Gamma(delta) T cells: non-classical ligands for non-classical cells

Pneumococcal colonization impairs mucosal immune responses to live attenuated influenza vaccine

Influenza virus infections affect millions of people annually, and current available vaccines provide varying rates of protection. However, the way in which the nasal microbiota, particularly established pneumococcal colonization, shape the response to influenza vaccination is not yet fully understood. In this study, we inoculated healthy adults with live Streptococcuspneumoniae and vaccinated them 3 days later with either tetravalent-inactivated influenza vaccine (TIV) or live attenuated influenza vaccine (LAIV). Vaccine-induced immune responses were assessed in nose, blood, and lung. Nasal pneumococcal colonization had no impact upon TIV-induced antibody responses to influenza, which manifested in all compartments. However, experimentally induced pneumococcal colonization dampened LAIV-mediated mucosal antibody responses, primarily IgA in the nose and IgG in the lung. Pulmonary influenza-specific cellular responses were more apparent in the LAIV group compared with either the TIV or an unvaccinated group. These results indicate that TIV and LAIV elicit differential immunity to adults and that LAIV immunogenicity is diminished by the nasal presence of S. pneumoniae. Therefore, nasopharyngeal pneumococcal colonization may affect LAIV efficacy.

CD4(+) T-cell subsets and host defense in the lung

CD4(+) T-helper subsets are lineages of T cells that have effector function in the lung and control critical aspects of lung immunity. Depletion of these cells experimentally or by drugs or human immunodeficiency virus (HIV) infection in humans leads to the development of opportunistic infections as well as increased rates of bacteremia with certain bacterial pneumonias. Recently, it has been proposed that CD4(+) T-cell subsets may also be excellent targets for mucosal vaccination to prevent pulmonary infections in susceptible hosts. Here, we review recent findings that increase our understanding of T-cell subsets and their effector cytokines in the context of pulmonary infection.

Alphabeta versus gammadelta lineage choice at the first TCR-controlled checkpoint

Alphabeta and gammadelta T cells develop in the thymus from a common precursor. Although lineages initially were defined by the type of TCR they express, it soon became clear that the TCR type per se does not play a deterministic role in the lineage decision, since in various transgenic and knockout models, as well as in a small fraction of cells in wt mice, the TCRgammadelta can drive the differentiation of alphabeta lineage cells and the TCRalphabeta can drive differentiation of gammadelta lineage cells. Thus until recently it was unclear what determines lineage choice and at which stage the two lineages diverge. Recent observations suggest that TCR signal strength determines lineage fate and that lineage choice is made at or shortly after the first TCR-controlled checkpoint. While it is clear that the decision between alphabeta and gammadelta lineages is made at the first TCR-controlled checkpoint and the alphabeta sublineages split off later, it is less clear whether gammadelta sublineages divert already at the first TCR-controlled checkpoint or later. Recent experiments support the former view.

Progress on the development of therapeutics against West Nile virus

A decade has passed since the appearance of West Nile virus (WNV) in humans in the Western Hemisphere in New York City. During this interval, WNV spread inexorably throughout North and South America and caused millions of infections ranging from a sub-clinical illness, to a self-limiting febrile syndrome or lethal neuroinvasive disease. Its entry into the United States triggered intensive research into the basic biology of WNV and the elements that comprise a protective host immune response. Although no therapy is currently approved for use in humans, several strategies are being pursued to develop effective prophylaxis and treatments. This review describes the current state of knowledge on epidemiology, clinical presentation, pathogenesis, and immunobiology of WNV infection, and highlights progress toward an effective therapy.

gammadelta T cells develop independently of Aire

Mutations in the transcriptional regulator Aire disrupt thymic alphabeta T cell selection, causing in humans Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). However, it is not known whether Aire is needed for normal gammadelta T cell development. We show that Aire(-/-) mice have a normal frequency of gammadelta T cells, with TCR repertoire comparable to that of wild-type mice, and normal amount of TCR Cdelta mRNA in ileum and skin. gammadelta T cells did not express increased amounts of CD25 or display hyperproliferation, and were not involved in pathological salivary gland infiltrates. Lastly, the frequency of circulating gammadelta T cells was similar in APECED patients and healthy controls. These data indicate that gammadelta T cells develop independently of Aire and are unlikely to have a significant pathogenetic or protective role in APECED. The antigens responsible for gammadelta and alphabeta T cell selection are thus probably largely different.

Genomic organization and recombinational unit duplication-driven evolution of ovine and bovine T cell receptor gamma loci

BACKGROUND

In humans and mice ("gammadelta low species") less than 5% of the peripheral blood T lymphocytes are gamma/delta T cells, whereas in chicken and artiodactyls ("gammadelta high species") gamma/delta T cells represent about half of the T cells in peripheral blood. In cattle and sheep (Bovidae) two paralogous T cell receptor gamma loci (TRG1 and TRG2) have been found. TRG1 is located on 4q3.1, within a region of homology with the human TRG locus on chromosome 7, while TRG2 localizes on 4q2.2 and appears to be unique to ruminants. The purpose of this study was the sequencing of the genomic regions encompassing both loci in a "gammadelta high" organism and the analysis of their evolutionary history.

RESULTS

We obtained the contiguous genomic sequences of the complete sheep TRG1 and TRG2 loci gene repertoire and we performed cattle/sheep sequence analysis comparison using data available through public databases. Dot plot similarity matrix comparing the two sheep loci with each other has shown that variable (V), joining (J) and constant (C) genes have evolved through a series of duplication events involving either entire cassettes, each containing the basic V-J-J-C recombinational unit, or single V genes. The phylogenetic behaviour of the eight enhancer-like elements found in the sheep, compared with the single copy present in the human TRG locus, and evidence from concordant insertions of repetitive elements in all analyzed TRGJ blocks allowed us to infer an evolutionary scenario which highlights the genetic "flexibility" of this region and the duplication-driven evolution of gene cassettes. The strong similarity of the human and Bovidae intergenic J-J-C regions, which display an enhancer-like element at their 3' ends, further supports their key role in duplications.

CONCLUSION

We propose that only duplications of entire J-J-C regions that possessed an enhancer-like element at their 3' end, and acquired at least one V segment at their 5' end, were selected and fixed as functional recombinational units.

Non-classical major histocompatibility complex proteins as determinants of tumour immunosurveillance

Tumours develop in vertebrate organisms endowed with immune systems that are potentially able to eradicate them. Nevertheless, our ever-increasing understanding of the complex interactions between lymphocytes and tumour cells fuels the long-standing hope of developing efficient immunotherapies against cancer. This review focuses on a versatile family of proteins, the major histocompatibility complex class Ib, which has been recently implicated in both the establishment of anti-tumour immune responses and in tumour immune response evasion. We focus on a subset of class Ib proteins, human leukocyte antigen (HLA)-G, Qa-2, CD1d and NKG2D ligands, which bind to either stimulatory or inhibitory receptors expressed on T, natural killer (NK) and NKT lymphocytes, and thereby modulate their anti-tumour activity.

WC1+ gammadelta T cell memory population is induced by killed bacterial vaccine

Limited studies have addressed the ability of gammadelta T cells to become memory populations. We previously demonstrated that WC1.1(+) gammadelta T cells from ruminants vaccinated with killed Leptospira borgpetersenii proliferate and produce IFN-gamma in recall responses. Here we show that this response is dependent upon antigen-responsive CD4 T cells, at least across transwell membranes; this requirement cannot be replaced by IL-2. The response was also dependent upon in vivo priming, since gammadelta T cells from leptospira vaccine-naive animals did not respond to antigen even when co-cultured across membranes from antigen-responsive PBMC. Gammadelta T cells were the major antigen-responding T cell population for the first 4 wks following vaccination and replicated more rapidly than CD4 T cells. Primed WC1(+) gammadelta T cells circulated as CD62L(hi)/CD45RO(int)/CD44(lo), characteristics of T(CM) cells. When stimulated with antigen, they decreased CD62L, increased CD44 and CD25, and had no change in CD45RO expression. These changes paralleled those of the leptospira antigen-responsive CD4 T cells but differed from those of gammadelta T cells proliferating to mitogen stimulation. This system for in vivo gammadelta T cell priming is unique, since it relies on a killed antigen to induce memory and may be pertinent to designing vaccines that require type 1 pro-inflammatory cytokines.

Gammadelta T cells do not require fully functional cytotoxic pathways or the ability to recognize recipient alloantigens to prevent graft rejection

Gammadelta T cells are a unique and minor T-cell subset that differs from conventional alphabeta T cells by virtue of their tissue localization and antigen processing requirements. We have previously shown that ex vivo-activated gammadelta T cells are able to prevent graft rejection without causing clinically significant graft-versus-host disease (GVHD). In the present study, we examined how gammadelta T cells facilitate alloengraftment and to what extent mechanisms used by conventional alphabeta T cells are also used by gammadelta T cells. We observed that, unlike alphabeta T cells, for which CD8(+) T cells are primarily responsible for facilitating engraftment, purified CD8(+)gammadelta(+) T cells administered at the same fractional dose as for the unseparated activated gammadelta T-cell population were insufficient to prevent graft rejection. Furthermore, the ability to prevent graft rejection was not affected by the absence of fully functional fas ligand or perforin cytotoxic pathways, nor was it contingent on the ability of gammadelta T cells to recognize recipient major histocompatibility process alloantigens. Repetitive infusions of a suboptimal dose of gammadelta T cells however were able to rescue mice from graft rejection, suggesting that the persistence of these cells in vivo was critical in facilitating alloengraftment. These studies demonstrate that gammadelta T cells do not use mechanisms used by conventional nontolerant alphabeta T cells to prevent graft rejection. The ability of these cells to promote engraftment without causing GVHD further distinguishes these cells from alphabeta T cells and may be an attribute that can be exploited in the clinical transplantation setting.

Gamma delta T cells facilitate adaptive immunity against West Nile virus infection in mice

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, and gammadelta T cells are involved in the protective immune response against viral challenge. We have now examined whether gammadelta T cells contribute to the development of adaptive immune responses that help control WN virus infection. Approximately 15% of TCRdelta(-/-) mice survived primary infection with WN virus compared with 80-85% of the wild-type mice. These mice were more susceptible to secondary challenge with WN virus than the wild-type mice that survived primary challenge with the virus. Depletion of gammadelta T cells in wild-type mice that survived the primary infection, however, does not affect host susceptibility during secondary challenge with WN virus. Furthermore, gammadelta T cells do not influence the development of Ab responses during primary and at the early stages of secondary infection with WN virus. Adoptive transfer of CD8(+) T cells from wild-type mice that survived primary infection with WN virus to naive mice afforded partial protection from lethal infection. In contrast, transfer of CD8(+) T cells from TCRdelta(-/-) mice that survived primary challenge with WN virus failed to alter infection in naive mice. This difference in survival correlated with the numeric and functional reduction of CD8 memory T cells in these mice. These data demonstrate that gammadelta T cells directly link innate and adaptive immunity during WN virus infection.

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.

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.

Attenuation of gammadeltaTCR signaling efficiently diverts thymocytes to the alphabeta lineage

The role of the T cell antigen receptor complex (TCR) in alphabeta/gammadelta lineage commitment remains controversial, in particular whether different TCR isoforms intrinsically favor adoption of a certain lineage. Here, we demonstrate that impairing the signaling capacity of a gammadeltaTCR complex enables it to efficiently direct thymocytes to the alphabeta lineage. In the presence of a ligand, a transgenic gammadeltaTCR mediates almost exclusive adoption of the gammadelta lineage, while in the absence of ligand, the same gammadeltaTCR promotes alphabeta lineage development with efficiency comparable to the pre-TCR. Importantly, attenuating gammadeltaTCR signaling through Lck deficiency causes reduced ERK1/2 activation and Egr expression and diverts thymocytes to the alphabeta lineage even in the presence of ligand. Conversely, ectopic Egr overexpression favors gammadelta T cell development. Our data support a model whereby gammadelta versus alphabeta lineage commitment is controlled by TCR signal strength, which depends critically on the ERK MAPK-Egr pathway.

γδ T-lymphocyte cytotoxic activity against Mycobacterium bovis analyzed by flow cytometry

Gamma Delta (gammadelta) T lymphocytes contain the unique capability of responding to pathogens in both an innate and acquired immune response. Previously, gammadelta lymphocytes have been reported to respond to Mycobacteria tuberculosis determined by proliferation and IFN-gamma production. Unlike alpha beta (alphabeta) lymphocytes, gammadelta lymphocytes constitutively express a natural killer receptor providing gammadelta lymphocytes the capability for innate cytolytic functions. A new cytolytic assay by flow cytometry was reported capable of determining natural killer activity using K562 cells as targets without the need for radioactive materials. The objectives of this study were to first apply the flow cytometer-based assay to assess gammadelta lymphocytes natural killer activity following animal vaccination with Mycobacterium bovis Bacillus Calmette-Guerin (BCG). Secondly, to optimize the flow cytometer assay in order to detect antigen specific cytolytic activity to mycobacterium and to compare the cytolytic activity of gammadelta lymphocytes to CD-8 lymphocytes. gammadelta lymphocytes increased in NK activity (P=0.012) following animal vaccination with M. bovis BCG. Both innate (P=0.02) and acquired antigen-specific cytolytic activity (P=0.04) increased following incubation with M. bovis-infected monocytes. In conclusion, flow cytometric-based assay is a sensitive and reliable tool to determine cytolytic activity of gammadelta T-lymphocytes against mycobacterium.

Enumeration of peripheral lymphocyte subsets using 6 vs. 4 color staining: A clinical evaluation of a new flowcytometer

Technological advances in instruments allow the evaluation of many lymphocyte subsets in one step. The aim of this study was to evaluate the new FACSCanto flowcytometer in routine conditions, using a 6 color combination, single platform, whole blood, lysis, no wash protocol.

METHODS

Two systems were simultaneously compared on 67 blood samples and external quality controls, using CD3,CD4, CD8, CD19, CD16/56, and CD45 in one tube TRUCOUNT beads (BD Biosciences) or two tubes (TetraChrome and Flowcount, Beckman-Coulter and DakoCytomation).

RESULTS

The day-to-day instrument detection but automatic compensations were stable. Manual compensation settings were satisfactory using available facilities. Commercial and UK NEQAS quality control results were acceptable. The intra-experiment reproducibility was good (coefficient of variation (CV)<3%) but highly operator-dependent (CD4+ T cell count CVs from 1.2 to 9.7, six operators). Storage of samples was acceptable, but storage of stained samples altered absolute count reliability. Serial dilutions show a good count accuracy. The FACScanto T subsets and B cell data were highly correlated with our reference values (r2>0.87) and absolutes values were very close (slopes>0.89). The gating strategy, fluorochrome choice, and compensation setting are discussed. A few improvements are expected (sample loader, data management, auto-gating, acquisition parameters, sample mixing, absolute values calculation, etc). In conclusions, despite its complexity, 6 color staining is a reliable, stable, and highly informative technique for lymphocyte subset monitoring but remains to be optimized.

Infection-induced expansion of a MHC Class Ib-dependent intestinal intraepithelial gammadelta T cell subset

Salmonella species invade the host via the intestinal epithelium. Hence, intestinal intraepithelial lymphocytes (iIELs) are potentially the first element of the immune system to encounter Salmonella during infection. In this study, we demonstrate, in a mouse model, the expansion of a CD8alphabeta(+)CD94(-)TCRgammadelta(+) T cell subset within the iIEL population in response to oral infection with virulent or avirulent Salmonella. This population can be detected 3 days following infection, represents up to 15% of the TCRgammadelta(+) iIELs, and is dependent on the MHC class Ib molecule T23 (Qa-1). Qa-1 is expressed by intestinal epithelial cells and thus accessible for iIEL recognition. Such cells may play a role in the early immune response to Salmonella.

CD3 bright lymphocyte population reveal ?? T cells

BACKGROUND

In routine CD3/CD4/CD8 T-cell analysis, a CD3 bright population of lymphocytes is frequently observed. The aim of the present study was to identify the immunological significance of such CD3 bright lymphocytes.

METHODS

We analyzed samples from 31 healthy adult volunteers, 78 human immunodeficiency virus (HIV)-positive, and 78 renal transplanted patients.

RESULTS

A clearly distinct CD3 bright (frequently CD4-/CD8-) T-cell fraction was observed in 84% of donors and was directly correlated with the fraction of gammadelta T cells (r2 = 0.64). CD3 overexpression on gammadelta T cells was confirmed by a combination of monoclonal antibody staining (CD3-ECD, gammadeltaTCR-FITC, and alphabetaTCR-PE-Cy5) or immunomagnetic purification of gammadelta T cells (i.e., MdFI 20 vs 8.86). The gammadelta T cells expressed CD8 polypeptide chains (alpha and beta) in all possible combinations. The largest proportion, surprisingly, were cells expressing CD8betabeta homodimers (43.8 +/- 16.5%). CD8alphaalpha homodimers were expressed on 14.2% (+/- 12.3) of total gammadelta T cells, whereas CD8alphabeta heterodimers were expressed on 12.2% (+/- 7.5). We also observed a bimodal distribution of the intensity of CD3 fluorescence of gammadelta T cells in immunocompromised patients with a threshold at 105 cell/microl. CD3 bright gammadelta T cells were more frequently observed in HIV patients (29%) compared with renal transplant patients (11%) and healthy donors (3%; chi2 test: P = 0.0007).

CONCLUSIONS

The simple observation of a CD3 bright T-cell subset on CD3/CD4/CD8 routine analysis suggests a high gammadelta T-cell fraction and, in our opinion, should be followed by a complementary analysis to determine precisely the number of gammadelta T cells and to identify their CD8alpha/beta phenotype. When CD3 bright T cells/microl were more than 40%, high gammadelta T cells were detected in more than 87% of cases, with a specificity of 76%. Occasionally, the CD3 bright subset appeared to be strongly homogeneous, suggesting an oligoclonal proliferation that could possibly reveal a chronic localized stimulation or an early lymphoproliferative disorder. Because the gammadelta T cells have interesting immunological peculiarities, the clinical significance of their quantitative abnormality should be clarified in diseases such as HIV, organ transplantation, autoimmunity and lymphoma.

IFN-gamma-producing gamma delta T cells help control murine West Nile virus infection

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, thereby partially mimicking human disease. Using this model, we have demonstrated that mice deficient in gammadelta T cells are more susceptible to WN virus infection. TCRdelta(-/-) mice have elevated viral loads and greater dissemination of the pathogen to the CNS. In wild-type mice, gammadelta T cells expanded significantly during WN virus infection, produced IFN-gamma in ex vivo assays, and enhanced perforin expression by splenic T cells. Adoptive transfer of gammadelta T cells to TCRdelta(-/-) mice reduced the susceptibility of these mice to WN virus, and this effect was primarily due to IFN-gamma-producing gammadelta T cells. These data demonstrate a distinct role for gammadelta T cells in the control of and prevention of mortality from murine WN virus infection.

Immunoregulation in the tissues by gammadelta T cells

For a T-cell subset to be classified as immunoregulatory, it might reasonably be predicted that in its absence, animals would experience pathological immune dysregulation. Moreover, reconstitution of the subset should restore normal immune regulation. So far, these criteria have been satisfied by only a few of the candidate regulatory T-cell subsets, but among them is the intraepithelial gammadelta T-cell receptor (TCR)+ subset of mouse skin. In this article, we look at immunoregulatory gammadelta T cells, and the growing evidence for tissue-associated immunoregulation mediated by both gammadelta T cells and alphabeta T cells.

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.

An autoreactive gamma delta TCR derived from a polymyositis lesion

To investigate the role of gammadelta T cells in human autoimmune disease we expressed and characterized a gammadelta TCR from an autoimmune tissue lesion. The TCR was first identified in a rare form of polymyositis characterized by a monoclonal infiltrate of gammadelta T cells which invaded and destroyed skeletal muscle fibers. The Vgamma1.3-Jgamma1-Cgamma1/Vdelta2-Jdelta3 TCR cDNA of the original muscle invasive gammadelta T cell clone was reconstructed from unrelated cDNA and transfected into the mouse hybridoma BW58alpha(-)beta(-). Appropriate anti-human gammadelta TCR Abs stimulated the TCR transfectants to produce IL-2, thus demonstrating that the human gammadelta TCR functionally interacted with murine signaling components. The transfected Vgamma1.3/Vdelta2 TCR recognized a cytosolic protein expressed in cultured human myoblasts and TE671 rhabdomyosarcoma cells. The Ag was recognized in the absence of presenting cells. Using a panel of control gammadelta TCR transfectants with defined exchanges in different positions of both TCR chains, we showed that the gammadelta TCR recognized its Ag in a TCR complementarity-determining region 3-dependent way. To our knowledge, this is the first example of a molecularly defined gammadelta TCR directly derived from an autoimmune tissue lesion. The strategy used in this study may be applicable to other autoimmune diseases.

CD4-CD8-"Double-negative" cutaneous T-cell lymphomas share common histologic features and an aggressive clinical course

We report 15 patients with CD4-CD8-"double-negative" T-cell lymphoma arising in skin. There were seven women and eight men with a mean age at diagnosis of 53 years (range 19-77 years). All but two patients presented with solitary or multiple cutaneous nodule(s). Initial and recurrent biopsy specimens showed a dense infiltrate centered in the mid-dermis (extending into subcutis when sampled) of small to intermediate-sized lymphocytes with indistinct nucleoli and frequently irregular nuclear contours. Periadnexal infiltration and epidermal ulceration were present in five cases with the intraepidermal cells being primarily reactive CD4+ T cells. All cases were negative for CD30 and terminal deoxynucleotidyltransferase; one showed expression of CD56, and six of eight tested cases were positive for T-cell receptor-delta expression. Despite systemic chemotherapy, all 12 patients with clinical follow-up showed recurrent or progressive disease with widespread cutaneous dissemination in 10 of 12. Eventual dissemination to lymph nodes or bone marrow occurred in two patients each, with at least nine patients dead of disease or treatment complications. Only two patients achieved lasting clinical remission (with 2'-deoxycoformycin/pentostatin and nelarabine, respectively). CD4-CD8-"double-negative" CTCL has distinctive histologic features and cytomorphology with a marked propensity for rapid multifocal cutaneous dissemination.

Is antigen presentation the primary function of HLA-G?

Human histocompatibility leukocyte antigen (HLA)-G is an antigen-presenting molecule. This review discusses the possibility that this might not be its primary function. HLA-G indeed modulates innate immunity by interacting with immunoglobulin-like receptors and by regulating HLA-E expression and its subsequent interaction with CD94/NKG2 receptors. HLA-G also down-modulates both CD8(+) and CD4(+) T-cell responsiveness.

The ins and outs of body surface immunology

Rather than being confined to the secondary lymphoid tissue of the spleen and lymph nodes, large numbers of lymphocytes are intrinsically associated with the epithelial surfaces of the body. The best studied is gut-associated lymphoid tissue, but distinct epithelium-associated lymphoid tissue also exists in the reproductive tract, the lung, and the skin. The multiple cell types and functions composing these lymphoid tissues are increasingly seen as the key to how antigens delivered to body surfaces can elicit either immunogenic or tolerogenic responses. In some instances, these responses occur purely within the local body surface tissue, yet in other cases both local and systemic responses are elicited.