The interaction between the costimulatory molecules CD80/86 and CD28 contributed to CD4+ T lymphocyte activation in flounder (Paralichthys olivaceus)

CD28 and CD80/86 are crucial co-stimulatory molecules for the T cell activation. Previous study illustrated that CD28 and CD80/86 present on T cells and antigen-presenting cells in flounder (Paralichthys olivaceus), respectively. The co-stimulatory molecules were closely associated with cell immunity. In this paper, recombinant protein of flounder CD80/86 (rCD80/86) and phytohemagglutinin (PHA) were added to peripheral blood leukocytes (PBLs) in vitro. Lymphocytes were significantly proliferated with CFSE staining, and the proportion of CD4+ and CD28+ lymphocytes significantly increased. In the meantime, genes related to the CD28-CD80/86 signaling pathway or T cell markers were significantly upregulated (p < 0.05). For further study, the interaction between CD80/86 and CD28 was confirmed. The plasmid of CD28 (pCD28-FLAG and pVN-CD28) or CD80/86 (pVC-CD80/86) was successfully constructed. In addition, pVN-ΔCD28 without the conserved motif "TFPPPF" was constructed. The results showed that bands of pCD28-FLAG bound to rCD80/86 were detected by both anti-FLAG and anti-CD80/86. pVN-CD28 complemented to pVC-CD80/86 showing positive fluorescent signals, and pVN-ΔCD28 failed to combine with pVC-CD80/86. The motif "TFPPPF" in CD28 played a crucial role in this linkage. These results indicate that CD28 and CD80/86 molecules interact with each other, and their binding may modulate T lymphocytes immune response in flounder. This study proved the existence of CD28-CD80/86 signaling pathway in flounder.

Characterization of Co-Stimulatory Ligand CD80/86 and Its Effect as a Molecular Adjuvant on DNA Vaccine Against Vibrio anguillarum in Flounder (Paralichthys olivaceus)

The CD80/86 molecule is one of the important co-stimulatory ligands and involves antigen-specific immune responses by ligating with CD28 and then delivering the required second signal to T-cell activation. In this study, a CD80/86 homolog was identified, and its expression characteristics were studied in flounder (Paralichthys olivaceus). The open reading frame (ORF) of CD80/86 is 906 bp, encoding 301 aa, and the extracellular amino acid sequence encoded two IgV- and IgC-like structural domains; fCD80/86 is highly expressed in head kidney, peripheral blood leukocytes (PBLs), and spleen, and has relatively high expression in muscle. Antibodies specific for CD80/86 were produced, and CD80/86 was colocalized with MHCII+, CD40+, and CD83+ leukocytes but not with IgM+, CD3+, or CD4+ lymphocytes. The cloned CD80/86 in flounder shares conserved structural features with its mammalian counterparts and is mainly distributed on antigen-presenting cells. Based on these data, CD80/86 as an adjuvant to enhance the immune response of DNA vaccine was investigated. A bicistronic DNA vaccine expressing both CD80/86 and the outer membrane protein (OmpK) of Vibrio anguillarum (p-OmpK-CD80/86) was successfully constructed. After immunization, p-OmpK-CD80/86 could induce the upregulation of the proportion of IgM+ and CD4+ cells in flounder, compared to the p-OmpK- or p-CD80/86-immunized group; CD28 genes were significantly induced in the p-CD80/86 and p-OmpK-CD80/86 groups. Compared to the p-OmpK group, the higher expression of CD83, MHCI, CD4, CD8, and IL-2 was detected at the injection site. The relative percent survival (RPS) produced by p-OmpK-CD80/86 is 66.11% following the V. anguillarum challenge, while the RPS of p-OmpK or p-CD80/86 is 46.30% and 5.56%, respectively. The results revealed that CD80/86 is mainly found in antigen-presenting cells, and could help elicit humoral immune responses in teleost through the CD80/86-CD28 signaling pathway involving CD4+ lymphocytes.

Inhibitory Role of an Aeromonas hydrophila TIR Domain Effector in Antibacterial Immunity by Targeting TLR Signaling Complexes in Zebrafish

The Toll/interleukin-1 receptor (TIR) domain is a structural unit responsible for the assembly of signal protein complexes in Toll-like receptor (TLR) and interleukin-1 receptor signaling pathways. TIR domain homologs are found in a considerable number of bacteria and enhance bacterial infection and survival in host organisms. However, whether TIR domain homologs exist in Aeromonas hydrophila, a ubiquitous waterborne bacterium in aquatic environments, remains poorly understood. In this study, a TIR domain protein (TcpAh) was identified from A. hydrophila JBN2301. TIR domain of TcpAh is highly homologous to the counterpart domains in TLRs and myeloid differentiation factor 88 (MyD88). The zebrafish infected with mutant A. hydrophila with tcpAh deletion had a remarkably lower mortality than those infected with the wild-type strain. This result suggests that TcpAh is a crucial virulence factor for A. hydrophila infection. TcpAh exhibited a strong ability to associate with MyD88, tumor necrosis factor receptor-associated factor 3 (TRAF3) and TRAF-associated NF-κB activator-binding kinase 1 (TBK1) in TIR-TIR, TIR-Death domain (DD), and other alternative interactions. This finding suggests that TcpAh extensively interferes with MyD88 and TIR domain-containing adapter inducing interferon (IFN)-β (TRIF) signaling pathways downstream of TLRs. Consequently, CD80/86 expression was suppressed by TcpAh via attenuating TLR-stimulated NF-κB activation, which ultimately led to the impairment of the major costimulatory signal essential for the initiation of adaptive humoral immunity against A. hydrophila infection. We believe that this study is the first to show a previously unrecognized mechanism underlying A. hydrophila evades from host antibacterial defense by intervening CD80/86 signal, which bridges innate and adaptive immunity. The mechanism will benefit the development of therapeutic interventions for A. hydrophila infection and septicemia by targeting TcpAh homologs.

The Association Between CTLA-4, CD80/86, and CD28 Gene Polymorphisms and Rheumatoid Arthritis: An Original Study and Meta-Analysis

Background: Rheumatoid arthritis (RA) is related to several pivotal susceptibility genes, including cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and costimulatory molecule (CD80/CD86) genes. Although the connection between polymorphisms of CTLA-4 and CD86 genes in different populations of RA have been studied extensively, the results are controversial. Objective: To clarify the correlation in the Chinese Han population between CTLA-4, CD80/86, and CD28 gene polymorphisms, and RA susceptibility. Methods: A case-control study (574 RA patients and 804 controls) was conducted to determine the correlation between CTLA-4 rs231775 and rs16840252 gene polymorphisms, CD86 rs17281995 gene polymorphisms, and the risk of RA for the Chinese Han population. Furthermore, an additional meta-analysis, including three single nucleotide polymorphisms (SNPs) (CTLA-4 rs231775, CTLA-4 rs3087243, and CTLA-4 rs5742909) from 32 citations, including 43 studies, 24,703 cases and 23,825 controls was performed to elucidate the relationship between known SNPs in the CTLA-4 genes and RA for more robust conclusions. Results: The results showed that CTLA-4 rs231775 gene polymorphism decreased the RA risk (GA vs. AA, OR = 0.77, P = 0.025), whereas CTLA-4 rs16840252 and CD86 rs17281995 gene polymorphisms were not related to RA susceptibility. Stratification analyses by RF, ACPA, CRP, ESR, DAS28, and functional class identified significant associations for CTLA-4 rs231775 and rs16840252 gene polymorphisms in the RF-positive and RF-negative groups. A meta-analysis of the literature on CTLA-4 gene polymorphisms and RA risk revealed that the risk of RA was decreased by CTLA-4 rs231775 gene polymorphisms. Conclusions: The CTLA-4 rs231775 gene polymorphism decreased the risk of RA, whereas CTLA-4 rs16840252 and CD86 rs17281995 gene polymorphisms were not related to RA risk. A meta-analysis indicated that CTLA-4 rs231775 and rs3087243 gene polymorphisms decreased the risk of RA. To support these analytical results, additional clinical cases should be investigated in further studies.

CCR7, CD80/86 and CD83 in yellow catfish (Pelteobagrus fulvidraco): Molecular characteristics and expression patterns with bacterial infection

Dendritic cells (DCs) have a strong ability to stimulate naive T lymphocyte proliferation, so DCs play an important regulatory role in the initiation of the specific immune response. DCs cannot play the role of antigen presentation without the expression of surface molecules. The chemokine receptor CCR7 and the costimulatory molecules CD80/86 and CD83 are not only markers of DC maturation but also important functional molecules in the immune response of DC-T cells. In this study, partial cDNA sequences of CCR7, CD80/86 and CD83 were obtained by rapid amplification of cDNA ends (RACE) technology from yellow catfish. Bioinformatics analysis of deduced amino acid sequences of these three genes showed that CCR7, CD80/86 and CD83 genes in yellow catfish have similar functional domains to the homologs in other vertebrates, which indicated that the functions of these genes may be somewhat conserved during the evolution process. Afterward, the expression characteristics of these three genes in different tissues were detected by q-PCR. This result indicated that CCR7, CD80/86 and CD83 were expressed in all examined tissues, and the highest expression levels of CCR7 and CD80/86 and CD83 were detected in the trunk kidney, muscle and midgut, respectively. Meanwhile, the expression levels of CCR7 and CD80/86 were lowest in the gill, and the expression of CD83 was lowest in the stomach. Finally, healthy yellow catfish were infected with A.hydrophila (1.0 × 10⁷ CFU/mL) or E.ictaluri (1.0 × 10⁶ CFU/mL), q-PCR results indicated that both pathogenic bacteria can induce significant upregulation of CCR7, CD80/86 and CD83 in immune organs, and the expression levels of these genes in the intestine were higher than those in the skin and gill. Our results in this study provide a molecular basis for exploring the role of CCR7, CD80/86 and CD83 in the immune responses induced by bacteria, and can help us to understand the difference of immune responses induced by extracellular and intracellular bacteria.

Insights into CD8 T Cell Activation and Exhaustion from a Mouse Gammaherpesvirus Model

(S.R.S.) I was introduced to viral immunology while working in Peter Doherty's laboratory in the early stages of my research career, inspiring a lifelong interest in this area. During those early years under Peter's mentorship, we studied a mouse gammaherpesvirus model (murine gammaherpesvirus-68 [MHV-68]) that provided a useful small animal model for investigating the immunological control of gammaherpesvirus infection. Interestingly, while CD4 T cells were not required for acute control of MHV-68 in the lung, CD8 T cell-mediated control was progressively lost in the absence of CD4 T cell help, leading to viral recrudescence. This was one of several early studies showing that CD8 T cell control of persistent viral infections was lost in the absence of CD4 T cell help, preceding the concept of CD8 T cell exhaustion. Further studies showed that MHV-68 infection of mice offered a unique model for comparing the mechanisms of acute and long-term control of a persistent viral infection and developing strategies for reversing T cell exhaustion. Here, we provide a brief review of the literature on CD8 T cell activation and exhaustion in this model, focusing on the role of CD40 and B7 family members and including some previously unpublished data.

Identification of another primordial CD80/86 molecule in rainbow trout: Insights into the origin and evolution of CD80 and CD86 in vertebrates

In mammals, the binding of distinct costimulatory ligands CD80 and CD86 to their receptors is essential for optimal T cell activation. Previous studies have shown that only a single CD80/86 gene exists in rainbow trout (termed rtCD80/86A) and other teleost fish, suggesting that CD80 and CD86 arose by gene duplication in the tetrapod branch, after the separation of fish and tetrapods. However, in this study, another CD80/86 gene has been cloned from rainbow trout, termed rtCD80/86B. The sequence identity between trout CD80/86 is significantly higher than that between CD80 and CD86 in tetrapods, indicating that CD80 and CD86 underwent divergent evolution in vertebrates, especially in tetrapods. Gene synteny analyses showed that the CD80 and CD86 genes are closely located in the same chromosome in tetrapods. However, CD80/86 genes are located in two distinct chromosomes in rainbow trout and Atlantic salmon, suggesting that salmonid CD80/86 genes arose by the salmonid-specific whole-genome duplication (WGD) event. Expression analysis showed that rtCD80/86A was more abundant and inducible than rtCD80/86B in various tissues, indicating the important role of rtCD80/86A in trout immunity. Interestingly, we found that head kidney B cells showed higher expression level of rtCD80/86A and rtCD80/86B when compared with the other leukocytes, suggesting a potential role for trout B cells as antigen-presenting cells (APCs).

T-cell responses against CD19+ pediatric acute lymphoblastic leukemia mediated by bispecific T-cell engager (BiTE) are regulated contrarily by PD-L1 and CD80/CD86 on leukemic blasts

T-cell immunotherapies are promising options in relapsed/refractory B-precursor acute lymphoblastic leukemia (ALL). We investigated the effect of co-signaling molecules on T-cell attack against leukemia mediated by CD19/CD3-bispecific T-cell engager. Primary CD19+ ALL blasts (n≥10) and physiologic CD19+CD10+ bone marrow precursors were screened for 20 co-signaling molecules. PD-L1, PD-1, LAG-3, CD40, CD86, CD27, CD70 and HVEM revealed different stimulatory and inhibitory profiles of pediatric ALL compared to physiologic cells, with PD-L1 and CD86 as most prominent inhibitory and stimulatory markers. PD-L1 was increased in relapsed ALL patients (n=11) and in ALLs refractory to Blinatumomab (n=5). Exhaustion markers (PD-1, TIM-3) were significantly higher on patients' T cells compared to physiologic controls. T-cell proliferation and effector function was target-cell dependent and correlated to expression of co-signaling molecules. Blockade of inhibitory PD-1-PD-L and CTLA-4-CD80/86 pathways enhanced T-cell function whereas blockade of co-stimulatory CD28-CD80/86 interaction significantly reduced T-cell function. Combination of Blinatumomab and anti-PD-1 antibody was feasible and induced an anti-leukemic in vivo response in a 12-year-old patient with refractory ALL. In conclusion, ALL cells actively regulate T-cell function by expression of co-signaling molecules and modify efficacy of therapeutic T-cell attack against ALL. Inhibitory interactions of leukemia-induced checkpoint molecules can guide future T-cell therapies.

Conservation of structural and interactional features of CD28 and CD80/86 molecules from Nile tilapia (Oreochromis niloticus)

Interaction of CD28 with CD80 or CD86 molecules provides a costimulatory signals required in T cell activation. In this study, we cloned and analyzed a CD28 gene (On-CD28) and a CD80/86 gene (On-CD80/86) from Nile tilapia (Oreochromis niloticus). Sequence analysis revealed the typical characteristics of On-CD28 protein; for instance, the proline-based motif (¹¹⁷TYPPPL¹²²) is essential in binding of CD28 to CD80/86 ligands. Moreover, an extracellular Ig domain was found in On-CD80/86; this domain is responsible in binding of CD28 to CD80/86 receptors. Subcellular localization analysis showed that both On-CD28 and On-CD80/86 were distributed predominantly in the cytomembrane. Yeast two-hybrid assay showed that On-CD28 directly interacted with On-CD80/86. On-CD28 and On-CD80/86 transcripts were detected in all the examined tissues of healthy Nile tilapia, and the highest expression levels of On-CD28 and On-CD80/86 were detected in the brain and heart, respectively. Following a bacterial challenge using Streptococcus agalactiae in vivo, On-CD28 and On-CD80/86 were upregulated in head kidney, spleen, intestines, and brain. However, they showed different expression profiles in response to stimulation with inactivated S. agalactiae in vitro. These findings indicated that the interaction of On-CD28 with On-CD80/86 provides a costimulatory signals that possibly play an important role in T cell activation during S. agalactiae infection.

Characterization and expression analysis of grouper (Epinephelus coioides) co-stimulatory molecules CD83 and CD80/86 post Cryptocaryon irritans infection

Co-stimulatory molecules (CD83, CD80 and CD86), belong to immunoglobulin superfamily, are type I membrane glycoprotein, which express on antigen presenting cells and provide the second signal for the activation of T lymphocytes. In the present study, we cloned the grouper's CD83 (675 bp) and CD80/86 (876 bp). Homology analysis showed that both EcCD83 and EcCD80/86 shares the highest amino acid similarity (51% and 47%) for the overall sequence with puffer fish (Takifugu rubripes). Some conserved features and important functional residues in mammalian CD83, CD80 and CD86 were also identified from these molecules of teleosts including grouper, suggesting the function of both molecules may be conserved among vertebrates. In transfected HEK293T cells, both molecules localized on the membrane surface. Tissue distribution analysis showed both EcCD83 and EcCD80/86 mRNAs were mainly expressed in immune organs, and EcCD80/86 was extremely higher expressed in mucosal immune tissues including skin and gill than systematic immune organs, which indicates these co-stimulatory molecules may prime T cell activation in local mucosal tissues. In Cryptocaryon irritans infected groupers, the expression level of EcCD83 and EcCD80/86 were both seen significant up-regulation in the skin at most tested time points.

CD28-mediated T cell response is upregulated by exogenous application of autologous Hsp70-peptide complex in a tumor-bearing host

Hsp70, a highly conserved protein, has gained plenty of attention by virtue of its adjuvant capability to induce peptide-specific cytotoxic T lymphocyte responses. In this study, we have investigated the effect of autologous Hsp70-peptide complex (or simply autologous Hsp70) on the expression of CD28 on T cells and its effector functions through macrophage activation. Further, we investigated the effect of Hsp70 on the expression of CD80 and CD86 on macrophages isolated from normal and tumor-bearing host to provide costimulatory signal for T cell activation and secretion of IL-2 and IFN-γ during interaction. We found that treatment of autologous Hsp70 effectively activated TAMs to induce higher expression of CD28 on T cells through T cells-macrophage interaction. Treatment of autologous Hsp70 induces higher expression of CD80 and CD86 on TAMs, as a result, increases B7/CD28 interaction, which in turns activates T cells and induces higher production of IL-2 and IFN-γ, thereby increasing antigen-specific T cell proliferation. With our novel study, we have provided the strong insights into the role of extracellular Hsp70 on the expression of CD28 costimulatory molecule on T cells, which helps in the activation and generation of antigen-specific T cell effector functions in a tumor-bearing host to curb malignancy.

Impact of PRRSV on activation and viability of antigen presenting cells

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important diseases of swine industry. The causal agent, PRRS-virus (PRRSV), is able to evade the host immune response and survive in the organism causing transient infections. Despite all scientific efforts, there are still some gaps in the knowledge of the pathogenesis of this disease. Antigen presenting cells (APCs), as initiators of the immune response, are located in the first line of defense against microorganisms, and are responsible for antigen recognition, processing and presentation. Dendritic cells (DCs) are the main type of APC involved in antigen presentation and they are susceptible to PRRSV infection. Thus, PRRSV replication in DCs may trigger off different mechanisms to impair the onset of a host effective immune response against the virus. On the one side, PRRSV may impair the basic functions of DCs by regulating the expression of major histocompatibility complex class II and CD80/86. Other strategy followed by the virus is the induction of cell death of APCs by apoptosis, necrosis or both of them. The impairment and/or cell death of APCs could lead to a failure in the onset of an efficient immune response, as long as cells could not properly activate T cells. Future aspects to take into account are also discussed in this review.