian-amniotes split.

CONCLUSION

FcR- and KIR-related receptors evolved through continual species-specific diversification, most likely by extensive domain shuffling and birth-and-death processes. This mode of evolution raises the possibility that the ancestral function of these paired receptors was a direct interaction with pathogens and that many physiological functions found in the mammalian receptors were secondary acquisitions or specializations.

Natural human gene correction by small extracellular genomic DNA fragments

Classical gene targeting employs natural homologous recombination for a gene correction using a specially designed and artificially delivered DNA construct but the method is very inefficient. On the other hand, small DNA fragments in the form of tiny chromatin-like particles naturally present in blood plasma can spontaneously penetrate into human cells and cell nuclei. We hypothesized that these natural DNA nanoparticles with recombinagenic free ends might be effective agents for gene replacement therapy. We demonstrate that a mixture of small fragments of total human chromatin from non-mutant cells added to a culture medium without transfection agents efficiently repaired a 47 base pair deletion in the CASP3 gene in 30% of treated human MCF7 breast cancer cells, as shown by restoration of caspase-3 apoptotic function and CASP3 DNA and mRNA structure. Such an innate gene replacement mechanism might function naturally in an organism using its own apoptotic DNA fragments. This mechanism might enable human cancer cell phenotype normalization in the presence of excess normal cells.

Generation and Characterization of Monoclonal Antibodies Specific for Human FCRLA

FCRLA is a recently identified intracellular protein structurally related to the classic Fc receptors and expressed primarily in the germinal centers of B cells. We generated six monoclonal antibodies (MAbs) specific to the human protein. The MAbs recognize three different epitopes, which were shown to be localized on the D3 domain of the FCRLA molecule. The clones M101 and M616 were demonstrated to be applicable in various immunochemical analyses, such as immunoblotting, immunohistochemistry, and immunoprecipitation. In addition, this pair of antibodies was used for development of a sandwich version of ELISA to quantitatively detect FCRLA in cell lysates. Using these MAbs, we studied FCRLA expression in a panel of human B cell lines, such as Raji, Daudi, Bjab, BL-2, RPMI 1788, RPMI 8226, IM-9, and SKW6.4. It was found that all these lines, except RPMI 8226, produce FCRLA but may vary in the proportion of FCRLA-positive cells. The MAbs we established can be a useful tool to investigate the functional role of FCRLA and its applicability as a B cell development and malignant transformation marker.

[Expression patterns of the human and mouse IFGP family genes]

The IFGP family is a recently identified group of human and mouse genes structurally related to the genes of leukocyte Fc-receptors. In this study we compared expression patterns of six human and four mouse IFGP genes. With the exception of mouse IFGP2, the genes of the family were found to be predominantly expressed in haemopoietic cells. Expression of human IFGP1-IFGP5 and mouse IFGP3 was B cell-specific. Mouse IFGP1 transcripts were mainly found in B cells, but this gene may be either expressed by nonlymphoid cells. Expression of the human IFGP6 was detected in CD8+ T cells and NK cells. We further demonstrated that alternative splicing of human IFGP1 and IFGP6 mRNA may generate transcripts coding for the previously unknown isoforms. The novel IFGP1 isoform lacks transmembrane domain, whereas the IFGP6 isoform has altered cytoplasmic tail. The data obtained indicate that the receptors of family may contribute to the regulation of development and/or functions of three effector types of lymphocytes, namely B cells, CD8 T cells and NK cells.

Cloning and characterization of the human FCRL2 gene

We report cloning and characterization of FCRL2, a novel human gene that belongs to the FcR family. The gene is closely linked and structurally similar to the recently identified FCRL/FREB/FcRX gene. The encoded protein is composed of three Ig-like domains and a C-terminal mucin-like domain containing a conserved alpha-helical motif with dileucine signals. Intraexonic splicing may generate two alternative transcripts, coding for isoforms with the third and fourth domains replaced by entirely different amino acid sequences. Like FCRL, the full-length isoform of FCRL2 is expressed intracellularly in transfected 293T cells. Expression analysis revealed FCRL2 mRNA only in placenta. The gene transcripts were not detected in lymphoid tissues or in the main leukocyte subsets isolated from peripheral blood. However, we found that FCRL2 is differentially expressed by transformed B cell lines. Of interest is also the finding that the gene expression may be up-regulated in the progression of melanocytic tumors.

Expression pattern of FCRL (FREB, FcRX) in normal and neoplastic human B cells

FCRL (also known as FREB and FcRX) is a recently described member of the family of Fc receptors for immunoglobulin G (IgG). In the present study we analysed its expression in normal and neoplastic lymphoid tissue using immunohistochemical techniques. FCRL was preferentially expressed in a proportion of germinal centre cells and, more weakly, in mantle zone B cells. In addition, strong labelling was observed in marginal zone B cells in the spleen, representing one of the few markers for this cell type. The majority of cases of small B-cell lymphoma, diffuse large B-cell lymphoma and lymphocyte predominance Hodgkin's disease were positive for FCRL. However, the number of positive cells varied widely, and in consequence we could not define a cut-off that distinguished subsets of diffuse large B-cell lymphoma. Our results also showed that FCRL tended to be negative in T-cell-rich B-cell lymphoma and in classical Hodgkin's disease. FCRL may therefore represent a novel marker for normal B cells (e.g. splenic marginal zone cells) and may also be useful as a potential marker of B-cell neoplasms.

Identification of CD16-2, a novel mouse receptor homologous to CD16/Fc gamma RIII

It is believed that mouse Fc gamma RIII arose by an evolutionarily recent recombination, which brought together the extracellular domains from Fc gamma RII with the transmembrane/cytoplasmic region from the ancestor Fc gamma RIII. Here, we report identification of a mouse gene encoding a transmembrane receptor that may be regarded as the true ortholog of nonrodent CD16/Fc gamma RIII. Designated CD16-2, the novel protein is highly similar to human Fc gamma RIIIA in the signal peptide (60% identical residues), and in the extracellular domains (65%). Although the similarity between the two proteins is less conspicuous in the transmembrane/cytoplasmic region (54%), it is higher than between human Fc gamma RIIIA and mouse Fc gamma RIII (44%). However, the conserved transmembrane motif LFAVDTGL shared by rodent and human Fc gamma RIII and Fc epsilon RI has two replacements in CD16-2. The CD16-2 gene is tightly linked to the Fc gamma RIII and Fc gamma RII genes and consists of five exons. Northern blot analysis revealed that CD16-2 is expressed in peripheral blood leukocytes, as well as in spleen, thymus, colon and intestine. RT-PCR showed prominent expression in macrophage cell line J774. Based on sequence comparisons, it is suggested that the modern repertoire of the mammalian low affinity Fc receptors has resulted from repetitive duplications and/or recombinations of three ancestral genes.

A family of highly diverse human and mouse genes structurally links leukocyte FcR, gp42 and PECAM-1

A group of genes encoding proteins structurally related to the leukocyte Fc receptors (FcRs) and termed the IFGP family was identified in human and mouse. Sequences of four human and two mouse cDNAs predict proteins differing by domain composition. One of the mouse cDNAs encodes a secreted protein, which, in addition to four immunoglobulin (Ig)-like domains, contains a scavenger receptor superfamily-related domain at the C-terminus. The other cDNAs code for the type I transmembrane proteins with the extracellular parts comprised of one to six Ig-like domains. Five homologous types of the Ig-like domains were defined and each protein was found to have a unique combination of the domain types. The cytoplasmic tails of the transmembrane proteins show different patterns of the tyrosine-based signal motifs. While the human IFGP members appear to be B-cell antigens, the mouse genes have a broader tissue distribution with predominant expression in brain. Sequence comparisons revealed that the IFGP family may be regarded as a phylogenetic link joining the leukocyte FcRs with the rat NK cell-specific gp42 antigen and platelet endothelial cell adhesion molecule-1 (PECAM-1), two mammalian leukocyte receptors whose close relatives were not found previously. It is suggested that FcRs, the IFGP proteins and gp42 have arisen by a series of duplications from a common ancestor receptor comprised of five Ig-like domains. The organization of the human genes shows that the IFGP family evolved through differential gain and loss of exons due to recombination and/or mutation accumulation in the duplicated copies.

FCRL, a novel member of the leukocyte Fc receptor family possesses unique structural features

A novel conserved member of the leukocyte Fc receptor (FcR) family was identified in human and mouse. The presumably secreted protein, designated FCRL (FcR-like) is comprised of four domains. The three N-terminal domains are related to the extracellular region of FcgammaRI, with the second (35-37% residue identity) and the third (46-52%) domains showing highest similarity. The C-terminal domain is a unique sequence enriched with proline residues. In humans, alternative transcripts for six FCRL isoforms were revealed. Spleen and tonsils were found to be the major sources of FCRL mRNA in human tissues. Western blotting of tonsil cell lysate using FCRL-specific antibodies recognized a 44-kDa protein produced as a monomer containing free sulfhydryl groups. The monomer, however, was able to form disulfide-linked homo-oligomer upon oxidation. In COS-7 cells transiently transfected with two human FCRL isoforms, both resided intracellularly. Immunohistochemical staining of tonsil sections demonstrated the FCRL expression in germinal centers, suggesting that the protein may be implicated in germinal center-specific stages of B cell development. The phylogenetic analysis of the FCRL relationships with the leukocyte FcR supports a view that the three-domain structure was primordial in the evolution of the family.

Cloning of a CXCR4 homolog in chondrostean fish and characterization of the CXCR4-specific structural features

The chemokine receptor CXCR4 and its ligand SDF-1 are essential components of hematopoiesis, organogenesis and immunomodulation in mammalian species. We cloned a cDNA encoding CXCR4 homolog of sterlet (Acipenser ruthenus), a representative of chondrostean fishes. The deduced amino acid sequence of sterlet CXCR4 is almost equally distant from mammalian and teleost CXCR4 (66-68% identical residues). Percent identity with the other chemokine receptors varies in the 30-35% range. The CXCR4 sequences from the three phylogenetically diverged lineages were compared with the sequences of the other chemokine receptors to determine the CXCR4-specific structural elements that were conserved during vertebrate evolution. The characteristic residues and/or motifs are located predominantly in the intracellular and extracellular regions and in the third, fourth and fifth transmembrane domains. The data presented may be helpful for structure-function analysis of the CXCR4 ligand binding and signal transduction.

CD3epsilon homologues in the chondrostean fish Acipenser ruthenus

CD3epsilon is an essential component of the T-cell receptor (TCR) complex for antigen. We report here molecular cloning and characterization of cDNAs encoding the CD3epsilon homologues in sterlet (Acipenser ruthenus), a representative of primitive chondrostean fishes. Sequence analysis of the cDNA clones demonstrated unexpectedly high CD3epsilon gene heterogeneity in this species. While some cDNAs encoded proteins with the structure typical of mammalian CD3epsilon, others coded for proteins lacking the membrane-proximal half of the extracellular domain. Two cDNAs contained in-frame stop codons in the region encoding the cytoplasmic domain. Based on genomic blot analysis and RT-PCR typing of individual spleen RNAs, we suggest that sterlet may possess two highly polymorphic CD3epsilon loci, of which one can produce alternatively spliced transcripts. The structural elements shown to be functionally important in the mammalian CD3epsilon are strongly conserved in the sterlet CD3epsilon. The cytoplasmic region contains an immunoreceptor tyrosine-based activation motif (ITAM) with YEPI and YSGL tyrosine-containing sequences that are characteristic of only this TCR subunit. The pattern of sequence conservation indicates also that strong selection pressure was imposed on a motif VYYW at the C-end of the transmembrane domain and on a CD3epsilon-specific proline-rich motif RXPPVP juxtaposed to the N-terminus of the ITAM. Weak similarity of the sterlet CD3epsilon with the chicken and Xenopus CD3gamma/delta indicates that these two TCR subunits diverged before radiation of bony fishes and tetrapods. While the role of CD3epsilon heterogeneity in sterlet remains to be elucidated, the data obtained show that the basic mechanisms of TCR signaling have ancient evolutionary origin.

Identification of an IL-8 homolog in lamprey (Lampetra fluviatilis): early evolutionary divergence of chemokines

Subtractive hybridization was used to study river lamprey (Lampetra fluviatilis) leukocyte-specific cDNA. A clone representing the most abundant component (12%) of the leukocyte library subtracted with liver cDNA was isolated and characterized. The cDNA encodes a presumably secreted polypeptide of 101 residues. The 3' untranslated region of the cDNA contains motifs characteristic of the transiently expressing genes. Comparison of the deduced amino acid sequence with known protein sequences revealed its homology to the members of the chemokine superfamily. Designated as LFCA-1, the lamprey protein contains four conserved cysteines, of which the first two are separated by a residue, and a number of other CXC family characteristic residues. LFCA-1 has the highest similarity to the chicken EMF-1 (40%) and to the mammalian IL-8 (32-33%). However, it lacks the ELR motif essential for the function of the mammalian IL-8-related chemokines. Based on the phylogenetic analysis of the LFCA-1 relationship to the higher vertebrate chemokines, it is concluded that the evolutionary origin of the chemokine superfamily is ancient, and that the divergence of the CXC and CC families most likely occurred at the time or before the first vertebrates emerged.

Expression of immunoglobulin kappa and lambda chains in mink

The ratio of kappa and lambda chains of immunoglobulins varies significantly from one species to another. It has previously been thought that lambda was only type expressed in mink. We tested mink immunoglobulin light chains using two monoclonal antibodies G80 and G88. It has been shown that G80 and G88 specifically recognize two antigenically different subpopulations of the light chains. Immunochemical analysis of these subpopulations separated by affinity chromatography suggested that they represent lambda and kappa types of light chains, respectively. Screening of a mink cDNA library with monoclonal antibody G88 resulted in the isolation of clone pIGK-1 containing kappa chain-encoding sequence. The cDNA insert of pIGK-1 included most of the V segment, as well as the J, C and 3' untranslated sequences. Mink V kappa sequence shown the highest homology with the human V kappa II subgroup genes (76-79%). Mink C kappa sequence was 53-63% homologous to C kappa of other species. The striking feature of mink C kappa chain is the presence of glutamine in the C-terminal position. Southern blot analysis suggested that mink haploid genome has one C kappa gene and multiple V kappa genes. The kappa:lambda chain ratio in the 12 minks studied was, on the average, 46:54. The same ratio was observed for the kappa- and lambda-producing cells in the mesenteric lymph nodes. The five previously identified mink light chain allotypes were assigned to the lambda chains, thereby confirming that lambda chains in this species are additionally subdivided into several subtypes.

Monoclonal antibodies against heavy and light chains of domestic mink IgG

A panel of 26 monoclonal antibodies (MAbs) specific to mink IgG was produced and analyzed by ELISA, immunodiffusion assay (IDA) and immunoblotting assay. All the raised MAbs were directed against the isotypic IgG epitopes. Immunoblotting assay demonstrated that 11 MAbs reacted only with the Fc-fragments of IgG and 7 only with the light chains. Four antibodies bound to the Fab-containing fragments and failed to react with the Fc-fragments or isolated L-chains. Three MAbs did not react with IgG in IDA. Based on the results of IDA and cross-blocking assays, the MAbs were divided into 10 groups, with the MAbs of each group recognizing the same epitope. In IDA some MAbs were able to react with the epitopes which are common to the IgGs of some other representatives of Mustelidae family and also to some mammalian species remote from mink (dog, horse, pig, fox and rabbit).

Mink-mouse hybridomas that secrete mink immunoglobulin G

Optimum conditions were established to obtain mink-mouse interspecific hybridomas secreting mink IgG in fusions of mouse myelomas with mink immune spleen cells. Minks were immunized with allogeneic IgG, and the spleen cells were fused with three mouse myeloma lines P3-X63-Ag8.653, NSO and Sp2/0-Ag14. Of these, P3-X63-Ag8.653 and NSO were found to be the best fusion partners giving the highest yield of hybrid clones and number of IgG secreting clones. Cloning of mink-mouse hybridomas was efficient when BALB/c nu/nu peritoneal and spleen cells were used as feeders. The ten clonal lines produced secreted intact mink IgG molecules as shown by SDS-PAGE and subsequent immunoblotting. The secretion level of IgG ranged from 5 to 200 ng/ml in the clonal lines.