Mouse gamma delta TCR+NK1.1+ thymocytes specifically produce interleukin-4, are major histocompatibility complex class I independent, and are developmentally related to alpha beta TCR+NK1.1+ thymocytes

E proteins control the development of NKγδT cells through their invariant T cell receptor

T cell receptor (TCR) signaling regulates important developmental transitions, partly through induction of the E protein antagonist, Id3. Although normal γδ T cell development depends on Id3, Id3 deficiency produces different phenotypes in distinct γδ T cell subsets. Here, we show that Id3 deficiency impairs development of the Vγ3+ subset, while markedly enhancing development of NKγδT cells expressing the invariant Vγ1Vδ6.3 TCR. These effects result from Id3 regulating both the generation of the Vγ1Vδ6.3 TCR and its capacity to support development. Indeed, the Trav15 segment, which encodes the Vδ6.3 TCR subunit, is directly bound by E proteins that control its expression. Once expressed, the Vγ1Vδ6.3 TCR specifies the innate-like NKγδT cell fate, even in progenitors beyond the normally permissive perinatal window, and this is enhanced by Id3-deficiency. These data indicate that the paradoxical behavior of NKγδT cells in Id3-deficient mice is determined by its stereotypic Vγ1Vδ6.3 TCR complex.

Recognition of synthetic polyanionic ligands underlies "spontaneous" reactivity of Vγ1 γδTCRs

Although γδTCRs were discovered more than 30 yr ago, principles of antigen recognition by these receptors remain unclear and the nature of these antigens is largely elusive. Numerous studies reported that T cell hybridomas expressing several Vγ1-containing TCRs, including the Vγ1Vδ6 TCR of γδNKT cells, spontaneously secrete cytokines. This property was interpreted as recognition of a self-ligand expressed on the hybridoma cells themselves. Here, we revisited this finding using a recently developed reporter system and live single cell imaging. We confirmed strong spontaneous signaling by Vγ1Vδ6 and related TCRs, but not by TCRs from several other γδ or innate-like αβ T cells, and demonstrated that both γ and δ chains contributed to this reactivity. Unexpectedly, live single cell imaging showed that activation of this signaling did not require any interaction between cells. Further investigation revealed that the signaling is instead activated by interaction with negatively charged surfaces abundantly present under regular cell culture conditions and was abrogated when noncharged cell culture vessels were used. This mode of TCR signaling activation was not restricted to the reporter cell lines, as interaction with negatively charged surfaces also triggered TCR signaling in ex vivo Vγ1 γδ T cells. Taken together, these results explain long-standing observations on the spontaneous reactivity of Vγ1Vδ6 TCR and demonstrate an unexpected antigen presentation-independent mode of TCR activation by a spectrum of chemically unrelated polyanionic ligands.

Resolving the mystery-How TCR transgenic mouse models shed light on the elusive case of gamma delta T cells

Cutting-edge questions in αβ T cell biology were addressed by investigating a range of different genetically modified mouse models. In comparison, the γδ T cell field lacks behind on the availability of such models. Nevertheless, transgenic mouse models proved useful for the investigation of γδ T cell biology and their stepwise development in the thymus. In general, animal models and especially mouse models give access to a wide range of opportunities of modulating γδ T cells, which is unachievable in human beings. Because of their complex biology and specific tissue tropism, it is especially challenging to investigate γδ T cells in in vitro experiments since they might not reliably reflect their behavior and phenotype under physiologic conditions. This review aims to provide a comprehensive historical overview about how different transgenic mouse models contributed in regards of the understanding of γδ T cell biology, whereby a special focus is set on studies including the elusive role of the γδTCR. Furthermore, evolutionary and translational remarks are discussed under the aspect of future implications for the field. The ultimate full understanding of γδ T cells will pave the way for their usage as a powerful new tool in immunotherapy.

Growth and the Growth Hormone-Insulin Like Growth Factor 1 Axis in Children With Chronic Inflammation: Current Evidence, Gaps in Knowledge, and Future Directions

Growth failure is frequently encountered in children with chronic inflammatory conditions like juvenile idiopathic arthritis, inflammatory bowel disease, and cystic fibrosis. Delayed puberty and attenuated pubertal growth spurt are often seen during adolescence. The underlying inflammatory state mediated by proinflammatory cytokines, prolonged use of glucocorticoid, and suboptimal nutrition contribute to growth failure and pubertal abnormalities. These factors can impair growth by their effects on the GH-IGF axis and also directly at the level of the growth plate via alterations in chondrogenesis and local growth factor signaling. Recent studies on the impact of cytokines and glucocorticoid on the growth plate further advanced our understanding of growth failure in chronic disease and provided a biological rationale of growth promotion. Targeting cytokines using biological therapy may lead to improvement of growth in some of these children, but approximately one-third continue to grow slowly. There is increasing evidence that the use of relatively high-dose recombinant human GH may lead to partial catch-up growth in chronic inflammatory conditions, although long-term follow-up data are currently limited. In this review, we comprehensively review the growth abnormalities in children with juvenile idiopathic arthritis, inflammatory bowel disease, and cystic fibrosis, systemic abnormalities of the GH-IGF axis, and growth plate perturbations. We also systematically reviewed all the current published studies of recombinant human GH in these conditions and discussed the role of recombinant human IGF-1.

Differential dependence on nuclear factor-κB-inducing kinase among natural killer T-cell subsets in their development

Natural killer T cells (NKT cells) are comprised of several subsets. However, the possible differences in their developmental mechanisms have not been fully investigated. To evaluate the dependence of some NKT subpopulations on nuclear factor-κB-inducing kinase (NIK) for their generation, we analysed the differentiation of NKT cells, dividing them into subsets in various tissues of alymphoplasia (aly/aly), a mutant mouse strain that lacks functional NIK. The results indicated that the efficient differentiation of both invariant NKT (iNKT) and non-iNKT cells relied on NIK expression in non-haematopoietic cells; however, the dependence of non-iNKT cells was lower than that of iNKT cells. Especially, the differentiation of CD8(+) non-iNKT cells was markedly resistant to the aly mutation. The proportion of two other NKT cell subsets, NK1.1(+) γδ T cells and NK1.1(-) iNKT cells, was also significantly reduced in aly/aly mice, and this defect in their development was reversed in wild-type host mice given aly/aly bone marrow cells. In exerting effector functions, NIK in NKT-αβ cells appeared dispensable, as NIK-deficient NKT-αβ cells could secrete interleukin-4 or interferon-γ and exhibit cytolytic activity at a level comparable to that of aly/+ NKT-αβ cells. Collectively, these results imply that the NIK in thymic stroma may be critically involved in the differentiation of most NKT cell subsets (although the level of NIK dependence may vary among the subsets), and also that NIK in NKT-αβ cells may be dispensable for their effector function.

The Jekyll and Hyde story of IL17-Producing γδT Cells

In comparison to conventional αβT cells, γδT cells are considered as specialized T cells based on their contributions in regulating immune response. γδT cells sense early environmental signals and initiate local immune-surveillance. The development of functional subtypes of γδT cells takes place in the thymus but they also exhibit plasticity in response to the activating signals and cytokines encountered in the extrathymic region. Thymic development of Tγδ1 requires strong TCR, CD27, and Skint-1 signals. However, differentiation of IL17-producing γδT cells (Tγδ17) is independent of Skint-1 or CD27 but requires notch signaling along with IL6 and TGFβ cytokines in the presence of weak TCR signal. In response to cytokines like IL23, IL6, and IL1β, Tγδ17 outshine Th17 cells for early activation and IL17 secretion. Despite expressing similar repertoire of lineage transcriptional factors, cytokines, and chemokine receptors, Tγδ17 cells differ from Th17 in spatial and temporal fashion. There are compelling reasons to consider significant role of Tγδ17 cells in regulating inflammation and thereby disease outcome. Tγδ17 cells regulate mobilization of innate immune cells and induce keratinocytes to secrete anti-microbial peptides thus exhibiting protective functions in anti-microbial immunity. In contrast, dysregulated Tγδ17 cells inhibit Treg cells, exacerbate autoimmunity, and are also known to support carcinogenesis by enhancing angiogenesis. The mechanism associated with this dual behavior of Tγδ17 is not clear. To exploit, Tγδ17 cells for beneficial use requires comprehensive analysis of their biology. Here, we summarize the current understanding on the characteristics, development, and functions of Tγδ17 cells in various pathological scenarios.

γδ T Lymphocytes Coordinate Eosinophil Influx during Allergic Responses

Tissue eosinophil infiltration, which is a hallmark of allergic and helminthic diseases, is mainly coordinated by T lymphocytes, via the production of eosinophilotactic chemokines. Among T lymphocyte subsets, lymphocytes expressing γδ T cell receptor have been determined as a key factor for eosinophil accumulation via direct and indirect mechanisms. This knowledge is strongly supported by the fact that, in different experimental models of eosinophilic airway inflammation and helminth-induced Th2 lung inflammation, an evident tissue accumulation of γδ T lymphocytes is observed. In addition, the depletion of γδ T lymphocytes is correlated with the impairment of eosinophil accumulation in inflamed tissue. γδ T lymphocytes are non-conventional T lymphocytes, which comprise a minor T lymphocyte subset, mainly distributed in the tissue, and present crucial roles in innate and acquired immune responses. γδ T lymphocytes recognize several danger- and pathogen-associated molecular pattern molecules and stress antigens in a MHC-independent fashion and can provide rapid tissue-specific responses, via the production of a wide range of chemical mediators capable to modulate other cell populations. These mediators include chemoattractant cytokines and chemokines that attract eosinophils into the tissue by either direct recognition (such as IL-5, CCL11/eotaxin), or indirect mechanisms via the modulation of αβ T lymphocytes and macrophages (through the production of interferon-γ, IL-4, and CCL2/Monocyte chemoattractant protein-1, MCP-1, for example). The present review presents an overview of how γδ T lymphocytes coordinate eosinophil accumulation in allergy, by focusing on their role in airway inflammation and by discussing the involvement of cytokines and chemokines in this phenomenon.

A comprehensive review of the phenotype and function of antigen-specific immunoregulatory double negative T cells

Double negative T cells that lack the expression of both CD4 and CD8 T cell co-receptors exhibit a most unique antigen-specific immunoregulatory potential first described over a decade ago. Due to their immunoregulatory function, this rare T cell population has been studied in both mice and humans for their contribution to peripheral tolerance and disease prevention. Consequently, double negative cells are gaining interest as a potential cellular therapeutic. Herein, we review the phenotype and function of double negative T cells with emphasis on their capacity to induce antigen-specific immune tolerance. While the phenotypic and functional similarities between double negative T cells identified in mouse and humans are highlighted, we also call attention to the need for a specific marker of double negative T cells, which will facilitate future studies in humans. Altogether, due to their unique properties, double negative T cells present a promising therapeutic potential in the context of various disease settings.

Dok-1 overexpression promotes development of γδ natural killer T cells

In T cells, two members of the Dok family, Dok-1 and Dok-2, are predominantly expressed. Recent evidence suggests that they play a negative role in T-cell signaling. In order to define whether Dok proteins regulate T-cell development, we have generated transgenic mice overexpressing Dok-1 in thymocytes and peripheral T cells. We show that overexpression of Dok-1 retards the transition from the CD4(-) CD8(-) to CD4(+) CD8(+) stage. Moreover, there is a specific expansion of PLZF-expressing Vγ1.1(+) Vδ6.3(+) T cells. This subset of γδ T cells acquires innate characteristics including rapid IL-4 production following stimulation and requiring SLAM-associated adaptor protein (SAP) for their development. Moreover, Dok-1 overexpression promotes the generation of an innate-like CD8(+) T-cell population that expresses Eomesodermin. Altogether, these findings identify a novel role for Dok-1 in the regulation of thymic differentiation and in particular, in the development of PLZF(+) γδ T cells.

T-cell signaling regulated by the Tec family kinase, Itk

The Tec family tyrosine kinases regulate lymphocyte development, activation, and differentiation. In T cells, the predominant Tec kinase is Itk, which functions downstream of the T-cell receptor to regulate phospholipase C-gamma. This review highlights recent advances in our understanding of Itk kinase structure and enzymatic regulation, focusing on Itk protein domain interactions and mechanisms of substrate recognition. We also discuss the role of Itk in the development of conventional versus innate T-cell lineages, including both alphabeta and gammadelta T-cell subsets. Finally, we describe the complex role of Itk signaling in effector T-cell differentiation and the regulation of cytokine gene expression. Together, these data implicate Itk as an important modulator of T-cell signaling and function.

gammadelta T cell subsets: a link between TCR and function?

The gammadelta T lmphocytes are often divided into subsets based upon expression of certain TCR components. This division was initially made because gammadelta T cells residing in particular epithelia were found to show tissue specific differences in their TCRs. Many examples now show that gammadelta T cell subsets also appear to be biased to carry out particular functions. This suggests that particular gammadelta TCR types direct the cells to acquire a certain type of functional programming during thymic development. Here, we describe functionally distinct, TCR-defined gammadelta T cell subsets, and evidence that their functions are predetermined in the thymus.

Analysis of gamma delta T cell functions in the mouse

Mouse models of disease and injury have been invaluable in investigations of the functional role of gammadelta T cells. They show that gammadelta T cells engage in immune responses both early and late, that they can function both polyclonally and as peripherally selected clones, and that they can be effector cells and immune regulators. They also suggest that functional development of gammadelta T cells occurs stepwise in thymus and periphery, and that it is governed by gammadelta TCR-signaling and other signals. Finally, they indicate that gammadelta T cell functions often segregate with TCR-defined subsets, in contrast to conventional T cells. From the functional studies in mice and other animal models, gammadelta T cells emerge as a distinct lymphocyte population with a unique and broad functional repertoire, and with important roles in Ab responses, inflammation and tissue repair. They also are revealed as a potentially useful target for immune intervention.

CCR6 and NK1.1 distinguish between IL-17A and IFN-gamma-producing gammadelta effector T cells

Gammadelta T cells are a potent source of innate IL-17A and IFN-gamma, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24(low) CD44(high) effector gammadelta T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6+ gammadelta T cells produced IL-17A, while NK1.1+ gammadelta T cells were efficient producers of IFN-gamma but not of IL-17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1+ gammadelta T cells. Accordingly, both gammadelta T-cell subsets were rare in gut-associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL-17A and IFN-gamma in response to TCR-specific and TCR-independent stimuli. IL-12 and IL-18 induced IFN-gamma and IL-23 induced IL-17A production by NK1.1+ or CCR6+ gammadelta T cells, respectively. Importantly, we show that CCR6+ gammadelta T cells are more responsive to TCR stimulation than their NK1.1+ counterparts. In conclusion, our findings support the hypothesis that CCR6+ IL-17A-producing gammadelta T cells derive from less TCR-dependent selection events than IFN-gamma-producing NK1.1+ gammadelta T cells.

Tec kinase Itk in gammadeltaT cells is pivotal for controlling IgE production in vivo

In conventional alphabeta T cells, the Tec family tyrosine kinase Itk is required for signaling downstream of the T cell receptor (TCR). Itk also regulates alphabeta T cell development, lineage commitment, and effector function. A well established feature of Itk(-/-) mice is their inability to generate T helper type 2 (Th2) responses that produce IL-4, IL-5, and IL-13; yet these mice have spontaneously elevated levels of serum IgE and increased numbers of germinal center B cells. Here we show that the source of this phenotype is gammadelta T cells, as normal IgE levels are observed in Itk(-/-)Tcrd(-/-) mice. When stimulated through the gammadelta TCR, Itk(-/-) gammadelta T cells produce high levels of Th2 cytokines, but diminished IFNgamma. In addition, activated Itk(-/-) gammadelta T cells up-regulate costimulatory molecules important for B cell help, suggesting that they may directly promote B cell activation and Ig class switching. Furthermore, we find that gammadelta T cells numbers are increased in Itk(-/-) mice, most notably the Vgamma1.1(+)Vdelta6.3(+) subset that represents the dominant population of gammadelta NKT cells. Itk(-/-) gammadelta NKT cells also have increased expression of PLZF, a transcription factor required for alphabeta NKT cells, indicating a common molecular program between alphabeta and gammadelta NKT cell lineages. Together, these data indicate that Itk signaling regulates gammadelta T cell lineage development and effector function and is required to control IgE production in vivo.

Intracellular bacterial infection and invariant NKT cells

The invariant (i) natural killer (NK)T cells represent a unique subset of T lymphocytes which express the V alpha 14 chain of the T cell receptor (TCR), that recognizes glycolipid antigens presented by the nonpolymorphic major histocompatibility complex (MHC) class I-like antigen presentation molecule CD1d, and they participate in protection against some microbial pathogens. Although iNKT cells have originally been regarded as T cells co-expressing NKR-P1B/C (NK1.1: CD 161), they do not seem to consistently express this marker, since NK1.1 surface expression on iNKT cells undergoes dramatic changes following facultative intracellular bacterial infection, which is correlated with functional changes of this cell population. Accumulating evidence suggests that NK1.1 allows recognition of "missing-self", thus controlling activation/inhibition of NK1.1-expressing cells. Therefore, it is tempting to suggest that iNKT cells participate in the regulation of host immune responses during facultative intracellular bacterial infection by controlling NK1.1 surface expression. These findings shed light not only on the unique role of iNKT cells in microbial infection, but also provide evidence for new aspects of the NK1.1 as a regulatory molecule on these cells.

Outgrowth of CD4low/negCD25+ T cells with suppressor function in CD4+CD25+ T cell cultures upon polyclonal stimulation ex vivo

CD4(+)CD25(+) regulatory T cells (Tregs) play an essential role in controlling autoimmunity and allograft rejection. Several ex vivo activation and expansion protocols have been developed to amplify cell numbers and suppressor function of murine and human Tregs. We demonstrate in this study that ex vivo activation and expansion of murine Tregs resulted in an enrichment of a CD4(low/neg)CD25(+) T cell population that was more than 20-fold more potent than expanded conventional Tregs in suppressing an in vitro CD4(+)CD25(-) T cell response to allo-Ag. The generation of CD4(low/neg)CD25(+) T cells was independent of the presence of Tregs in the culture, and suppressor function was acquired only after activation and expansion. CD4(low/neg)CD25(+) T cells expressed either an alphabeta or gammadelta TCR, had an activated phenotype, and did not express the transcription factor FoxP3. Despite expressing the cell surface Ags lymphocyte activation gene-3 (CD223) and CD103, neither was essential for suppressor cell function. Suppression by CD4(low/neg)CD25(+) T cells was prevented by a semipermeable membrane and was independent of IL-10 and TGF-beta. In summary, we describe in this study CD4(low/neg)CD25(+) FoxP3(neg) T cells with highly potent suppressor cell function derived from cultures of an enriched population of CD4(+)CD25(+) T cells that may contribute to the suppressor activity of ex vivo expanded bone fide Tregs.

Marking a path to transplant tolerance

Long-term allograft survival requires lifelong immunosuppression, which comes with serious side effects. Inducing immune tolerance to the transplant would enable immunosuppression withdrawal and revolutionize the quality of life of transplant recipients. In this issue of the JCI, Martínez-Llordella et al. identify a profile of biomarkers that predict tolerance in liver transplant recipients (see the related article beginning on page 2845). These findings translate into a new means for prospectively selecting liver transplant patients who would benefit from immunosuppression withdrawal and ultimately may guide development of tolerogenic therapies that allow for allograft acceptance without the use of long-term immunosuppression.

The role of NKT cells in tumor immunity

NKT cells are a relatively newly recognized member of the immune community, with profound effects on the rest of the immune system despite their small numbers. They are true T cells with a T cell receptor (TCR), but unlike conventional T cells that detect peptide antigens presented by conventional major histocompatibility (MHC) molecules, NKT cells recognize lipid antigens presented by CD1d, a nonclassical MHC molecule. As members of both the innate and adaptive immune systems, they bridge the gap between these, and respond rapidly to set the tone for subsequent immune responses. They fill a unique niche in providing the immune system a cellular arm to recognize lipid antigens. They play both effector and regulatory roles in infectious and autoimmune diseases. Furthermore, subsets of NKT cells can play distinct and sometimes opposing roles. In cancer, type I NKT cells, defined by their invariant TCR using Valpha14Jalpha18 in mice and Valpha24Jalpha18 in humans, are mostly protective, by producing interferon-gamma to activate NK and CD8(+) T cells and by activating dendritic cells to make IL-12. In contrast, type II NKT cells, characterized by more diverse TCRs recognizing lipids presented by CD1d, primarily inhibit tumor immunity. Moreover, type I and type II NKT cells counter-regulate each other, forming a new immunoregulatory axis. Because NKT cells respond rapidly, the balance along this axis can greatly influence other immune responses that follow. Therefore, learning to manipulate the balance along the NKT regulatory axis may be critical to devising successful immunotherapies for cancer.

Airway hyperresponsiveness through synergy of gammadelta} T cells and NKT cells

Mice sensitized and challenged with OVA were used to investigate the role of innate T cells in the development of allergic airway hyperresponsiveness (AHR). AHR, but not eosinophilic airway inflammation, was induced in T cell-deficient mice by small numbers of cotransferred gammadelta T cells and invariant NKT cells, whereas either cell type alone was not effective. Only Vgamma1+Vdelta5+ gammadelta T cells enhanced AHR. Surprisingly, OVA-specific alphabeta T cells were not required, revealing a pathway of AHR development mediated entirely by innate T cells. The data suggest that lymphocytic synergism, which is key to the Ag-specific adaptive immune response, is also intrinsic to T cell-dependent innate responses.

Visualization of the earliest steps of γδ T cell development in the adult thymus

The checkpoint in gammadelta cell development that controls successful T cell receptor (TCR) gene rearrangements remains poorly characterized. Using mice expressing a reporter gene 'knocked into' the Tcrd constant region gene, we have characterized many of the events that mark the life of early gammadelta cells in the adult thymus. We identify the developmental stage during which the Tcrd locus 'opens' in early T cell progenitors and show that a single checkpoint controls gammadelta cell development during the penultimate CD4- CD8- stage. Passage through this checkpoint required the assembly of gammadelta TCR heterodimers on the cell surface and signaling via the Lat adaptor protein. In addition, we show that gammadelta selection triggered a phase of sustained proliferation similar to that induced by the pre-TCR.

Human alpha beta and gamma delta thymocyte development: TCR gene rearrangements, intracellular TCR beta expression, and gamma delta developmental potential--differences between men and mice

To evaluate the role of the TCR in the alphabeta/gammadelta lineage choice during human thymocyte development, molecular analyses of the TCRbeta locus in gammadelta cells and the TCRgamma and delta loci in alphabeta cells were undertaken. TCRbeta variable gene segments remained largely in germline configuration in gammadelta cells, indicating that commitment to the gammadelta lineage occurred before complete TCRbeta rearrangements in most cases. The few TCRbeta rearrangements detected were primarily out-of-frame, suggesting that productive TCRbeta rearrangements diverted cells away from the gammadelta lineage. In contrast, in alphabeta cells, the TCRgamma locus was almost completely rearranged with a random productivity profile; the TCRdelta locus contained primarily nonproductive rearrangements. Productive gamma rearrangements were, however, depleted compared with preselected cells. Productive TCRgamma and delta rearrangements rarely occurred in the same cell, suggesting that alphabeta cells developed from cells unable to produce a functional gammadelta TCR. Intracellular TCRbeta expression correlated with the up-regulation of CD4 and concomitant down-regulation of CD34, and plateaued at the early double positive stage. Surprisingly, however, some early double positive thymocytes retained gammadelta potential in culture. We present a model for human thymopoiesis which includes gammadelta development as a default pathway, an instructional role for the TCR in the alphabeta/gammadelta lineage choice, and a prolonged developmental window for beta selection and gammadelta lineage commitment. Aspects that differ from the mouse are the status of TCR gene rearrangements at the nonexpressed loci, the timing of beta selection, and maintenance of gammadelta potential through the early double positive stage of development.

Most IL-4-producing gamma delta thymocytes of adult mice originate from fetal precursors

Thy-1(dull) gammadelta T cells constitute a distinct adult gammadelta T cell subset characterized by the expression of a TCR composed of Vgamma1Cgamma4 and Vdelta6Cdelta chains with limited junctional sequence diversity. However, several features of the expressed Thy-1(dull) TCR-gammadelta genes, in particular the absence or minimal presence of N region diversity and the almost invariable Ddelta2-Jdelta1 junction, are typical of rearrangements often found in the fetal thymus. In this study, we have investigated the origin of these cells. Few Thy-1(dull) gammadelta thymocytes developed in syngeneic radiation adult chimeras, regardless of whether the recipient mice were given adult bone marrow or fetal liver cells as a source of hemopoietic precursors. In contrast, normal numbers of Thy-1(dull) gammadelta T cells developed in fetal thymi grafted into adult syngeneic recipients. Interestingly, the majority of Thy-1(dull) gammadelta thymocytes present in the grafts were of graft origin, even when most conventional gammadelta and alphabeta thymocytes in the grafted thymi originated from T cell precursors of recipient origin. Single-cell PCR analyses of the nonselected TCR-gamma rearrangements present in adult Thy-1(dull) gammadelta thymocytes revealed that more than one-half of these cells represent the progenies of a limited number of clones that greatly expanded possibly during the first weeks of life. Finally, the second TCR-delta allele of a large number of Thy-1(dull) gammadelta T cells contained incomplete TCR-delta rearrangements, thus providing an explanation for the adult-type rearrangements previously found among nonfunctional V(D)J rearrangements present in Thy-1(dull) gammadelta thymocytes.

Hepatic T cells and liver tolerance

The T-cell biology of the liver is unlike that of any other organ. The local lymphocyte population is enriched in natural killer (NK) and NKT cells, which might have crucial roles in the recruitment of circulating T cells. A large macrophage population and the efficient trafficking of dendritic cells from sinusoidal blood to lymph promote antigen trapping and T-cell priming, but the local presentation of antigen causes T-cell inactivation, tolerance and apoptosis. These local mechanisms might result from the need to maintain immunological silence to harmless antigenic material in food. The overall bias of intrahepatic T-cell responses towards tolerance might account for the survival of liver allografts and for the persistence of some liver pathogens.

Critical role of NK cells rather than V alpha 14(+)NKT cells in lipopolysaccharide-induced lethal shock in mice

Although macrophages play a central role in the pathogenesis of septic shock, NK1(+) cells have also been implicated. NK1(+) cells comprise two major populations, namely NK cells and V alpha 14(+)NKT cells. To assess the relative contributions of these NK1(+) cells to LPS-induced shock, we compared the susceptibility to LPS-induced shock of beta(2)-microglobulin (beta(2)m)(-/-) mice that are devoid of V alpha 14(+)NKT cells, but not NK cells, with that of wild-type (WT) mice. The results show that beta(2)m(-/-) mice were more susceptible to LPS-induced shock than WT mice. Serum levels of IFN-gamma following LPS challenge were significantly higher in beta(2)m(-/-) mice, and endogenous IFN-gamma neutralization or in vivo depletion of NK1(+) cells rescued beta(2)m(-/-) mice from lethal effects of LPS. Intracellular cytokine staining revealed that NK cells were major IFN-gamma producers. The J alpha 281(-/-) mice that are exclusively devoid of V alpha 14(+)NKT cells were slightly more susceptible to LPS-induced shock than heterozygous littermates. Hence, LPS-induced shock can be induced in the absence of V alpha 14(+)NKT cells and IFN-gamma from NK cells is involved in this mechanism. In WT mice, hierarchic contribution of different cell populations appears likely.

gammadelta T cells are critical for the induction of anterior chamber-associated immune deviation

Anterior chamber-associated immune deviation (ACAID) is a systemic form of tolerance that is elicited by introducing antigens into the anterior chamber of the eye. ACAID is characterized by deficiencies in delayed-type hypersensitivity and complement-fixing antibodies upon subsequent challenge with antigen. The mechanisms responsible for the generation of this form of tolerance are not yet completely clear. Here we asked whether gammadelta T cells, which are critical in the induction of oral tolerance and nasal tolerance, play a role in ACAID. The percentage of splenic gammadelta T cells was higher in mice that received antigen via the anterior chamber compared to untreated mice. In addition, CD44 was up-regulated on some splenic gammadelta and alphabeta T cells after the intraocular injection of antigen. Moreover, administration of antigen into the anterior chamber did not induce ACAID in the C57BL/6 mice pretreated with anti-mouse delta-chain monoclonal antibody or in the gammadelta T-cell-receptor-deficient (delta-/-) mice. gammadelta T cells from wild-type mice reconstituted ACAID when transferred into the delta-/- mice before injection of antigen, verifying that the deficiency in delta-/- mice results from the lack of gammadelta T cells rather than from an inadvertent change caused by deletion of the delta-chain. These findings indicate that gammadelta T cells play a very important role in ocular tolerance.

Tissue-specific segregation of TCRgamma delta+ NKT cells according to phenotype TCR repertoire and activation status: parallels with TCR alphabeta+NKT cells

Whereas the majority of NKT cells in the mouse express an alpha beta TCR (NKTalpha beta cells), a small subset of NKT cells express a gamma delta TCR (NKTgamma delta). Here we have systematically analyzed the phenotype, TCR repertoire and activation status of NKTgamma delta cells in the thymus, liver, spleen and bone marrow of normal C57BL/6 mice. Our data indicate that NKTgamma delta cells segregate in a tissue-specific manner according to these parameters. While most NKTgamma delta cells in the thymus and liver have a recently activated CD62L(lo) phenotype and a TCR repertoire that is heavily biased to Vgamma1.1 and Vdelta6.3, the majority of NKTgamma delta cells in the spleen and bone marrow are CD62L(hi) and have a much less biased TCR repertoire. Moreover, expression of NK markers is high on NKTgamma delta cells in spleen and bone marrow but low in thymus and liver. Collectively our results reveal a tissue-specific segregation of NKTgamma delta cells that is strikingly similar to that recently described for CD1d-dependent and Cd1d-independent NKTalpha beta cells. We therefore propose that chronic TCR activation by tissue-specific endogenous ligands is a generic property of NKT cells of both the alpha beta and gamma delta lineages.

Defective development of NK1.1+ T-cell antigen receptor alphabeta+ cells in zeta-associated protein 70 null mice with an accumulation of NK1.1+ CD3- NK-like cells in the thymus

Development of natural killer 1.1+ (NK1.1+) CD3+ (NK1.1+ T) cells was analyzed in zeta-associated protein 70 (ZAP-70) null ((-/-)) mice. Both NK1.1+ TCRalphabeta+ and NK1.1+ TCRgammadelta+ cell populations were absent in the thymus and spleen. By contrast, the number of NK1.1+ CD3- cells was increased in these tissues. The NK1.1+ CD3- thymocytes in ZAP-70(-/-) mice had surface phenotypes in common with NK or NK1.1+ T cells. However, some of them were discordant either with NK cells or with NK1.1+ T cells. The NK1.1+ CD3- cells produced interferon-gamma upon stimulation with NK1.1 cross-linking in the presence of interleukin-2 and exhibited a substantial cytotoxicity against YAC-1 cells. Moreover, the generation of NK1.1+ T cells with invariant Valpha14Jalpha281 chains was induced from the NK1.1+ CD3- thymocytes following stimulation with phorbol myristate acetate and ionomycin in a neonatal thymic organ culture. An introduction of TCRalpha and beta transgenes to the ZAP-70(-/-) mice resulted in generation of an NK1.1+ TCRalphabeta(dim) population, whereas no substantial CD4+ CD8- or CD4- CD8+ population that expressed the introduced TCRalphabeta was generated in the mainstream T lineage. These findings demonstrate that ZAP-70 kinase is indispensable for the development of NK1.1+ T cells and that the unique NK1.1+ CD3- thymocytes in ZAP-70(-/-) mice contain immediate precursors of NK1.1+ T cells.

Strain-specific TCR repertoire selection of IL-4-producing Thy-1 dull gamma delta thymocytes

Thy-1 dull gamma delta thymocytes constitute an unusual subset of mature TCR gamma delta cells which share with NK T cells the expression of cell surface markers usually associated with activated or memory cells and the simultaneous production of high levels of IL-4 and IFN-gamma upon activation. In DBA / 2 mice, Thy-1 dull gamma delta thymocytes express a restricted repertoire of TCR that are composed of the V1 gene product mainly associated with V6.4 chains exhibiting very limited junctional sequence diversity. In this study we have characterized this gamma delta T cell population in different strains of mice and show that Thy-1 dull gamma delta thymocytes are present in every strain tested, albeit at different frequencies. Moreover IL-4 production by gamma delta thymocytes is mainly confined to the Thy-1 dull population in every strain tested. Finally, the repertoire of TCR expressed by Thy-1 dull gamma delta thymocytes varies in different strain of mice, although a biased expression of Vgamma1 and Vdelta6 chains was observed in all strains studied. However, the extent of junctional diversity of the V1 and V6 chains expressed by Thy-1 dull gamma delta thymocytes varied from oligoclonal in DBA/2 mice to polyclonal in FVB/N mice. Thy-1 dull gamma delta thymocytes from mouse strains such as C3H/HeJ and BALB/c contain cells with diverse Vdelta6(D)Jdelta junctions together with cells with relatively homogeneous Vdelta6(D)Jdelta junctions, similar to those found in DBA/2. Thus, the Thy-1 dull gamma delta population appears to contain two subsets of cells which differ in the diversity of their TCR.

Cellular and cytokine correlates of mucosal protection in murine model of oral candidiasis

Host protection against Candida albicans infection in a model of oral candidiasis involving infection-prone [DBA/2 (H-2(d))] and less infection-prone [BALB/c (H-2(d))] mouse strains was analyzed in terms of antibody and cellular responses, and in terms of cytokine patterns from regional lymph node cells. There was a selective expansion of gamma/delta(+) T-cell receptor cells, which correlated with the patterns of colonization in both mouse strains, with higher numbers of gamma/delta T cells detected in BALB/c mice. Antigen-induced T-cell proliferation was significantly higher in BALB/c mice than in DBA/2 mice. Higher levels of serum immunoglobulin G (IgG) and salivary IgA antibodies were detected in BALB/c mice than in DBA/2 mice, but only after the infection was cleared. The cervical lymph node cells from infected mice were assessed for interleukin-4 (IL-4), IL-12, and gamma interferon (IFN-gamma) mRNA gene expression by reverse transcription-PCR and protein production in the culture supernatants following restimulation in vitro. In BALB/c mice, an early increase in levels of IL-4, IFN-gamma, and IL-12 correlated with rapid elimination of C. albicans. In DBA/2 mice, where resolution of infection was delayed, IL-4 message expression was delayed and the IL-4 secretion level was lower. Neutralization of IL-4 by multiple injections of an anti-IL-4 monoclonal antibody in BALB/c mice resulted in increased carriage rate and delayed clearance of the yeasts. Collectively, the data suggest that the T-cell response to C. albicans in the regional lymph nodes which correlates best with rapid oral clearance of C. albicans is a balanced Th0 cytokine response involving early secretion of both IFN-gamma and IL-4.

Relationships between natural T cells, atopy, IgE levels, and IL-4 production

BACKGROUND

Th2 cells govern allergic disorders. Mechanisms leading to the Th2 commitment are dominated by the requirement of IL-4. A potential source of this triggering IL-4 could be the CD4 + subset of a small population of T cells, natural T (NT) cells. Indeed, this subset is involved in IgE responses in mice and produces promptly high amounts of IL-4 in both mice and man.

METHODS

NT cells were identified in peripheral blood by flow cytometry with antibodies against Valpha24 and Vbeta11, recognizing the T-cell receptor specific for NT cells. Simultaneous staining with anti-CD3, anti-CD4, or anti-CD8 antibodies was performed. The frequency of NT cells in man was studied according to the presence of atopy defined by the positivity of skin tests, according to total IgE levels in serum, and according to IL-4 concentration of whole-blood culture supernatants determined by a flow cytometer microsphere-based assay.

RESULTS

Seventy subjects were included, of whom 30 were atopic. The number of CD4+ NT cells was higher in atopics than in nonatopics (P=0.009). This number was correlated to the total IgE levels (r = 0.34, P = 0.03). In addition, the number of CD4 + NT cells, but also of CD8 + NT cells, was correlated to the levels of IL-4 (r=0.71, P=0.01, and r=0.6, P=0.03, respectively).

CONCLUSIONS

These results show that the number of NT cells, particularly the CD4+ subset, is related to atopy, IL-4 production, and IgE levels. Therefore, this population of T cells is likely to play a role in the Th2 commitment initiating atopic diseases.

Naive human T cells can be a source of IL-4 during primary immune responses

IL-4 plays a key role in driving the differentiation of CD4+ Th precursors into Th2 cells, both in mice and in humans. The source of IL-4 during primary immune responses is, however, still debated. When IL-4 consumption in in vitro T cell cultures was blocked with a MoAb to the IL-4 receptor alpha-chain (IL-4Ralpha), it became evident that freshly isolated naive (CD45RO-) CD4+ T cells from adults or cord blood produce IL-4 upon activation with anti-CD3 and CD80. IL-4 production by naive T cells is strictly IL-2-dependent. Endogenous IL-4 activity in naive CD4+ T cell cultures modulates the production of interferon-gamma (IFN-gamma) on the one hand and IL-5 and IL-13 on the other hand in opposite directions, and it is partly responsible for the low IFN-gamma production by cord blood T cells. Comparison of the ratio of IL-4/IFN-gamma in supernatants of T cell cultures reveals a skewing towards IL-4 production by cord blood T cells, while naive T cells from (non-atopic) adults predominantly produce IFN-gamma. We conclude that CD4+ naive T cells can produce IL-4 without the need for Th2 differentiation, and therefore that they can be the initial source of IL-4 required at the time of priming for T cell differentiation into Th2 cells.

IL-4-Producing γδ T Cells That Express a Very Restricted TCR Repertoire Are Preferentially Localized in Liver and Spleen

IL-4-producing γδ thymocytes in normal mice belong to a distinct subset of γδ T cells characterized by low expression of Thy-1. This γδ thymocyte subset shares a number of phenotypic and functional properties with the NK T cell population. Thy-1dull γδ thymocytes in DBA/2 mice express a restricted repertoire of TCRs that are composed of the Vγ1 gene product mainly associated with the Vδ6.4 chain and exhibit limited junctional sequence diversity. Using mice transgenic for a rearranged Vγ1Jγ4Cγ4 chain and a novel mAb (9D3) specific for the Vδ6.3 and Vδ6.4 murine TCRδ chains, we have analyzed the peripheral localization and functional properties of γδ T cells displaying a similarly restricted TCR repertoire. In transgenic mice, IL-4 production by peripheral γδ T cells was confined to the γδ+9D3+ subset, which contains cells with a TCR repertoire similar to that found in Thy-1dull γδ thymocytes. In normal DBA/2 mice such cells represent close to half of the γδ T cells present in the liver and around 20% of the splenic γδ T cells.

Tissue-Specific Segregation of CD1d-Dependent and CD1d-Independent NK T Cells

NKT cells, defined as T cells expressing the NK cell marker NK1.1, are involved in tumor rejection and regulation of autoimmunity via the production of cytokines. We show in this study that two types of NKT cells can be defined on the basis of their reactivity to the monomorphic MHC class I-like molecule CD1d. One type of NKT cell is positively selected by CD1d and expresses a biased TCR repertoire together with a phenotype found on activated T cells. A second type of NKT cell, in contrast, develops in the absence of CD1d, and expresses a diverse TCR repertoire and a phenotype found on naive T cells and NK cells. Importantly, the two types of NKT cells segregate in distinct tissues. Whereas thymus and liver contain primarily CD1d-dependent NKT cells, spleen and bone marrow are enriched in CD1d-independent NKT cells. Collectively, our data suggest that recognition of tissue-specific ligands by the TCR controls localization and activation of NKT cells.

Characterization of subpopulations of T-cell receptor intermediate (TCRint) T cells

CD1-autoreactive T cells of two types have been demonstrated among T cells expressing the T-cell receptor (TCR) alphabeta at intermediate levels (TCRint cells). One type constitutes a major fraction of the natural killer (NK)1.1+ TCRint population in C57BL/6 (B6) mice and carries a restricted TCR composed of an alpha-chain with an invariant Valpha14-J281 rearrangement, and a beta-chain using Vbeta8. 2, 7 or 2. The second type utilises a variety of TCR and was derived from CD4+ cells in mice lacking MHC class II. To increase our understanding of the two different CD1-reactive subsets, we have investigated and compared the populations of origin: NK1.1+ and NK1. 1- TCRint subsets from MHC class II-deficient mice and CD4+NK1.1+ T cells from B6 mice. The three TCRint populations shared a phenotype indicating previous activation, and contained low frequencies of cells expressing NK receptors of the Ly49 family. In contrast to control CD4+ cells, the three TCRint subsets produced high amounts of interleukin (IL)-4 and interferon (IFN)-gamma after activation. Importantly, no IL-10 could be detected in either TCRint population, implying a distinct function for these cells, different from those of conventional CD8+ and CD4+ cells, including the typical T-helper 2 (Th2) cell. Analysis of TCR expression indicated that the proportion of cells using the semi-invariant Valpha14/Vbeta8.2-type TCR was lower in NK1.1+ cells from MHC class II-negative mice than in CD4+NK1.1+ B6 cells. Further, usage of the Valpha14-J281 rearrangement was also demonstrated among NK1.1- TCRint cells.

MHC Class II-Dependent NK1.1+ γδ T Cells Are Induced in Mice by Salmonella Infection

We observed the emergence of a novel population of γδ T cells expressing NK1.1 Ag in the peritoneal cavity of mice infected with Salmonella choleraesuis. The NK1.1+γδ T cells accounted for approximately 20% of all γδ T cells emerging in the peritoneal cavity of C57BL/6 mice and expressed preferentially rearranged Vγ4-Jγ1 and Vδ6.3-Dδ1-Dδ2-Jδ1 genes with N diversity. The γδ T cells proliferated vigorously in response to PHA-treated spleen cells and produced IFN-γ in the culture supernatant. However, spleen cells from Aβb-deficient mice were unable to stimulate the γδ T cells. Furthermore, the NK1.1+γδ T cells were stimulated not only by Chinese hamster ovary (CHO) cells expressing wild-type IAb but also by those expressing IAb/Eα52-68 or IAb/pigeon cytochrome c-derived analogue peptide complex. These proliferation activities were inhibited by mAb specific for IAb chain. Consistent with these findings, the emergence of NK1.1+γδ T cells was reduced in the peritoneal cavity of Aβb-deficient mice after Salmonella infection, whereas NK1.1+γδ T cells were rather abundant in the peritoneal cavity of Salmonella-infected β2m-deficient mice. Moreover, the NK1.1+γδ T cells were easily identified in the thymus of β2m-deficient but not Aβb-deficient mice. Our results indicated that MHC class II expression is essential for development and activation of NK1.1+γδ T cells in the thymus and the periphery.

A Limited Role for β-Selection During γδ T Cell Development

T cells belong to two distinct lineages expressing either αβ or γδ TCR. During αβ T cell development, it is clearly established that productive rearrangement at the TCR β locus in immature precursor cells leads to the expression of a pre-TCR complex. Signaling through the pre-TCR results in the selective proliferation and maturation of TCR β+ cells, a process that is known as β-selection. However, the potential role of β-selection during γδ T cell development is controversial. Whereas PCR-RFLP and sequencing techniques have provided evidence for a bias toward in-frame VDJβ rearrangements in γδ cells (consistent with β-selection), γδ cells apparently develop normally in mice that are unable to assemble a pre-TCR complex due to a deficiency in TCR β or pTα genes. In this report, we have directly addressed the physiologic significance of β-selection during γδ cell development in normal mice by quantitating intracellular TCR β protein in γδ cells and correlating its presence with cell cycle status. Our results indicate that β-selection plays a significant (although limited) role in γδ cell development by selectively amplifying a minor subset of γδ precursor cells with productively rearranged TCR β genes.

The homogeneity of the TCRdelta repertoire expressed by the Thy-1dull gammadelta T cell population is due to cellular selection

Thy-1dull gammadelta T cells are an unusual subset of mature TCRgammadelta T cells characterized by their highly restricted TCR repertoire. In DBA/2 mice, they predominantly express the product of the Vgamma1 gene together with that of a member of the Vdelta6 subfamily (the Vdelta6.4 gene) and their junctional sequences show very little diversity. To address the mechanisms underlying the expression of the restricted TCRgammadelta repertoire, we have cloned all Vdelta6 subfamily members present in DBA/2 mice and studied their frequency of expression in Thy-1dull and Thy-1bright gammadelta thymocyte populations. Furthermore, we have also cloned non-functional Vdelta6DdeltaJdelta1 rearrangements present in the Thy-1dull gammadelta T cell population and compared their Vdelta6 gene utilization and their junctional sequences with those expressed by this population. Our results indicate that the restricted TCRdelta repertoire expressed by the Thy-1dull gammadelta thymocytes results from cellular selection, rather than molecular constraints suggesting the existence of a limited set of self-ligands. Finally, phenotypic, functional and TCRgammadelta repertoire analysis of Thy-1dull gammadelta T cells in beta2-microglobulin (beta2m)-deficient mice indicated that these putative ligands are not beta2m-dependent major histocompatibility complex class I or class I-like molecules.

Kinetics of T cell receptor beta, gamma, and delta rearrangements during adult thymic development: T cell receptor rearrangements are present in CD44(+)CD25(+) Pro-T thymocytes

We performed a comprehensive analysis of T cell receptor (TCR) gamma rearrangements in T cell precursors of the mouse adult thymus. Using a sensitive quantitative PCR method, we show that TCRgamma rearrangements are present in CD44(+)CD25(+) Pro-T thymocytes much earlier than expected. TCRgamma rearrangements increase significantly from the Pro-T to the CD44(-)CD25(+) Pre-T cell transition, and follow different patterns depending on each Vgamma gene segment, suggesting that ordered waves of TCRgamma rearrangement exist in the adult mouse thymus as has been described in the fetal mouse thymus. Recombinations of TCRgamma genes occur concurrently with TCRdelta and D-Jbeta rearrangements, but before Vbeta gene assembly. Productive TCRgamma rearrangements do not increase significantly before the Pre-T cell stage and are depleted in CD4(+)CD8(+) double-positive cells from normal mice. In contrast, double-positive thymocytes from TCRdelta-/- mice display random proportions of TCRgamma rearranged alleles, supporting a role for functional TCRgamma/delta rearrangements in the gammadelta divergence process.

The role of the T-cell receptor (TCR) in alpha beta/gamma delta lineage commitment: clues from intracellular TCR staining

T cells belong to two mutually exclusive lineages expressing either alpha beta or gamma delta T-cell receptors (TCR). Although alpha beta and gamma delta cells are known to share a common precursor the role of TCR rearrangement and specificity in the lineage commitment process is controversial. Instructive lineage commitment models endow the alpha beta or gamma delta TCR with a deterministic role in lineage choice, whereas separate lineage models invoke TCR-independent lineage commitment followed by TCR-dependent selection and maturation of alpha beta and gamma delta cells. Here we review the published data pertaining to the role of the TCR in alpha beta/gamma delta lineage commitment and provide some additional information obtained from recent intracellular TCR staining studies. We conclude that a variant of the separate lineage model is best able to accommodate all of the available experimental results.

The developmental fate of T cells is critically influenced by TCRgammadelta expression

Differentiation of gammadelta and alphabeta T cells from a common precursor cell depends on productive rearrangement and expression of TCRgammadelta or TCRbeta genes, but whether it is an instructive or a stochastic mechanism that is responsible for this process is unclear. We report that expression of the productively rearranged TCRgamma transgene competitively inhibits alphabeta thymocyte development under conditions where TCRbeta gene rearrangement is limiting. The status of TCRdelta gene rearrangements in the remaining alphabeta-lineage cells indicates that the effect is mediated by the intact gammadelta receptor. Paradoxically, in TCRbeta-/- mice, gammadelta receptor expression can also drive differentiation of some alphabeta-lineage cells. To resolve this paradox, we provide evidence for a minor population of gammadelta-dependent alphabeta-lineage cells in normal mice. The results indicate that the T cell lineage commitment process is either error-prone or stochastic.

Differential regulation of rejection of small intestinal and skin allografts in rats by injection of antibodies to ICAM-1 or the integrins alpha 4, alpha L, or beta 2

Female Lewis (LEW) rats received orthotopic small intestinal transplantation (SIT), or tail skin grafts from female (Lewis x Brown Norway)F1 (LBNF1) rats, along with peritransplant portal venous (pv) infusion of LBNF1 bone marrow-derived dendritic cells derived from male donors. All animals received im injection with cyclosporin A (5 mg/kg) for 3 consecutive days following transplantation. In some cases rats received intravenous injections, at 2-day intervals, with 1 mg of monoclonal antibodies to ICAM-1 or the integrins alpha 4, alpha L, or beta 2, or combinations of these reagents. Cells were harvested from the recipient rats at different times posttransplantation, and single cell suspensions were analyzed by FACS for expression of CD3+, CD4+, CD8+, alpha beta TcR+, and gamma delta TcR+ cells. Other tissue samples were used for histopathological assessment of rejection. We also investigated donor-specific and third-party (Wistar-Furth, Wi) restimulation of host lymphocytes from MLN, PLN, and PP for production of different cytokines in vitro. Of the various antibodies tested, only anti-alpha 4, but not anti-alpha L, -beta 2, nor -ICAM-1 led to further increased graft survival of LBNF1 SIT beyond that seen with pv-infused cells alone (30 days vs 19 days), while the combination of anti-alpha L (or beta 2) and ICAM-1 produced further significantly increased survival of skin grafts (30 days vs 21 days). For both SIT and skin-grafted animals increased graft survival was associated with decreased production of IL-2 and IFN-gamma and increased production of IL-4 and IL-10 from tissues local to the graft (PP and draining LN, respectively), with less significant alterations in tissues distant to the graft (PLN for SIT, and MLN for skin grafts). While, as reported previously, pv-immunized SIT rats showed increased gamma delta TCR+ cells within the SIT in association with increased graft survival, treatment with anti-alpha 4 diminished this increase in gamma delta TCR+ cells, while simultaneously increasing SIT survival. Nevertheless, the bias toward increased IL-10 production, and decreased IFN-gamma production, from cells of animals showing increased survival was maintained. These data suggest that local graft infiltration with gamma delta TCR+ cells following pv immunization is not necessary for prolongation of survival in this model system, although functional changes in the local cytokines milieu may be important.