Cattle CTLA-4, CD28 and chicken CD28 bind CD86: MYPPPY is not conserved in cattle CD28

Prediction of CD28-CD86 protein complex structure using different level of resolution approach

Immune system plays essential role in functioning of higher organisms. Its hyperactivity can lead to autoimmune diseases or even anaphylactic shock while hypoactivity leads to proneness to infections or even cancer. T-cells play crucial role in immunity mechanisms and their activation and inhibition is strictly controlled by the regulatory proteins, such as CD28 and CTLA-4. Activity of these proteins is controlled by a pair of ligands, named CD80 and CD86, which can non-covalently bound to their receptors. While structure of human CTLA-4-CD86 complex in known, there is still no available structure for the CD28-CD86 system. To obtain the reliable structure of CD28-CD86 complex we first validated our methodology on the CTLA-4-CD86 system. Then coarse-grained UNRES-dock molecular docking simulation was performed followed by all-atom molecular dynamics simulations. As a result, we obtained a complete CD28-CD86 complex structure on atomistic level, in which interaction interface is consistent with available data. We also determined the kinetic properties for CTLA4-CD86 and CD28-CD86 complexes with use of coarse-grained model and determined the key residues for complex formation with use of Robetta, PPCheck and HawkDock servers. Our results not only verify high accuracy of the UNRES-dock method, but also provide a highly reliable model of the CD28-CD86 complex, which can be used in further studies and drug design.

Molecular characterization of a T cell co-stimulatory receptor, CD28 of rock bream (Oplegnathus fasciatus): Transcriptional expression during bacterial and viral stimulation

CD28 is a co-stimulatory receptor that provides a critical second signal alongside T cell receptors for the activation of naive T cells. We characterized the CD28 gene of rock bream, which has a deduced amino acid sequence of 221 residues with an extracellular Ig-superfamily V domain, transmembrane region, and cytoplasmic tail. The conservation in domain structures and other motifs shows that it is highly likely that RbCD28 is a homologue of mammalian CD28 and may have related co-stimulatory functions. RbCD28 is constitutively expressed in most tissues that were analysed, with a relatively higher expression in teleost lymphoid organs, such as spleens, gills, trunk kidneys and skin. Unlike human CD28, RbCD28 is highly expressed in skin and gill-associated lymphoid organs. Although gills showed constitutive expression of RbCD28 in control animals, after a pathogen challenge, induction of CD28 was low, particularly in RSIV and E. tarda infection. Whereas induction of RbCD28 was observed in kidney during E. tarda and S. iniae infection, downregulation was observed during RSIV infection. In the case of the liver, E. tarda caused an initial upregulation of RbCD28. RbCD28 activation of T cells in the spleen was limited to S. iniae infection. Activation of RbCD28 observed in lymphoid organs during infection of various pathogens shows its key role as a co-stimulatory receptor of T cells.

Comparative Analysis of Immune Checkpoint Molecules and Their Potential Role in the Transmissible Tasmanian Devil Facial Tumor Disease

Immune checkpoint molecules function as a system of checks and balances that enhance or inhibit immune responses to infectious agents, foreign tissues, and cancerous cells. Immunotherapies that target immune checkpoint molecules, particularly the inhibitory molecules programmed cell death 1 and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), have revolutionized human oncology in recent years, yet little is known about these key immune signaling molecules in species other than primates and rodents. The Tasmanian devil facial tumor disease is caused by transmissible cancers that have resulted in a massive decline in the wild Tasmanian devil population. We have recently demonstrated that the inhibitory checkpoint molecule PD-L1 is upregulated on Tasmanian devil (Sarcophilus harrisii) facial tumor cells in response to the interferon-gamma cytokine. As this could play a role in immune evasion by tumor cells, we performed a thorough comparative analysis of checkpoint molecule protein sequences among Tasmanian devils and eight other species. We report that many of the key signaling motifs and ligand-binding sites in the checkpoint molecules are highly conserved across the estimated 162 million years of evolution since the last common ancestor of placental and non-placental mammals. Specifically, we discovered that the CTLA-4 (MYPPPY) ligand-binding motif and the CTLA-4 (GVYVKM) inhibitory domain are completely conserved across all nine species used in our comparative analysis, suggesting that the function of CTLA-4 is likely conserved in these species. We also found that cysteine residues for intra- and intermolecular disulfide bonds were also highly conserved. For instance, all 20 cysteine residues involved in disulfide bonds in the human 4-1BB molecule were also present in devil 4-1BB. Although many key sequences were conserved, we have also identified immunoreceptor tyrosine-based inhibitory motifs (ITIMs) and immunoreceptor tyrosine-based switch motifs (ITSMs) in genes and protein domains that have not been previously reported in any species. This checkpoint molecule analysis and review of salient features for each of the molecules presented here can serve as road map for the development of a Tasmanian devil facial tumor disease immunotherapy. Finally, the strategies can be used as a guide for veterinarians, ecologists, and other researchers willing to venture into the nascent field of wild immunology.

A targeted fimA DNA vaccine prevents alveolar bone loss in mice after intra-nasal administration

AIM

To construct a dendritic cell (DC)-targeted DNA vaccine against FimA of Porphyromonas gingivalis and evaluate the immunogenicity and protection in mice.

MATERIALS AND METHODS

A targeted DNA plasmid pCTLA4-FimA, which encodes the signal peptide and extracellular regions of mouse cytotoxic T lymphocyte-associated antigen 4 (CTLA4), the hinge and Fc regions of human Igγ1 and FimA of P. gingivalis, was constructed. Mice were immunized with pCTLA4-FimA, the non-targeted DNA plasmid pFimA, which contains only fimA gene, or pCI vector intra-nasally. Serum and saliva antibody responses were detected by enzyme-linked immunosorbent assay. The protection against P. gingivalis-induced periodontitis was evaluated by measuring alveolar bone loss in mice.

RESULTS

Mice immunized with pCTLA4-FimA showed elevated levels of specific serum IgG and salivary IgA antibody responses compared with mice immunized with pFimA (p<0.01). Both pFimA and pCTLA4-FimA immunized groups showed significantly lower alveolar bone loss, with the magnitude protection greater in the latter (p<0.01), compared with the pCI immunized group.

CONCLUSIONS

The DC-targeted DNA construct pCTLA4-FimA enhanced both systemic and mucosal immunity following intra-nasal immunization. A DNA-based immunization strategy may be an effective way to attenuate periodontitis induced by P. gingivalis.

Identification of cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) isoforms in the Pekin duck

Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4, CD152) is an inhibitory T cell receptor predominately expressed on activated T cells. The duck CTLA-4 (DuCTLA-4) cDNA and a transcript lacking the predicted transmembrane encoding region (DuCTLA-4DeltaTM) were isolated from splenocytes using RT-PCR. The predicted DuCTLA-4 protein showed an identity of 92%, 49% and 47% with chicken, human and mouse homologues, respectively. Sequence comparison revealed conservation of residues implicated in the B7 ligand binding, disulfide linkages, glycosylation and intracellular signaling. DuCTLA-4 mRNA was predominately expressed in primary and secondary immune organs. DuCTLA-4 and DuCTLA-4DeltaTM transcripts were differentially regulated in PBMCs. Flow cytometric analysis showed constitutive expression of DuCTLA-4 protein on freshly isolated PBMCs and a modest increase upon mitogen stimulation. Our observations suggest that DuCTLA-4 and its isoform DuCTLA-4DeltaTM evolved before the divergence of birds and mammals. Both DuCTLA-4 isoforms have significant structural homology to mammalian CTLA-4 proteins but their individual roles in the regulation of duck immune responses remains to be elucidated.

Structure and function of programmed death (PD) molecules

Programmed death (PD) molecules belong to the B7 family of co-stimulatory proteins and function in adaptive immunity. PD-1 (CD279) is expressed on lymphocytes and macrophages, and its ligand (PD-L1, CD274) on immune cells and non-hematopoietic cells. Ligation of PD-1 on lymphocytes inhibits T-cell proliferation, cytokine production, and cytolytic function by phosphorylation of immunoreceptor tyrosine-based switch motifs and blockade of T cell receptor signaling. PD-1 and PD-L1 interactions are essential to maintain peripheral immune tolerance and to modulate activation of naïve T cells. Decreased expression results in autoimmunity in mouse models, and increased expression is a key feature of chronic viral infections in humans.

Fusion protein encoded by a CTLA-4 targeted DNA construct binds to human dendritic cells

Fusing antigens to cytotoxic T-lymphocyte antigen 4 (CTLA-4) represents an effective approach to enhance DNA vaccine efficacy. It has been speculated that the direct targeting of CTLA-4 fusion antigens to antigen-presenting cells (APCs) causes antigens to be processed and presented to T cells more efficiently, leading to a stronger immune response. In the present study, dendritic cells (DCs), the most potent APCs, were generated from human monocytes. The specific binding of CTLA-4 fusion protein to DCs was investigated by flow cytometry. The results showed that the CTLA-4 fusion protein was capable of binding to the B7 molecules on human DCs with specificity.

Corynebacterium pseudotuberculosis and its role in ovine caseous lymphadenitis

Caseous lymphadenitis (CLA) of sheep, caused by Corynebacterium pseudotuberculosis, has been a significant disease in the majority of sheep-rearing regions for over a century. Because of the chronic and often sub-clinical nature of the infection, it has proved difficult to control and prevalence is high in many parts of the world, which in turn leads to significant economic losses for farmers. This review describes the important characteristics of C. pseudotuberculosis and examines the pathogenesis and epidemiology of the infection in sheep. The review also discusses the immune response to infection and describes the methods that have been developed to control CLA, with particular emphasis on the use of vaccination and serological testing.

Immunogenicity and persistence of a targeted anti-caries DNA vaccine

We have previously reported that a targeted anti-caries DNA vaccine, pGJA-P, induced accelerated and increased antibody responses compared with a non-targeted anti-caries DNA vaccine. Recently, pGJA-P/VAX, a new targeted anti-caries DNA vaccine for human trials, was constructed by replacing the pCI vector used in the construction of pGJA-P with pVAX1, the only vector authorized by the US Food and Drug Administration in clinical trials. Here, we report on our exploration of the kinetics of the antibody responses generated following pGJA-P/VAX immunization and the persistence of pGJA-P/VAX at both the inoculation site and the draining lymph nodes. Intranasal vaccination of mice with pGJA-P/VAX induced strong antibody responses that lasted for more than 6 months. Furthermore, pGJA-P/VAX could still be detected at both the inoculation site and the draining cervical lymph nodes 6 months after immunization. Thus, the persistent immune responses are likely due to the DNA depot in the host, which acts as a booster immunization.

Protective efficacy of a targeted anti-caries DNA plasmid against cariogenic bacteria infections

We have previously reported that a targeted anti-caries DNA plasmid pGJA-P/VAX which was constructed against the antigenic determinants of Streptococcus mutans (S. mutans) successfully induced antibody responses in mice and monkeys. The present study explored the protective efficacy of pGJA-P/VAX against cariogenic bacterial challenge. Groups of rats were orally challenged with S. mutans or Streptococcus sobrinus (S. sobrinus) and then immunized with pGJA-P/VAX or the vector pVAX1 intranasally. Serum IgG and salivary IgA antibody levels were assessed by an enzyme-linked immunosorbent assay and caries activity was evaluated by the Keyes method. The results showed that specific salivary IgA antibody responses were induced following intranasal vaccination with pGJA-P/VAX. Moreover, immunization with pGJA-P/VAX resulted in significantly reduced enamel and dentinal caries lesions in rats after S. mutans infection and significantly reduced enamel caries lesions after S. sobrinus infection. Thus, pGJA-P/VAX was not only protective toward S. mutans infection, but also provided cross-strain protection against S. sobrinus infection in rats.

Immunogenicity and protective efficacy of a targeted fusion DNA construct against dental caries

Targeting antigens to antigen-presenting cells by fusion to cytotoxic T lymphocyte-associated antigen 4 (CTLA4) has been shown to be a highly efficient method to enhance the efficacy of DNA vaccines. The purpose of this study was to determine the immunogenicity and protective efficacy of the targeted fusion DNA construct pGJA-P, which contains the signal peptide and extracellular regions of human CTLA4 gene, the hinge and Fc regions of human Iggamma1 gene, the glucan-binding domain of the Streptococcus mutans gtfB gene and the A-P fragment of the S. mutans pac gene, compared with the fusion DNA construct pGLUA-P, which contains only the glucan-binding domain of the S. mutansgtfB gene and the A-P fragment of the S. mutans pac gene. BALB/c mice were immunized with pGJA-P, pGLUA-P, or pCI (vector) by the intramuscular or intranasal route. Specific anti-PAc and anti-GTF-I serum IgG and salivary IgA antibody responses were assessed by an enzyme-linked immunosorbent assay. Wistar rats were orally challenged with S. mutans and immunized with pGJA-P, pGLUA-P, or pCI intramuscularly or intranasally, and caries activity was evaluated by the Keyes method. pGJA-P induced accelerated and increased serum and salivary antibody responses in mice compared with pGLUA-P. Rats immunized with pGJA-P had significantly fewer caries lesions than rats immunized with pGLUA-P (p < 0.01). Thus, this study demonstrates that the targeted DNA construct pGJA-P can enhance both systemic and mucosal immunity and may be a useful strategy for improving the protective efficacy of anticaries DNA vaccines.

Immunization with the gene expressing woodchuck hepatitis virus nucleocapsid protein fused to cytotoxic-T-lymphocyte-associated antigen 4 leads to enhanced specific immune responses in mice and woodchucks

A number of options are available to modify and improve DNA vaccines. An interesting approach to improve DNA vaccines is to fuse bioactive domains, like cytotoxic-T-lymphocyte-associated protein 4 (CTLA-4), to an antigen. Such fusion antigens are expressed in vivo and directed to immune cells by the specific bioactive domain and therefore possess great potential to induce and modulate antigen-specific immune responses. In the present study, we tested this new approach for immunomodulation against hepadnavirus infection in the woodchuck model. Plasmids expressing the nucleocapsid protein (WHcAg) and e antigen (WHeAg) of woodchuck hepatitis virus (WHV) alone or in fusion to the extracellular domain of woodchuck CTLA-4 and CD28 were constructed. Immunizations of mice with plasmids expressing WHcAg or WHeAg led to a specific immunoglobulin G2a (IgG2a)-dominant antibody response. In contrast, fusions of WHcAg to CTLA-4 and CD28 induced a specific antibody response with comparable levels of IgG1 and IgG2a. Furthermore, the specific IgG1 response to WHcAg/WHeAg developed immediately after a single immunization with the CTLA-4-WHcAg fusion. Woodchucks were immunized with plasmids expressing WHeAg or the CTLA-4-WHcAg fusion and subsequently challenged with WHV. CTLA-4-WHcAg showed an improved efficacy in induction of protective immune responses to WHV. In particular, the anti-WHsAg antibody response developed earlier after challenge in woodchucks that received immunizations with CTLA-4-WHcAg, consistent with the hypothesis that anti-WHs response is dependent on a Th cell response to WHcAg. In conclusion, the use of fusion genes represents a generally applicable strategy to improve DNA vaccination.

Molecular characterization of CD28 and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) of woodchuck (Marmota monax)

Eastern woodchuck (Marmota monax) became an important animal model to study the immunological processes in hepatitis B virus infection. To facilitate further study of T-cell responses in this model, we cloned and sequenced the cDNAs of Woodchuck CD28 and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), which play important roles for the regulation of T-cell activation by delivering the costimulation signals. According to the deduced amino-acid sequences, Woodchuck CD28 showed a similarity of 70% to 80% to its mammalian homologues. Woodchuck CTLA-4 has a higher similarity of 74% to 85% to corresponding mammalian CTLA-4 molecules. The strict conservation of critical amino-acid residues like cystein and asparagine residues in Woodchuck CD28 and CTLA-4 suggests that both molecules may structurally resemble their human or mouse homologues. A hexapeptide motif, MYPPPY, which has been supposed to be essential for the interaction with CD80, is present in both Woodchuck CD28 and CTLA-4. The cloned cDNAs of Woodchuck CD28 and CTLA-4 were placed under the control of the cytomegalovirus (CMV) promoter of the mammalian expression vector pcDNA3. Both proteins were expressed and detected by respective crossreactive antibodies in transiently transfected mammalian cells. By immunohistochemical staining with these antibodies, CD28 and CTLA-4 were also detected on cultured woodchuck peripheral blood lymphocytes. The molecular characterization of Woodchuck CD28 and CTLA-4 will facilitate studies on the T-cell response to hepadnavirus in the woodchuck model.

Optimization of DNA vaccination immune responses in dairy cows: effect of injection site and the targeting efficacy of antigen-bCTLA-4 complex

The objectives of this study were to evaluate the effects of immunization site and antigen presenting cell targeting on cattle immune responses to DNA immunization. Cows were vaccinated with the plasmid expression vector pCI alone, pCI encoding the bacterial antigen beta-galactosidase (pCI-beta-gal) or pCI encoding bCTLA 4 fused to beta-gal (pCI-bCTLA-hIgG-beta-gal). The plasmids were delivered by intramuscular, intradermal, intramammary gland, or intra supramammary lymph node needle-injection. Both vaccines induced significant humoral and cellular immune responses. pCI-beta-gal elicited a higher IgG response than immunization with pCI-bCTLA-hIgG-beta-gal. Cows injected intramuscularly and intramammary had higher IgG and IgG-1 humoral responses than cows immunized intradermaly or in the lymph nodes. The injection site did not significantly affect the magnitude of the IgG2 and IgM antibody responses, although a trend similar to the IgG results was observed. The lymphocyte proliferation index was higher with pCI-beta-gal but was not affected by the injection site. These results suggest that in bovine, the injection site can affect immune responses but they do not provide evidence that bCTLA-4-hIgG-antigen targeting is effective in cattle.

Efficacy of DNA vaccination by different routes of immunisation in sheep

DNA vaccination, delivered through various routes, has been used extensively in laboratory animals. Few studies have focused on veterinary species and while results obtained in laboratory animals can often be extrapolated to veterinary species this is not always the case. In this study we have compared the effect of the route of immunisation with DNA on the induction of immune responses and protection of sheep to challenge with live Corynebacterium pseudotuberculosis. Intramuscular injection of plasmid DNA encoding an inactivated form of the phospholipase D (PLD) antigen linked to CTLA4-Ig resulted in the induction of a strong memory response and sterile immunity following challenge in 45% of the animals. In contrast, gene gun delivery or subcutaneous (SC) injection of the DNA vaccine induced comparatively poor responses and insignificant levels of protection. Thus, DNA vaccine efficacy in sheep is strongly influenced by the route of vaccination. Amongst intramuscular vaccinates, protected sheep had significantly elevated IgG2 responses compared to unprotected animals, while both subgroups had equivalent IgG1 levels. This suggests that the presence of IgG2 antibodies and hence a Th1-like response, induced by the DNA vaccine gave rise to protective immunity against C. pseudotuberculosis.

The comparative efficacy of CTLA-4 and L-selectin targeted DNA vaccines in mice and sheep

The access of antigens to antigen presenting cells (APCs) appears to be a rate-limiting step in the generation of immune responses to DNA vaccines. The cytotoxic T lymphocyte antigen 4 (CTLA-4) and L-selectin represent attractive ligands for use in the targeting of antigen to APCs and lymph nodes. CTLA-4 binds with high affinity to the B7 membrane antigen on APCs, while L-selectin functions as a lymphocyte homing marker and binds to CD34 on the surface of high endothelial venule cells. DNA vaccines encoding human immunoglobulin (HIg), fused to either CTLA-4 or L-selectin, have been shown to generate up to 10,000-fold higher anti-HIg antibody responses than DNA vaccines encoding HIg alone. In this study, the ability of CTLA-4 or L-selectin mediated targeting to enhance the humoral immune response to an alternate vaccine antigen was investigated. DNA vaccines encoding CTLA-4-HIg and L-selectin-HIg fused to the host-protective 45W antigen from Taenia ovis were constructed. In BALB/c mice, the L-selectin targeted vaccine did not improve either the magnitude or speed of antibody responses of vaccinated mice. In contrast, the CTLA-4 targeted DNA vaccine generated 45W-specific antibody responses which were up to 30-fold higher than those achieved with non-targeted DNA vaccination. The kinetic of the antibody response generated following CTLA-4 targeted DNA vaccination was also significantly faster than that achieved with non-targeted DNA vaccination, or with adjuvanted protein vaccination. Vaccination of outbred sheep with DNA vaccines expressing either murine or ovine CTLA-4 targeted antigen failed to enhance immune responses. These findings indicate that CTLA-4 targeting may find application in the improvement of DNA vaccines, but requires further development for applications in large animal species.

Molecular cloning and sequencing of canine T-cell costimulatory molecule (CD28)

T-cells express CD28 and CTLA-4, and through binding to their shared ligands (CD80/CD86) on antigen presenting cells, provide a potent co-stimulatory signal for T-cell activation and proliferation. To investigate the role of CD28 in canine immune system, we hereby report the molecular cloning and sequencing of the full-length complementary DNA (cDNA) coding for canine CD28, from pokeweed mitogen stimulated canine peripheral blood lymphocytes. The cloned cDNA contains an open reading frame of 663 nucleotides, encoding for a polypeptide of 221 amino acids. The amino acid sequence of the canine CD28 showed 91.9, 80, and 79.6% similarities with those of the cat, cattle, and human counterparts, respectively. Five sequence motifs of TATT or ATTTA involved in the regulation of gene expression by influencing mRNA stability are found in the 3' untranslated region. The hexapeptide motif (MYPPPY), five cysteine residues, a potential N-glycosylation site and a cytoplasmic phosphatidylinositol 3-kinase binding site in canine CD28 molecule are completely conserved in canine CTLA-4. The availability of full length canine CD28 will provide a useful molecule for studying its role in dog immune system.

Porcine CTLA4-Ig lacks a MYPPPY motif, binds inefficiently to human B7 and specifically suppresses human CD4+ T cell responses costimulated by pig but not human B7

The CTLA4 receptor (CD152) on activated T lymphocytes binds B7 molecules (CD80 and CD86) on APC and delivers a signal that inhibits T cell proliferation. Several regions involved in binding to B7 are known, but the relative importance of these is not clear. We have cloned porcine CTLA4 (pCTLA4). Although highly homologous to human CTLA4 (hCTLA4), the predicted protein sequence contains a leucine for methionine substitution at position 97 in the MYPPPY sequence. A fusion protein constructed from the extracellular regions of pCTLA4 and the constant regions of human IgG1 (pCTLA4-Ig) bound porcine CD86 with equivalent affinity to that of hCTLA4-Ig. However, pCTLA4-Ig bound poorly to human CD80 and CD86 expressed on transfectants and EBV-transformed human B cells. In functional assays with MHC class II-expressing porcine endothelial cells and human B cells, pCTLA4-Ig blocked human CD4+ T cell responses to pig but not human cells, whereas control hCTLA4-Ig inhibited responses to both. Comparison between mouse, human, and porcine CTLA4-Ig suggests that the selective binding of pCTLA4-Ig to porcine CD86 molecules is due to the L for M substitution at position 97. Our results indicate that pCTLA4-Ig may be a useful reagent to define the precise nature of the interaction between B7 and CTLA4. By failing to inhibit the delivery of costimulatory signals provided by human B7, it may also prove to be a relatively specific inhibitor of the direct human T cell response to immunogenic pig tissue.

Molecular cloning and expression of feline CD28 and CTLA-4 cDNA

Feline CD28 and CTLA-4 (CD152) cDNA were cloned from Con-A stimulated feline peripheral blood mononuclear cells (PBMC) by rapid amplification of cDNA end-PCR (RACE-PCR). Both CD28 and CTLA-4 proteins belong to the immunoglobulin superfamily (Ig SF) and are composed of a signal sequence, an extracellular domain, a transmembrane domain and a cytoplasmic domain. The open reading frame (ORF) of CD28 cDNA encoded a predicted protein of 221 amino acids and that of CTLA-4 cDNA encoded a predicted protein of 223 amino acids. The B7 ligands binding motif MYPPPY hexamer was found on the extracellular Ig V-like domains of both receptors and phosphatidylinositol 3-kinase (PI 3-kinase) binding motifs pYMNM for CD28 and pYVKM for CTLA-4 were identified in the cytoplasmic domains. Comparisons of amino acid sequences of feline proteins with known sequences of other species indicated that rabbit CD28 and CTLA-4 were most closely related and mouse molecules were the least conserved with feline molecules. Comparison of each domain of both molecules with that of other animals showed that the cytoplasmic domain of CTLA-4 was 100% conserved and that of CD28 was the most conserved domain. The cloned CD28 and CTLA-4 cDNA could be expressed in transfected mammalian cells. Expression of feline CD28 and CTLA-4 mRNA in freshly isolated feline PBMC was demonstrated by RT-PCR. Stimulation of PBMC with Con-A similarly increased the expression of both CD28 and CTLA-4 mRNA.

Molecular cloning and sequencing of a cDNA encoding the feline cytotoxic T-lymphocyte-associated protein 4 (CTLA4) homologue

The feline CTLA4 cDNA encodes a transmembrane protein which shares 87.9% sequence identity with the human CTLA4 molecule. The cytoplasmic region of the feline CTLA4 is identical to that of humans and mice, which suggests conserved function(s) such as the regulation of cell-surface expression of this molecule.

Targeting improves the efficacy of a DNA vaccine against Corynebacterium pseudotuberculosis in sheep

A large-scale DNA vaccination trial was performed with sheep to investigate whether an antigen targeted by CTLA-4 enhanced and accelerated the humoral immune response. Vaccination with genetically detoxified phospholipase D (DeltaPLD) has been shown to be effective, at least partially, against Corynebacterium pseudotuberculosis, the causal agent of caseous lymphadenitis in sheep. CTLA-4 binds to B7 on antigen-presenting cells and thus was used to direct the fusion antigens to sites of immune induction. Here we demonstrated that targeting DeltaPLD as a CTLA-4 fusion protein significantly enhanced the speed, magnitude, and longevity of the antibody response compared to that obtained with DNA encoding DeltaPLD. While all groups of sheep vaccinated with DNA encoding DeltaPLD were afforded better protection against an experimental challenge with C. pseudotuberculosis than those immunized with an irrelevant plasmid or those left unimmunized, the best protection was provided by the targeted DNA vaccine. We propose that targeting antigens to antigen-presenting cells offers a generic strategy for enhancing the efficacy of DNA vaccines.

Complete sequence determination of the mouse and human CTLA4 gene loci: cross-species DNA sequence similarity beyond exon borders

CTLA4 (CD152), a receptor for the B7 costimulatory molecules (CD80 and CD86), is considered a fundamental regulator of T-cell activation. In this paper, we present the complete primary structure of the mouse and human CTLA4 gene loci. Sequence comparison between the mouse and the human CTLA4 gene loci revealed a high degree of sequence conservation both for homologous noncoding regions (65-78% identity) and for coding regions (72-98% identity), with an overall score of 71% over the entire length of the two genes. Of the CTLA4 genomic regions aligned, five simple repetitive elements were found in the mouse locus, whereas two simple repetitive sequences were localized on the human locus. RNA blot analysis of mouse and human primary tissues indicated that both CTLA4 and T-cell receptor transcripts were found in most organs with generally higher levels in lymphoid tissues. The conservation of CTLA4 gene patterning raises the possibility that constrained gene evolution of CTLA4 may be linked to conserved transcriptional control of this locus.

Role of the CTLA-4 receptor in T cell activation and immunity. Physiologic function of the CTLA-4 receptor

Costimulatory molecules of the B7 family regulate the activation of T lymphocytes. T cell activation is promoted by binding of B7 molecules to CD28 and inhibited by binding to CTLA-4 (CD152). The balance between positive signals through CD28 and negative signals through CTLA-4 is critical for the fate of the T cell and is subject to tight regulation. Recent in vitro and in vivo studies have significantly advanced our understanding of the function of the CTLA-4 receptor. The results of these experiments suggest that CTLA-4 is critical for the induction of self-tolerance, and that it may have distinct signaling functions in resting and activated T cells. In resting T cells, CTLA-4 crosslinking leads to cell-cycle arrest, whereas in activated T cells, CTLA-4 crosslinking induces apoptosis. In this article, we will review the physiologic functions of the CTLA-4 receptor.

Cloning of two members of the SIRP alpha family of protein tyrosine phosphatase binding proteins in cattle that are expressed on monocytes and a subpopulation of dendritic cells and which mediate binding to CD4 T cells

Recent experimental studies have greatly clarified the function of cell surface molecules in the induction and modulation of T cell responses by antigen-presenting cells (APC). However, the differences in ability to stimulate T cells evident for different types and subpopulations of the same APC, such as dendritic cell subsets, is less well understood. This report details an investigation of an antigen expressed on monocytes that is also expressed on a subset of cattle afferent lymph veiled cells (ALVC). A cDNA library derived from cattle monocytes was screened with monoclonal antibodies (mAb) for expression in COS-7 cells. Using separate mAb for screening, two cDNA were cloned, the sequences of which showed a single long open reading frame encoding a predicted type I glycoprotein of 506 amino acids that contained three immunoglobulin superfamily domains and a long 112-amino acid cytoplasmic tail. We have termed this antigen MyD-1, reflecting its myeloid and dendritic cell distribution. Analysis of the EMBL database revealed that the molecule is a member of the recently described family of signal regulatory proteins (SIRP). The outeremost Ig domain was of the adhesion/receptor I-type, suggesting that MyD-1 might bind to a ligand on another cell. Evidence for this was subsequently obtained by demonstrating that COS-7 cells transfected with MyD-1 cDNA bound CD4 T cells and this binding was blocked by specific mAb. The potential importance of this interaction was supported by the finding that the proliferation of resting memory CD4 T cells to ovalbumin-pulsed monocytes was significantly reduced in the presence of mAb to MyD-1. A role for the molecule in the modulation of the monocyte/dendritic APC response is also predicted from the existence of multiple potential tyrosine phosphorylation sites in the cytoplasmic domain, including the presence of an immunoreceptor tyrosine-based inhibitory motif (ITIM) and the observation that the SIRP alpha family members have been shown to bind to SHP-1 and SHP-2. Together these data indicate a possible functional importance for MyD-1 in the regulation of monocyte and dendritic cell function.

Afferent lymph veiled cells stimulate proliferative responses in allogeneic CD4+ and CD8+ T cells but not gamma delta TCR+ T cells

Dendritic cells were identified in afferent lymph derived by lymphatic cannulation of cattle, stained with monoclonal antibody (mAb) to the bovine workshop cluster 6 (WC6) antigen, which is highly expressed on bovine afferent lymph veiled cells, and sorted with a fluorescence-activated cell sorter. These cells expressed major histocompatibility complex (MHC) class I and II and CD1b but not CD14. They bound human and murine CTLA4-immunoglobulin (CTLA4-Ig) fusion proteins indicating expression of CD80 and or CD86. Dendritic cells induced proliferative responses in allogeneic CD4+ and CD8+ cells sorted from blood but did not induce responses in purified allogeneic WC1+, gamma/delta T cells, which are CD2-, CD4-, CD8- and are the major gamma delta T-cell population in cattle blood, even when interleukin-2 (IL-2) was added to cultures. A WC1-, CD2+ gamma delta T-cell receptor (TCR)+ population predominates in cattle spleens and proliferation of a T-cell line with this phenotype was not induced by allogeneic dendritic cells, with or without added IL-2. The observations imply that the ligand for the gamma delta TCR expressed on the two populations is not present on allogeneic dendritic cells or that the costimulatory molecules expressed on dendritic cells that render them highly effective at stimulating MHC class I- and class II-restricted CD8+ and CD4+ T cells are not recognized by the WC1+ or WC1- gamma/delta T cells. Expression of CD28 by the four cell types was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). Purified CD4+ and CD8+ cells both produced CD28 transcripts but neither purified WC1+ cells nor the WC1- gamma delta TCR+ cell line did so. The findings indicate that CD80 and or CD86 are involved in the stimulation of CD4+ and CD8+ alpha beta TCR+ T cells but not in the stimulation of either of the two gamma delta TCR+ populations.