MHC class I allele dosage alters CD8 expression by intestinal intraepithelial lymphocytes

The development of TCR alphabeta(+), CD8alphabeta(+) intestinal intraepithelial lymphocytes (IEL) is dependent on MHC class I molecules expressed in the thymus, while some CD8alphaalpha(+) IEL may arise independently of MHC class I. We examined the influence of MHC I allele dosage on the development CD8(+) T cells in RAG 2(-/-) mice expressing the H-2D(b)-restricted transgenic TCR specific for the male, Smcy-derived H-Y Ag (H-Y TCR). IEL in male mice heterozygous for the restricting (H-2D(b)) and nonrestricting (H-2D(d)) MHC class I alleles (MHC F(1)) were composed of a mixture of CD8alphabeta(+) and CD8alphaalpha(+) T cells, while T cells in the spleen were mostly CD8alphabeta(+). This was unlike IEL in male mice homozygous for H-2D(b), which had predominantly CD8alphaalpha(+) IEL and few mostly CD8(-) T cells in the spleen. Our results demonstrate that deletion of CD8alphabeta(+) cells in H-Y TCR male mice is dependent on two copies of H-2D(b), whereas the generation of CD8alphaalpha(+) IEL requires only one copy. The existence of CD8alphabeta(+) and CD8alphaalpha(+) IEL in MHC F(1) mice suggests that their generation is not mutually exclusive in cells with identical TCR. Furthermore, our data imply that the level of the restricting MHC class I allele determines a threshold for conventional CD8alphabeta(+) T cell selection in the thymus of H-Y TCR-transgenic mice, whereas the development of CD8alphaalpha(+) IEL is dependent on, but less sensitive to, this MHC class I allele.     

Oligoclonality of rat intestinal intraepithelial T lymphocytes: overlapping TCR beta-chain repertoires in the CD4 single-positive and CD4/CD8 double-positive subsets

Previous studies in humans and mice have shown that gut intraepithelial lymphocytes (IELs) express oligoclonal TCR beta-chain repertoires. These studies have either employed unseparated IEL preparations or focused on the CD8+ subsets. Here, we have analyzed the TCR beta-chain repertoire of small intestinal IELs in PVG rats, in sorted CD4+ as well as CD8+ subpopulations, and important differences were noted. CD8alphaalpha and CD8alphabeta single-positive (SP) IELs used most Vbeta genes, but relative Vbeta usage as determined by quantitative PCR analysis differed markedly between the two subsets and among individual rats. By contrast, CD4+ IELs showed consistent skewing toward Vbeta17 and Vbeta19; these two genes accounted collectively for more than half the Vbeta repertoire in the CD4/CD8 double-positive (DP) subset and were likewise predominant in CD4 SP IELs. Complementarity-determining region 3 length displays and TCR sequencing demonstrated oligoclonal expansions in both the CD4+ and CD8+ IEL subpopulations. These studies also revealed that the CD4 SP and CD4/CD8 DP IEL subsets expressed overlapping beta-chain repertoires. In conclusion, our results show that rat TCR-alphabeta+ IELs of both the CD8+ and CD4+ subpopulations are oligoclonal. The limited Vbeta usage and overlapping TCR repertoire expressed by CD4 SP and CD4/CD8 DP cells suggest that these two IEL populations recognize restricted intestinal ligands and are developmentally and functionally related.     

IL-15 promotes survival but not effector function differentiation of CD8+ TCRalphabeta+ intestinal intraepithelial lymphocytes

CD8 single-positive cells, including CD8alphaalpha+ and CD8alphabeta+ subsets, constitute the majority of TCRalphabeta+ intestinal intraepithelial lymphocytes (alphabeta iIEL) in mice. CD8+ alphabeta iIEL show significantly weaker responses to TCR stimulation in the presence of exogenous IL-2 than do CD8+ T cells of the central immune system. IL-15 is a T cell growth factor likely expressed in the intestine mucosa. To understand the role of IL-15 in CD8+ alphabeta iIEL biology, we compared the effects of exogenous IL-15 and IL-2 on the survival and primary responses of the two CD8+ alphabeta iIEL subsets in vitro. In contrast to the death of approximately 60% of both CD8alphaalpha+ and CD8alphabeta+ iIEL cultured in IL-2 with or without TCR stimulation, IL-15 promoted survival of the CD8alphaalpha+ subset in the presence of TCR stimulation and promoted survival of both subsets in the absence of TCR stimulation. The higher proliferation level of TCR stimulated CD8alphaalpha+ alphabeta iIEL cultured in IL-15 compared with those cultured in IL-2 is likely due to IL-15's prosurvival effects. In addition, unlike exogenous IL-2, exogenous IL-15 did not support the effector functions of either iIEL subsets, including IFN-gamma production, IL-4-induced Th2 cytokine production, and anti-TCR mAb-redirected cytotoxicity. These findings demonstrate that IL-15 and IL-2 are functionally distinct and suggest that IL-15 plays a unique role in the maintenance of the CD8+ alphabeta iIEL pool in the absence of Ag stimulation and in the survival and expansion of CD8alphaalpha+ alphabeta iIEL upon Ag stimulation.     

Dietary nucleotides increase the proportion of a TCR gammadelta+ subset of intraepithelial lymphocytes (IEL) and IL-7 production by intestinal epithelial cells (IEC); implications for modification of cellular and molecular cross-talk between IEL and IEC by dietary nucleotides

We have investigated the effects of dietary nucleotides on intraepithelial lymphocytes (IEL) and intestinal epithelial cells (IEC) in weanling mice. The proportion of T-cell receptor (TCR) gammadelta+ IEL in BALB/c mice fed a diet supplemented with nucleotides (NT(+) diet) was significantly higher than that in mice fed the nucleotide-free diet, while the proportion of TCR alphabeta+ IEL in NT(+) diet-fed mice was significantly decreased. The change of the TCR alphabeta+/TCR gammadelta+ ratio was mainly observed in a CD8 alphaalpha+ subset of IEL. IEC from NT(+) diet-fed mice produced a higher level of IL-7, which is important in the development of TCR gammadelta+ IEL, than those from control diet-fed mice. The expression levels of IL-7 and IL-2 receptors on IEL were not different between the two dietary groups. Our findings suggest that the increased population of a TCR gammadelta+ IEL subset by feeding nucleotides may be caused by the increased production of IL-7 by IEC.     

Intestinal intraepithelial lymphocytes exert potent protective cytotoxic activity during an acute virus infection

After systemic infection of mice with 104 PFU of lymphocytic choriomeningitis virus (LCMV), infected cells are detected simultaneously in various organs, including spleen and intestinal mucosa. Most notably, virus-infected cells are also present among CD11c+ dendritic cells in the subepithelial area of the small intestinal mucosa. Some of these virus-infected cells are in close spatial association with intestinal intraepithelial lymphocytes (IEL). Therefore, we compared virus-specific cytotoxic activity of CD8 splenocytes with that of IEL subsets. While ex vivo isolated TCRalphabeta+CD8alphaalpha+ IEL exert only minimal virus-specific cytotoxicity, maximum specific killing mediated by TCRalphabeta+CD8alphabeta+ IEL on day 8 postinfection exceeds maximum cytotoxic activity observed with CD8 splenocytes when assessed in vitro. Maximum cytotoxic activity of IEL is preceded by peak perforin and granzyme B mRNA expression in IEL around day 6 postinfection, suggesting a recent activation in situ. The antivirus cytotoxicity of in vivo primed IEL is further demonstrated by the protection from virus production in the spleen of mice infected with LCMV 10 h before adoptive cell transfer. These data indicate a potent priming of LCMV-specific IEL in situ after systemic LCMV infection and suggest that cytotoxic IEL markedly contribute to the elimination of virus-infected cells in the intestinal mucosa.     

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.     

Differential intra-epithelial lymphocyte phenotypes following Cryptosporidium parvum challenge in susceptible and resistant athymic strains of mice

The lack of immunocompetent laboratory animal models has limited our understanding of functional immune responses to Cryptosporidium parvum infection, but such responses have been studied in susceptible laboratory rodents with genetic, acquired, or induced immunodeficiencies. We previously observed that athymic C57BL/6J nude mice inoculated with C. parvum oocysts had lower or absent fecal oocyst excretion when compared to inoculated athymic BALB/cJ nude mice. This discrepancy prompted us to explore potential differences in intestinal immune responses in both strains. Prior to and after C. parvum challenge, BALB/cJ nude and C57BL/6J nude mice did not differ in either spleen cell numbers or in parasite-specific proliferation. However, both strains of mice exhibited a significant increase in intra-epithelial lymphocyte (IEL) numbers prior to and following C. parvum inoculation when compared to uninoculated controls (P<0.05). Prior to challenge, C57BL/6J nude mice had a higher percentage of both CD8+ and CD8+ gammadelta+ IEL than BALB/cJ nude mice. Following challenge, resistant C57BL/6J nude mice had a higher percentage of gammadelta+, CD4+, and CD8+ gammadelta+ IEL than uninoculated C57BL/6J nude mice and than susceptible BALB/cJ nude mice (P<0.05). Conversely, inoculated C57BL/6J nude mice had a significantly lower percentage of alphabeta+ IEL than inoculated BALB/cJ nude mice (P<0.05). We conclude that gammadelta+, CD4+, and/or CD8+ gammadelta+ IEL may influence responses to cryptosporidiosis in athymic murine models, and that the increased percentage of alphabeta+ IEL in susceptible BALB/cJ nude mice could reflect a preferential expression during chronic C. parvum infection and/or might downregulate local protective responses.     

Regulatory function for murine intraepithelial lymphocytes. Two subsets of CD3+, T cell receptor-1+ intraepithelial lymphocyte T cells abrogate oral tolerance

The murine intraepithelial lymphocyte (IEL) population is enriched in T cells that express the gamma delta-TCR, however, the biologic function served by these T cells remains obscure. IEL are considered to be major effector cells in mucosal immunity, and we have investigated whether IEL subsets could reverse orally induced systemic unresponsiveness (oral tolerance; OT) and support secondary type responses when adoptively transferred to mice orally tolerized with SRBC. When purified CD3+ IEL from mice orally primed with SRBC were transferred to adoptive hosts and challenged with SRBC, splenic IgM, IgG1, IgG2b, and IgA anti-SRBC plaque-forming cell responses were observed. However, CD3+ IEL from HRBC orally primed mice did not abrogate SRBC induced OT. Further, HRBC-primed CD3+, IEL converted HRBC-specific OT but not SRBC-specific OT. CD3+ IEL could be separated into four subsets based on expression of CD4 and CD8. CD3+, CD4-, 8+ T cells were the major subset (74.5%), with smaller numbers of CD4- and CD8- (double negatives, DN) (7.8%), CD4+, 8- (7.6%) and CD4+, CD8+ (double positives) (10.1%) T cells. Interestingly, both the CD3+, CD8+, and the CD3+, DN IEL subsets abrogated OT, resulting in significant IgM, IgG1, IgG2b, and IgA anti-SRBC plaque-forming cell responses when adoptively transferred to mice with OT. However, neither CD3+, CD4+, CD8-, nor double positive T cells affected OT when studied in this system. The CD3+, CD8+ IEL subset could be further separated into Thy-1+ (16.6%) and Thy-1- (83.4%) cells; adoptive transfer of Thy-1- cells abrogated oral tolerance whereas the Thy-1+ subset was without effect. When the expression of TCR on IEL with this biologic function was determined by use of monoclonal anti-alpha beta TCR (H57.597), TCR2-, CD3+ IEL possessed immunoregulatory function whereas the alpha beta-TCR+ (TCR2+) fraction did not abrogate OT. Immunoprecipitation of membrane fractions obtained from purified CD3+, CD4-, CD8+, Thy-1- IEL with polyclonal anti-delta peptide (Tyr-Ala-Asn-Ser-Phe-Asn-Asn-Glu-Lys-Leu) antibody revealed bands of 45 and 35 kDa, corresponding to the delta- and gamma-chains, respectively. These results suggest that gamma delta-TCR+ IEL possess a regulatory function, namely the restoration of immune responses in a state of oral tolerance. Further, both CD3+, CD4-, CD8+, Thy-1-, and CD3+, DN IEL T cells exhibit this effector contrasuppressor function.     

Cutting edge: TCR alpha beta+ CD8 alpha alpha+ T cells are found in intestinal intraepithelial lymphocytes of mice that lack classical MHC class I molecules.

TCR alpha beta+ intestinal intraepithelial lymphocytes (IEL) can express either the typical CD8 alpha beta heterodimer or an unusual CD8 alpha alpha homodimer. Both types of CD8+ IEL require class I molecules for their differentiation, since they are absent in beta2m-/- mice. To gain insight into the role of class I molecules in forming TCR alpha beta+ CD8+ IEL populations, we have analyzed the IEL in mice deficient for either TAP, beta 2m, CD1, or K and D. We find that K-/-D-/- mice have TCR alpha beta+ CD8 alpha alpha+ IEL, although they are deficient for TCR alpha beta+ CD8 alpha beta+ cells. This indicates that at least some TCR alpha beta+ CD8 alpha alpha+ IEL require only nonclassical class I molecules for their development. Surprisingly, the TCR alpha beta+ CD8 alpha alpha+ IEL are significantly increased in K-/-D-/- mice, suggesting a complex interaction between CD8+ IEL and class I molecules that might include direct or indirect negative regulation by K and D, as well as positive effects mediated by nonclassical class I molecules.     

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.     

Antigen feeding increases frequency and antigen-specific proliferation ability of intraepithelial CD4+ T cells in alphabeta T cell receptor transgenic mice

To study how intestinal intraepithelial lymphocytes (IEL) are affected by orally ingested antigen, the phenotypes and responses of the IEL in mice expressing a transgenic T cell receptor alphabeta (TCR alphabeta) specific for ovalbumin (OVA) were analyzed after feeding OVA. In the OVA-fed mice, the abundance of alphabeta-IEL as a proportion of the total IEL population increased and the frequency of CD4+ cells increased within the TCR alphabeta+ IEL population. CD4(+) IEL from OVA-fed transgenic mice proliferated in vitro more markedly in response to antigen stimulation than IEL from mice fed the control diet. These results indicate that antigen-specific proliferation of CD4+ IEL was amplified as a result of oral administration of antigen.     

Virus-induced activation of self-specific TCR alpha beta CD8 alpha alpha intraepithelial lymphocytes does not abolish their self-tolerance in the intestine

TCRalphabeta CD8alphaalpha intestinal intraepithelial lymphocytes (IEL) represent an enigmatic subset of T cells, particularly, in regard to their potential functions and the apparent persistence of cells expressing self-specific TCR. We have used mice that are transgenic for the TCRalphabeta specific for the lymphocytic choriomeningitis virus (LCMV)-derived peptide gp33, and TCRalphabeta-transgenic mice that coexpress the gp33 Ag ubiquitously, to analyze the functional properties of TCRalphabeta CD8alphaalpha IEL in the presence, or absence, of their specific MHC-restricted Ag, and to assess the impact of molecular mimicry during a potent LCMV infection on potentially self-reactive TCRalphabeta CD8alphaalpha IEL. In this study, we show that the presence of the specific self-Ag results in reduced expression of IL-2, IFN-gamma, and IL-10 by resident TCRalphabeta CD8alphaalpha IEL while expression of mRNA for TGFbeta is not affected. We further demonstrate that despite their secluded location in the epithelium, TCRalphabeta CD8alphaalpha IEL are activated after infection of the intestinal mucosa with LCMV. Importantly, LCMV-induced activation of self-specific TCRalphabeta CD8alphaalpha IEL does not reverse their tolerance as no cytotoxic activity or up-regulated expression of proinflammatory cytokines is detected and no overt signs of autoimmunity are seen. Taken together, these results are in support of an immunoregulatory role for self-specific TCRalphabeta CD8alphaalpha in the intestinal mucosa and clearly speak against an involvement of this cell subset in inflammatory reactions and tissue destruction.     

Resistance to viral infection by intraepithelial lymphocytes in HIV-1 P18-I10-specific T-cell receptor transgenic mice

For the analysis of mucosal immunity to HIV-1, we have recently established a line of transgenic (Tg) mice expressing the TCRalpha and TCRbeta genes of the murine CTL clone RT1 specific for P18-I10 (RGPGRAFVTI), an immunodominant gp160 envelope-derived epitope of IIIB isolate, restricted by the H-2D(d) MHC-I molecule. Here we examine those cells bearing specific TCR among the intraepithelial lymphocytes (IELs), with flow cytometric analysis using H-2D(d)/P18-I10 tetramers. We observed three distinct CD3(+), tetramer positive populations among the IELs: extra-thymic CD8alphabeta(+), alphabetaTCR T-cells; CD8 alphaalpha+, gammadeltaTCR T-cells; and thymus-derived CD8alphabeta+, alphabetaTCR T-cells. Challenge of these Tg mice with P18-I10 encoded by a vaccinia virus vector, either intrarectally (i.r.) or intraperitoneally (i.p.), revealed that the intraepithelial compartment seems to be a major site for prevention of the spread of viral infection. Such immunity appears due to the thymus-derived, CD8alphabeta+ antigen-specific CTLs together with CD8alphaalpha+ gammadelta cells, which regulate virus spread. This model system for studying CTL based immunity at mucosal sites should prove helpful in developing rational approaches for HIV control.     

Stepwise differentiation of CD4 memory T cells defined by expression of CCR7 and CD27

To study the steps in the differentiation of human memory CD4 T cells, we characterized the functional and lineage relationships of three distinct memory CD4 subpopulations distinguished by their expression of the cysteine chemokine receptor CCR7 and the TNFR family member CD27. Using the combination of these phenotypic markers, three populations were defined: the CCR7+CD27+, the CCR7-CD27+, and the CCR7-CD27- population. In vitro stimulation led to a stepwise differentiation from naive to CCR7+CD27+ to CCR7-CD27+ to CCR7-CD27-. Telomere length in these subsets differed significantly (CCR7+CD27+ > CCR7-CD27+ > CCR7-CD27-), suggesting that these subsets constituted a differentiative pathway with progressive telomere shortening reflecting antecedent in vivo proliferation. The in vitro proliferative response of these populations declined, and their susceptibility to apoptosis increased progressively along this differentiation pathway. Cytokine secretion showed a differential functional capacity of these subsets. High production of IL-10 was only observed in CCR7+CD27+, whereas IFN-gamma was produced by CCR7-CD27+ and to a slightly lesser extent by CCR7-CD27- T cells. IL-4 secretion was predominantly conducted by CCR7-CD27- memory CD4 T cells. Thus, by using both CCR7 and CD27, distinct maturational stages of CD4 memory T cells with different functional activities were defined.     

CD8 Raft localization is induced by its assembly into CD8alpha beta heterodimers, Not CD8alpha alpha homodimers

The coreceptor CD8 is expressed as a CD8alphabeta heterodimer on major histocompatibility complex class I-restricted TCRalphabeta T cells, and as a CD8alphaalpha homodimer on subsets of memory T cells, intraepithelial lymphocytes, natural killer cells, and dendritic cells. Although the role of CD8alphaalpha is not well understood, it is increasingly clear that this protein is not a functional homologue of CD8alphabeta. On major histocompatibility complex class I-restricted T cells, CD8alphabeta is a more efficient TCR coreceptor than CD8alphaalpha. This property has for the mouse protein been attributed to the recruitment of CD8alphabeta into lipid rafts, which is dependent on CD8beta palmitoylation. Here, these divergent distributions of CD8alphabeta and CD8alphaalpha are demonstrated for the human CD8 proteins as well. However, although palmitoylation of both CD8alpha and CD8beta chains was detected, this modification did not contribute to raft localization. In contrast, arginines in the cytoplasmic domain are crucial for raft localization of CD8betabeta. Most strikingly, the assembly of a non-raft localized CD8beta chain with a non-raft localized CD8alpha chain resulted in raft-localized CD8alphabeta heterodimers. Using chimeric CD8 proteins, this property of the heterodimer was found to be determined by the assembly of CD8alpha and CD8beta extracellular regions. The presence of two CD8alpha extracellular regions, on the other hand, appears to preclude raft localization. Thus, heterodimer formation and raft association are intimately linked for CD8alphabeta. These results emphasize that lipid raft localization is a key feature of human CD8alphabeta that clearly distinguishes it from CD8alphaalpha.     

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.     

Homing and function of human skin gammadelta T cells and NK cells: relevance for tumor surveillance

Normal (noninflamed) human skin contains a network of lymphocytes, but little is known about the homing and function of these cells. The majority of alphabeta T cells in normal skin express CCR8 and produce proinflammatory cytokines. In this study we examined other subsets of cutaneous lymphocytes, focusing on those with potential function in purging healthy tissue of transformed and stressed cells. Human dermal cell suspensions contained significant populations of Vdelta1(+) gammadelta T cells and CD56(+)CD16(-) NK cells, but lacked the subsets of Vdelta2(+) gammadelta T cells and CD56(+)CD16(+) NK cells, which predominate in peripheral blood. The skin-homing receptors CCR8 and CLA were expressed by a large fraction of both cell types, whereas chemokine receptors associated with lymphocyte migration to inflamed skin were absent. Neither cell type expressed CCR7, although gammadelta T cells up-regulated this lymph node-homing receptor upon TCR triggering. Stimulation of cutaneous Vdelta1(+) gammadelta T cell lines induced secretion of large amounts of TNF-alpha, IFN-gamma, and the CCR8 ligand CCL1. In contrast to cutaneous alphabeta T cells, both cell types had the capacity to produce intracellular perforin and displayed strong cytotoxic activity against melanoma cells. We therefore propose that gammadelta T cells and NK cells are regular constituents of normal human skin with potential function in the clearance of tumor and otherwise stressed tissue cells.