Inhibition of Cyclosporine A or rapamycin on T lymphocyte counts and the influence on the immune responses of B lymphocytes in flounder (Paralichthys olivaceus)

CD4+ T lymphocyte responses to viruses and virus-relevant stimuli in teleost fish

Fish diseases caused by viruses are a major threat to aquaculture. Development of disease protection strategies for sustainable fish aquaculture requires a better understanding of the immune mechanisms involved in antiviral defence. The innate and adaptive arms of the vertebrate immune system collaborate to mount an effective defence against viral pathogens. The T lymphocyte components of the adaptive immune system, comprising two major classes (helper T, Th or CD4+ and cytotoxic T lymphocytes, CTLs or CD8+ T cells), are responsible for cell-mediated immune responses. In particular, CD4+ T cells and their different subsets orchestrate the actions of various other immune cells during immune responses, making CD4+ T cells central drivers of responses to pathogens and vaccines. CD4+ T cells are also present in teleost fish. Here we review the literature that reported the use of antibodies against CD4 in a few teleost fish species and transcription profiling of Th cell-relevant genes in the context of viral infections and virus-relevant immunomodulation. Studies reveal massive CD4+ T cell proliferation and expression of key cytokines, transcription factors, and effector molecules that evoke mammalian Th cell responses. We also discuss gaps in the current understanding and evaluation of teleost CD4+ T cell responses and how development and application of novel tools and approaches to interrogate such responses could bridge these gaps. A greater understanding of fish Th cell responses will further illuminate the evolution of vertebrate adaptive immunity, inform strategies to address viral infections in aquaculture, and could further foster fish as model organisms.

Cytokine networks provide sufficient evidence for the differentiation of CD4+ T cells in teleost fish

Cytokines, a class of small molecular proteins with a wide range of biological activities, are secreted mainly by immune cells and function by binding to the corresponding receptors to regulate cell growth, differentiation and effects. CD4⁺ T cells can be defined into different lineages based on the unique set of signature cytokines and transcription factors, including helper T cells (Th1, Th2, Th17) and regulatory T cells (Treg). In teleost, CD4⁺ T cells have been identified in a variety of fish species, thought to play roles as Th cells, and shown to be involved in the immune response following specific antigen stimulation. With the update of sequencing technologies, a variety of cytokines and transcription factors capable of characterizing CD4⁺ T cell subsets also have been described in fish, including hallmark cytokines such as IFN-γ, TNF-α, IL-4, IL-17, IL-10, TGF-β and unique transcription factors such as T-bet, GATA3, RORγt, and Foxp3. Hence, there is increasing evidence that the subpopulation of Th and Treg cells present in mammals may also exist in teleost fish. However, the differentiation, plasticity and precise roles of Th cell subsets in mammals remain controversial. Research on the identification and differentiation of fish Th cells is still in its infancy and requires more significant effort. Here we will review recent research advances in characterizing the differentiation of fish CD4⁺ T cells by cytokines and transcription factors, mainly including the identification of Th and Treg cell hallmark cytokines and transcription factors, the regulatory role of cytokines on Th cell differentiation, and the function of Th and Treg cells in the immune response. The primary purpose of this review is to deepen our understanding of cytokine networks in characterizing the differentiation of CD4⁺ T cells in teleost.

Full-length transcriptome sequencing of lymphocytes respond to IFN-γ reveals a Th1-skewed immune response in flounder (Paralichthys olivaceus)

Interferon gamma (IFN-γ), the member of type II interferons, is a major driver and effector cytokine for Th1 cells and plays broad roles in regulating the function of immune cells. Teleost fish represents the oldest living bony vertebrates containing T-lymphocyte subsets. However, whether or how the regulatory mechanisms of IFN-γ on Th1 cells occur in teleost fish remain unknown. In this study, full-length transcriptome sequencing was performed to analyze the differentially expressed genes (DEGs) and signaling pathways in the IFN-γ stimulated lymphocytes of flounder (Paralichthys olivaceus), the data showed 811 genes were upregulated and 1107 genes were downregulated, Th1 and Th2 cell differentiation pathway was remarkably enriched from DEGs, and the genes in the Th1 cell differentiation pathway were upregulated and verified. Accordingly, variations on Th1 cell differentiation marker genes and CD4⁺ cells were investigated after IFN-γ stimulation, the results confirmed that CD4⁺ T lymphocytes proliferated significantly after IFN-γ stimulation, accompanied by eight genes significant upregulation and increased T-bet expression in lymphocytes. In conclusion, the results revealed an induction of IFN-γ on Th1-type immune response, providing novel perspectives into the differentiation of CD4⁺ T lymphocytes in teleost.

Matrix metalloproteinase 9 modulates immune response along with the formation of extracellular traps in flounder (Paralichthys olivaceus)

MMP-9 belongs to the Matrix Metalloprotease family, which is mainly involved in the protein hydrolysis process of extracellular matrix and plays important roles in many biological processes, such as embryogenesis, tissue remodeling, angiogenesis, inflammatory processes and wound healing. In this study, we described the sequence characteristics of the MMP-9 gene in flounder (PoMMP-9). PoMMP-9 was highly homologous to MMP-9 from turbot, medaka, and Fugu rubripes. The mRNA of PoMMP-9 was constitutively expressed in all tested tissues of healthy flounder with the highest expression levels in the head kidney and spleen. A time-dependent expression pattern of PoMMP-9 in the head kidney and spleen was found after the bacterial and virus challenge. This indicates that PoMMP-9 is inducible and involved in immune responses. Indirect immunofluorescence assay showed that the PoMMP-9 was co-localization in the extracellular traps (ETs) released by the leukocytes. After overexpression, PoMMP-9 can recruit more inflammatory cells and play a broad immune process from pathogen elimination to wound healing at the inflammatory site through ETs. In summary, this study provided new insights into the biological function of MMP-9 in teleost.

CD4-1 and CD8α T lymphocytes subsets in spotted sea bass (Lateolabrax maculatus) and comparison on antigenicity of T lymphocytes subsets in other three marine fish species

CD4 and CD8 molecules play an important role in the identification of T lymphocytes, and diverse among fish species. In this study, CD4-1 and CD8α gene of spotted sea bass (Lateolabrax maculatus) were cloned, polyclonal antibodies against CD4-1 (CD4-1 pAbs) and CD8α (CD8α pAbs) were produced, respectively. And the variations in CD4-1⁺ and CD8α⁺ T-lymphocytes in spotted sea bass and the cross-reactivity with leukocytes in pearl gentian grouper (Epinephelus fuscoguttatus x E. lanceolatus), schlegel's black rockfish (Sebastes schlegelii) and flounder (Paralichthys olivaceus) were investigated using CD4-1 pAbs and CD8α pAbs. The results showed that CD4-1 molecule ORF was 1413 bp and CD8α was 690 bp, both molecules are transmembrane glycoproteins with high amino acid homology to grouper. The CD4-1 pAbs specifically recognized both the CD4-1 recombinant and natural proteins, as does the CD8α pAbs to CD8α molecule, and no cross-reactivity between the two antibodies. CD4-1⁺ and CD8α⁺ T lymphocytes were detected in peripheral blood, spleen and head kidney leukocytes in spotted sea bass. In cross-reactivity assay with other three fish, CD4-1 pAbs could recognize the lymphocytes from pearl gentian grouper and schlegel's black rockfish, both with highest proportions in the spleen leukocytes, 5.3 ± 0.4% and 2.6 ± 0.3%, respectively, and CD8α pAbs could only recognize the lymphocytes in pearl gentian grouper, and no cross-reactivities to lymphocytes of flounder. These data suggested that the CD4-1 and CD8α molecules varied by fish species in the genes features and antigenicity, which might result in the diversities of T lymphocytes subpopulations. This will be a key to elucidating the classification and evolution of T lymphocytes in fish.

Splenic protection network revealed by transcriptome analysis in inactivated vaccine-immunized flounder (Paralichthys olivaceus) against Edwardsiella tarda infection

The protective immune response produced by fish after vaccination is crucial for vaccine effectiveness. Our previous studies have shown inactivated vaccine against Edwardsiella tarda can induce immune response in flounder (Paralichthys olivaceus). To elucidate the protective immune response at the genetic level, in this study, flounder was immunized with inactivated E. tarda for 5 weeks, and then they were challenged with E. tarda. The spleen was dissected at 7th day post immunization, 1st and 7th day post challenge, respectively. Transcriptome analysis showed that average of 46 million clean reads were obtained per library, while percentage of clean reads being mapped to reference genome was more than 89% in all cases, which suggested good quality of samples. As for differentially expressed genes (DEGs) identification in inactivated E. tarda groups, at 7th day post immunization, 1422 DEGs were identified and significantly enriched in innate immune-related pathways, such as Phagosome, Cell adhesion molecules and NF-kappa B signaling pathway; At 1st post challenge day, 1210 DEGs were identified and enriched to Antigen processing and presentation and Cell adhesion molecules, indicating that the pathogen was rapidly recognized and delivered; At 7th post challenge day, 1929 DEGs were identified, belonged to Toll-like receptor signaling pathway, Antigen processing and presentation, Th1 and Th2 cell differentiation and Th17 cell differentiation. Compared to 7th post immunization day, 73 immune-associated DEGs were identified at 1st post challenge day. Protein-protein interaction networks analysis revealed 11 hub genes (TLR7, TLR3, CXCR4, IFIH1, TLR8 etc), associated with recognition of pathogens and activation of innate immunity; while for 7th post challenge day, 141 immune-associated DEGs were identified. 30 hub genes (IL6, STAT1, HSP90A.1, TLR7, IL12β etc) were associated with stimulation of lymphocyte differentiation and activation of cellular immunity. Ten immune-related genes were randomly selected for RT-qPCR validation at each time point. In conclusion, data revealed protection of flounder against E. tarda infection by inactivated vaccine is mediated via immediate recognition of pathogen and subsequently activation of cellular immunity. Results give new aspect for vaccine protection cascades, is good references for vaccine evaluation.

Conserved Role of mTORC1 Signaling in B Cell Immunity in Teleost Fish

Mammalian studies have demonstrated that B cell immune responses are regulated by mechanistic target of rapamycin complex 1 (mTORC1) signaling. Teleost fish represent the oldest living bony vertebrates that contain bona fide B cells. So far, whether the regulatory mechanism of mTORC1 signaling in B cells occurred in teleost fish is still unknown. In this study, we developed a fish model by using rapamycin (RAPA) treatment to inhibit mTORC1 signaling and demonstrated the role of mTORC1 signaling in teleost B cells. In support, we found inhibition of mTORC1 signaling by RAPA decreased the phagocytic capacity, proliferation, and Ig production of B cells. Critically, Flavobacterium columnare induced specific IgM binding in serum, and these titers were significantly inhibited by RAPA treatment, thus decreasing Ab-mediated agglutination of F. columnare and significantly increasing the susceptibility of fish upon F. columnare reinfection. Collectively, our findings elucidated that the mTORC1 pathway is evolutionarily conserved in regulating B cell responses, thus providing a new point for understanding the B cells functions in teleost fish.

Cluster of differentiation antigens: essential roles in the identification of teleost fish T lymphocytes

Cluster of differentiation (CD) antigens are cell surface molecules expressed on leukocytes and other cells associated with the immune system. Antibodies that react with CD antigens are known to be one of the most essential tools for identifying leukocyte subpopulations. T lymphocytes, as an important population of leukocytes, play essential roles in the adaptive immune system. Many of the CD antigens expressed on T lymphocytes are used as surface markers for T lymphocyte classification, including CD3, CD4 and CD8 molecules. In this review, we summarize the recent advances in the identification of CD molecules on T lymphocytes in teleosts, with emphasis on the functions of CD markers in the classification of T lymphocyte subsets. We notice that genes encoding CD3, co-receptors CD4 and CD8 have been cloned in several fish species and antibodies have been developed to study protein expression in morphological and functional contexts. T lymphocytes can be divided into CD4⁺ and CD8⁺ cells discriminated by the expression of CD4 and CD8 molecules in teleost, which are functionally similar to mammalian helper T cells (Th) and cytotoxic T cells (Tc), respectively. Further studies are still needed on the particular characteristics of teleost T cell repertoires and adaptive responses, and results will facilitate the health management and development of vaccines for fish.

Expression of Interleukin-2 receptor subunit gamma (IL-2Rγ) and its binding with IL-2 induced activation of CD4 T lymphocytes in flounder (Paralichthys olivaceus)

Interleukin-2 receptor (IL-2R), as the specific ligand of interleukin-2 (IL-2), binds to IL-2 and transmits signals and then can induce the proliferation of T lymphocytes in mammals. In this paper, the subunit of IL-2R in flounder (Paralichthys olivaceus), interleukin-2 receptor subunit gamma (IL-2Rγ) was cloned, and polyclonal antibodies (Abs) against its extracellular region were produced, then the expression of flounder IL-2Rγ (fIL-2Rγ) at transcriptional and cellular levels were characterized. Moreover, the interaction of flounder IL-2 (fIL-2) with fIL-2Rγ was investigated, and the variations on CD4+/IL-2Rγ+ cells in flounder after treatment with recombinant IL-2 (rIL-2), anti-IL-2Rγ Abs were detected, respectively. The results showed that fIL-2Rγ protein had a typical fibronectin type III (FN3) domain. The Abs could specifically recognize native fIL-2Rγ molecules at 39.9 kDa. FIL-2Rγ was localized on both T and B lymphocytes, and the percentages of CD4+/IL-2Rγ+ and IgM+/IL-2Rγ+ lymphocytes were high in spleen. In addition, pBiFC-VN173-IL-2Rγ plasmids could bind to pBiFC-VC155-IL-2 plasmids. The percentage of CD4+/IL-2Rγ+ lymphocytes was significantly decreased after blocking with anti-IL-2Rγ Abs both in vivo and in vitro. In the meantime, four T cell markers genes and six IL-2-IL-2R pathway genes were down-regulated in anti-IL-2Rγ Abs group. These results first demonstrated that fIL-2Rγ molecules were expressed on both T and B lymphocytes in flounder, and the bond between fIL-2Rγ and fIL-2 activated the CD4 T lymphocytes. This study gave a new sight into the exploration of IL-2R function on T lymphocytes proliferation in fish.

The Expression of CD28 and Its Synergism on the Immune Response of Flounder (Paralichthys olivaceus) to Thymus-Dependent Antigen

CD28 is well known as a critical T-cell costimulatory receptor involved in T cell activation by binding to its ligands. In this study, CD28 was cloned, and its expression profiles were characterized in flounder (Paralichthys olivaceus); variations of CD28+ cells after being stimulated with different types of antigens and the function of the CD28 costimulatory pathway on T-cell activation were investigated in vitro. fCD28 consists of four exons and three introns, and the full-length cDNA of fCD28 was 675-bp encoded 224 amino acids. The conserved motif (121TFPPPF126) binding to the CD80/86 ligand exists in the Ig-superfamily homology domain. The high expression of fCD28 is in gills, PBLs, head kidney, and spleen. CD28+ cells were co-localized with CD4+ T lymphocytes but not on IgM+ B lymphocyte cells. Moreover, the expression of CD28 was significantly varied in flounder after being stimulated by keyhole limpet hemocyanin (KLH) at both the transcriptional and cellular levels, while no significant differences were observed between lipopolysaccharide (LPS) stimulation and the control group. Notably, treatment of PBLs cultured in vitro with CD28 molecule-specific antibody (anti-CD28 Abs) and PHA produced more cell colonies and stimulated the proliferation of cultured leukocytes compared to PHA stimulation alone and the control group, and a higher level of IL-2 was detected in the culture medium. Meanwhile, anti-CD28 Abs increased the percent of CD28+ cells (10.41 ± 1.35%), CD4+ T lymphocytes (18.32 ± 2.15%), and CD28+/CD4+ double-positive cells (6.24 ± 1.52%). This effect also resulted in significant variations in the genes of cell membrane-bound molecules, cytokines, and related signaling pathways in cultured leukocytes, with significant changes in the genes of interleukin-2 (IL-2) and nuclear factor of activated T cells (NFAT) in the early stages of culture, and the expression of other molecules increased over time. These results proved the localization of the CD28 molecule on T lymphocytes in flounder, and anti-CD28 may act as the B7 ligand involved in T cell activation after antigen stimulation. These data provide a basis for a more in-depth study of the mechanism of the CD28 costimulatory pathway in T cell activation.

Cyclosporine reduces the spleen dimensions in rabbits

Purpose

To assess the influence of prolonged cyclosporine use on the macro- and microscopic morphology of the spleen.

Methods

16 adult rabbits were divided into two groups (n = 8): group 1 – a placebo group, which was followed-up over a period of nine months; group 2 – which had taken an oral dose of cyclosporine (10 mg·kg^–1·day^–1) over nine months. At the end of this period, the splenic histoarchitecture of all animals was evaluated and the splenic corpuscles were measured.

Results

The spleens of the first group presented normal characteristics and dimensions. The second group, however, had a reduction in all dimensions and its tissue texture had become soft. The white pulp and the perivascular sheath had become reduced in size and the number of lymphoid follicles had also fallen (p = 0.002), manifesting less splenic corpuscles (p = 0.0012) and lymphocyte nuclear pigments (p = 0.03).

Conclusions

Prolonged use of cyclosporine reduces the spleen size, transforming it into a soft organ associated with a decrease in white pulp, perivascular sheath, lymphoid follicles and nuclear pigments in rabbits.

Testicular subcutaneous allografting followed by immunosuppressive treatment promotes maintenance of spermatogonial cells in rainbow trout (Oncorhynchus mykiss)

Germ cell transplantation and testis graft represent promising biotechnologies that can be applied for the reproduction of commercial or endangered species. However, mechanisms of rejection from the host immune system might remove the transplanted donor cells/tissues and limit the surrogate production of gametes. In this work, we administered emulsion containing-immunosuppressants to verify whether they are capable to prevent immune rejection and promote survival of testis allografts in rainbow trout. In the first part of this study, we demonstrated in vitro that tacrolimus and cyclosporine were able to affect viability, inhibit leucocyte proliferation, and suppress il2 expression in vitro. In in vivo experiments, both doses of tacrolimus (0.5 and 1.5 mg/kg) and the lower dose of cyclosporine (20 mg/kg) significantly inhibited the expression of il2 in head kidney, three days post-injection. A higher dose of cyclosporine (40 mg/kg) was able to inhibit il2 expression for up to seven days post-injection. In the second part, testis allografts were conducted in fish treated weekly with emulsion containing-tacrolimus. Immunohistochemical, conventional histology, and qRT-PCR (vasa) analysis demonstrated the presence of spermatogonial cells by the fifth week, in animals treated with 0.5 mg/kg of tacrolimus similar as found in autografted group. In the group treated with the highest tacrolimus dose (1.5 mg/kg) and in the non-treated group (without immunosuppressant), no germ cells or their respective markers were detected. il2 expression in head kidney was also suppressed in grafted animals treated with tacrolimus compared to non-treated group. These results suggest that tacrolimus may be a promising immunosuppressant for testis allografts or germ cell transplantation in rainbow trout. Co-administration combining tacrolimus (at lower dose) with other immunosuppressive drugs for inhibiting other activation pathways of the immune system, as performed in human organ transplantation, could be an alternative approach to optimize the immunosuppressive effects in host organisms.

Interleukin-2 (IL-2) Interacts With IL-2 Receptor Beta (IL-2Rβ): Its Potential to Enhance the Proliferation of CD4+ T Lymphocytes in Flounder (Paralichthys olivaceus)

Interleukin-2 (IL-2) is an important immunomodulatory cytokine that primarily promotes the activation, proliferation, and differentiation of CD4+ T helper subsets and CD4+ T regulatory cells. In our previous studies, IL-2 and IL-2 receptor beta (IL-2Rβ) genes of flounder (Paralichthys olivaceus) were cloned, and IL-2Rβ molecules expressed on both B and T lymphocytes were identified. In the present study, the interaction of flounder IL-2 (fIL-2) with the IL-2 receptor beta (fIL-2Rβ) was investigated. The proportion of CD4+ T lymphocytes and IL-2Rβ+ cells were detected both in vivo and in vitro. Firstly, the binding of recombinant flounder IL-2 protein (rfIL-2) and rfIL-2Rβ was verified by pull-down assay and enzyme-linked immunosorbent assay. Indirect immunofluorescence assay showed that rfIL-2 enhanced the proliferation of CD4+ and IL-2Rβ+ cells in the gill and spleen. Furthermore, CD4-1+, CD4-2+ T lymphocytes and IL-2Rβ+ cells were significantly upregulated in cultured peripheral blood lymphocytes (PBLs) with addition of rfIL-2, as shown by Flow cytometry. The related genes were examined by Q-PCR in cultured PBLs with added rfIL-2. The results showed that the IL-2-IL-2R interaction induced upregulated expression of T lymphocyte surface makers, Th1-related cytokines or transcription factors, and critical genes of the IL-2 signaling pathway. In addition, these IL-2-elicited biological functions and immune responses were downregulated by blocked with anti-rfIL-2Rβ and anti-rfIL-2 Abs, showing that IL-2Rβ plays an indispensable role in IL-2 elicited biological function. Our results demonstrated that the interaction between IL-2 and IL-2Rβ showed its potential to enhance the proliferation of CD4+ T lymphocytes in flounder. As found in mammals, a Th1-mediated mechanism regulated by this interaction exists in teleost.

Kinetics of T lymphocyte subsets and B lymphocytes in response to immunostimulants in flounder (Paralichthys olivaceus): implications for CD4+ T lymphocyte differentiation

CD4⁺ T lymphocytes play crucial roles in the adaptive immune system. CD4, as the most effective marker to delineate the T-helper subsets, was identified in many fish species. Two CD4 homologs, CD4-1 and CD4-2, have been reported in flounder (Paralichthys olivaceus). In this study, monoclonal antibodies (mAbs) against CD4-1 and CD4-2 of flounder were produced, CD4⁺ T lymphocytes were isolated and identified, and the variations in CD4⁺ and CD8⁺ T lymphocytes and IgM⁺ B lymphocytes after Poly I:C, PMA or β-glucan stimulation were investigated. Then, the expression of transcription factors and cytokines in sorted CD4⁺ T lymphocytes was analyzed. The results showed that the mAbs were specific to flounder CD4-1⁺ and CD4-2⁺ T cells. CD4-1⁺ and CD4-2⁺ cells responded to all three stimulants, while CD8⁺ T lymphocytes only give a strong response to Poly I:C, and the percentages of IgM⁺ B lymphocytes showed a tendency to increase. After stimulation, the expression of transcription factors and cytokines of Th1, Th2 and Th17 cells varied in CD4⁺ T cells. These results will provide crucial foundations for the differentiation and function of teleost CD4⁺ T lymphocytes.

In vivo phagocytosis and hematology in Astyanax altiparanae, a potential model for surrogate technology

Abstract Although the potential of surrogate propagation technology for aquaculture and conservation of Neotropical fish, the poor understanding of the host immune system may results in rejection and destruction of the donor material. Thus, it is necessary to study and to develop methods to evaluate the effects of immunosuppressive drugs employment and to evaluate the immunocompatibility between donor and receptor. Thus, the present study aimed to optimize a methodology to assess in vivo phagocytosis in Astyanax altiparanae using Saccharomyces cerevisiae and to evaluate their hematological response resultant from the inflammatory induction. To this, S. cerevisiae were labeled with Congo red and injected in the coelomic cavity of A. altiparanae at the concentration of 2.5 x 106 cells mL-1. A PBS solution and a non-injected group were kept as control. Fish blood was sampled and the phagocytic capacity and index were determined at 1, 2, 3 and 6 h post-injection (hpi). The yeast injection successfully stimulated phagocytosis, with the best result for phagocytosis assessment after 2 hpi. Moreover, it was achieved a high traceability of phagocytized and non-phagocytized yeast under optic microscopy analysis due to the Congo red labeling. The hematological profile was similar to usually observed in early infections, indicating lymphocyte migration to inflammatory site and increase in number of circulating phagocytes due to natural response to inflammatory stimulus. In conclusion, our method was efficient to assess in vivo phagocytosis in A. altiparanae and will be an important tool to evaluate the efficacy of immunosuppressive drugs in this species. Additionally, these results may serve as support for further studies in fish immunocompetence, both in laboratory and in field conditions.

Systemic immunobiological, immunosuppressant, and oncologic agents for the treatment of dermatologic diseases during the SARS-CoV-2 (COVID-19) pandemic emergency: A quick review for a quick consultation

The precision medicine era has helped to better manage patients with immunological and oncological diseases, improving the quality of life of this class of patients. Regarding the management of these patients and positivity to severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), currently, limited data are available and information is evolving. In this quick review, we have analyzed the mechanisms of action and related infective risk of drugs used for the treatment of immune‐mediated and oncologic skin conditions during the daily clinical practice. In general, immunosuppressant and antineoplastic agents for dermatologic treatments do not require suspension and do not require special measures, if not those commonly observed. In the case of a coronavirus disease (COVID‐19) patient with complications (such as pneumonia, respiratory failure), treatment suspension should always be considered after taking into account the general condition of the patient, the risk‐benefit ratio, and the pathophysiology of COVID‐19 infection. The COVID‐19 emergency pandemic does not imply undertreatment of existing skin conditions, which together with the SARS‐CoV‐2 infection may jeopardize the patient's life.

T and B lymphocytes immune responses in flounder (Paralichthys olivaceus) induced by two forms of outer membrane protein K from Vibrio anguillarum: Subunit vaccine and DNA vaccine

To further elucidate the roles of T and B lymphocytes in fish subunit and DNA candidate vaccines for immunisation, the immune responses of T and B lymphocytes to recombinant protein (rOmpK) and plasmid OmpK (pOmpK) from Vibrio anguillarum plus cyclosporine A (CsA) were investigated in flounder (Paralichthys olivaceus). The results showed that in the rOmpK-immunised groups, the percentages of CD4-1⁺ and CD4-2⁺ T (PCD4-1⁺ and PCD4-2⁺ T) lymphocytes significantly increased to a peak on days 5 or 7. The percentages of IgM⁺ B (PIgM⁺ B) lymphocytes and specific antibodies markedly increased to a peak at weeks 4 or 5. The nine immune-related genes were significantly up-regulated and the expression levels of CD4-1, CD4-2 and MHC II genes were higher than that of CD8α, CD8β and MHC I genes. The CD4⁺ T lymphocytes, IgM⁺ B lymphocytes, and specific antibodies were significantly inhibited by CsA. Therefore, the responses of CD4⁺ T lymphocytes influenced the responses of the B lymphocytes and antibodies. In the pOmpK-immunised groups, the PCD4-1⁺, PCD4-2⁺, and PCD8β⁺ T lymphocytes significantly increased to a peak on days 11 or 14, days 9 or 11, and days 7 or 9, respectively. The PIgM⁺ B lymphocytes and specific antibodies significantly increased to a peak at weeks 5 or 6. Immune related genes upregulated, and CD4⁺ and CD8⁺ T lymphocytes, IgM⁺ B lymphocytes and specific antibodies all suppressed by CsA, suggesting that the responses of T lymphocytes subpopulations influenced B lymphocytes and antibodies responses. Therefore, the subpopulations of T lymphocytes played an important role in the immune responses induced by subunit and DNA candidate vaccines of OmpK and regulated the immune responses of B lymphocytes in flounder.

Immunological characteristics of Interleukin-2 receptor subunit beta (IL-2Rβ) in flounder (Paralichtlys olivaceus): Implication for IL-2R function

Interleukin-2 receptor subunit beta of flounder (Paralichthys olivace, fIL-2Rβ) was annotated on the NCBI, its gene was cloned and characterized functionally in this study. And then the amino acids sequences and tertiary structure of fIL-2Rβ were analyzed, respectively. RT-PCR and ImageJ analyzed showed that fIL-2Rβ mRNA were expressed in the gill, spleen, kidney, intestines, liver, blood, muscle and skin, which showed high signals in spleen and blood. And then the recombinant protein of fIL-2Rβ extracellular region and its polyclonal antibodies were produced, native fIL-2Rβ molecules in flounder peripheral blood leukocytes (PBLs) were identified at 60.7 kDa by Mass spectrometry, which were in accordance with the molecular mass of full fIL-2Rβ protein calculated on the predicted protein sequence. Then the IL-2Rβ+ cell in T/B lymphocytes were characterized by Flow cytometry and indirect immunofluorescence assay, respectively. The results showed that the percentages of IL-2Rβ+ leukocytes, IL-2Rβ+/CD4+, IL-2Rβ+/IgM+ lymphocytes were 18.4 ± 2.7%, 4.5 ± 0.8%, 4.3% ± 0.5 in PBLs, and were 13.6 ± 0.9%, 4.6 ± 1.1%, 6.1% ± 0.4 in spleen, similarly, the percentages of IL-2Rβ+ leukocytes, IL-2Rβ+/CD4+, IL-2Rβ+/IgM+ lymphocytes were 9.4 ± 0.3%, 4.0 ± 0.5%, 5.7 ± 0.1% in head kidney, respectively. After KLH injection, compared with control group, the gene expression of IL-2, IL-2Rβ, CD3, TCR, CD79b and IgM in spleen of flounder were up-regulated, respectively (p < 0.05). And the FCM results showed that the percentages of IL-2Rβ+ leukocytes in PBLs were significantly increased post Keyhole limpet hemocyanin (KLH) injection, which peaked 23.9 ± 0.9% at 9^th day (p < 0.05). To our knowledge, those results first reported that the characteristics of IL-2R and IL-2R + molecules were expressed on both B and T lymphocytes in fish. At the same time, this study lays a foundation for further exploring the interaction between IL-2 and IL-2R to promote cell proliferation and carrying out biological functions.

Intramuscular administration of a DNA vaccine encoding OmpK antigen induces humoral and cellular immune responses in flounder (Paralichthys olivaceus) and improves protection against Vibrio anguillarum

Outer membrane protein K (OmpK) is an immunogenic protein that could act as subunit vaccine candidate for Vibrio anguillarum. In this study, a DNA vaccine encoding the OmpK gene of V. anguillarum was constructed and confirmed to express OmpK in vitro and in vivo. To evaluate the potential of pcDNA3.1-OmpK (pOmpK) as vaccine candidate, the humoral and cellular immune responses, and protective effects were analyzed in flounder model. The results showed that the transcription and translation of OmpK gene occurred in both transfected hirame natural embryo (HINAE) cells and injected fish muscles, indicating the functionality of pOmpK to express OmpK. Fish immunized with pOmpK showed significant increase of surface IgM positive (sIgM⁺), CD4-1⁺, CD4-2⁺ lymphocytes and production of specific anti-V. anguillarum or anti-rOmpK antibodies, which indicate the activation of humoral and cellular immune responses after vaccination. Moreover, a relative percent survival (RPS) rate of 50.00% against V. anguillarum infection was obtained for flounder immunized with pOmpK. In conclusion, this study indicates that pOmpK is able to induce humoral and cellular immune responses and can be used as a DNA vaccine candidate.

Influence of CD4-1+, CD4-2+ and CD8+ T lymphocytes subpopulations on the immune response of B lymphocytes in flounder (Paralichthys olivaceus) immunized with thymus-dependent or thymus-independent antigen

In order to elucidate the influence of T lymphocytes subpopulations on B lymphocytes immune response, in this paper, CD4-1⁺, CD4-2⁺, CD8⁺ T lymphocytes and B lymphocytes responses to thymus-independent (TI) or thymus-dependent (TD) antigen plus immunosuppressant were investigated in flounder (Paralichthys olivaceus). The results showed that in LPS-immunized group, the percentages of CD4-1⁺, CD4-2⁺, CD8β⁺ T (PCD4-1⁺ T, PCD4-2⁺ T and PCD8β⁺ T) lymphocytes in peripheral blood leucocytes (PBLs) had no significant variations, the percentages of IgM⁺ B (PIgM⁺ B) lymphocytes and LPS-specific antibodies (LA) significantly increased and peaked at 3^rd or 4^th week post-injection; CsA had no inhibition on both T/B lymphocytes and LA; RaPa only suppressed the PIgM⁺ B lymphocytes and LA, and the inhibition maximum (Imax) were about 35% and 20%, respectively. In KLH-immunized group, the PCD4-1⁺, PCD4-2⁺ and PCD8β⁺ T lymphocytes significantly increased and peaked at 3^rd or 5^th day, successively the PIgM⁺ B lymphocytes and KLH-specific antibodies (KA) significantly increased to the peak at 5^th week; the PCD4-1⁺, PCD4-2⁺ T and PIgM⁺ B lymphocytes and LA were inhibited significantly by both CsA and RaPa, and the Imax on them were 13%-33%, 11%-25%, 19%-34%, 22%-26%, respectively, while the PCD8β⁺ T lymphocytes showed no significant suppression. The results indicated that the suppression of PIgM⁺ B lymphocytes in KLH + CsA group was not directly derived from CsA, but due to the suppression of T lymphocytes, especially CD4⁺ T lymphocytes subpopulations. The results showed for the first time that, similar to higher vertebrates, T lymphocytes didn't respond to TI antigen, moreover, T lymphocyte subpopulations had a regulation on the immune response of B lymphocyte for TD antigen in flounder.

Characterization of CD40+ leukocytes in flounder (Paralichthys olivaceus) and its response after Hirame novirhabdovirus infection and immunization

CD40 is a crucial signal mediating factor in T-dependent B cell responses and involved in many aspects of cellular and humoral immunity. In this paper, recombinant protein of CD40 in flounder (Paralichthys olivaceus) and its antibodies (Abs) were produced, native CD40 molecules in flounder tissues were identified, then the CD40⁺ leukocytes in T/B lymphocytes were characterized, and the variations of CD40⁺ leukocytes in flounder after Hirame novirhabdovirus (HIRRV) infection and immunization were investigated, respectively. The results showed that the Abs could specifically recognize native flounder CD40 molecule at 32 kDa. The proportions of CD40⁺ leukocytes were varied by flounder tissues. CD40⁺/IgM⁺ B lymphocytes, CD40⁺/CD4-1⁺ T lymphocytes, CD40⁺/CD4-2⁺ T lymphocytes and CD40⁺/CD8⁺ T lymphocytes in peripheral blood leukocytes (PBLs) were 1.18 ± 0.27%, 0.69 ± 0.17%, 0.75 ± 0.14% and 0.25 ± 0.14%; were 2.80 ± 0.32%, 0.71 ± 0.19%, 0.88 ± 0.23% and 0.33 ± 0.17% in spleen; 4.11 ± 0.47%, 0.92 ± 0.18%, 1.09 ± 0.17% and 0.9 ± 0.17% in head kidney; 1.92 ± 0.39%, 1.02 ± 0.23%, 1.33 ± 0.38% and 0.67 ± 0.24% in intestine; 1.24 ± 0.36%, 1.21 ± 0.24%, 1.70 ± 0.3% and 0.97 ± 0.21% in gill, respectively. The percentages of CD40⁺ leukocytes in PBLs were significantly increased in both HIRRV infection and immunization groups, and reached their peak levels at 3rd day with 5.70 ± 0.16% and 6.40 ± 0.13%, respectively. Concluded with our previous study, these data first reported that CD40 molecules were expressed on both B and T lymphocytes in teleost, and had a coordination with T and B lymphocytes in immune responses.

Evaluation of bivalent vaccines candidates among VAA, OmpK and OmpR from Vibrio anguillarum in flounder (Paralichthys olivaceus)

Outer membrane protein (Omp) K, OmpR and VAA have been identified with good immunogenicity from Vibrio anguillarum, and their recombinant proteins showed variable relative percent survival (RPS) in previous study. In order to develop effective bivalent vaccine candidates, recombinant (r) VAA + rOmpK (AK), rVAA + rOmpR (AR), rOmpK + rOmpR (KR) among VAA, OmpK and OmpR, or formalin-killed cells (FKC) of V. anguillarum were immunized in flounder, respectively. Results revealed that AK, AR, KR and FKC could induce the proliferation of surface membrane immunoglobulin-positive B lymphocytes or CD3⁺ T lymphocytes in peripheral blood lymphocytes, and significantly enhance the total antibodies, specific antibodies and immune-related gene than those of control group. AK, AR, KR or FKC showed RPS of 74.92%, 78.49%, 82.09% and 56.99%, respectively. These results indicated that three bivalent vaccines AK, AR and KR could induce strong cellular and humoral immunity, and had high protection against V. anguillarum infection in flounders.

Generation, characterization and application of monoclonal antibodies against matrix protein of hirame novirhabdovirus (HIRRV) in flounder

Hirame novirhabdovirus (HIRRV) causes severe disease in fish cultures, resulting in great economic loss in Asia and Europe. In this study, the matrix protein (M) of HIRRV was recombinantly expressed as the immunogen to produce monoclonal antibodies (MAbs) using hybridoma cell fusion technology, and 3 MAbs were produced and characterized by indirect ELISA, Western blotting and immunofluorescence assay (IFA). Western blotting and mass spectrometric analysis showed that the MAbs could specifically react with the nature M protein of HIRRV. The MAbs were employed to detect virions in HIRRV-infected epithelioma papulosum cyprini (EPC) cells and flounder Paralichthys olivaceus by IFA and immunohistochemistry (IHC). In the virus-infected EPC cells, the virions were mainly located in the cytoplasm, whereas in flounder, HIRRV was present in all 10 tested tissues, and the positive signals in spleen, head-kidney and heart were higher than in other tissues, consistent with the results obtained by RT-PCR. Moreover, strong positive signals were observed in the endothelial cells of blood vessels, but only the leukocytes were infected by HIRRV in the whole blood cells. These results indicate that the high susceptibility to HIRRV of leukocytes and endothelial cells may facilitate the spread of HIRRV and finally cause systemic infection in flounder. This study provides a foundation for further studies on rapid diagnosis of HIRRV and its infection mechanisms.

Immunomodulatory effect of Schisandra polysaccharides in cyclophosphamide-induced immunocompromised mice

As a strategy to prevent the well-known immunosuppressant effects of cyclophosphamide (Cyp), the immunomodulatory effects of the polysaccharide extract of the fruit of Schisandra chinensis (Turcz.) Baill. were investigated in the present study. The crude Schisandra polysaccharide (SCP) was obtained by water extraction and alcohol precipitation methods. The total carbohydrate, uronic acid and protein contents were determined using the phenol-sulfuric acid, m-hydroxydiphenyl and Bradford method, respectively. The monosaccharide composition of SCP was determined by high-performance liquid chromatography. ICR mice were randomly divided into control, model, low-dose SCP (0.4 mg/10 g), medium-dose SCP (0.8 mg/10 g) and high-dose SCP (1.6 mg/10 g) groups. The mice in the SCP groups were intragastrically administered SCP once a day for 21 days and those from the control and model groups were administered the same volume of distilled water. Subsequently, the mice in the model and SCP groups were intraperitoneally injected with Cyp (20 mg/kg) once a day for 5 days. The mouse leukocyte count in the peripheral blood as well as thymus and spleen indexes were determined, and the phagocytic function of macrophages was estimated using a carbon clearance test. The thymus and spleen were histomorphologically observed. The levels of tumor necrosis factor-α and interferon-γ were measured by ELISA. Furthermore, antibody formation and spleen lymphocyte proliferation were measured by the serum hemolysin and the MTT method, respectively. The apoptotic rate of splenic lymphocytes was determined by flow cytometric analysis. The results indicated that SCP prevents Cyp-induced impairment of the cellular, humoral and non-specific immunity, and may be an auxiliary immune enhancer for the prevention of immune hypofunction.

Recombinant Hsp33 and OmpC protein can serve as promising divalent vaccine with protection against Vibrio anguillarum and Edwardsiella tarda in flounder (Paralichthys olivaceus)

Vibrio anguillarum and Edwardsiella tarda are severe aquaculture pathogens shared similar epidemiological characteristics and susceptible to flounder (Paralichthys olivaceus). In our previous studies, recombinant(r) protein heat shock protein 33 (rHsp33) from V. anguillarum and outer membrane protein C (rOmpC) from E. tarda were proved to have protection against V. anguillarum and E. tarda, respectively. In this paper, the cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, and the protection of divalent vaccine candidate (rHsp33 + rOmpC, rHC) against both V. anguillarum and E. tarda were evaluated. RHC, rHsp33, and rOmpC were vaccinated to flounder, respectively, and the percentages of surface immunoglobulin-positive (sIg+) cells in peripheral blood lymphocytes (PBLs), serum IgM, specific antibodies against V. anguillarum or E. tarda, specific antibodies against rHsp33, rOmpC or rHC, the expression of immune-related genes and relative percent survival (RPS) against V. anguillarum or E. tarda were measured. The results showed that: RHC could induced the enhancement of sIg + cells and high levels of specific antibodies against both V. anguillarm and E. tarda; Also a significant increase of specific antibodies against rHsp33, rOmpC or rHC, and up-regulation of gene expression of CD3, CD4-1, CD4-2, CD8α, CD8β and IgM in spleen, head-kidney, and hindgut, RPS of 70 ± 3.45% against V. anguillarum and 60 ± 1.48% against E. tarda, respectively. In addition, rHsp33 induced specific antibodies against E. tarda and rOmpC, and had a RPS of 43.3 ± 3.73% against E. tarda; rOmpC could evoke specific antibodies against V. anguillarum and rHsp33, and had a RPS of 44 ± 1.27% against V. anguillarm; The results demonstrated that there was cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, rHC as a divalent vaccine can induce significant immune response and efficient protection against both E. tarda and V. anguillarum in flounder.