Immunological characterization of a gammadelta T-cell stimulatory ligand on autologous monocytes

IMGT® Biocuration and Comparative Analysis of Bos taurus and Ovis aries TRA/TRD Loci

The adaptive immune response provides the vertebrate immune system with the ability to recognize and remember specific pathogens to generate immunity, and mount stronger attacks each time the pathogen is encountered. T cell receptors are the antigen receptors of the adaptive immune response expressed by T cells, which specifically recognize processed antigens, presented as peptides by the highly polymorphic major histocompatibility (MH) proteins. T cell receptors (TR) are divided into two groups, αβ and γδ, which express distinct TR containing either α and β, or γ and δ chains, respectively. The TRα locus (TRA) and TRδ locus (TRD) of bovine (Bos taurus) and the sheep (Ovis aries) have recently been described and annotated by IMGT^® biocurators. The aim of the present study is to present the results of the biocuration and to compare the genes of the TRA/TRD loci among these ruminant species based on the Homo sapiens repertoire. The comparative analysis shows similarities but also differences, including the fact that these two species have a TRA/TRD locus about three times larger than that of humans and therefore have many more genes which may demonstrate duplications and/or deletions during evolution.

The bovine model for elucidating the role of γδ T cells in controlling infectious diseases of importance to cattle and humans

There are several instances of co-investigation and related discoveries and achievements in bovine and human immunology; perhaps most interesting is the development of the BCG vaccine, the tuberculin skin test and the more recent interferon-gamma test that were developed first in cattle to prevent and diagnosis bovine tuberculosis and then applied to humans. There are also a number of immune-physiological traits that ruminant share with humans including the development of their immune systems in utero which increases the utility of cattle as a model for human immunology. These are reviewed here with a particular focus on the use of cattle to unravel γδ T cell biology. Based on the sheer number of γδ T cells in this γδ T cell high species, it is reasonable to expect γδ T cells to play an important role in protective immune responses. For that reason alone cattle may provide good models for elucidating at least some of the roles γδ T cells play in protective immunity in all species. This includes fundamental research on γδ T cells as well as the responses of ruminant γδ T cells to a variety of infectious disease situations including to protozoan and bacterial pathogens. The role that pattern recognition receptors (PRR) play in the activation of γδ T cells may be unique relative to αβ T cells. Here we focus on that of the γδ T cell specific family of molecules known as WC1 or T19 in ruminants, which are part of the CD163 scavenger receptor cysteine rich (SRCR) family that includes SCART1 and SCART2 expressed on murine γδ T cells. We review the evidence for WC1 being a PRR as well as an activating co-receptor and the role that γδ T cells bearing these receptors play in immunity to leptospirosis and tuberculosis. This includes the generation of memory responses to vaccines, thereby continuing the tradition of co-discovery between cattle and humans.

Differential chemokine and cytokine production by neonatal bovine γδ T-cell subsets in response to viral toll-like receptor agonists and in vivo respiratory syncytial virus infection

γδ T cells respond to stimulation via toll-like receptors (TLR). Bovine γδ T cells express TLR3 and TLR7, receptors that are key for the recognition of viruses such as bovine respiratory syncytial virus (BRSV); however, responses of γδ T cells to stimulation via these receptors, and their role during viral infections, remains unclear. Here, we demonstrate that neonatal bovine γδ T cells exhibit robust chemokine and cytokine production in response to the TLR3 agonist, Poly(I:C), and the TLR7 agonist, Imiquimod. Importantly, we observe a similar phenotype in γδ T-cell subsets purified from calves infected with BRSV. Bovine γδ T cells are divided into subsets based upon their expression of WC1, and the response to TLR stimulation and viral infection differs between these subsets, with WC1.1(+) and WC1(neg) γδ T cells producing macrophage inflammatory protein-1α and granulocyte-macrophage colony-stimulating factor, and WC1.2(+) γδ T cells preferentially producing the regulatory cytokines interleukin-10 and transforming growth factor-β. We further report that the active vitamin D metabolite 1,25-dihydroxyvitamin D3 does not alter γδ T-cell responses to TLR agonists or BRSV. To our knowledge, this is the first characterization of the γδ T-cell response during in vivo BRSV infection and the first suggestion that WC1.1(+) and WC1(neg) γδ T cells contribute to the recruitment of inflammatory populations during viral infection. Based on our results, we propose that circulating γδ T cells are poised to rapidly respond to viral infection and suggest an important role for γδ T cells in the innate immune response of the bovine neonate.

Annotation and classification of the bovine T cell receptor delta genes

Background

γδ T cells differ from αβ T cells with regard to the types of antigen with which their T cell receptors interact; γδ T cell antigens are not necessarily peptides nor are they presented on MHC. Cattle are considered a "γδ T cell high" species indicating they have an increased proportion of γδ T cells in circulation relative to that in "γδ T cell low" species such as humans and mice. Prior to the onset of the studies described here, there was limited information regarding the genes that code for the T cell receptor delta chains of this γδ T cell high species.

Results

By annotating the bovine (Bos taurus) genome Btau_3.1 assembly the presence of 56 distinct T cell receptor delta (TRD) variable (V) genes were found, 52 of which belong to the TRDV1 subgroup and were co-mingled with the T cell receptor alpha variable (TRAV) genes. In addition, two genes belonging to the TRDV2 subgroup and single TRDV3 and TRDV4 genes were found. We confirmed the presence of five diversity (D) genes, three junctional (J) genes and a single constant (C) gene and describe the organization of the TRD locus. The TRDV4 gene is found downstream of the C gene and in an inverted orientation of transcription, consistent with its orthologs in humans and mice. cDNA evidence was assessed to validate expression of the variable genes and showed that one to five D genes could be incorporated into a single transcript. Finally, we grouped the bovine and ovine TRDV1 genes into sets based on their relatedness.

Conclusions

The bovine genome contains a large and diverse repertoire of TRD genes when compared to the genomes of "γδ T cell low" species. This suggests that in cattle γδ T cells play a more important role in immune function since they would be predicted to bind a greater variety of antigens.

Antigen-independent priming: a transitional response of bovine γδ T-cells to infection

Analysis of global gene expression in immune cells has provided unique insights into immune system function and response to infection. Recently, we applied microarray and serial analysis of gene expression (SAGE) techniques to the study of γδ T-cell function in humans and cattle. The intent of this review is to summarize the knowledge gained since our original comprehensive studies of bovine γδ T-cell subsets. More recently, we have characterized the effects of mucosal infection or treatment with microbial products or mitogens on gene expression patterns in sorted γδ and αβ T-cells. These studies provided new insights into the function of bovine γδ T-cells and led to a model in which response to pathogen-associated molecular patterns (PAMPs) induces ‘priming’ of γδ T-cells, resulting in more robust responses to downstream cytokine and/or antigen signals. PAMP primed γδ T-cells are defined by up-regulation of a select number of cytokines, including MIP1α and MIP1β, and by antigens such as surface IL2 receptor α (IL-2Rα) and CD69, in the absence of a prototypic marker for an activated γδ T-cell, IFN-γ. Furthermore, PAMP primed γδ T-cells are more capable of proliferation in response to IL-2 or IL-15 in the absence of antigen. PAMPs such as endotoxin, peptidoglycan and β-glucan are effective γδ T-cell priming agents, but the most potent antigen-independent priming agonists defined to date are condensed oligomeric tannins produced by some plants.

Characterization of the gammadelta T cell response to acute leukemia

BACKGROUND

Previous work from our center has suggested a correlation between increased donor-derived Vdelta1+ gammadelta T cells and long-term relapse-free survival following bone marrow transplantation for leukemia. Questions remain, however, as to whether this observation can be explained by a gammadelta T cell-based immune response against primary leukemia.

METHODS

We examined gammadelta T cell receptor (TCR) phenotype, cell proliferation, and cytolytic activity following culture with irradiated primary leukemia blasts from a haploidentical first-degree relative. Subsequently, we also studied the gammadelta TCR phenotype and complimentarity determining region 3 (CDR3) cDNA sequences from 17 newly diagnosed leukemia patients.

RESULTS

In 17/28 (61%) of in vitro cultures, gammadelta T cells proliferated in culture with primary blasts. Vdelta1+ T cells were proportionally increased in all cultures and were the predominant cell population in 6/17. In the 7 cultures where cytotoxicity could be assessed, 6 (86%) showed some degree of cytotoxicity to the primary leukemia. Vdelta1+ T cells were also the predominant gammadelta T cell subtype in pre-treatment leukemia patients principally due to loss of Vdelta2+ T cells rather than expansion of Vdelta1+ cells. The Vdelta1 CDR3-region cDNA sequence from these patients revealed exclusive use of the Jdelta1 constant region and sequence conservation in 4/11 patients.

CONCLUSIONS

gammadelta T cells exhibit an in vitro response to primary leukemia blasts that is manifested by proliferation, an increased proportion of Vdelta1+ T cells, and cytotoxicity to the primary leukemia blasts. The Vdelta1+ T cell population is also predominant in newly diagnosed leukemia patients likely due to a loss of circulating Vdelta2+ T cells. A small proportion of newly diagnosed patients showed Vdelta1 CDR3 region similarity. These findings suggest a role for gammadelta T cells in the immune response to leukemia.

Identification of three new bovine T-cell receptor delta variable gene subgroups expressed by peripheral blood T cells

To understand the biology of gammadelta T cells in ruminants, it is necessary to have a comprehensive picture of gammadelta T-cell receptor gene diversity and expression. In this study, three new subgroups of bovine T-cell receptor delta (TRD) variable genes were identified by RT-PCR and sequencing and homology with TRDV genes from other mammals determined. Previously unidentified TRDV subgroup genes described in this study include the bovine homologues of ovine TRDV2, TRDV3, and TRDV4 which were named accordingly. TRDV2 subgroup has two genes (TRDV2-1 and TRDV2-2) while we found the previously identified TRDV1 has at least eight genes corresponding to separate genomic sequences. Nucleotide and amino acid sequences for particular gene subgroups between cattle and sheep were more than 87% identical but identities among TRDV subgroups within a species were much less, with bovine TRDV4 having <45% identity to the other three bovine TRDV gene subgroups. Analysis of circulating bovine gammadelta T cells revealed that genes from all four TRDV subgroups were expressed in combination with TRDJ1, TRDJ3, and TRDC, although TRDV4 was the least represented, and all displayed a variety of CDR3 junctional lengths. Finally, some genes within the TRDV1, TRDV2, and TRDV3 subgroups recombined with TRAV incorporating TRAJs, suggesting dual use.

Differential TCR gene usage between WC1 − and WC1 + ruminant γδ T cell subpopulations including those responding to bacterial antigen

Ruminant gammadelta T cells are divided into subpopulations based on the presence or absence of WC1 co-receptors (scavenger-receptor-cysteine-rich family members uniquely expressed on gammadelta T cells). Evidence suggests WC1+ are inflammatory while WC1- are regulatory and that they also differ in their tissue distribution. Recently, this paradigm was refined further as cells that produce interferon-gamma and proliferate to autologous antigens, leptospira antigens, or IL-12 were largely found within the WC1+ subpopulation that bears the WC1.1 antigenic epitope but not that bearing the WC1.2 epitope. Here, the T cell receptor gene expression by these different subpopulations (WC1-, WC1.1+, and WC1.2+) was compared using flow cytometrically-purified cells and reverse transcriptase-polymerase chain reaction (RT-PCR). The WC1- gammadelta T cells had transcripts for all 11 possible combinations of the TRG subgroup V and C genes while those in both WC1+ subpopulations were restricted to TRGV3-TRGC5 and TRGV7-TRGC5. In contrast, all three subpopulations expressed transcripts from all four known bovine TRDV genes. Further analysis of the WC1+ gammadelta T cells that proliferated in leptospira antigen-stimulated cultures indicated that they do not represent a unique subpopulation within the larger WC1+ population based on their TCR gene usage. Moreover, sequencing of 65 transcripts showed that their junctional regions were diverse as TRGJ5-1, TRGJ5-2, TRDJ1, and TRDJ3 were used, and CDR3s ranged from 9 to 24 amino acids. The restricted but shared gammadelta TCR gene usage for WC1.1+, WC1.2+, and WC1(+)-antigen-responsive cells leaves open the possibility that the WC1 co-receptor is an important determining element in the activation process and subsequent response.

Bovine T cell receptor gamma variable and constant genes: combinatorial usage by circulating gammadelta T cells

Studies here describe expression and sequence of several new bovine T cell receptor gamma (TRG) genes to yield a total of 11 TRG variable (TRGV) genes (in eight subgroups) and six TRG constant (TRGC) genes. Publicly available genomic sequences were annotated to show their placement. Homologous TRG genes in cattle and sheep were assigned, using four accepted criteria. New genes described here include the bovine TRGC6, TRGV2, and TRGV4, homologues of ovine TRGC4, TRGV2, and TRGV4, respectively. The bovine Vgamma7 and BTGV1 clones (previously TRGV4 and TRGV2, respectively) were reassigned to new subgroups TRGV7 and TRGV8, respectively, with approval by the IMGT Nomenclature Committee. Three TRGV subgroups (TRGV5, TRGV6, and TRGV8) were further designated as TRGV5-1 and TRGV5-2, TRGV6-1 and TRGV6-2, and TRGV8-1 and TRGV8-2 because each subgroup is comprised of two mapped genes. The complete sequence of bovine TRGC5 is also reported, for which a limited number of nucleotides was previously available, and shown to be most closely related to ovine TRGC5. Analysis of circulating gammadelta T cells revealed that rearrangement of TRGV genes with TRGC genes is largely dictated by their proximity within one of the six genomic V-J-C cassettes, with all TRG genes expressed by bovine peripheral blood gammadelta T cells. Cattle are useful models for gammadelta T cell biology because they have gammadelta T cells that respond to isopentenylpyrophosphate (IPP) antigens, while mice do not, and some bovine TRGV genes cluster closely with human genes.

Function of ruminant gammadelta T cells is defined by WC1.1 or WC1.2 isoform expression

WC1 is a transmembrane glycoprotein and member of the scavenger receptor cysteine rich (SRCR) family that is uniquely expressed on gammadelta T cells. The WC1 isoforms referred to as WC1.1, WC1.2, and WC1.3 are expressed on discrete subpopulations of gammadelta T cells with WC1.1 and WC1.2 expressed on mostly nonoverlapping gammadelta T cell populations. Studies have demonstrated a potential role for WC1 in modulating the response of gammadelta T cells but have not converged into a single accepted paradigm. Recent investigations that examined changing representation among mononuclear cells with age and patterns of proliferation and cytokine production by subsets bearing one or more of the previously identified variants of the WC1 molecule are summarized here. While the decrease in percentages within blood in the first year of life was found to be precipitous for WC1.1+ gammadelta T cells it was not for WC1.2+ cells. While both populations proliferated to mitogen stimulation there was a bias towards responses by WC1.2+ cells. In leptospira antigen-stimulated cultures and autologous mixed lymphocyte reaction (AMLR) cultures WC1.1+ cells proliferated and produced interferon-gamma (IFN-gamma) while WC1.2+ cells did to a much lower extent. This suggested functional differences related to the isoform of WC1 expressed. Under Th1-polarizing conditions, the WC1.1+ cells also made IFN-gamma whereas the vast majority of cells expressing WC1.2 did not. Despite the difference in IFN-gamma production, cells bearing either WC1 isoform had similar transcription levels of the high affinity IL-12 receptor subunit (IL-12Rbeta2) as well as of the transcription factors T-bet and GATA-3 when cultured with IL-12. Both populations transcribed low levels of IL-10 mRNA under Th1-polarizing conditions and TGF-beta transcripts were ubiquitously expressed by each of these cell types. Cloning and sequencing of the cytoplasmic tails of the WC1 isoforms revealed a consensus ITAM in all three isoforms but a DENY sequence adjacent to one of the SH-2 binding sites of WC1.1 only. The results suggest that WC1+ gammadelta T cells differentiated on the basis of WC1 isoform expression play distinct roles in immune responses that may be dictated by WC1 intracellular signaling.

Mononuclear cell subsets in bronchoalveolar lavage fluid during Dictyocaulus viviparus infection of calves: a potential role for gamma/delta TCR-expressing cells in airway immune responses?

Mononuclear cell populations in the lungs of calves infected with Dictyocaulus viviparus were studied during primary infection and reinfection in order to identify cells involved in development of protective immunity to parasitic bronchitis. Three groups of calves were either inoculated with 500 third-stage larvae at both weeks 0 and 10 (n = 6), inoculated only at week 10 (n = 6), or remained uninfected (n = 3). The animals were monitored weekly by collection of bronchoalveolar lavage fluid (BALF), blood and faeces. Among mononuclear BALF-cell populations, the gamma/delta TCR-expressing cells showed a pronounced transient increase in proportion as well as in relative cell size 2 weeks post primary infection, whereas CD4-, CD8-, Ig- and CD14-expressing cells showed no significant differences related to the infection. The increase in gamma/delta TCR-expressing cells coincided with significantly increased proportions of eosinophils and recovery of adult worms in BALF. After reinfection, gamma/delta TCR-expressing cells increased again, but not until week 3 post inoculation, whereas eosinophils were increased by week 2 and reached higher levels than after primary infection. After reinfection, establishment of D. viviparus was less successful than after primary infection. In conclusion, these results indicate a role for gamma/delta TCR-expressing lymphocytes in the pathogenesis of D. viviparus infection.

Regulation of Numbers of Macrophages in the Endometrium of the Sheep by Systemic Effects of Pregnancy, Local Presence of the Conceptus, and Progesterone

Many species exhibiting hemochorial placentation experience an accumulation of macrophages in the endometrium during pregnancy. For the present study, it was tested whether macrophages also accumulate in the endometrium of the sheep, which is a species undergoing an epitheliochorial placentation. An additional objective was to determine whether regulation of endometrial macrophage number occurs via systemic or local signals and whether progesterone is one of these signals. The approach was to evaluate presence of macrophages immunohistochemically using antibodies to CD68 and CD14. Tissues examined were from cyclic ewes in the luteal phase of the estrous cycle, unilaterally-pregnant ewes at day 140 of pregnancy in which pregnancy was surgically confined to one uterine horn, ovariectomized ewes, and ovariectomized ewes treated with progesterone for 44 days. Macrophages were localized predominately to the stromal compartment of the stratum compactum region of the endometrium. In non-pregnant ewes, macrophages were not abundant regardless of physiological status. Increased numbers of endometrial macrophages were seen for both the pregnant and non-pregnant uterine horns of unilaterally pregnant ewes. Numbers of macrophages were higher in the endometrium from the pregnant uterine horn than from endometrium from the non-pregnant uterine horn. Results indicate that macrophages accumulate in the endometrium by day 140 of pregnancy in the sheep and that this induction is because of both systemic and local signals. Progesterone appears not to be an important regulator of numbers of endometrial macrophages.

Differential requirements for proliferation of CD4+ and γδ+ T cells to spirochetal antigens

Alphabeta+ and gammadelta+ T cells have different mechanisms of epitope recognition and are stimulated by antigens of different chemical nature. An immunization model with antigens from the spirochete Brachyspira hyodysenteriae was used to examine the requirements for proliferation of circulating porcine CD4+ and gammadelta+ T cells in mixed lymphocyte cultures. CD4+ T cells only responded to stimulation with B. hyodysenteriae antigens, whereas gammadelta+ T cells proliferated when cultures were stimulated with either spirochetal antigens or interleukin-2 (IL-2). T cells that had proliferated expressed high levels of IL-2-receptor-alpha (IL-2Ralpha). Furthermore, neutralization of IL-2 at the beginning of the culture period was more efficient in blocking gammadelta+ than CD4+ T cell proliferation. Immunization induced interferon-gamma (IFN-gamma) production by CD4+ T cells, whereas only a small fraction of the antigen-stimulated gammadelta+ T cells produced this cytokine. Our results indicate that, under the same environmental conditions, CD4+ T cell functions are more tightly regulated when compared to gammadelta+ T cells. We conclude that these differences are due, in part, to the enhanced gammadelta+ T cell responsiveness to IL-2.

The WC1(+) gammadelta T-cell population in cattle: a possible role in resistance to intracellular infection

Intracellular infections are important in veterinary medicine and detailed understanding of the associated immune responses is needed for optimal development of strategies based on diagnosis and vaccination. It is generally accepted that cell-mediated immune responses are of greatest importance in intracellular infections and recent studies from several bovine models of infection indicate that WC1(+) gammadelta T-cells have a number of possible levels of involvement, which remain incompletely defined. Investigations of experimental infection with Mycobacterium bovis in cattle have indicated that WC1(+) gammadelta T-cells are among the first cells to accumulate at initial sites of infection, an observation which has been linked with decreased numbers of these cells in the circulation within days of infection. These WC1(+) gammadelta T-cells have been shown to respond in vitro, both to protein antigens and to non-protein, phosphate containing antigens of M. bovis and to be capable of producing IFN-gamma. Studies of M. bovis infection in calves depleted of WC1(+) gammadelta T-cells by monoclonal antibody have suggested that the presence of these cells is associated with development of a Th1-biased acquired immune response. In combination, these observations allow speculation regarding a possible role for WC1(+) gammadelta T-cells as a link between the innate and acquired immune systems which is instrumental in establishing an appropriate response.

Activation of bovine peripheral blood gammadelta T cells for cell division and IFN-gamma production

Bovine peripheral blood gammadelta T cells have been evaluated for effector function (IFN-gamma production) and clonal expansion in a variety of systems including following activation by mitogens, IL-12, and stimulation, through the T cell receptor (TCR) with anti-CD3 monoclonal antibody (mAb), a cell-bound molecule and a soluble antigenic extract. To evaluate cell division, carboxyfluorescein succinimidyl ester (CFSE) loading of cells and flow cytometric analysis were used, while IFN-gamma production was evaluated by intracytoplasmic staining. It was found that bovine gammadelta T cells produced IFN-gamma and clonally expanded when stimulated through the TCR/CD3 complex by a cell-associated autologous molecule on monocyte, by bacterial components following in vivo sensitization of gammadelta T cells with a leptospira vaccine or by anti-CD3 mAb. In addition, gammadelta T cells were activated efficiently for effector function but not clonal expansion by culturing with IL-12. In contrast, stimulation by Con A or PMA/ionomycin induced efficient replication but only low level IFN-gamma production which was not enhanced by the presence of IL-12. In several systems the amount of IFN-gamma produced per cell by gammadelta T cells was less than that produced by CD4 T cells in the same cultures.