Teleost fish mount complex clonal IgM and IgT responses in spleen upon systemic viral infection

Abstract

Upon infection, B-lymphocytes expressing antibodies specific for the intruding pathogen develop clonal responses triggered by pathogen recognition via the B-cell receptor. The constant region of antibodies produced by such responding clones dictates their functional properties. In teleost fish, the clonal structure of B-cell responses and the respective contribution of the three isotypes IgM, IgD and IgT remain unknown. The expression of IgM and IgT are mutually exclusive, leading to the existence of two B-cell subsets expressing either both IgM and IgD or only IgT. Here, we undertook a comprehensive analysis of the variable heavy chain (VH) domain repertoires of the IgM, IgD and IgT in spleen of homozygous isogenic rainbow trout (Onchorhynchus mykiss) before, and after challenge with a rhabdovirus, the Viral Hemorrhagic Septicemia Virus (VHSV), using CDR3-length spectratyping and pyrosequencing of immunoglobulin (Ig) transcripts. In healthy fish, we observed distinct repertoires for IgM, IgD and IgT, respectively, with a few amplified m and t junctions, suggesting the presence of IgM-and IgT-secreting cells in the spleen. In infected animals, we detected complex and highly diverse IgM responses involving all VH subgroups, and dominated by a few large public and private clones. A lower number of robust clonal responses involving only a few VH were detected for the mucosal IgT, indicating that both IgM + and IgT + spleen B cells responded to systemic infection but at different degrees. In contrast, the IgD response to the infection was faint. Although fish IgD and IgT present different structural features and evolutionary origin compared to mammalian IgD and IgA, respectively, their implication in the B-cell response evokes these mouse and human counterparts. Thus, it appears that the general properties of antibody responses were already in place in common ancestors of fish and mammals, and were globally conserved during evolution with possible functional convergences.

The pyloric caeca area is a major site for IgM+ and IgT+ B cell recruitment in response to oral vaccination in rainbow trout

“…As more data become available, it seems probable that IgT also plays a role in non-mucosal defense as demonstrated by the fact that IgT expansion in the spleen of virus-infected animals has been observed, revealing that these spleen IgT + cells contribute to increase IgT plasma levels [30]. Our results suggest that both IgM and IgT together respond at an early stage upon mucosal immunization.…”

DNA vaccination against a fish rhabdovirus promotes an early chemokine-related recruitment of B cells to the muscle

“…On the other hand, we detected CD4 transcripts but we could not analyse the presence of CD4 + cells through flow cytometry because there is no antibody available to date. Interestingly, our results reveal a novel non-mucosal role for IgT + cells, as also observed by Castro et al [20]. In any case, more work should be performed to establish the role of all these cells mobilized to the muscle in the immunity to DNA vaccination.…”

“…Although it seems that IgT + cells play an important role in mucosal responses [19], recent evidence implicates IgT in systemic responses as well [20]. Our results demonstrate that both IgM + and IgT + cells are recruited to the muscle upon DNA vaccination, in contrast to reports in mammals, in which macrophages, T cells and neutrophils are the predominant recruited cell types [21,22].…”

“…To verify that IgM and IgT transcripts quantified were not sterile Ig transcripts, PCRs were performed using a forward primer specific for a subgroup or a set of IGHV genes in combination with a reverse primer C or C specific for IGHM or IGHT genes, in a pooled cDNA sample from each experimental group as previously described [20] ( Supplementary Fig. 1).…”

Virus genomes and virus-host interactions in aquaculture animals

“…After such viruses pass the first line of defense and enter the host cell, the infected cell immediately initiates a series of innate immune responses; these include an inflammatory response, complement system activation, interferon production, induction of antiviral reactions, cell apoptosis, and innate immune cell responses from macrophages, neutrophils, dendritic cells, natural killer and other immune cells that prevent viral replication and inhibit virus propagation [153,156,167]. Subsequently or concurrently, acquired (adaptive) immune responses, such as thymus-derived T lymphocyte activation, specific immunoglobulins (IgT or IgZ), polymeric Ig receptor production, and differential cytokine network activation, amongst others, enables collaboration between the cellular and humoral immune systems leading to destruction of the invading viruses [168][169][170][171]. Additionally, some aquatic viruses have developed immune evasion mechanisms and strategies to combat host immune systems through IFN suppression and apoptosis inhibition; such viruses have increased pathogenicity and have acquired the ability to cross species barriers in their transmission [153,167,172].…”