A large proportion of bovine T cells express the gamma delta T cell receptor and show a distinct tissue distribution and surface phenotype

The numbers, phenotype, and tissue distribution of gamma delta T cells in cattle were studied using two monoclonal antibodies (mAbs) which react with the bovine gamma delta T cell receptor (TCR). Both mAbs stained 20-40% of T cells in peripheral blood, and immunoprecipitated molecules of 44 and 36 kd (reduced) and 70-80 kd (non-reduced). In cattle the majority of circulating gamma delta T cells showed a distinct surface phenotype; they expressed T19, a 215 kd molecule described in sheep and cattle which marks only gamma delta T cells. Bovine gamma delta T cells were also CD2-, CD4-, and mostly CD8-, and failed to express CD6, a molecule possibly involved in T cell activation. The distribution of gamma delta T cells in cattle lymphoid tissues differed markedly from that in humans, in that bovine gamma delta T cells were concentrated around lymph node trabeculae and were usually sparse or absent from the B cell and T cell domains of lymph nodes. Like most other species studied, gamma delta T cells in cattle were localized to epithelial surfaces, particularly within the skin and intestine, indicating that it was at these sites where gamma delta T cells functioned. Our results provide further evidence for the unusual localization, recirculation pattern, and phenotype of gamma delta T cells, and also show that some features of gamma delta T cells can differ quite markedly from species to species.     

Sequence and organization of the human T cell delta chain gene

A novel human T cell receptor (TcR) gene, located 85 kbp upstream to the C alpha coding regions, was isolated using human genomic clones to identify cDNA homologous to messages encoded by this region. The deduced protein sequence of this gene is highly homologous to that of the newly identified constant region found in the murine TcR alpha chain locus. This gene undergoes rearrangements and is expressed at the RNA level in human thymocytes, peripheral T cells and several leukemic T cell lines which have been shown to express the surface gamma-delta heterodimer, suggesting that this gene encodes the human T cell delta chain.     

T cell receptor gene rearrangements in cells with natural killer activity in the mouse

Cell-mediated recognition can operate at different levels of complexity and specificity based largely on the time of appearance of effector mechanisms during the course of evolution. Antigen-specific cytotoxic T lymphocytes require both T cell receptor genes and lectin-like cell adhesion molecules (LFA-1, LFA-2, lymphocyte function-associated) to initiate and maintain stable effector target cell conjugates. Natural killer (NK) cells, on the other hand, do not require expression of T cell receptor genes in the recognition and killing of tumor cells and virally infected cells. Adhesion is mediated by a family of glycoprotein molecules, of which the LFA-1 and LFA-2 molecules appear as the most likely candidates. NK-mediated cytolysis proceeds in the absence of MHC restriction, but nevertheless appears to be triggered by depressed levels of self MHC products on the cell surface of target cells. Finally, interleukin 2-dependent, cloned cell lines with NK-like cytotoxic activity should no longer be considered as bona-fide NK cells but rather reclassified as a subset of T cells which displays NK function.     

Detection of a T cell receptor delta chain with an anti-TCR alpha chain serum.

Two types of T cell antigen-specific receptors have been described. Most peripheral blood T lymphocytes express, at their surface, an antigen receptor consisting of alpha and beta subunits, while a small subset of thymocytes and a minority of mature T lymphocytes express a heterodimeric receptor termed gamma delta. Whereas the gene segments localization corresponding to the TCR gamma and beta chains are separate, genes encoding the joining and the constant regions of TCR delta chain are located between the TCR V alpha region and the J alpha-C alpha gene cluster. To determine whether V alpha gene segments are used by delta chains, immunoprecipitations from human TCR gamma delta expressing cell clones were performed with an anti-alpha serum. The results show that a rabbit antiserum raised against the purified REX TCR alpha subunit immunoprecipitates a TCR delta chain from the cell surface of only one human T cell clone termed SO1. However, since no SO1 RNA hybridization is observed with REX TCR V alpha probe and SO1 cloned cells do react with an anti-V delta 2 monoclonal antibody, we conclude that TCR delta and alpha chains expressed a limited structural homology and that REX TCR V alpha gene do not seem to be frequently used in a functional delta chain.     

Natural killer T cells and the regulation of asthma

A crucial role has been suggested for invariant natural killer T cells (iNKT) in regulating the development of asthma, a complex and heterogeneous disease characterized by airway inflammation and airway hyperreactivity (AHR). iNKT cells constitute a unique subset of T cells responding to endogenous and exogenous lipid antigens, rapidly secreting a large amount of cytokines, which amplify both innate and adaptive immunity. Herein, we review recent studies showing a requirement for iNKT cells in various models of asthma in mice and monkeys as well as studies in human patients. Surprisingly, in several different murine models of asthma, distinct subsets of iNKT cells were required, suggesting that iNKT cells serve as a common critical pathogenic element for many different forms of asthma. The importance of iNKT cells in both allergic and non-allergic forms of asthma, which are independent of adaptive immunity and associated with airway neutrophils, may explain situations previously found to be incompatible with the Th2 paradigm of asthma.     

Murine epidermal gamma/delta T cells express Fc gamma receptor II encoded by the Fc gamma R alpha gene.

Short-term bulk cultures and some long-term clones and lines of murine T cell receptor (TcR) gamma/delta-bearing epidermal T cells (dEC) were found to express an Fc gamma receptor II (Fc gamma RII), as revealed by reactivity with the monoclonal antibody 2.4G2. Northern blot analysis showed that the Fc gamma RII expressed on dEC is encoded solely by the Fc gamma R alpha gene. While all the various cultured dEC cell populations analyzed exhibit lectin-dependent cellular cytotoxicity, only those which expressed Fc gamma R alpha were also capable of mediating antibody-dependent cellular cytotoxicity (ADCC). These results in combination with the previous demonstration of Fc gamma R alpha on mouse natural killer cells support an essential role for Fc gamma R alpha in ADCC and extend an analogy with surface CD16 (Fc gamma RIII) expression and ADCC in human natural killer cells and peripheral TcR gamma/delta T cells.     

Functional double-negative T cells in the periphery express T cell receptor Vβ gene products that cause deletion of single-positive T cells

A proportion of peripheral T cells lack surface expression of the CD4 or CD8 coreceptor molecules and hence are designated as “double negative” (DN). Most DN T lymphocytes express the Γ/β T cell receptor (TcR), but a minor fraction of them, in both humans and mice, express the α/β TcR. Whereas α/β⁺ DN T lymphocytes are infrequent (< 1%) in conventional lymphoid organs (spleen, blood, lymph node), they account for two-thirds of the T cells residing in adult bone marrow. Analysis of the TcR Vβ repertoire expressed by peripheral DN T cells revealed a high frequency of cells bearing autoreactive TcR that cause deletion of “single-positive” (SP) (CD4⁺CD8^? or CD4^?CD8⁺) T cells. Peripheral DN cells thus represent a cell type that is relatively resistant to clonal deletion. Furthermore, such cells have not been inactivated (anergized) in vivo since they proliferate and secrete interleukins in response to cross-linking by monoclonal antibodies specific for these Vβ gene products that are deleted in SP T cells. These results might help to understand the association of peripheral expansion of DN cells and development of autoimmune diseases.     

Two distinct immunogenic epitopes on the alpha chain of human T cell antigen receptor

Monoclonal antibodies (MAb) to human T Cell Antigen Receptor (TCR) have been used to study the structure and function of TCR. Using purified alpha/beta heterodimeric protein, we have generated two MAb against human TCR alpha protein. The two MAb, alpha F1 and alpha F2, recognized amino acid residues 141-159 and 212-231 of the constant region of the alpha chain TCR. Although neither MAb reacted with viable T cells, both antibodies immunoprecipitated TCR alpha/beta heterodimer from HPB-ALL, Jurkat, PBL and a 32 kDa in vitro translation product of alpha chain cDNA. These antibodies have been shown to be useful in the immunohistochemical staining of human tissues. These two MAb, together with other anti-framwork MAb to TCR, should provide valuable reagents in the study of TCR and clinical classification of T cell lineage neoplasms.     

Role of T cell receptor delta gene in susceptibility to celiac disease

There is a strong genetic influence on the susceptibility to celiac disease. Although in the vast majority of patients with celiac disease, the HLA-DQ(l ^* 0501, 1 ^* 0201) heterodimer encoded by the alleles HLADQA1 ^* 0501 and HLA-DQB1 ^* 0201 seems to confer the primary disease susceptibility, it cannot be excluded that other genes contribute to disease susceptibility, as indicated by the difference in concordance rates between monozygotic twins and HLA identical siblings (70% vs. 30%). Obviously other genes involved in the genetic control of T cell mediated immune response could potentially influence susceptibility to celiac disease. The density of T cells using the T cell receptor (TCR) is considerably increased in the jejunal epithelium of patients with celiac disease, an abnormality considered to be specific for celiac disease. This suggests an involvement of T cells in the pathogenesis of the disease. To ascertain whether the TCR delta (TCRD) gene contributes to celiac disease susceptibility we carried out an association study and genetic linkage analysis using a highly polymorphic microsatellite marker at the TCRD locus on chromosome 14q11.2. The association study demonstrated no significant difference in allele frequencies of the TCRD gene marker between celiac disease patients and controls; accordingly, the relative risk estimates did not reach the level of statistical significance. In the linkage analysis, performed in 23 families, the logarithm of the odds (LOD) scores calculated for celiac disease versus the TCRD gene marker excluded linkage, suggesting that there is no determinant contributing to celiac disease status at or 5 cM distant to the analyzed TCRD gene marker. In conclusion, the results of the present study provide no evidence that the analyzed TCRD gene contributes substantially to celiac disease susceptibility.Abbreviations AGA Antigliadin antibodies - EMA Antiendomysium antibodies - LOD score Logarithmic odds ratio - PCR Polymerase chain reaction - RR Relative risk - TCR T cell receptor     

Pro-T cells in fetal thymus express c-kit and RAG-2 but do not rearrange the gene encoding the T cell receptor β chain

Ten percent of 15-day fetal thymocytes of mice were Pgp-1⁺Thy-1^lo cells. Half were strongly stained with monoclonal antibodies (mAb) recognizing the oncogene product, c-kit, but were not stained with mAb against non-T cell markers such as B220, Mac-1 and Gr-1. The isolated Pgp-1⁺c-kit⁺ thymocytes showed no rearranged bands for V-DJ and D-J of T cell receptor (TcR) β, but Pgp-1^?-c-kit^? thymocytes showed D-J rearranged bands. Both cells expressed the RAG-2 gene which is required for the V(D)J recombination process. When Pgp-1⁺c-kit⁺ thymocytes were cultured in 2-deoxyguanosine-treated alymphocytic fetal thymus, they became TcR-expressing mature type T cells, but this differentiation was reduced by the addition of anti c-kit mAb. These data indicate that Pgp-1⁺c-kit⁺ thymocytes are pro-T cells with the potential to differentiate mature T cells in the thymic environment. This study also indicates that c-kit-mediated signals promote the differentiation of thymocytes during their early stages.     

Human Vgamma9/Vdelta2 effector memory T cells express the killer cell lectin-like receptor G1 (KLRG1)

The killer cell lectin-like receptor G1 (KLRG1) is expressed in natural killer (NK) cells and effector memory alphabeta T cells. Gammadelta T cells represent an unconventional lymphocyte population that shares characteristics of NK cells and T cells and links innate and adaptive immunity. Vgamma9/Vdelta2 T cells comprise the majority of peripheral human gammadelta T cells and respond to the microbial metabolite (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP). Here, we demonstrate that KLRG1 is expressed in a significant proportion of Vgamma9/Vdelta2 T cells in cord blood and in the majority of peripheral Vgamma9/Vdelta2 T cells from adult donors. KLRG1+ Vgamma9/Vdelta2 T cells displayed an effector memory phenotype, as KLRG1 was expressed mainly in Vgamma9/Vdelta2 T cells lacking CD27, CD45RA, CD62L, and CC chemokine receptor 7 (CCR7). Unlike alphabeta T cells, where possession of KLRG1 identified effector memory cells with impaired proliferative capacity, KLRG1+ Vgamma9/Vdelta2 T cells were able to proliferate vigorously upon stimulation with HMB-PP in the presence of interleukin-2. Moreover, KLRG1 ligation on Vgamma9/Vdelta2 T cells by antibodies did not inhibit HMB-PP-induced proliferation and cytokine production nor cytolysis of Daudi cells.     

Intra- and inter-allelic ordering of T cell receptor beta chain gene assembly

Allelic exclusion at the TCRbeta locus mandates that gene assembly be regulated in a manner that permits feedback inhibition of further complete TCRbeta rearrangements upon pre-TCR expression. Here we show that assembly of TCRbeta chain genes from Vbeta, Dbeta and Jbeta gene segments is intra-allelically ordered, proceeding primarily through DJbeta, and not VDbeta, intermediates. This ensures that Vbeta to DJbeta rearrangement, which can be feedback inhibited, is the final step in the assembly process. A newly assembled VDJbeta rearrangement must be tested to determine if it is in-frame before Vbeta to DJbeta rearrangement is permitted on the alternate allele. This inter-allelic ordering may occur through a general inefficiency of Vbeta to DJbeta rearrangement and/or through static differences in accessibility of the two TCRbeta alleles. However, we find that within the regulatory context of allelic exclusion, Vbeta to DJbeta rearrangement proceeds to completion on both alleles. Furthermore, all possible VDJbeta rearrangements are not completed on one allele before Vbeta to DJbeta rearrangement is initiated on the alternate allele. Together, these data support a dynamic model of inter-allelic accessibility that permits the ordered and efficient assembly of complete variable region genes on both TCRbeta alleles during T cell development.