Local expansion of allergen-specific CD30+Th2-type gamma delta T cells in bronchial asthma

BACKGROUND: T lymphocytes infiltrating airways during the allergic immune response play a fundamental role in recruiting other specialized cells, such as eosinophils, by secreting interleukin 5 (IL-5), and promoting local and systemic IgE synthesis by producing IL-4. Whether these presumed allergen-specific T cells are of mucosal or systemic origin is still a matter of conjecture. MATERIALS AND METHODS: Immunophenotype, IL-4 production, and in vitro proliferative response to specific or unrelated allergens were analyzed in the bronchoalveolar lavage (BAL) fluid lymphocyte suspensions obtained from untreated patients with allergic asthma. Healthy subjects and patients affected by pulmonary sarcoidosis, a granulomatous lung disease characterized by infiltrating Th1 CD4+ lymphocytes, served as controls. RESULTS: The proportions of gamma delta T lymphocytes, mostly CD4+ or CD4- (-)CD8-, was higher in asthmatic subjects than in controls (p < 0.05). Most BAL gamma delta CD4+ lymphocytes of asthmatic patients displayed the T cell receptor (TCR)-gamma delta V delta 1 chain. While CD30 antigen coexpression on the surface of BAL alpha beta(+) T lymphocytes was low (ranging from 5 to 12%), about half of pulmonary gamma delta T cells coexpressed it. These cells produced IL-4 and negligible amounts of interferon-gamma (IFN gamma), and proliferated in vitro in response to purified specific but not unrelated allergens. In contrast, control or sarcoidosis gamma delta T cells never displayed the CD30 surface molecule or produced significant quantities of IL-4. CONCLUSIONS: These findings not only confirm our previous hypothesis that the allergen-specific Th2-type lymphocytes found in the lungs of asthmatic patients are gamma delta T cells belonging to airway mucosal immunocytes, but also strongly support the notion that asthma is a local rather than a systemic disease.     

Selective expansion of activated V delta 4+ cells during experimental infection of mice with Leishmania major

Previous work from this laboratory has revealed that infection of mice with Leishmania major leads to an expansion of gamma delta+ T cells in the spleen. Further examination of the gamma delta+ T cells expanding in infected mice has shown that the majority of these cells in the spleen, lymph nodes, blood and liver expressed the V delta 4 gene segment. Cell cycle analysis, using propidium iodide incorporation, demonstrated that while only 1% of alpha beta+ T cells in the spleen were in either S + G2/M phase, up to 10% of the gamma delta+ T cells were in cycling phase 8 weeks after infection. Comparison of the state of activation of the two populations in different organs after infection, confirmed that gamma delta+ T cells are actively dividing in lymph nodes, liver and blood, but not in the thymus or among intraepithelial lymphocytes. Examination of the expression of different activation markers on the surface of gamma delta+ T cells in the spleen of both normal and chronically infected BALB/c mice by FACS analysis, revealed increased expression of LFA-1, CD25, CD44, 4F2, CD28 and the heat-stable antigen, whereas Thy-1 and CD5 decreased. Collectively, these results suggest an oligoclonal expansion and activation of gamma delta+ T cells in response to L. major infection.     

Differences in the kinetics of T cell accumulations in C3H/HeN (Bcg-resistant) and C57BL/6 (Bcg-susceptible) mice infected with Mycobacterium paratuberculosis

The accumulation of various T cell subsets in Bcg-susceptible (C57BL/6) and- resistant (C3H/HeN) strains of mice were compared following an intraperitoneal infection with Mycobacterium paratuberculosis. Groups of mice from both strains were killed at 3, 5, 10, 15, 30, and 150 days after infection and lymphocytes were harvested from the peritoneal exudate cells (PEC), spleen, intestinal epithelial lymphocytes (IEL), lamina propria lymphocytes (LPL), Peyer's patches, and mesenteric lymph node (MLN) and labelled with monoclonal antibodies to CD3, CD4, CD8, gamma delta TCR, CD25, and CD44 for flow cytometric analysis. Uninfected C3H/HeN mice had higher proportions of CD4+ cells in the spleen, MLN, LPL, IEL, and Peyer's patches, while uninfected C57BL/6 mice had higher proportions of CD8+ and/or gamma delta T cells. Significant increases in accumulation of CD8+ and gamma delta T cells were detected in the peritoneum and other tissues in both strains of mice after infection. Higher CD4/CD8 ratios were observed in most lymphoid tissues of C3H/HeN mice, while increased proportions of CD8+ and/or gamma delta T cells were present in C57BL/6 mice. These results indicate that significant differences in T cell profiles exist between these two strains of mice, both inherently and in response to infection with M. paratuberculosis. Innately lower levels of CD4+ cells and/or higher percentages of CD8+ and gamma delta T cells may play a role in the increased suspectibility of C57BL/6 mice to infection with M. paratuberculosis.     

A novel subset of adult gamma delta thymocytes that secretes a distinct pattern of cytokines and expresses a very restricted T cell receptor repertoire

We have characterized the function, phenotype, ontogenic development, and T cell receptor (TCR) repertoire of a subpopulation of gamma delta thymocytes, initially defined by expressing low levels of Thy-1, that represents around 5% and 30% of total gamma delta thymocytes in adult C57BL/6 and DBA/2 mice, respectively. Activation of FACS-sorted Thy-1dull gamma delta thymocytes from DBA/2 mice with anti-gamma delta monoclonal antibodies in the presence of interleukin-2 (IL-2) results in the secretion of high levels of several cytokines, including interferon-gamma (IFN-gamma), IL-4, IL-10, and IL-3. In contrast, only IFN-gamma was detected in parallel cultures of Thy-1bright gamma delta thymocytes. Virtually all Thy-1dull gamma delta thymocytes express high levels of CD44 and low levels of the heat-stable antigen and CD62 ligand, while around half of them express the NK1.1 marker. Thy-1dull gamma delta thymocytes are barely detectable in newborn animals, and their representation increases considerably during the first 2 weeks of postnatal life. The majority of Thy-1dull gamma delta thymocytes from DBA/2 mice express TCR encoded by the V gamma 1 gene and a novel V delta 6 gene named V delta 6.4. Sequence analysis of these functionally rearranged gamma and delta genes revealed highly restricted V delta-D delta-J delta junctions, and somewhat more diverse V gamma-J gamma junctions. We conclude that Thy-1dull gamma delta thymocytes exhibit properties that are equivalent to those of natural killer TCR alpha beta T cells. Both cell populations produce the same distinct pattern of cytokines upon activation, share a number of phenotypic markers originally defined for activated or memory T cells, display similar postnatal kinetics of appearance in the thymus and express a very restricted TCR repertoire.     

Nickel subsulfide is genotoxic in vitro but shows no mutagenic potential in respiratory tract tissues of BigBlue rats and Muta Mouse mice in vivo after inhalation

The immunostimulatory capacity of Acanthospermum hispidum, a tropical plant which is used in the traditional medicine of Benin for the treatment of infectious diseases, was studied in the porcine immune system. These in vitro studies revealed the capacity of A. hispidum to enhance the proliferation of T lymphocytes after stimulation with ConA or allogeneic stimulator cells in the mixed leucocyte culture (MLC). The virus-specific MHC class II-restricted in vitro immune response against pseudorabies virus (PRV) was also enhanced in a co-stimulating manner. Phenotyping of T lymphocytes that had been activated in vitro in the presence of A. hispidum revealed an increase of activated gamma delta T lymphocytes with the phenotype CD2-CD5low+CD8-. In vitro analysis of the influence on the lymphocyte function demonstrated neither an increase of the immunoglobulin synthesis, nor of the interleukin-2 production, nor of the cytolytic activities. Experiments using separated T-lymphocyte subpopulations showed that the co-stimulatory activity was based on a synergism between T helper and gamma delta T lymphocytes, and that gamma delta T lymphocytes were the targets of the plant-derived extract. The gamma delta T cells which could not activated in mixed leukocyte cultures or with pseudorabies virus antigen in a secondary immune response, were reactive to the interleukin-2 released from antigen-stimulated T helper lymphocytes.     

Diminution of the number of gamma delta T lymphocytes in hepatocellular carcinoma patients treated with transcatheter arterial embolization

gamma delta T lymphocytes, which are CD3+ lymphocytes that express gamma delta chains of the T-cell antigen receptor (TCR) on their surface, are functionally distinct from alpha beta T lymphocytes, which express alpha beta chains of the TCR. gamma delta T lymphocytes are thought to differentiate in mouse hepatic sinusoids, to play a role in antitumor action, and to act as natural killer cells. The purpose of this study was to examine whether gamma delta T lymphocytes in the peripheral blood are suppressed when hepatic sinusoids are damaged during transcatheter arterial embolization (TAE). The numbers of alpha beta T lymphocytes and gamma delta T lymphocytes in the peripheral blood were examined with monoclonal antibodies and flow cytometry before and after TAE in 32 patients (from 46 to 78 years of age) with liver cirrhosis and hepatocellular carcinoma. The number of alpha beta T lymphocytes before and after TAE was unchanged. However, the number of gamma delta T lymphocytes and the ratio of gamma delta T lymphocytes to CD3+ lymphocytes were significantly decreased for 3 weeks after TAE treatment. This decrease suggests that TAE suppresses the supply of gamma delta T lymphocytes to the peripheral blood. In addition, TAE may weaken a patient's antitumor immunity, because gamma delta T lymphocytes that have antitumor activity decrease after TAE.     

Peritoneal gamma delta T cells induced by Escherichia coli infection in mice. Correlation between Thy-1 phenotype and host minor lymphocyte-stimulating phenotype

We found that gamma delta T cells increased in number in the peritoneal cavity after i.p. inoculation with Escherichia coli (ATCC 26) in mice. The increase of the gamma delta T cells was most prominent on day 5 after inoculation when the pathogens had been already eliminated from the hosts. Two-color flow cytometric (FCM) analysis revealed that these gamma delta T cells in infected C57BL/6 mice expressed Thy-1 Ag on their cell surface. On the other hand, gamma delta T cells induced by E. coli inoculation in C3H/He mice contained Thy-1-negative gamma delta T cells in addition to the Thy-1-positive gamma delta T cells. In both strains, irrespective of Thy-1 Ag expression, these gamma delta T cells were CD5 negative, CD44 positive, L-selectin negative, Ly-6C negative, and IL-2R low positive. Analyses of peritoneal exudate cells (PEC) from several other strains of mice after E. coli inoculation suggested that Thy-1-negative gamma delta T cells appear in mice carrying endogenous superantigen specific for V beta 3, especially mammary tumor virus-6. These findings suggest that Thy-1 Ag expression on the gamma delta T cells appearing in the peritoneal cavity after i.p. E. coli inoculation is correlated to the Mls phenotype of the host mice.     

T lymphocytes bearing the gamma/delta T-cell receptor in cutaneous lesions of dermatitis herpetiformis

T lymphocytes bearing the gamma/delta T-cell receptor are a rare component of normal human GI epithelium and skin. Recently, however, an unusually high percentage of T lymphocytes with gamma/delta receptors has been described in gastrointestinal biopsies from patients with dermatitis herpetiformis, implicating the gamma/delta T cell subset in the pathogenesis of this disease. We investigated a possible role for this subset of lymphocytes in the pathogenesis of the cutaneous lesions of dermatitis herpetiformis. Using a standard immunoperoxidase technique, we labelled perilesional skin biopsies from patients with dermatitis herpetiformis and other inflammatory dermatoses with monoclonal antibodies to CD3, CD4, CD8, alpha/beta T cell receptor, gamma/delta T cell receptor, and IL-2 receptor. We found no differences in the percentage of gamma/delta positive T lymphocytes in skin lesions of dermatitis herpetiformis as compared to other selected inflammatory conditions. These findings suggest that the pathogenesis of the cutaneous lesions of dermatitis herpetiformis is not mediated through gamma/delta T cells, and that the cutaneous lesions may develop through mechanisms different from those operative in the gastrointestinal tract.     

Common whiplash: psychosomatic or somatopsychic?

We have previously demonstrated that gamma/delta T lymphocytes may participate in the host immune response against lung adenocarcinomas. Here we show that, in about one-fourth of human lung cancers, gamma/delta T cells represented a significant proportion of freshly isolated tumor-infiltrating lymphocytes. Moreover, these cells selectively expand in vitro upon culture in the presence of IL-2, thus suggesting a prior activation in vivo. Finally, when we evaluated the expression of heat shock proteins and of a panel of tumor-associated antigens in lung cancers infiltrated by gamma/delta vs. alpha/beta T cells, we found that the former displayed a distinct antigenic pattern, characterized by over-expression of HSP72 and of the 67-kDa high-affinity laminin receptor, which might account for gamma/delta T-cell recognition.     

Immune responses of tuberculosis patients

Immunity to tuberculosis (TB) required a Th1 pattern of cytokine release. In experimental models even a minor Th2 component abrogates immunity, and leads to an immunopathology that mimics the human disease. There to determine if Th2 cells are present in a peripheral blood, we analyzed the intracellular IL-4 using a flow cytometer. IL-4 producing cells were founded in CD4+ and CD4- Tells. Moreover, we studied about gamma delta (gamma delta) T cells in TB patients. V gamma 9-expressing gamma delta T cells were decreased in patients. However, the proliferative response to PPD by V gamma 9-expressing gamma delta T cells from some patients were higher levels compared with controls. The roles of gamma delta T cells of TB were not yet revealed completely.     

Control of self-reactive cytotoxic T lymphocytes expressing gamma delta T cell receptors by natural killer inhibitory receptors

The majority of peripheral blood gamma delta T cells in human adults expresses T cell receptors (TCR) with identical V regions (V gamma 9 and V delta 2). These V gamma 9 V delta 2 T cells recognize the major histocompatibility complex (MHC) class I-deficient B cell line Daudi and broadly distributed nonpeptidic antigens present in bacteria and parasites. Here we show that unlike alpha beta or V gamma 9- gamma delta T cells, the majority of V gamma 9V delta 2 T cells harbor natural killer inhibitory receptors (KIR) (mainly CD94/NKG2A heterodimers), which are known to deliver inhibitory signals upon interaction with MHC class I molecules. Within V gamma 9V delta 2 T cells, KIR were mainly expressed by clones exhibiting a strong lytic activity against Daudi cells. In stark contrast, almost all V gamma 9V delta 2 T cell clones devoid of killing activity were KIR-, thus suggesting a coordinate acquisition of KIR and cytotoxic activity within V gamma 9V delta 2 T cells. In functional terms, KIR inhibited lysis of MHC class I-positive tumor B cell lines by V gamma 9V delta 2 cytotoxic T lymphocytes (CTL) and raised their threshold of activation by microbial antigens presented by MHC class I-positive cells. Furthermore, masking KIR or MHC class I molecules revealed a TCR-dependent recognition by V gamma 9V delta 2 CTL of ligands expressed by activated T lymphocytes, including the effector cells themselves. Taken together, these results suggest a general implication of V gamma 9V delta 2 T cells in immune response regulation and a central role of KIR in the control of self-reactive gamma delta CTL.     

The effects of oophorectomy and female sex steroids on glucose kinetics in the rat

In the present study, we have analyzed the appearance and maturation of gamma/delta T cells, recognized with a new mAb V65, in the central and peripheral lymphoid organs of fetal, neonatal, and adult Wistar rats. Cytofluorometrical analysis demonstrated the first V65+ gamma/delta T cells in the thymus of 16-17-day embryonic rats, although by immunohistology, they were identified only in 19-day rat embryos in both the cortico-medullary border and thymic medulla. Phenotypically, gamma/delta thymocytes from fetal and neonatal thymus expressed CD3, CD2, and CD5, but only 60-80% were CD8+ and approximately 40-50% expressed the alpha chain (p55) of the IL-2R. In the periphery, the immunohistological study identified for the first time gamma/delta T cells in the splenic white pulp and the gut of 21-day fetal rats, where they occurred within the epithelium as well as in the lamina propria. After birth, gamma/delta lymphocytes appeared in the skin, where they were present as dendritic epidermal T cells in increasing numbers during postnatal life. Whereas these gamma/delta T cells formed the predominant T-cell population in the rat skin, gamma/delta T cells in peripheral lymphoid organs, BALT, or the gut only represented a minor T-cell population. These results are discussed in comparison to gamma/delta T cells of other vertebrate species.     

Identification of gamma delta T lymphocyte subsets that populate calf ileal mucosa after birth

Ileal intraepithelial and lamina propria lymphocytes from newborn, 1.5-week-old, and 3-week-old calves were compared to determine to what extent the mucosa becomes populated after birth. Single and dual fluorescence flow cytometry were used with monoclonal antibodies to bovine (Bo) CD molecules to identify lymphocyte subpopulations. Few ileal mucosal lymphocytes were present in calves at birth. However, by 1.5 weeks of age, the villi were populated with large numbers of lymphocytes, and by 3 weeks of age, the numbers had increased further. These included a prominent subpopulation of gamma delta T cells. Several subsets of gamma delta T cells populated ileal mucosa after birth. The predominant subset coexpressed BoCD2, and a smaller subset coexpressed BoCD8. WC1+ gamma delta T cells comprised the smallest subset. All gamma delta T cell subsets coexpressed ACT2, a molecule expressed on activated WC1+ and WC1- gamma delta T cells from cattle.     

Differential effects of IL-2 and IL-15 on the death and survival of activated TCR gamma delta+ intestinal intraepithelial lymphocytes

TCR gamma delta+ cells are enriched in the intestine mucosa and constitute approximately half of the intestinal intraepithelial lymphocytes (iIEL) in mice. They are likely activated by self and foreign Ags in situ, but little is known about how the activated gamma delta iIEL are regulated. In the iIEL compartment, IL-2 is produced by activated TCR alpha beta+ iIEL, and IL-15 message is detected in iIEL and in the epithelial cells. We found surface expression of IL-2 as well as IL-15Rs on activated gamma delta iIEL, and examined the effects of IL-2 and IL-15 on the survival and death of gamma delta iIEL during secondary stimulation through TCR. We found that both cytokines supported growth of the restimulated gamma delta iIEL, but exerted different effects on their survival. A significant higher number of live cells were recovered from the gamma delta iIEL cultures restimulated in IL-15 than in IL-2. Quantitation of apoptotic cells showed more cell death in the IL-2 group than in the IL-15 group. The cell death was associated with restimulation through TCR and was not caused by insufficient growth factor, thus representing activation-induced cell death. Western blot analyses found no difference in the levels of Bcl-2 and Bax proteins between the two groups. However, the level of Bcl-xL protein diminished with time in the IL-2 group whereas the level was sustained in the IL-15 group, which may contribute to the pro-survival effect of IL-15. These results demonstrated that the survival of activated gamma delta iIEL is differentially regulated by IL-2 and IL-15.     

Gamma delta T cells of the murine vagina: T cell response in vivo in the absence of the expression of CD2 and CD28 molecules

While little is known about their activation requirements and function, the intraepithelial T cells of the murine vagina express TCR complexes in which the antigen recognition components and the signaling components have unusual features. These vaginal T cells express an invariant V gamma 4/V delta 1 TCR and appear to be the only intraepithelial gamma delta T cells that exclusively use FcR gamma chains in their TCR complex. To further characterize the vaginal gamma delta T cells we isolated them from normal mice and from mice injected systemically with an activation-inducing dose of anti-TCR mAb. The isolated gamma delta T cells were examined by flow cytometry for their surface expression of a panel of adhesion, proteins, activation antigens and cellular interaction molecules (CD44, CD62L, CD45RB, LFA-1, CD2 and CD28). The patterns of expression observed indicate that the vaginal gamma delta T cells of normal mice show the phenotype of effector T cells. The adhesion/co-stimulatory molecules CD28 and CD2 were not detected on vaginal gamma delta T cells, an interesting finding since the absence of CD2 from other T cells has been suggested to result in anergy. However, vaginal gamma delta T cells are responsive to TCR-mediated signals since injection of normal mice with pan-anti-TCR antibody or stimulating anti-gamma delta TCR antibody resulted in an increase in cell number and increased expression of transferrin and IL-2 receptors. These results indicate that vaginal gamma delta T cells might utilize other co-stimulatory molecules, if any, in connection with TCR-induced activation and differentiation. While the physiological function of vaginal gamma delta T cells remains unknown, the expression of an invariant V gamma 4/V delta 1 TCR, their exclusive use of gamma chain homodimers in their TCR, and the absence of CD2 and CD28 co-stimulatory molecules are a novel combination of properties that suggests specialized functional properties. Although vaginal gamma delta T cells share some features in common with gamma delta T cells that reside in other epithelial tissues, such as skin and intestine, the present studies provide additional evidence that vaginal gamma delta T cells are a highly specialized and distinct T cell population.     

Peripheral V gamma 9/V delta 2 T cell deletion and anergy to nonpeptidic mycobacterial antigens in asymptomatic HIV-1-infected persons

Gamma delta T cells represent a minor population of human peripheral lymphocytes, the majority of them expressing the V delta 2/V gamma 9 TCR. Their accumulation in infectious disease lesions and their reactivity toward mycobacterial Ags suggest that V gamma 9/V delta 2 T cells play a role during infectious diseases. We have shown previously a significant expansion of the V delta 1 subset parallel to a dramatic decrease of the V delta 2 subset in PBMC from HIV-infected persons. To understand the mechanisms involved in the deletion of V delta 2 T cells, we analyzed their ability to respond in vitro to several V gamma 9/V delta 2 t cell-specific ligands. We observed that in 60% of asymptomatic HIV-infected persons, V delta 2 T cells exhibited a functional anergy to Daudi and to Mycobacterium tuberculosis stimulations. These observations were supported by the defective expansion of this subset to the recently described nonpeptidic phosphorylated Ag, TUBAg-1. Since V delta 2 responsiveness to mycobacterial Ags was shown to be normally dependent on IL-2 secretion by Th1-type CD4 T cells, the ability of IL-2 to restore V delta 2 T cells' responsiveness to TUBAg-1 was tested. V delta 2 T cell anergy persisted in spite of the presence of IL-2, and was frequently correlated with a defect in CD25 expression on stimulated V delta 2 T cells. Since V delta 2 anergy was associated with an in vivo depletion of this subset, we studied whether programmed cell death could be involved in this process, particularly because of their activated phenotype. Although peripheral V delta 2 T cells from some HIV-infected persons showed an increased susceptibility to spontaneous and activation-induced apoptosis, statistical comparison between HIV+ and HIV- donors indicated that there was no difference between both groups in the rate of V delta 2 apoptosis. Finally, V delta 2 complementarity-determining region 3 TCR analysis indicated that, in vivo, the remaining V delta 2 T cells were still polyclonal. All together these results suggest that the qualitative and quantitative alterations of the V delta 2 subset in the course of HIV infection are the consequence of a chronic antigenic stimulation, and raise the question of the contribution of a cellular ligand induced or modified by chronic HIV infection.     

Natural killer cells determine development of allergen-induced eosinophilic airway inflammation in mice

The earliest contact between antigen and the innate immune system is thought to direct the subsequent antigen-specific T cell response. We hypothesized that cells of the innate immune system, such as natural killer (NK) cells, NK1.1(+) T cells (NKT cells), and gamma/delta T cells, may regulate the development of allergic airway disease. We demonstrate here that depletion of NK1.1(+) cells (NK cells and NKT cells) before immunization inhibits pulmonary eosinophil and CD3(+) T cell infiltration as well as increased levels of interleukin (IL)-4, IL-5, and IL-12 in bronchoalveolar lavage fluid in a murine model of allergic asthma. Moreover, systemic allergen-specific immunoglobulin (Ig)E and IgG2a levels and the number of IL-4 and interferon gamma-producing splenic cells were diminished in mice depleted of NK1.1(+) cells before the priming regime. Depletion of NK1.1(+) cells during the challenge period only did not influence pulmonary eosinophilic inflammation. CD1d1 mutant mice, deficient in NKT cells but with normal NK cells, developed lung tissue eosinophilia and allergen-specific IgE levels not different from those observed in wild-type mice. Mice deficient in gamma/delta T cells showed a mild attenuation of lung tissue eosinophilia in this model. Taken together, these findings suggest a critical role of NK cells, but not of NKT cells, for the development of allergen-induced airway inflammation, and that this effect of NK cells is exerted during the immunization. If translatable to humans, these data suggest that NK cells may be critically important for deciding whether allergic eosinophilic airway disease will develop. These observations are also compatible with a pathogenic role for the increased NK cell activity observed in human asthma.     

Early preferential stimulation of gamma delta T cells by TNF-alpha

Although recent findings indicate that gamma delta T cells influence both early innate and Ag-specific adaptive host responses, it has remained unclear what triggers gamma delta T cell reactivity. Investigating very early T cell activation in mouse and human models of bacterial infection, we measured CD69 expression as an indicator of early cellular activation. Both murine alpha beta and gamma delta T cells responded polyclonally to systemic bacterial infections, and to LPS. However, gamma delta T cells responded more strongly to the bacteria and to LPS. In vitro LPS-stimulated human T cells showed a similar differential response pattern. We identified TNF-alpha as mediator of the early differential T cell activation, and of differential proliferative responses. The stronger response of gamma delta T cells to TNF-alpha was correlated with higher inducible expression levels of TNF-Rp75. Among unstimulated splenocytes, more gamma delta T cells than alpha beta T cells expressed CD44 at high levels. The data suggest that TNF-Rp75 determines the differential T cell reactivity, and that most gamma delta T cells in the normal spleen are present in a presensitized state. As TNF-alpha stimulates activated T cells, it may early preferentially connect gamma delta T cell functions with those of cells that produce this cytokine, including activated innate effector cells and Ag-stimulated T lymphocytes.