Novel function for intestinal intraepithelial lymphocytes. Murine CD3+, gamma/delta TCR+ T cells produce IFN-gamma and IL-5.

Intestinal intraepithelial lymphocytes (IEL) from mice are greater than 80% CD3+ T cells and could be separated into four subsets according to expression of CD4 and CD8. In our studies designed to assess the functions of IEL, namely, cytokine production, it was important to initially characterize the various subsets of T cells that reside in IEL. The major subset was CD4-, CD8+ (75% of CD3+ T cells), which contained approximately 45 to 65% gamma/delta TCR+ and 35 to 45% alpha/beta TCR+ T cells. Approximately 7.5% of IEL T cells were CD4-, CD8- (double negative) and gamma/delta+ population. On the other hand, CD4+, CD8+ (double positive) and CD4+, CD8- fractions represented 10% and 7.5% of CD3+ T cells, respectively, which were all alpha/beta TCR+. Inasmuch as CD3+, CD4-, CD8+ T cells are a major subset of IEL which contain both gamma/delta TCR or alpha/beta TCR-bearing cells, the present study was focused on the capability of this subset of IEL T cells to produce the cytokines IFN-gamma and IL-5. Both gamma/delta TCR+ and alpha/beta TCR+ IEL spontaneously produced IFN-gamma and IL-5, although higher frequencies of cytokine spot-forming cells were associated with the alpha/beta TCR+ subset. Approximately 30% of CD8+, gamma/delta TCR+ cells produced both cytokines, whereas approximately 90% of alpha/beta TCR+ T cells produced either IFN-gamma or IL-5. Both gamma/delta TCR+ and alpha/beta TCR+ IEL possessed large quantities of cytokine-specific mRNA, clearly showing that these IEL were programmed for cytokine production. When IEL were activated with anti-gamma/delta or anti-CD8 antibodies, higher numbers of IFN-gamma and IL-5 spot-forming cells were noted. The present study has provided direct evidence that a major function of IEL involves cytokine production, and this is the first evidence that gamma/delta TCR+ cells in IEL possess the capability of producing both IL-5 and IFN-gamma.     

Mucosal T lymphocyte numbers are selectively reduced in integrin alpha E (CD103)-deficient mice.

The mucosal lymphocyte integrin alpha E(CD103)beta 7 is thought to be important for intraepithelial lymphocyte (IEL) localization or function. We cloned the murine integrin gene encoding alpha E, localized it to chromosome 11, and generated integrin alpha E-deficient mice. In alpha E-/- mice, intestinal and vaginal IEL numbers were reduced, consistent with the known binding of alpha E beta 7 to E-cadherin expressed on epithelial cells. However, it was surprising that lamina propria T lymphocyte numbers were diminished, as E-cadherin is not expressed in the lamina propria. In contrast, peribronchial, intrapulmonary, Peyer's patch, and splenic T lymphocyte numbers were not reduced in alpha E-deficient mice. Thus, alpha E beta 7 was important for generating or maintaining the gut and vaginal T lymphocytes located diffusely within the epithelium or lamina propria but not for generating the gut-associated organized lymphoid tissues. Finally, the impact of alpha E deficiency upon intestinal IEL numbers was greater at 3-4 wk of life than in younger animals, and affected the TCR alpha beta+ CD8+ T cells more than the gamma delta T cells or the TCR alpha beta+ CD4+CD8- population. These findings suggest that alpha E beta 7 is involved in the expansion/recruitment of TCR alpha beta+ CD8+ IEL following microbial colonization. Integrin alpha E-deficient mice will provide an important tool for studying the role of alpha E beta 7 and of alpha E beta 7-expressing mucosal T lymphocytes in vivo.     

Expression of murine IL-2 receptor beta-chain on thymic and splenic lymphocyte subpopulations as revealed by the IL-2-induced proliferative response in human IL-2 receptor alpha-chain transgenic mice

Lymphocytes from the human (h) IL-2R alpha chain transgenic mice (TGM) constitutively express high affinity binding sites for hIL-2, consisting of transgenic h-IL-2R alpha and endogenous murine IL-2R beta, and therefore easily proliferate in vitro in response to hIL-2. Our study was undertaken to clarify the hIL-2-responsive lymphocyte subsets in the TGM, which should most likely reflect the normal distribution of m IL-2R beta expression. In both thymus and spleen, the majority of expanded cells by hIL-2 was CD3+CD4-CD8+ TCR alpha beta+ cells. The proliferation of CD4+ cells was not observed at all from either organ despite the expression of transgenic hIL-2R alpha. Potent cellular proliferation was also observed from the thymocytes that had been depleted of CD8+ cells, the expanded cells consisting of CD3- (15-40%) and CD3+ populations (60-85%). Among CD3+ cells, approximately the half portion expressed TCR alpha beta, whereas the other half was suggested to express TCR gamma delta. A variable portion (5-20%) of the CD3+ cells expressed CD8 (Lyt-2) in the absence of Lyt-3, and the CD3+CD8+ cells were confined preferentially to the TCR alpha beta- (TCR gamma delta+) population. In the culture of splenocytes depleted of CD8+ cells, however, the proliferated cells were mostly CD3-CD4-CD8-TCR-Mac1-, whereas a minor portion (10-30%) was CD3+CD4-CD8-TCR alpha beta- (TCR gamma delta+. Analysis of TCR genes at both DNA and mRNA levels confirmed the phenotypical observations. These results strongly suggested that IL-2R beta was constitutively and selectively expressed on the primary murine thymocytes and splenic T and NK cells, except for CD4+ cells in both organs.     

Phenotypic complexity of intraepithelial lymphocytes of the small intestine.

A detailed phenotypic analysis of intraepithelial lymphocytes (IEL) of the small intestine was performed using multicolor fluorescence flow cytometry. CD4+8+ IEL (double positives; DP) could be detected in significant numbers in preparations from several mouse strains. DP IEL expressed Tcr alpha, beta and Thy1. Comparison of Tcr alpha, beta levels of thymocytes and IEL revealed that whereas the majority of DP thymocytes expressed low Tcr levels, DP IEL expressed high, mature T cell levels of Tcr. In addition, DP IEL were generally Ly3- (CD8 beta), unlike their thymic counterparts, which are Ly3+. Ly3 was not present on Tcr gamma, delta IEL, whereas CD4-8+ Tcr alpha, beta IEL contained Ly3- and Ly3+ subsets. The Ly3- population in either Tcr-bearing subset could be further subdivided by Thy1 expression. Ly1 (CD5) expression was also examined, and none of the Tcr gamma, delta IEL were Ly1+. Based on Thy1, Ly3, and Ly1 expression, four CD4-8+ Tcr alpha, beta IEL subsets were detected. The results indicate the cellular complexity of the IEL compartment rivals that found in the thymus. These findings are discussed in light of recent data suggesting an extrathymic origin of some IEL.     

Intraepithelial gamma/delta T cells in duodenal mucosa are related to the immune state and survival time in AIDS.

The proportion of T-cell receptor gamma/delta+ cells and the CD4/CD8 ratio relative to all CD3+ intraepithelial lymphocytes (IEL) were determined by immunofluorescence in duodenal mucosa of late-stage (mostly CDC IVC1/D) subjects (n = 21) infected with human immunodeficiency virus type 1 (HIV-1). The gamma/delta fraction (median, 14.2%; range, 1.7 to 59.8%) was increased (P < 0.03) compared with that in HIV- controls (n = 11; median 2.8%; range, 0.3 to 38%). Also, the number of gamma/delta+ IEL per mucosal unit was increased (P < 0.05) in the HIV+ subjects (median, 11.1/U) compared with the controls (3.2/U). Approximately 100% of the gamma/delta+ IEL were CD8-, and most expressed the Vdelta1vJdelta1-encoded epitope (median, 90.9%). The total number of CD3+ IEL tended to be lower than in the controls (67.4 versus 72.9/U). Both the epithelium and the lamina propria contained mainly CD8+ T cells, the median ratios of CD4+ T cells being 1 and 7.6%, respectively. This result accorded with the reduced CD4 cell number in blood (median, 18 X 10(6)/liter). The HIV+ subjects had increased serum levels of neopterin and beta2-microglobulin (both P < 0.0001), probably reflecting immunostimulation. Serum neopterin and beta2-microglobulin were inversely related to duodenal gamma/delta IEL, particularly in the premortal group (r = -0.97 and r = -0.58, respectively). The increased gamma/delta IEL might reflect enhanced intestinal protection in late-phase HIV infection. Short survival expectancy (<7 months) was associated not only with high levels of neopterin and beta2-microglobulin but also with a reduced number of duodenal gamma/delta+ cells (P < 0.03).     

Developmental regulation of alpha beta T cell antigen receptor expression results from differential stability of nascent TCR alpha proteins within the endoplasmic reticulum of immature and mature T cells.

The alpha beta T cell antigen receptor (TCR) that is expressed on most T lymphocytes is a multisubunit transmembrane complex composed of at least six different proteins (alpha, beta, gamma, delta, epsilon and zeta) that are assembled in the endoplasmic reticulum (ER) and then transported to the plasma membrane. Expression of the TCR complex is quantitatively regulated during T cell development, with immature CD4+CD8+ thymocytes expressing only 10% of the number of surface alpha beta TCR complexes that are expressed on mature T cells. However, the molecular basis for low TCR expression in developing alpha beta T cells is unknown. In the present study we report the unexpected finding that assembly of nascent component chains into complete TCR alpha beta complexes is severely impaired in immature CD4+CD8+ thymocytes relative to their mature T cell progeny. In particular, the initial association of TCR alpha with TCR beta proteins, which occurs relatively efficiently in mature T cells, is markedly inefficient in immature CD4+CD8+ thymocytes, even for a matched pair of transgenic TCR alpha and TCR beta proteins. Inefficient formation of TCR alpha beta heterodimers in immature CD4+CD8+ thymocytes was found to result from the unique instability of nascent TCR alpha proteins within the ER of immature CD4+CD8+ thymocytes, with nascent TCR alpha proteins having a median survival time of only 15 min in CD4+CD8+ thymocytes, but > 75 min in mature T cells. Thus, these data demonstrate that stability of TCR alpha proteins within the ER is developmentally regulated and provide a molecular basis for quantitative differences in alpha beta TCR expression on immature and mature T cells. In addition, these results provide the first example of a receptor complex whose expression is quantitatively regulated during development by post-translational limitations on receptor assembly.     

CD3.TCR1, a human CD3 epitope expressed on viable gamma/delta lymphocytes exclusively.

T lymphocytes express either the alpha/beta or the gamma/delta receptor (TCR) in a mutually exclusive fashion. Both structures are associated on the cell membrane with the CD3 proteins which are thought to transduce signals resulting from antigen recognition. The CD3 complex is present in both alpha/beta and gamma/delta cells and includes at least five proteins (designated gamma, delta, epsilon, zeta and eta). We have developed here a novel mAb, anti-CD3.TCR1, which immunoprecipitates the CD3 molecules from both alpha/beta and gamma/delta cells lysates following solubilization with Triton X-100. While the SDS-PAGE migration profile of the material recognized by either anti-CD3.TCR1 or anti-OKT3 are superimposable in both cell types, this mAb recognizes viable untreated gamma/delta T lymphocytes exclusively. These findings further support the view that molecular interactions within the TCR/CD3 protein complex are distinct in the two T lymphocyte populations.     

The unfolding story of T cell receptor gamma

Antigen-specific, major histocompatibility complex-restricted recognition by classical T cells is mediated by a T cell receptor (TCR) consisting of a disulfide-linked alpha beta heterodimer. During the search for the genes encoding the alpha and beta proteins, a third immunoglobulin-like gene, termed gamma, was uncovered. Like the TCR alpha and beta genes, the TCR gamma gene consists of variable and constant segments that rearrange during T cell development in the thymus. Although the physiological role of TCR gamma remains an enigma, much has been learned with the recent identification of the protein products of this gene family in both mice and humans. The gamma chain is associated with a partner chain, termed delta. The gamma delta heterodimer is associated with an invariant T3 complex, very similar to that associated with the alpha beta heterodimer, and appears predominantly, if not exclusively, on cells with a CD4-, CD8- phenotype both in the thymus and in the periphery. TCR gamma delta is the first T3-associated receptor to appear during thymocyte development and defines a separate T cell lineage distinct from alpha beta-bearing cells. Although TCR alpha beta-bearing cells and TCR gamma delta-bearing cells follow parallel developmental pathways, the diversity of expressed gamma delta receptors is extremely limited relative to that of alpha beta receptors.     

T cell receptor gamma gene status of human alpha/beta+ and gamma/delta+ T cell clones: absence of V9JP rearrangements in alpha/beta+ clones is not a result of a lack of rearrangements involving more 5' J gamma segments

T cell receptor (TCR) gamma gene rearrangements were examined in panels of human T cell clones expressing TCR alpha/beta or gamma/delta heterodimers. Over half of the alpha/beta+ clones had both chromosomes rearranged to C gamma 2 but this was the case for only 20% of the gamma/delta+ clones. While more than half of the gamma/delta+ clones showed a V9JP rearrangement, this configuration was absent from all 49 alpha/beta+ clones analysed. However, this was not a result of all rearrangements being to the more 3' J gamma genes as 11 alpha/beta+ clones had rearrangement(s) to JP1, the most 5' J gamma gene segment. Both alpha/beta+ and gamma/delta+ clones showed a similar pattern of V gamma gene usage in rearrangements to J gamma 1 or J gamma 2 with a lower proportion of the more 3' genes being rearranged to J gamma 2 than for the more 5' genes. Several alpha/beta+ and several gamma/delta+ clones had noncoordinate patterns of rearrangement involving both C gamma 1 and C gamma 2. Eleven out of fourteen CD8+ clones tested had both chromosomes rearranged to C gamma 2 whereas all clones derived from CD4-8- cells and having unconventional phenotypes (CD4-8- or CD4+8+) had at least one C gamma 1 rearrangement. Twelve out of twenty-seven CD4+ clones also had this pattern, suggesting that CD4-8+ clones had a tendency to utilize more 3' J gamma gene segments than CD4+ clones. There was some evidence for interdonor variation in the proportions of TCR gamma rearrangements to C gamma 1 or C gamma 2 in alpha/beta+ clones as well as gamma/delta+ clones. The results illustrate the unique nature of the V9JP rearrangement in gamma/delta+ clones and the possible use of a sequential mechanism of TCR gamma gene rearrangements during T cell differentiation is discussed.     

Tissue localization and CD8 accessory molecule expression of T gamma delta cells in humans

In this study, we used TCR isotype-specific antibodies to examine the frequency, phenotype, and histologic localization pattern of T gamma delta cells in humans. The TCR delta 1+ cells comprised an average of 15% of the splenic CD3+ cells and 7% of circulating T cells. The T gamma delta cells in these human tissues, like their avian counterparts, were often not "double-negative" for the CD4 and CD8 accessory molecules. Approximately 50% of the splenic delta+ cells expressed CD8, and 30% of the delta+ cells in blood were CD8+. T cells of both gamma delta and alpha beta TCR isotypes were exceedingly rare in the skin. The T gamma delta cells exhibited preferential homing to the sinusoidal areas (red pulp) of the spleen and into the epithelial layer of the intestine in humans, as had been previously noted in chickens. Although 80% of the T gamma delta cells in the human intestinal mucosa were localized in the epithelial layer, these cells represented only 5 to 10% of all the CD3+ T cells in this microenvironment. We conclude that T gamma delta cells represent a sizeable subpopulation of the T cells in human peripheral tissues. The phylogenetic conservation of the CD8 expression by peripheral T gamma delta cells and of their preferential homing pattern suggests a special role in bodily defense for this T cell subpopulation.     

Self-reactive, T cell receptor-gamma delta+, lymphocytes from the intestinal epithelium of weanling mice.

Intraepithelial T lymphocytes (IEL) are dispersed throughout the intestinal epithelial lining but their role in cellular immune defense is unknown. Their location suggests that their highly activated state may be due to constant exposure to bacterial Ag. To study IEL specificity and function we have prepared a panel of IEL-T cell hybridomas from both adult and weanling C57B1/6 mice. Many of these expressed TCR-gamma delta, a cell type rare in peripheral lymph nodes and spleen but predominant at epithelial surfaces. We have identified a subset of gamma delta T cells from weanling mice which is self reactive, i.e., these hybrids secrete IL-2 spontaneously, without antigenic stimulation or a requirement for APC. Self-reactive TCR-gamma delta+ hybrids and lines, all of which bear a particular TCR (V gamma 1.1C gamma 4V delta 6), have previously been derived from neonatal thymus and the skin. Northern blot and immunoprecipitation analyses suggest that the self-reactive IEL hybrids also bear a C gamma 4/V delta 6 TCR. Antibody inhibition experiments showed that the self-reactivity of the IEL hybrids is TCR mediated. Spontaneous IL-2 production was blocked by soluble anti-CD3 and anti-TCR-gamma delta antibodies but not by antibodies to the TCR-alpha beta. The self-reactive IEL hybrids lack class II MHC and the class I-like proteins CD1 and TLA but express class I MHC. IEL hybrids may also require the vitronectin receptor as an accessory molecule for their activation because spontaneous IL-2 production is blocked by antibody to the vitronectin receptor as well as by the extracellular matrix protein active site peptide RGDS, but not the control peptide RGES. V gamma 1.1C gamma 4V delta 6 T cells in the thymus, skin, and intestine may represent a small and unique subpopulation of lymphocytes with a potential for autoimmune reactivity at peripheral sites.     

T cell differentiation model based on the expression of T cell receptor chains and genes--study in the human leukemia/lymphoma cell lines

A total of 33 human leukemia/lymphoma cell lines were classified into 4 groups with respect to the pattern of cell membrane (sm) expression of the CD3 and T cell receptor (TCR) molecules; (i) smCD3+TCR alpha beta (16 cell lines), (ii) smCD3+TCR beta delta (1 cell line), (iii) smCD3+TCR gamma delta (3 cell lines) amd (iv) smCD3-TCR- (13 cell lines), respectively. Using monoclonal antibodies (MoAbs) specific to CD3 (NU-T3), TCR alpha chain (alpha F1), TCR beta chain (beta F1), and TCR gamma chain (C gamma M1), respectively, cytoplasmic (cy) expression of these molecules was determined by immunofluorescence test. Expression of cyCD3 was present in all cell lines regardless of groups. In group (i), all 16 cell lines expressed both TCR alpha and beta chains. While only TCR beta chain was expressed in group (ii), TCR gamma chain was expressed in all 3 cell lines of group (iii). One (PEER) of the three in group (iii) expressed TCR beta chain as well. In group (iv), we found 8 cell lines with cyTCR alpha expression, 11 cell lines with cyTCR beta expression, and 10 cell lines with cyTCR gamma expression, respectively. For TCR genes, except 1 cell line all cell lines were found to present rearranged C beta gene and its mRNA, including all 3 TCR gamma/delta cell lines of group (iii). One of the TCR alpha beta cell lines exhibited rearranged C delta and J delta genes as well as its mRNA. Two cell lines of the 13 CD3-TCR- of group (iv) exhibited rearranged C delta and J delta and its mRNA. An NK-like activity and IL-2 production were induced in the TCR beta delta and gamma delta cell lines [group (ii) and (iii)] by treatment with PHA and PMA.     

Avian T cells expressing gamma delta receptors localize in the splenic sinusoids and the intestinal epithelium

A panel of murine mAb specific for the chicken homologues of the CD3, CD4, CD8, TCR gamma delta, and TCR alpha beta has been used to study the distribution of T cells expressing these markers in sections of chicken lymphoid tissues. These studies have revealed that the T cells possessing the two classes of TCR occupy distinct histologic microenvironments. The TCR1+ cells (gamma delta TCR homologue) are localized preferentially in the splenic sinusoids and the intestinal epithelium, where most of them express the CD8 homologue. The TCR2+ cells (alpha beta TCR homologue), a majority of which express the CD4 homologue, are found primarily in the splenic periarteriolar sheath and the lamina propria of the intestine. The frequency and distribution of the two classes of T cells in the thymus is also unique. The different tissue homing patterns of the TCR1 and TCR2 cells suggest that they represent separate lineages of T cells with distinctive physiologic roles.     

Preferential repopulation of the small intestine by gut-derived T cell precursors in the murine system.

The potential of intestinal intraepithelial lymphocyte (IEL) precursors to repopulate the lymphoid components of lethally-irradiated mice was evaluated. Mice injected with total IEL, or IEL depleted of mature T cells, died within 2 weeks post-irradiation. Injection of T cell-depleted Thy-1.1 IEL and Thy-1.2 bone marrow (BM) into lethally-irradiated Thy-1.2 mice resulted in survival rates greater than 90%. The vast majority of thymocytes analysed at 2, 6, and 10 weeks post-treatment were Thy-1.2+. The Thy-1.1+ and Thy-1.2+ cells were detected in the spleen 2 and 6 weeks post-reconstitution. After 10 weeks, the majority of splenic T cells were Thy-1.2+. The majority of Thy-1+ IEL were of the Thy-1.1 subtype at 2 and 6 weeks after reconstitution. After 10 weeks, Thy-1.2+ IEL became the predominant subtype. Flow cytometry (FCM) analyses of Thy-1.1+ IEL showed that Thy-1.1 was co-expressed with CD3, CD4, CD5, CD8, TCR alpha beta and TCR gamma delta T cell markers. These findings indicate that IEL precursors home preferentially to gut epithelia and generate complex IEL phenotypic subsets.     

Distribution of T cells bearing different forms of the T cell receptor gamma/delta in normal and pathological human tissues

Frozen sections from normal and pathologic human tissues were immunostained by the APAAP technique with three mAb directed against different epitopes of the TCR gamma delta; TCR delta 1 which binds to all cells bearing the TCR gamma delta; BB3 and delta TCS1 which, by immunoprecipitation studies, appear to react respectively with the disulfide-linked and nondisulfide-linked form of the TCR gamma delta. In normal thymus, TCR delta 1+ cells accounted for approximately 2% of the CD3+ thymocytes and were about three times more numerous in the medulla than in the cortex. TCR delta 1+ cells were mostly constituted by the delta TCS1 reactive subset (average ratio delta TCS1/BB3: 3.7). In the tonsil, the TCR delta 1+ cells (about 3% of CD3+ elements) were mainly located in the interfollicular area, where they frequently tended to arrange around high endothelium venules. In most samples, TCR delta 1+ cells were distributed beneath to the tonsil epithelium. Unlike thymus, the majority of TCR delta 1+ cells were usually constituted by the BB3-reactive subset (average BB3/delta TCS1 ratio: 2.0). A similar predominance of BB3+ over delta TCS1+ cells was also observed in normal peripheral blood. The spleen was the organ with the highest concentration of TCR delta 1+ cells that, like in the thymus, were mostly represented by delta TCS1+ elements. Noteworthy, the TCR delta 1+ cells were preferentially located in the splenic sinusoids while TCR alpha beta-bearing lymphocytes mostly occupied the periarteriolar sheaths of penicilliary arteries. The majority of neoplastic T cell proliferations studied lacked to express the TCR gamma delta. Two cases of beta F1-(TCR alpha beta-) T lymphoblastic lymphoma, however, were TCR gamma delta+ (delta TCS1+/BB3-). Both of them showed a stage II cortical phenotype, e.g., CD1+/CD3+/CD4+/CD8+/TCR delta 1+. Among inflammatory conditions, an increase of BB3+ cells was observed in close association with necrotic areas in cases of Kikuchi's and tuberculous lymphadenitis. The significance of this finding is under study.     

Size and frequency characteristics of alpha beta and gamma delta T cells in the spleens of normal and cyclophosphamide-suppressed virus-infected chickens.

The characteristics of avian lymphocytes expressing surface CD8 (CT8) and T cell receptor (TCR) glycoproteins have been monitored by two-color flow microfluorimetry. Exposure of 1-month-old birds to a lethal influenza A virus, which is known to be lympholytic, significantly decreased the frequency of both the alpha beta TCR2+CT8+ and gamma delta TCR1+CT8- subsets in spleen. However, all categories of T cells showed evidence of greater mean cell size, indicating that they are responding. Inoculation of baby chicks with fowl pox virus induced a response more typical of specific immunity in the TCR2+CT8+ set, in that the lymphocytes increased in both frequency and mean cell size. Greater numbers of lymphoblasts were also found for the TCR2+CT8-, TCR1+CT8+, and TCR1+CT8- subsets, but the total cell counts for the minority TCR1+CT8- cells in spleen were consistently decreased. Immunosuppression with cyclophosphamide prior to infection eliminated 90% of the white blood cells from spleen, with the greatest effect being on the TCR1+ populations. The CT8+ alpha beta T cell response in chick spleen following exposure to a poxvirus is thus comparable to the situation observed for this subset of lymphocytes in mice infected with other viruses. However, although the gamma delta T cells increase in size, their frequency in spleen either does not change (CT8+) or is significantly decreased (CT8-).     

Organization of the human T-cell receptor genes

T lymphocytes recognize antigens through their membrane bound T-cell receptors. Whereas the conventional T-cell receptors are heterodimers of alpha and beta chains, expressed at the surface of CD3+ CD4+ and CD3+ CD8+ T lymphocytes, the gamma delta T-cell receptors are found at the surface of a subset of T-lymphocytes of phenotype CD3+ CD4- CD8-. The synthesis of the T-cell receptor chains results from the junction (or rearrangement) of DNA segments: Variable (V) gene and joining (J) segment for the alpha and gamma chains, V gene, D (diversity) and J segments for the beta and delta chains. In this review, we summarize the recent findings on the genomic organization of the alpha, beta, gamma and delta T-cell receptor loci in human.     

Human decidual leukocytes from early pregnancy contain high numbers of gamma delta+ cells and show selective down-regulation of alloreactivity.

The mononuclear lymphoid cell population in human pregnant uterus mucosa, decidua, from early normal pregnancies was studied phenotypically and functionally. The phenotype was determined in situ by immunohistochemistry, and in isolated decidual mononuclear cell preparations by immunofluorescence and flow cytometry. A mild isolation procedure of gentle mechanical disruption followed by density gradient centrifugation was used. Leukocytes comprised a large part of the decidual tissue. They were present in aggregates mainly situated adjacent to the glandular epithelium. In addition, individual leukocytes were present intraepithelially, as well as scattered between the stromal cells and around vessels and lacunes. Four lymphocyte populations of approximately the same size were identified: TCR gamma delta+/CD56+ cells, TCR gamma delta+/CD56- cells, TCR gamma delta-/CD56+ cells, and TCR alpha beta+/CD8+ cells. TCR gamma delta- expressing cells comprised about 60% of the T cells. They were CD4-/CD8-, and about half of the TCR gamma delta+ cells expressed the memory/activation marker CD45RO. The Kp 43 Ag, earlier described on activated CD56+ and TCR gamma delta+ cells in peripheral blood, was essentially only expressed on the TCR gamma delta-/CD56+ cell population in decidua. At least 50% of the TCR alpha beta+ cells were CD8+. The function(s) of either one of these populations might be to prevent immunologic reactions against the fetus, to protect the uterus from unwanted extensive invasion of trophoblasts, or to protect the uteroplacental unit from infection. Decidual T cells did not respond to stimulation by alloantigens or mitogenic anti-CD3 mAb but responded to the same extent as PBMC to mitogenic lectins. The surface density of the TCR/CD3 complex was low on freshly isolated decidual lymphocytes, but could be up-regulated upon stimulation with PMA/Ionomycin. Local selective down-regulation of surface expression of the TCR/CD3 complex and of activation involving this complex might be one of the mechanisms by which a maternal immunologic reaction against the semiallogeneic fetus is prevented.