Differential production of interferon-gamma and interleukin-4 in response to Th1- and Th2-stimulating pathogens by gamma delta T cells in vivo

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

Mouse T cells co-expressing an alpha beta T cell receptor (TCR) and the NK1.1 antigen have been shown to be major interleukin (IL)-4-producing cells and could therefore regulate cell-mediated immune responses. We have identified a related sub-set of thymocytes co-expressing a gamma delta TCR and NK1.1 which also produce IL-4. Unlike alpha beta +NK1.1+ thymocytes, the selection of gamma delta +NK1.1+ thymocytes is not dependent upon beta 2-microglobulin (beta 2m)-associated class I molecule expression because these cells are present in beta 2m-deficient mice. This suggests that gamma delta +NK1.1+ T cells may regulate immune responses to a different variety of antigens. However, the development of alpha beta +NK1.1+ and gamma delta +NK1.1+ thymocytes appears to be related. Analysis of different mutant mice lacking alpha beta +NK1.1+ thymocytes revealed a specific increase in gamma delta +NK1.1+ thymocyte production when the block in alpha beta +NK1.1+ thymocyte differentiation occurs after beta TCR rearrangement.

Immunological determinants of disease caused by respiratory syncytial virus

Various disease syndromes caused by respiratory syncytial virus (RSV) may have a common mechanism of pathogenesis mediated by cytokines produced by type 2 T helper cells. The nature of the immune response to RSV is determined by the pattern of cytokines produced sequentially by many different cell types. Vaccination can influence the types of cytokine produced by selectively activating T cell subpopulations and inducing an immune response that clears the virus with minimal immunopathology.

Type 1 and type 2: a fundamental dichotomy for all T-cell subsets

Cytokine secretion is not confined to CD4+ T cells; rather, Type 1 and Type 2 populations of CD8+ and gamma delta T cells can also be generated in vitro and isolated from in vivo situations. These subsets and their physiological functions are significant.

A recombinant minigene vaccine containing a nonameric cytotoxic-T-lymphocyte epitope confers limited protection against Listeria monocytogenes infection

We have previously shown that vaccines expressing virus-derived cytotoxic-T-lymphocyte (CTL) epitopes as short minigenes can confer effective protection against virus challenges, and here we extend these studies to the bacterium Listeria monocytogenes. Host defense against this important human pathogen appears largely T cell mediated, and a nonamer CTL epitope from the listeriolysin O (LLO) protein has been identified in BALB/c mice. We have synthesized this nonamer as a minigene, expressed it in a recombinant vaccinia virus (VV-list), and used this to immunize mice. Memory CTLs cultured from VV-list-immunized mice specifically lyse target cells pulsed with a nonamer peptide identified at LLO amino acid residues 91 to 99. Four weeks postimmunization, mice were challenged with L. monocytogenes. By day 6 following challenge with a sublethal dose of L. monocytogenes, mice immunized with VV-list showed a approximately 2,000- to 6,000-fold reduction in bacteria CFU in the spleen and liver. At this time point, with control mice, bacterial were readily detectable by Gram stain of the liver but were undetectable in the VV-list-immunized animals. Additionally, when a normally lethal dose of bacteria was given, death was delayed in VV-list-immunized animals. This study has demonstrated that a single immunization with a recombinant vaccinia virus bearing only nine amino acids from a bacterial pathogen can induce specific CTLs able to confer partial protection against bacterial challenge.

Control of natural killer cell-mediated innate resistance against the intracellular pathogen Listeria monocytogenes by gamma/delta T lymphocytes

Listeria monocytogenes is an intracellular bacterium which causes an acute infectious disease in mice. Initial host resistance depends on innate immunity mediated primarily by natural killer (NK) cells followed by specific alpha/beta T cells, which are central to acquired specific immunity. Gamma/delta T lymphocytes seem to provide a link between the innate and the specific immune response. All these lymphocyte populations produce gamma interferon (IFN-gamma), which, because of its macrophage-activating potential, is central to antibacterial protection. IFN-gamma from NK cells not only contributes to early host resistance but also promotes development of protective T-cell responses of helper T type 1 (Th1) type. Here, we show that innate resistance and early IFN-gamma production in listeriosis are markedly impaired in T-cell receptor (TCR)-delta-/- but not TCR-beta-/- gene disruption mutant mice. By two-color cytofluorimetry, we demonstrate that NK cells rather than gamma/delta T lymphocytes are the major cellular source of IFN-gamma in immunocompetent mice and that IFN-gamma production by NK cells is impaired in the TCR-delta-/- mutants. Probably, reduced tumor necrosis factor production in listeria-infected TCR-delta-/- mutants contributed to impaired NK cell activation. Our data reveal a novel function of gamma/delta T cells as regulators of innate resistance against sublethal infection with an intracellular pathogen.

Germinal center formation, immunoglobulin class switching, and autoantibody production driven by "non alpha/beta" T cells

The production of class-switched antibodies, particularly immunoglobulin (Ig) G1 and IgE, occurs efficiently in T cell receptor (TCR) alpha-/- mice that are congenitally devoid of alpha/beta T cells. This finding runs counter to a wealth of data indicating that IgG1 and IgE synthesis are largely dependent on the collaboration between B and alpha/beta T cells. Furthermore, many of the antibodies synthesized in TCR alpha-/- mice are reactive to a similar spectrum of self-antigens as that targeted by autoantibodies characterizing human systemic lupus erythematosus (SLE). SLE, too, is most commonly regarded as an alpha/beta T cell-mediated condition. To distinguish whether the development of autoantibodies in TCR alpha-/- mice is due to an intrinsic de-regulation of B cells, or to a heretofore poorly characterized collaboration between B and "non-alpha/beta T" cells, the phenotype has been reconstituted by transfer of various populations of B and non-alpha/beta T cells including cloned gamma/delta T cells derived from TCR alpha-/- mice, to severe combined immunodeficient (SCID) mice. The results establish that the reproducible production of IgG1 (including autoantibodies) is a product of non-alpha/beta T cell help that can be provided by gamma/delta T cells. This type of B-T collaboration sustains the production of germinal centers, lymphoid follicles that ordinarily are anatomical signatures of alpha/beta T-B cell collaboration. Thus, non-alpha/beta T cell help may drive Ig synthesis and autoreactivity under various circumstances, especially in cases of alpha/beta T cell immunodeficiency.

γδ T cells in malaria infections

The association of a pronounced gammadelta T-cell response with Plasmodium infections is intriguing. The ability of parasite material to activate gammadelta T cells in vitro, and the localization of these cells in vivo in the red pulp of the spleen, suggests that these cells could play a role in the killing of bloodstage malaria parasites. However, the magnitude, the response and the predominance of inflammatory cytokines secreted by these cells may also indicate a role in the pathology of malaria infections. In this article, Jean Langhorne reveiws the current status of gammadelta T cells in malaria in the context of what is known about the function and specificity of gammadelta T cells in general.

Human basophils release interleukin-4 after stimulation with Schistosoma mansoni egg antigen

The elevated interleukin (IL)-4 and IgE production in Schistosoma mansoni infection seems to be induced essentially by the egg stage of the parasite. The underlying mechanism, however, is not known. Since basophils from human peripheral blood can produce IL-4, we asked, whether soluble S. mansoni egg antigens (SEA) would trigger basophils to release IL-4. Basophils from healthy human donors (n = 32) without prior history of schistosomiasis were incubated with SEA in the presence of IL-3. In all donors, IL-4 was produced at different concentrations. The IL-4 production was dependent on the dose of SEA, was correlated with the purity of the basophil preparation, and the IL-4 concentration in the culture supernatant was maximal 5 h after stimulation with SEA. In addition to its IL-4-stimulatory effect, SEA triggered basophils to degranulate, thereby releasing histamine and sulfidoleukotrienes. Stripping of receptor-bound IgE from basophils inhibited both SEA- and anti-IgE-induced, but not ionomycin-induced IL-4 production. Moreover, resensitization of stripped basophils with stripping supernatants or human serum restored SEA-induced IL-4 production. This suggests that IgE is involved in the mechanism of IL-4 induction by SEA. Since IL-4 is induced in basophils from nonexposed donors, basophils may play a role as an early source of IL-4 in S. mansoni infection.

The instructive role of innate immunity in the acquired immune response

Innate immunity has been considered only to provide rapid, incomplete antimicrobial host defense until the slower, more definitive acquired immune response develops. However, innate immunity may have an additional role in determining which antigens the acquired immune system responds to and the nature of that response. Knowledge of the molecules and pathways involved may create new therapeutic options for infectious and autoimmune diseases.

Endogenous interleukin-4, but not interleukin-10, is involved in suppression of host resistance against Listeria monocytogenes infection in interferon-depleted mice

The production and roles of endogenous interleukin-4 (IL-4) and IL-10 in a sublethal infection with Listeria monocytogenes were studies in normal mice and anti-gamma interferon (IFN-gamma) monoclonal antibody (MAb)-pretreated mice. In normal mice, the expression of mRNAs for IL-4 and IL-10, which was amplified by reverse transcription-PCR, was induced in the spleens and livers either early or late in infection, although the serum IL-4 and IL-10 were not detectable by enzyme-linked immunosorbent assays. In vivo administration of anti-IL-4 MAb showed no effect on antilisterial resistance, whereas anti-IL-10 MAb partially diminished the defense. In anti-IFN-gamma MAb-pretreated mice, a delay in the bacterial elimination from the spleens and livers was observed and high titers of serum IL-4 and IL-10 were induced late in infection. Production of endogenous IL-4 and IL-10 was suppressed in both CD4+ cell-and CD8+ cell depleted mice. The suppression of antilisterial resistance in anti-IFN-gamma MAb-pretreated mice was canceled when anti-IL-4 MAb was injected late in infection, whereas anti-IL-10 MAb showed no effect. These results suggest that the host immune responses were polarized into the T-helper 2 phenotype in anti-IFN-gamma MAb-pretreated mice and that inhibition of host resistance against L. monocytogenes by depletion of IFN-gamma might be attributable to IL-4 produced by T cells polarized into the T-helper 2 phenotype as well as the inhibition of the IFN-gamma effects.

Human intestinal Vdelta1+ lymphocytes recognize tumor cells of epithelial origin

gammadelta T cells can be grouped into discrete subsets based upon their expression of T cell receptor (TCR) variable (V) region families, their tissue distribution, and their specificity. Vdelta2+ T cells constitute the majority of gammadelta T cells in peripheral blood whereas Vdelta1+T cells reside preferentially in skin epithelium and in the intestine. gammadelta T cells are envisioned as first line host defense mechanisms capable of providing a source of immune effector T cells and immunomodulating cytokines such as interleukin (IL) 4 or interferon (IFN) gamma. We describe here the fine specificity of three distinct gammadelta+ tumor-infiltrating lymphocytes (TIL) obtained from patients with primary or metastatic colorectal cancer, that could be readily expanded in vitro in the presence of IL-1beta and IL-7. Irrespective of donor, these individual gammadelta T cells exhibited a similar pattern of reactivity defined by recognition of autologous and allogeneic colorectal cancer cells, renal cell cancer, pancreatic cancer, and a freshly isolated explant from human intestine as measured by cytolytic T cell responses and by IFN-gamma release. In contrast, tumors of alternate histologies were not lysed, including lung cancer, squamous cell cancer, as well as the natural/lymphocyte-activated killer cell-sensitive hematopoietic cell lines T2, C1R, or Daudi. The cell line K562 was only poorly lysed when compared with colorectal cancer targets. Target cell reactivity mediated by Vdelta1+ T cells was partially blocked with Abs directed against the TCR, the beta2 or beta7 integrin chains, or fibronectin receptor. Marker analysis using flow cytometry revealed that all three gammadelta T cell lines exhibit a similar phenotype. Analysis of the gammadelta TCR junctional suggested exclusive usage of the Vdelta1/Ddelta3/Jdelta1 TCR segments with extensive (< or = 29 bp) N/P region diversity. T cell recognition of target cells did not appear to be a major histocompatibility complex restricted or to be correlated with target cell expression of heat-shock proteins. Based on the ability of some epithelial tumors, including colorectal, pancreatic, and renal cell cancers to effectively cold target inhibit the lysis of colorectal cancer cell lines by these Vdelta1+ T cell lines, we suggest that intestinal Vdelta1+ T cell lines, we suggest that intestinal Vdelta1+ T cells are capable of recognizing cell surface Ag(s) shared by tumors of epithelial origin.

Resistance to cutaneous graft-vs.-host disease is not induced in T cell receptor delta gene-mutant mice

The function of murine dendritic epidermal cells (dEC) remains largely speculative, probably because of the lack of a suitable in vivo model, although previous studies suggest that gamma/delta+ dEC may have originally evolved to serve as a self-protection mechanism(s). Our previous study demonstrated that the epidermis of mice that had spontaneously recovered from cutaneous graft-vs-host disease (GVHD) induced by local injection of CD4+ autoreactive T cells contained unexpectedly large numbers of dEC and became resistant to subsequent attempts to induce GVHD in a site-restricted manner, suggesting that the resistance is mediated by dEC. However, because alpha/beta+ dEC as well as gamma/delta+ dEC were greatly increased in number in the epidermis, it was unclear whether gamma/delta+ dEC are indeed responsible for this protection. The availability of this murine model and mice selectively lacking gamma/delta T cells as a result of disruption of the T cell receptor C delta gene segment allowed us to investigate the role of gamma/delta+ dEC. In the epidermis of gamma/delta T cell-deficient mice (delta-/-), a congenital lack of gamma/delta+ dEC was substituted for by alpha/beta+ dEC of either a CD4-8+ or a CD4-8- phenotype. After intradermal injection of the autoreactive T cells, delta-/- mice developed significantly enhanced delayed-type hypersensitivity responses and cutaneous GVHD, which persisted longer than in heterozygous littermate controls (delta+/-). Surprisingly, resistance to the cutaneous GVHD was not induced in the epidermis of delta-/- mice after spontaneous recovery from the GVHD, whereas the "susceptible" epidermis of delta-/+ mice contained large numbers of alpha/beta dEC comparable to those in "resistant" epidermis of delta+/- mice. Injection of day 16 fetal thymocytes from wild-type mice into delta-/- mice resulted in the appearance of donor-type gamma/delta+ dEC in the epidermis, and reconstitution with gamma/delta+ dEC restored the protective immune response of the epidermis against the GVHD to nearly normal levels. These results indicate that gamma/delta+ dEC are responsible for the site-restricted protection against cutaneous GVHD.

Recognition by gamma/delta T cells

In contrast with the study of alpha beta T cells, that of gamma delta T cells is relatively recent and stems from the discovery of their rearranged genes, rather than from any knowledge of their biological function. Thus, experiments designed to characterize their specificity and function have drawn heavily on our knowledge of alpha beta T cells. During the past few years, many studies, especially with mice lacking either alpha beta or gamma delta T cells, have demonstrated that gamma delta T cells can contribute to immune competence, but they do so in a way that is distinct from alpha beta T cells. It is also evident that gamma delta T cells may not recognize antigen the same way as do alpha beta T cells. Analysis of three protein antigens-the murine MHC class II IEk, the nonclassical MHC T10/T22, and the Herpes virus glycoprotein gI-indicates that gamma delta T cell recognition does not require antigen processing and that the proteins are recognized directly. In all three cases, recognition by these T cell clones involves neither peptides bound to these proteins nor peptides derived from them. Moreover, a group of small phosphate-containing nonpeptide compounds derived from mycobacterial extracts has been found to stimulate a major population of human peripheral gamma delta T cells in a T cell receptor (TCR)-dependent manner. This indicates that gamma delta T cells can respond to ligands that are different from those of alpha beta T cells. Analysis of complementarity determining region (CDR3) length distributions of gamma and delta chains indicates that they are more similar to those of immunoglobulins than to TCR alpha and beta. This further supports the idea that gamma delta and alpha beta T cells recognize antigens differently and suggests that gamma delta T cells may be more like immunoglobulins in their recognition properties. gamma delta T cells share many cell surface proteins with alpha beta T cells and are able to secrete lymphokines and express cytolytic activities in response to antigenic stimulation. These, together with the results cited above, indicate that gamma delta T cells can mediate cellular immune functions without a requirement for antigen processing. Thus, pathogens, damaged tissues, or even B and T cells can be recognized directly, and cellular immune responses can be initiated without a requirement for antigen degradation or specialized antigen-presenting cells. This would give gamma delta T cells greater flexibility than the more classical type of alpha beta T cell-mediated cellular immunity.

Role of gamma delta T cells in pathogenesis and diagnosis of Behcet's disease

BACKGROUND

Behcet's disease (BD) is a multisystem disorder of unknown pathogenesis. The diagnosis is based on a set of international clinical criteria. Previous investigations have suggested that immunological cross-reactivity between peptides within streptococcal heat-shock proteins and human peptides might be involved in the pathogenesis of BD. We tested four peptides from mycobacterial heat-shock proteins to see if they specifically stimulated gamma delta T cells from BD patients. We then investigated this response to see whether it could be used as a laboratory test to diagnose BD.

METHODS

We used a T-cell proliferative test to assay responses to four mycobacterial 65 kDa heat-shock-protein peptides and to four homologous peptides derived from the sequence of the human 60 kDa heat-shock protein.

FINDINGS

We elicited significant gamma delta T-cell responses to the mycobacterial peptides in 25 (76%) of 33 patients with BD, compared with 2 (3.6%) of 55 controls with recurrent oral ulcers, systemic disease, or no disorders. The proportion of BD patients who had false-negative results decreased if the test was done during clinical manifestation of disease activity. There was a correlation between disease activity and T-cell responses. Four homologous peptides from human 60 kDa heat-shock protein also specifically stimulated T cells from patients with BD but with lower stimulation indices.

INTERPRETATION

Activation of peripheral-blood mononuclear cells with the four heat-shock-protein peptides elicited significant T-cell proliferative responses by the gamma delta subset of T cells, which may regulate alpha beta T cells. Because these peptides have a high specificity for BD, this assay can be used as a laboratory diagnostic test for BD.

gamma/delta and other unconventional T lymphocytes: what do they see and what do they do?

T lymphocytes recognize specific ligands by clonally distributed T-cell receptors (TCR). In humans and most animals, the vast majority of T cells express a TCR composed of an alpha chain and a beta chain, whereas a minor T-cell population is characterized by the TCR gamma/delta. Almost all of our knowledge about T cells stems from alpha/beta T cells and only now are we beginning to understand gamma/delta T cells. In contrast to conventional alpha/beta T cells, which are specific for antigenic peptides presented by gene products of the major histocompatibility complex, gamma/delta T cells directly recognize proteins and even nonproteinacious phospholigands. These findings reveal that gamma/delta T cells and alpha/beta T cells recognize antigen in a fundamentally different way and hence mitigate the dogma of exclusive peptide-major histocompatibility complex recognition by T cells. A role for gamma/delta T cells in antimicrobial immunity has been firmly established. Although some gamma/delta T cells perform effector functions, regulation of the professional and the nonprofessional immune system seems to be of at least equal importance. The prominent residence of gamma/delta T cells in epithelial tissues and the rapid mobilization of gamma/delta T cells in response to infection are consistent with such regulatory activities under physiological and pathologic conditions. Thus, although gamma/delta T cells are a minor fraction of all T cells, they are not just uninfluential kin of alpha/beta T cells but have their unique raison d'être.

Orchestration of the protective immune response to intracellular bacteria: Francisella tularensis as a model organism

Francisella tularensis is used as a model organism in studies of mechanisms behind the induction of a protective T-cell response in the mammalian host. Protective immunity is associated with a CD4 and CD8 T-cell response towards a mosaic of proteins of F. tularensis and due to HLA restriction, each individual selects her own mosaic. No single protein has so far been shown to be immunodominant. Only live F. tularensis affords effective host protection. Subcellular antigen preparations induce only a marginal protective response even when combined with potent adjuvants such as immunostimulating complexes (ISCOMs). In mice, intradermal injection of live F. tularensis but not of killed bacteria results in an early cytokine expression in the infected liver, including interleukin-12, tumor necrosis factor-alpha, and interferon-gamma. This cytokine response seems to be a prerequisite for effective priming of T cells to an array of proteins of F. tularensis to occur.

Reversibility of T helper 1 and 2 populations is lost after long-term stimulation

Commitment of T helper 1 (Th1) or Th2 populations developing during an immune response to a pathogen, or an inappropriate immune response to an allergen or autoantigen, may determine the difference between health and chronic disease. We show that strongly polarized Th1 and Th2 populations assessed by immunoassay are heterogeneous using flow cytometry to detect single cells producing interferon gamma (IFN-gamma) and interleukin 4 (IL-4). Th1 populations arising after 1 wk of stimulation in IL-12 plus anti-IL-4 antibodies could convert to Th2 cells when restimulated in IL-4. Th2 populations resulting from stimulation for 1 wk in IL-4 could give rise to Th1 cells upon restimulation in IL-12 plus anti-IL-4. In contrast, the cytokine profiles of long-term Th1 and Th2 populations arising originally from repeated stimulation in IL-12 or IL-4 appeared more homogeneous and were not reversible, although IL-4 dramatically reduced the number of IFN-gamma-producing Th1 cells. This may explain previous reports that Th1 cells can be converted to Th2 cells.

Cytokine imbalance and autoantibody production in T cell receptor-alpha mutant mice with inflammatory bowel disease

Spontaneous inflammatory bowel disease (IBD) resembling human ulcerative colitis develops in mice mutant for the T cell receptor alpha gene (TCR-alpha-/-). TCR-alpha-/- mice lack TCR-alpha/beta+ cells but contain TCR-gamma/delta+ cells and a small population of a unique CD4+, TCR-alpha-/beta+(low) cells. Since all the immunoglobulin (Ig) classes are present in these mice, help to B cells must be provided by cells other than TCR-alpha/beta+ cells. In the present study, we found serum levels of IgG1 and IgG2 to be markedly increased in TCR-alpha-/- mice with IBD as compared to TCR-alpha-/- mice without IBD or TCR-alpha+/- controls. An increase in IgG1-, IgG2a- and IgA- but not IgM-secreting mesenteric lymph node (MLN) B cells was detected in TCR-alpha-/- mutant mice. There was also a marked increase in MLN B cells secreting autoantibody (IgG) to tropomyosin, a cytoskeletal protein. Examination of the hyperplastic MLN showed a marked increase in the number of B, TCR-delta+, and CD4+ TCR-alpha-/beta+ cells, similar to the cell population observed at the site of colonic inflammation. Analysis of spontaneous cytokine production by MLN cells using an enzyme-linked immunospot assay, immunohistochemistry, and reverse transcription/polymerase chain reaction showed a decrease of interleukin 2 (IL-2) but a marked increase of IL-4 and interferon gamma (IFN-gamma) production in TCR-alpha-/- mice with IBD as compared to TCR-alpha-/- mice without IBD and TCR alpha+/- control mice. Both TCR-alpha-/beta+ and TCR-delta+ cells were found to be capable of producing IL-4; IFN-gamma was produced mostly by non-T cells, many of which were shown to be CD3- NK 1.1+ cells. We propose that the cytokine imbalance present in these mice results in expansion of B cells, production and switching of autoantibodies to IgG2 subclass, and development of IBD. It is possible that the unusual CD4+ TCR-alpha-/beta+ population and expanded TCR-gamma/delta+ population present in TCR-alpha-/- mice plays a central role in this abnormal immune response.

The expanding universe of T-cell subsets: Th1, Th2 and more

Since their discovery nearly ten years ago, T helper 1 (Th1) and Th2 subsets have been implicated in the regulation of many immune responses. In this article, Tim Mosmann and Subash Sad discuss the increasing number of T-cell subsets defined by cytokine patterns; the differentiation pathways of CD4+ and CD8+ T cells; the contribution of other cell types to these patterns; and the cytokine interactions during infection and pregnancy.

Dynamic changes in circulating and antigen-responsive T-cell subpopulations post-Mycobacterium bovis infection in cattle

Bovine tuberculosis is a threat to animal and human health in several countries. Greater understanding of the immunology of the disease is required to develop improved tests and vaccines. This study has used a model of bovine tuberculosis, established in the natural host, to investigate the dynamic changes that occur in the circulating T-cell subpopulations after infection. When the phenotypic composition of the peripheral blood lymphocytes was determined pre- and post-experimental infection, the response to disease comprised three phases. Firstly, the WC1/gamma delta T cells decreased and then increased, suggesting localization to developing lesions and clonal expansion. Secondly, the CD4:CD8 ratio increased. Thirdly, the CD4:CD8 ratio decreased to less than pre-infection measurements. The latter changes suggested sequential involvement of CD4 and then CD8 T cells. The proportion of cells expressing interleukin-2 receptor (IL-2R) also increased. Panels of T-cell clones were established at various stages post-infection and all clones that exhibited antigen responsiveness were phenotyped. T-cell clones from early infection were WC1/gamma delta and CD4 in phenotype, while CD8 clones appeared later in infection, eventually becoming dominant. Therefore, from in vivo and in vitro evidence, it was suggested that there is a dynamic progression in the T-cell subpopulations involved dominantly in responses to mycobacteria.

T cells in murine lupus: propagation and regulation of disease

MRL/Mp-lpr/lpr mice develop a spontaneous lupus syndrome, including hypergammaglobulinemia, autoantibodies, glomerulonephritis, and lymphadenopathy. To investigate the role of lymphocytes subsets in the pathogenesis of disease, lupus-prone MRL mice deficient in alpha beta T cells, gamma delta T cells, or both were generated. Mice deficient in alpha beta T cells developed a partially penetrant lupus syndrome, characterized by lymphadenopathy, elevated levels of class-switched immunoglobulins, an increased incidence of antinuclear antibodies, and immune deposits in kidneys which progressed to renal insufficiency over time. In comparison to wild type animals, gamma delta T cell-deficient animals developed an accelerated and exacerbated disease phenotype, characterized by accelerated hypergammaglobulinemia and enhanced autoantibody production and mortality. Repertoire analysis of these latter animals identified polyclonal expansion (V beta) of alpha beta CD4+ B220-cells. Mice lacking both alpha beta and gamma delta T cells failed to generate class-switched autoantibodies and immune complex renal disease. First, these findings demonstrate that murine lupus in the setting of Fas-deficiency does not absolutely require the presence of alpha beta T cells, and they also suggest that a significant basis for MRL/lpr disease, including renal disease, involves alpha beta T cell-independent, gamma delta T cell dependent, polyreactive B cell autoimmunity, upon which alpha beta T cell-dependent mechanisms aggravate specific autoimmune responses. Second, these data indicate that gamma delta T cells partake in the regulation of systemic autoimmunity, presumably via their effects on alpha beta CD4+ B220-T cells that provide B cell help. Finally, these results demonstrate that MRL/lpr B cells, despite their intrinsic abnormalities, cannot per se cause tissue injury without T cell help.

Chagas' disease is attenuated in mice lacking gamma delta T cells

The role of gamma delta T cells in the immunopathology of Chagas' disease is evaluated by monitoring the course of Trypanosoma cruzi infection in mice lacking gamma delta T cells after disruption of the T-cell receptor C delta locus. Levels of parasitemia, states of lymphocyte activation, and levels of lymphokine production as well as tissue pathology are compared in delta knockout mice and their littermates in acute and chronic phases of infection. Although the levels of circulating parasites do not significantly differ in the two groups, mortality scores and numbers of inflammatory lesions of skeletal and cardiac muscles are lower in gamma delta T cell-deficient m ice than in littermate controls. Furthermore, polyclonal lymphocyte activation, as measured by proliferative activities and numbers of B- and T-cell blasts in the spleen, are reduced in deficient mice in the acute and chronic phases of infection. Levels of gamma interferon mRNA obtained from total spleen cells, known to be a critical lymphokine in resistance to T. cruzi infection, are significantly higher in uninfected gamma delta T cell-deficient mice than in control animals and slightly above levels for littermates in the course of acute infection. Interestingly, however, in chronic phases, the levels of this lymphokine are not statistically different between the two groups of mice. These results indicate that gamma delta T cells do not play a crucial role in parasite clearance during the acute phase of the disease but contribute to the mechanisms leading to tissue damage and pathology.

Effects of interferon-alpha therapy on immune parameters in immune thrombocytopenic purpura

Interferon-alpha (IFN alpha) has been shown to increase platelet numbers in patients with immune thrombocytopenic purpura (ITP), but the basis for this effect is not known. In this study changes in immune function were monitored following administration of IFN alpha to seven patients whose ITP had proved refractory to conventional therapy. Patients' peripheral blood mononuclear cells were cultured with phytohaemagglutinin and culture supernatants assayed for cytokine production. Production of the Th1 cytokines IL-2 and IFN-gamma was low in patients compared to healthy controls, and amounts of these tended to increase after IFN alpha therapy. In two patients high levels of IL-10 were detectable in culture, and these were reduced after IFN alpha. In patients who had high serum concentrations of IL-4 or IL-10, these were also decreased following therapy. Natural killer cell activity, which was low in the patients prior to therapy, was increased following administration of IFN alpha. In those patients with detectable platelet-associated autoantibody to gpIIb/IIIa, the amounts were reduced after treatment. Two patients had an unusually high percentage of T cells expressing the gamma delta T cell receptor, which decreased after therapy. The findings are consistent with an increase in Th 1 activity and a decrease in autoantibody production following IFN alpha therapy, which may be related to the beneficial effects of this cytokine.

Altered serum cytokines in hepatic and portal blood of rats at early times following portal venous infusion of semi-allogeneic cells

The liver of anaesthetized adult ( > 350 g) Lewis rats was perfused in vitro after cannulation of both the hepatic and portal vein, with clamping of the hepatic artery. Heparinized blood (400 microliters) was withdrawn at 0, 6, 12, 18, 24, 30 and 36 h from each site, and serum and peripheral blood lymphocytes (PBL) isolated after ficoll/hypaque separation. Serum was tested in bioassays for cytokines known to modulate lymphocyte:endothelial interactions in vivo and in vitro (IFN gamma, TGF beta, TNF alpha, IL-6, IL-1). In some experiments rats received, via portal venous infusion, a sterile inoculum of 150 x 10(6) semi-allogeneic (LBN F1) spleen cells immediately or 12 h after the start of the study. In animals which were unchallenged with cells via the portal vein, subtle differences in detectable cytokines were observed between hepatic and portal blood samples, as reported in earlier studies. Within 12 h the minor perturbations observed in cytokine profiles following surgical insult resolved, and the changes between hepatic and portal venous samples remained constant throughout the study in control rats. However, in rats treated with LBNF1 cells, changes in the cytokine profiles were seen compared with control animals, and as a function of time post F1 cell infusion. Changes in mRNAs for different cytokines were observed in PBL taken from portal/hepatic blood in these same animals. These data point to one possible mechanism whereby the liver may influence immunological processes following portal venous antigen challenge.

Role of NK1.1+ T cells in a TH2 response and in immunoglobulin E production

Immune responses dominated by interleukin-4 (IL-4)-producing T helper type 2 (TH2) cells or by interferon gamma (IFN-gamma)-producing T helper type 1 (TH1) cells express distinctive protection against infection with different pathogens. Interleukin-4 promotes the differentiation of naïve CD4+ T cells into IL-4 producers and suppresses their development into IFN-gamma producers. CD1-specific splenic CD4+NK1.1+ T cells, a numerically minor population, produced IL-4 promptly on in vivo stimulation. This T cell population was essential for the induction of IL-4-producing cells and for switching to immunoglobulin E, an IL-4-dependent event, in response to injection of antibodies to immunoglobulin D.

Differential production of intracellular gamma interferon in alpha beta and gamma delta T-cell subpopulations in response to peritonitis

Flow cytometry was used to measure T-cell intracellular gamma interferon and surface interleukin 2 re-ceptor expression in response to peritonitis in rats. Interleukin 2 receptor expression levels were similar in the two T-cell subsets, but gamma interferon production was increased fivefold in gamma delta T cells compared with pro-duction in alpha beta T cells. Our results provide further evidence of an early and vigorous gamma delta T-cell response to bac-terial infection.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.

Heterogeneity of intracellular cytokine synthesis at the single-cell level in polarized T helper 1 and T helper 2 populations

CD4+ T helper (Th) cells can be classified into different types based on their cytokine profile. Cells with these polarized patterns of cytokine production have been termed Th1 and Th2, and can be distinguished functionally by the production of IFN-gamma and IL-4, respectively. These phenotypes are crucial in determining the type of immune response that develops after antigen priming. There are no surface markers that define them, and cytokine immunoassay or mRNA analysis both have limitations for characterization of single cells. Using immunofluorescent detection of intracellular IFN-gamma and IL-4, we have studied the emergence of Th1 and Th2 cells in response to antigen exposure and the patterns of cytokine synthesis in established T cell clones. IFN-gamma production by Th1 clones was detectable in almost all cells by 4 h, and it continued in most cells for > 24 h. IL-4 production in Th2 cells peaked at 4 h, but declined rapidly. In Th0 cells containing both cytokines, fewer cells produced IFN-gamma, which did not appear until IL-4 synthesis declined. Cocultivation of clones showed no such cross-regulation. Antigen stimulation of transgenic T cells expressing an ovalbumin-specific T cell receptor generated Th2 cells, probably as a result of endogenous IL-4 production. Addition of IL-12 and/or anti-IL-4 caused Th1 cells to develop, while some Th0 cells were seen when IL-12 alone was added. These results show that stimulation in the presence of polarizing stimuli results in cells producing either IFN-gamma or IL-4, but that coproduction can occur in rare cells under defined conditions.

Direct presentation of nonpeptide prenyl pyrophosphate antigens to human gamma delta T cells

Human V gamma 2V delta 2+ T cells recognize mycobacterial nonpeptide antigens, such as isopentenyl pyrophosphate, and their synthetic analogs, such as monoethyl phosphate, through a TCR-dependent process. Here, we examine the presentation of these antigens. V gamma 2V delta 2+ T cells recognized secreted prenyl pyrophosphate antigens in the absence of other accessory cells but, under such conditions, required T cell-T cell contact. Recognition required neither the expression of classical MHC class I, MHC class II, or CD1a, CD1b, and CD1c molecules, nor MHC class I or class II peptide loading pathways. Fixed accessory cells also presented the prenyl pyrophosphate antigens to gamma delta T cells. Thus, in contrast with the presentation of conventional peptide antigens, protein antigens, and superantigens to alpha beta T cells, prenyl pyrophosphate antigens are presented to gamma delta T cells through a novel extracellular pathway that does not require antigen uptake, antigen processing, or MHC class I or class II expression. This pathway allows for the rapid recognition of bacteria by gamma delta T cells and suggests that gamma delta T cells play a role in the early response to bacterial infection.

Roles for both CD4+ and CD8+ T cells in protective immunity against Onchocerca lienalis microfilariae in the mouse

Mice inoculated with microfilariae of the filarial nematode Onchocerca lienalis clear their parasites from the skin over a period of 3 to 4 months and are highly resistant to a challenge infection. The adoptive transfer of spleen cells at various time points following primary and secondary infections of mice shows that exposures of 50 days or greater are required for the generation of lymphocytes capable of transferring protection to naive recipients. This adoptive transfer of protection with spleen cells from infection-primed mice partitions with the T lymphocyte population. In contrast, the passive transfer of protection with spleen-derived B cells, or sera taken at various time points following infection was not achieved. Moreover, there was no detectable synergistic effect when B and T cells were co-administered to recipient animals. Depletion of CD4+ and CD8+ T cells with monoclonal antibodies shows that CD8+ T cells have some regulatory effect on parasite establishment early in primary infection, but this is later superseded by CD4+ T cell reactivity that is predominant both when primary infection microfilariae are cleared and also during resistance to reinfection. Measurement of cytokines in the sera of mice undergoing primary and secondary infections support a microfilariae-induced Th2 activity, with high levels of IL-5 that are sustained upon reinfection, and low levels of IFN-gamma that are negligible at the time when mice are most strongly immune.

The enigmatic specificity of gamma delta T cells

In most scientific investigations, the study of mechanism follows the study of function. For example, alpha beta T cells were shown to be important mediators of immunity before the interaction between the T cell receptor (TCR) and peptide-MHC complexes was understood. However, sometimes the study of function follows from the study of mechanism. Research of gamma delta T cell receptors falls into this category. The gamma chain of the TCR was first cloned in 1984, which then led to the discovery of gamma delta T cells in 1985. Since then, research has focused on understanding ligands of the gamma delta TCR with the hope of better understanding the function of gamma delta T cells. An initial assumption was that gamma delta T cells, like alpha beta T cells, recognize peptides bound to MHC molecules; however, recent data indicate that gamma delta T cells are not biased towards MHC recognition in the same way as alpha beta T cells. Although there are intriguing new insights, the specificity and function of gamma delta T cells remains a mystery.

T-cell subsets. Who does the polarizing?

T cells can 'polarize' into T1 and T2 effector cell types in response to distinct cytokines. T cells and cells presenting antigen to the T cells are themselves candidate sources of these polarizing cytokines.

Preferential activation and expansion of human peripheral blood gamma delta T cells in response to Toxoplasma gondii in vitro and their cytokine production and cytotoxic activity against T. gondii-infected cells

Studies were conducted to determine if gamma delta T cells participate in the immune response to Toxoplasma gondii. Preferential expansion of human gamma delta T cells occurred when peripheral blood T cells from either T. gondii-seronegative or seropositive individuals were incubated with autologous PBMC infected with the parasite. That gamma delta T cells proliferated after incubation with infected cells was confirmed using purified of gamma delta T cells. These T. gondii-induced gamma delta T cell responses did not require prior exposure to the parasite since T cells obtained from umbilical cord blood from seronegative newborns also exhibited preferential expansion of gamma delta T cells. Cytofluorometric analysis of T cells obtained from either umbilical cord blood or peripheral blood from adults revealed that V gamma 9+ and V delta 2+ gamma delta T cells responded to stimulation with infected cells. Preferential expansion of gamma delta T cells was not restricted by polymorphic determinants of MHC molecules. PBMC that had internalized killed parasites but not PBMC incubated with T. gondii lysate antigens also stimulated preferential expansion and activation of gamma delta T cells as assessed by expression of CD25 and HLA-DR molecules. V gamma 9+V delta 2+ gamma delta T cells were cytotoxic for T. gondii-infected cells in an MHC-unrestricted manner, and produced IFN-gamma, IL-2, TNF-alpha, but not IL-4 when incubated with cells infected with the parasite. These results suggest that rapid induction of a remarkable primary gamma delta T cell response may be important in the early protective immune response to T. gondii.

Deregulated T cell activation and autoimmunity in mice lacking interleukin-2 receptor beta

In mice lacking the interleukin-2 receptor beta chain (IL-2R beta), T cells were shown to be spontaneously activated, resulting in exhaustive differentiation of B cells into plasma cells and the appearance of high serum concentrations of immunoglobulins G1 and E as well as autoantibodies that cause hemolytic anemia. Marked infiltrative granulocytopoiesis was also apparent, and the animals died after about 12 weeks. Depletion of CD4+ T cells in mutant mice rescued B cells without reversion of granulocyte abnormalities. T cells did not proliferate in response to polyclonal activators, nor could antigen-specific immune responses be elicited. Thus, IL-2R beta is required to keep the activation programs of T cells under control, to maintain homeostasis, and to prevent autoimmunity.

Gamma delta T cell-induced nitric oxide production enhances resistance to mucosal candidiasis

Despite the prevalence of gamma delta T cells in mucosae that are typically colonized by Candida albicans, little is known of the possible role of these cells in resistance to candidiasis. A sharp increase in the number of gamma delta T cells and macrophages following intraperitoneal inoculation of mice with C. albicans led us to examine the role of these cells in the immune response to C. albicans. We show that the gamma delta T cells enhance macrophage nitric oxide (NO) production and anti-candida activity, in vitro. We also propose that the gamma delta T cells regulate macrophage function during candidiasis in vivo as well, because depletion of these cells abrogated inducible NO synthase expression in mucosae and enhanced murine susceptibility to candidiasis.

Horse (Equus caballus) T-cell receptor alpha, gamma, and delta chain genes: nucleotide sequences and tissue-specific gene expression

Horse (Equus caballus) T-cell receptor alpha (TCRA), gamma (TCRG), and delta (TCRD) chain genes were isolated from a cDNA library and characterized. Five unique TCRAV families, including four full-length sequences, five distinct TCRAJ genes, and a single TCRAC gene were identified. TCRAV genes had closest homology with human sequences and least similarity to rat genes. Among eight horse TCRG genes, two distinct constant region genes with considerable variation in the connecting region were identified, but no variable or joining genes were present. Southern blot hybridization confirmed the presence of at least two TCRGC genes and indicated that the vast majority of horse alpha beta T cells rearrange either one or both TCRG alleles. Analysis of horse TCRD genes revealed the presence of eight unique TCRDV genes representing seven families, each having closest nucleotide homology with sheep sequences. Six unique TCRDJ genes were isolated; however, four of these sequences differed by only one base pair and thus likely represented alleles of a single gene. One horse TCRDC gene was present among fifteen clones analyzed and, based on Southern blot hybridizations, was deleted in polyclonal alpha beta T-cell populations, indicating that the TCRD locus is probably located within the TCRA locus as in other species. Polymerase chain reaction using horse-specific primers for the detection of TCRAC and TCRDC gene expression indicated that gamma delta T cells are located at numerous sites throughout the body, and with the exception of bone marrow where only TCRAC transcripts were detected, are closely associated with alpha beta T cells. This finding indicates that these two T-cell populations may be functionally interactive.

T helper cell subsets in insulin-dependent diabetes

It has been proposed that the development of insulin-dependent diabetes is controlled by the T helper 1 (TH1) versus TH2 phenotype of autoreactive TH cells: TH1 cells would promote diabetes, whereas TH2 cells would actually protect from disease. This proposition was tested by establishing cultures of TH1 and TH2 cells that express an identical diabetogenic T cell receptor and comparing their ability to initiate disease in neonatal nonobese diabetic mice. TH1-like cells actively promoted diabetes; TH2-like cells invaded the islets but did not provoke disease--neither did they provide substantial protection.