RESUMO
Introduction: Red blood cells (RBCs), also known as erythrocytes, are underestimated in their role in the immune system. In mammals, erythrocytes undergo maturation that involves the loss of nuclei, resulting in limited transcription and protein synthesis capabilities. However, the nucleated nature of non-mammalian RBCs is challenging this conventional understanding of RBCs. Notably, in bony fishes, research indicates that RBCs are not only susceptible to pathogen attacks but express immune receptors and effector molecules. However, given the abundance of RBCs and their interaction with every physiological system, we postulate that they act in surveillance as sentinels, rapid responders, and messengers. Methods: We performed a series of in vitro experiments with Cyprinus carpio RBCs exposed to Aeromonas hydrophila, as well as in vivo laboratory infections using different concentrations of bacteria. Results: qPCR revealed that RBCs express genes of several inflammatory cytokines. Using cyprinid-specific antibodies, we confirmed that RBCs secreted tumor necrosis factor alpha (TNFα) and interferon gamma (IFNγ). In contrast to these indirect immune mechanisms, we observed that RBCs produce reactive oxygen species and, through transmission electron and confocal microscopy, that RBCs can engulf particles. Finally, RBCs expressed and upregulated several putative toll-like receptors, including tlr4 and tlr9, in response to A. hydrophila infection in vivo. Discussion: Overall, the RBC repertoire of pattern recognition receptors, their secretion of effector molecules, and their swift response make them immune sentinels capable of rapidly detecting and signaling the presence of foreign pathogens. By studying the interaction between a bacterium and erythrocytes, we provide novel insights into how the latter may contribute to overall innate and adaptive immune responses of teleost fishes.
Assuntos
Aeromonas hydrophila , Carpas , Citocinas , Eritrócitos , Doenças dos Peixes , Infecções por Bactérias Gram-Negativas , Animais , Carpas/imunologia , Carpas/microbiologia , Eritrócitos/imunologia , Eritrócitos/metabolismo , Citocinas/metabolismo , Citocinas/imunologia , Aeromonas hydrophila/imunologia , Infecções por Bactérias Gram-Negativas/imunologia , Doenças dos Peixes/imunologia , Doenças dos Peixes/microbiologia , Fagocitose/imunologia , Moléculas com Motivos Associados a Patógenos/imunologia , Imunidade InataRESUMO
The myxozoan parasite Tetracapsuloides bryosalmonae is the causative agent of proliferative kidney disease (PKD)-a disease of salmonid fishes, notably of the commercially farmed rainbow trout Oncorhynchus mykiss. Both wild and farmed salmonids are threatened by this virulent/deadly disease, a chronic immunopathology characterized by massive lymphocyte proliferation and hyperplasia, which manifests as swollen kidneys in susceptible hosts. Studying the immune response towards the parasite helps us understand the causes and consequences of PKD. While examining the B cell population during a seasonal outbreak of PKD, we unexpectedly detected the B cell marker immunoglobulin M (IgM) on red blood cells (RBCs) of infected farmed rainbow trout. Here, we studied the nature of this IgM and this IgM+ cell population. We verified the presence of surface IgM via parallel approaches: flow cytometry, microscopy, and mass spectrometry. The levels of surface IgM (allowing complete resolution of IgM- RBCs from IgM+ RBCs) and frequency of IgM+ RBCs (with up to 99% of RBCs being positive) have not been described before in healthy fishes nor those suffering from disease. To assess the influence of the disease on these cells, we profiled the transcriptomes of teleost RBCs in health and disease. Compared to RBCs originating from healthy fish, PKD fundamentally altered RBCs in their metabolism, adhesion, and innate immune response to inflammation. In summary, RBCs play a larger role in host immunity than previously appreciated. Specifically, our findings indicate that the nucleated RBCs of rainbow trout interact with host IgM and contribute to the immune response in PKD.
Assuntos
Nefropatias , Oncorhynchus mykiss , Animais , Eritrócitos , Linfócitos B , Imunoglobulina MRESUMO
The immune system is a complex and sophisticated biological system, spanning multiple levels of complexity, from the molecular level to that of tissue. Our current understanding of its function and complexity, of the heterogeneity of leukocytes, is a result of decades of concentrated efforts to delineate cellular markers using conventional methods of antibody screening and antigen identification. In mammalian models, this led to in-depth understanding of individual leukocyte subsets, their phenotypes, and their roles in health and disease. The field was further propelled forward by the development of single-cell (sc) RNA-seq technologies, offering an even broader and more integrated view of how cells work together to generate a particular response. Consequently, the adoption of scRNA-seq revealed the unexpected plasticity and heterogeneity of leukocyte populations and shifted several long-standing paradigms of immunology. This review article highlights the unprecedented opportunities offered by scRNA-seq technology to unveil the individual contributions of leukocyte subsets and their crosstalk in generating the overall immune responses in bony fishes. Single-cell transcriptomics allow identifying unseen relationships, and formulating novel hypotheses tailored for teleost species, without the need to rely on the limited number of fish-specific antibodies and pre-selected markers. Several recent studies on single-cell transcriptomes of fish have already identified previously unnoticed expression signatures and provided astonishing insights into the diversity of teleost leukocytes and the evolution of vertebrate immunity. Without a doubt, scRNA-seq in tandem with bioinformatics tools and state-of-the-art methods, will facilitate studying the teleost immune system by not only defining key markers, but also teaching us about lymphoid tissue organization, development/differentiation, cell-cell interactions, antigen receptor repertoires, states of health and disease, all across time and space in fishes. These advances will invite more researchers to develop the tools necessary to explore the immunology of fishes, which remain non-conventional animal models from which we have much to learn.
Assuntos
Peixes/genética , Peixes/imunologia , Leucócitos/imunologia , Leucócitos/metabolismo , RNA-Seq , Análise de Célula Única , Animais , Imunidade , Análise de Célula Única/métodosRESUMO
AIMS: As the most abundant cell population in the blood, erythrocytes represent an attractive source of nutrients and a protective niche to a number of pathogens. Previously, we observed the attachment of the myxozoan parasite Sphaerospora molnari to erythrocytes of its host, common carp (Cyprinus carpio), raising a number of questions about the nature of this interaction. METHODS AND RESULTS: We elucidated the impact of S molnari on the number of erythrocytes in healthy and immunocompromised fish, over a period of 6 weeks. While we observed only a mild decrease in RBC numbers in healthy individuals, we witnessed gradual and finally severe haemolytic anaemia in immunosuppressed fish. Accompanying this overt loss was increased erythropoiesis as represented by an increase of erythroblasts in the blood. In vitro, we demonstrated the uptake of host proteins from CFSE-labelled erythrocytes, ultimately inducing death of host RBCs, likely for nutrient gain of the parasite. Nevertheless, the results do not exclude a possible role of erythrocyte-derived proteins in immune evasion. CONCLUSION: Overall, the obtained data provide first evidence for the previously unknown appetite of myxozoan parasites for host erythrocytes and create an important framework for future investigations into the molecular mechanisms underlining this interaction.
Assuntos
Eritrócitos/parasitologia , Comportamento Alimentar/fisiologia , Myxozoa/fisiologia , Anemia Hemolítica/parasitologia , Animais , Carpas/parasitologia , Eritropoese/fisiologia , Doenças dos Peixes/parasitologia , FilogeniaRESUMO
Memory B cells and plasma cells are antigen-experienced cells tasked with the maintenance of humoral protection. Despite these prominent functions, definitive cell surface markers have not been identified for these cells. We report here the isolation and characterization of the monoclonal variable lymphocyte receptor B (VLRB) N8 antibody from the evolutionarily distant sea lamprey that specifically recognizes memory B cells and plasma cells in humans. Unexpectedly, we determined that VLRB N8 recognizes the human leukocyte antigen-I (HLA-I) antigen in a tyrosine sulfation-dependent manner. Furthermore, we observed increased binding of VLRB N8 to memory B cells in individuals with autoimmune disorders multiple sclerosis and systemic lupus erythematosus. Our study indicates that lamprey VLR antibodies uniquely recognize a memory B cell- and plasma cell-specific posttranslational modification of HLA-I, the expression of which is up-regulated during B cell activation.