gp120-mediated induction of the MAPK cascade is dependent on the activation state of CD4(+) lymphocytes

The capacity of the HIV-1 envelope glycoprotein gp120 to induce intracellular signals is thought to contribute to HIV-1 pathogenesis. Here, we report that gp120 binding resulted in activation of the mitogen-activated protein kinase (MAPK) in CD4(+) lymphocytes prestimulated through their T-cell receptor (TCR). However, gp120 did not activate this pathway in either freshly isolated quiescent T cells or nonproliferating CD4(+) lymphocytes prestimulated with the interleukin-7 (IL-7) cytokine. This response was not solely dependent on proliferation per se because proliferating IL-7-prestimulated umbilical cord (UC)-derived T lymphocytes did not exhibit significant MAPK activation upon gp120 binding. Nevertheless, like peripheral blood lymphocytes, MAPK recruitment was induced by gp120 in UC T cells following TCR prestimulation. The lack of a gp120-mediated signaling response was not due to decreased gp120 receptor levels; CD4 expression was modified neither by IL-7 nor by TCR engagement, and high levels of functional CXCR4 were present on IL-7-treated lymphocytes. In addition to CD4 and CXCR4, recent evidence suggests that glycosphingolipids in raft microdomains serve as cofactors for HIV-1 fusion. The ganglioside GM1, a marker of rafts, was augmented in TCR-stimulated but not IL-7-stimulated T lymphocytes, and disruption of rafts inhibited gp120-induced signaling. Thus, stimulation of a mitogenic pathway by gp120 appears to require receptor binding in the context of membrane microdomains. These studies reveal a mechanism via which gp120 may differentially modulate the fate of activated and quiescent T cells in vivo.     

Innate signals overcome acquired TCR signaling pathway regulation and govern the fate of human CD161(hi) CD8α⁺ semi-invariant T cells

Type 17 programmed CD161(hi)CD8α(+) T cells contribute to mucosal immunity to bacteria and yeast. In early life, microbial colonization induces proliferation of CD161(hi) cells that is dependent on their expression of a semi-invariant Vα7.2(+) TCR. Although prevalent in adults, CD161(hi)CD8α(+) cells exhibit weak proliferative and cytokine responses to TCR ligation. The mechanisms responsible for the dichotomous response of neonatal and adult CD161(hi) cells, and the signals that enable their effector function, have not been established. We describe acquired regulation of TCR signaling in adult memory CD161(hi)CD8α(+) T cells that is absent in cord CD161(hi) cells and adult CD161(lo) cells. Regulated TCR signaling in CD161(hi) cells was due to profound alterations in TCR signaling pathway gene expression and could be overcome by costimulation through CD28 or innate cytokine receptors, which dictated the fate of their progeny. Costimulation with IL-1β during TCR ligation markedly increased proinflammatory IL-17 production, while IL-12-induced Tc1-like function and restored the response to TCR ligation without costimulation. CD161(hi) cells from umbilical cord blood and granulocyte colony stimulating factor-mobilized leukaphereses differed in frequency and function, suggesting future evaluation of the contribution of CD161(hi) cells in hematopoietic stem cell grafts to transplant outcomes is warranted.     

Expression of the interleukin-2 receptor gamma chain on cord blood mononuclear cells

Lymphocytes in umbilical cord blood and neonatal peripheral blood have been shown to have less ability in an immune reaction. In our present experimental approach to address this issue, we made use of the cord blood of full-term birth infants to investigate the expression of the interleukin- 2 receptor gamma (IL-2Rgamma) chain that is shared with receptors for IL-4, IL-7, IL-9, and IL-15 as well as IL-2. The gamma chain expression in cord blood lymphocytes was about one-third that in the lymphocytes of adults, whereas no significant difference between cord blood and adult monocytes was observed. A reduced expression of the gamma chain was observed in all of the CD4+ T cells, CD8+ T cells, gamma-delta T cells, B cells, CD16+ natural killer (NK) cells, and CD56(bright) NK cells of the cord blood lymphocytes. The reduced gamma chain expression reached two-thirds of that in adults after 3 days of culture in vitro and in infants 3 days after birth, thus implying that the increase in the gamma chain may significantly contribute to the prevention of neonatal infection.     

CD3 zeta dependence of the CD2 pathway of activation in T lymphocytes and natural killer cells.

In T lymphocytes, signal transduction through the CD2 adhesion molecule requires surface expression of the CD3-Ti T-cell receptor (TCR) complex. In contrast, in natural killer (NK) cells, CD2 functions in the absence of a TCR. Because the TCR on T lymphocytes and the CD16 low-affinity IgG Fc receptor (Fc gamma receptor type III) complex on NK cells share a common CD3 zeta subunit, we reasoned that CD3 zeta may be critical for CD2 signaling in T lymphocytes and NK cells. Here we show that transfection of a cDNA encoding a transmembrane form of CD16 into TCR- variants of the Jurkat T-cell line results in CD16 expression in association with endogenous CD3 zeta homodimers and restores CD2 signaling function. To test directly the role of CD3 zeta in CD2 triggering, we then transfected human CD2 into each of two murine T-T hybridomas that express TCRs containing either a full-length CD3 zeta subunit or a truncated CD3 zeta subunit incapable of transducing signals. Despite expression of equivalent surface levels of TCR, CD2-mediated signaling is seen only in the T cells containing wild-type CD3 zeta. These findings show that (i) CD16 on NK cells is functionally equivalent to the TCR on T lymphocytes for coupling CD2 to signaling pathways and (ii) CD2 signal transduction depends upon the CD3 zeta subunit of the TCR complex and, by inference, the CD3 zeta subunit of the CD16 complex.     

NKG2D receptor regulates human effector T-cell cytokine production

Although innate immune signals shape the activation of naive T cells, it is unclear how innate signals influence effector T-cell function. This study determined the effects of stimulating the NKG2D receptor in conjunction with the TCR on human effector CD8(+) T cells. Stimulation of CD8(+) T cells through CD3 and NKG2D simultaneously or through a chimeric NKG2D receptor, which consists of NKG2D fused to the intracellular region of CD3ζ, activated β-catenin and increased expression of β-catenin-induced genes, whereas T cells stimulated through the TCR or a combination of the TCR and CD28 did not. Activation by TCR and NKG2D prevented expression and production of anti-inflammatory cytokines IL-10, IL-9, IL-13, and VEGF-α in a β-catenin- and PPARγ- dependent manner. NKG2D stimulation also modulated the cytokine secretion of T cells activated simultaneously through CD3 and CD28. These data indicate that activating CD8(+) T cells through the NKG2D receptor along with the TCR modulates signal transduction and the production of anti-inflammatory cytokines. Thus, human effector T cells alter their function depending on which innate receptors are engaged in conjunction with the TCR complex.     

Glucose transporter 1 expression identifies a population of cycling CD4+ CD8+ human thymocytes with high CXCR4-induced chemotaxis

GLUT1, the major glucose transporter in peripheral T lymphocytes, is induced upon T cell receptor activation. However, the role of GLUT1 during human thymocyte differentiation remains to be evaluated. Our identification of GLUT1 as the human T lymphotrophic virus (HTLV) receptor has enabled us to use tagged HTLV-receptor-binding domain fusion proteins to specifically monitor surface GLUT1 expression. Here, we identify a unique subset of CD4+ CD8+ double-positive (DP) thymocytes, based on their GLUT1 surface expression. Whereas these cells express variable levels of CD8, they express uniformly high levels of CD4. Glucose uptake was 7-fold higher in CD4(hi) DP thymocytes than in CD4(lo) DP thymocytes (P = 0.0002). Further analyses indicated that these GLUT1+ thymocytes are early post-beta-selection, as demonstrated by low levels of T cell receptor (TCR)alphabeta and CD3. This population of immature GLUT1+ DP cells is rapidly cycling and can be further distinguished by specific expression of the transferrin receptor. Importantly, the CXCR4 chemokine receptor is expressed at 15-fold higher levels on GLUT1+ DP thymocytes, as compared with the DP GLUT1- subset, and the former cells show enhanced chemotaxis to the CXCR4 ligand CXCL12. Thus, during human thymopoiesis, GLUT1 is up-regulated after beta-selection, and these immature DP cells constitute a population with distinct metabolic and chemotactic properties.     

Priming of T cells to Fas-mediated proliferative signals by interleukin-7

T-cell depletion associated with HIV infection or cytoreductive therapies triggers potential T-cell regenerative mechanisms such as peripheral T-lymphocyte expansion to weak antigenic stimuli and the increased availability of interleukin-7 (IL-7), a cytokine with potent antiapoptotic and proliferative activities. Deleterious mechanisms also associated with lymphopenia, such as increased Fas expression and apoptosis of T cell, however, may result in opposing effects. In this study, we show that Fas molecules, primarily associated with T-cell depletion in lymphopenic settings, may also contribute to compensatory T-cell expansion through transmitting costimulatory signals to suboptimally activated T cells. Proliferation of T lymphocytes in response to concomitant Fas and T-cell receptor (TCR) triggering was shown to be increased in HIV-infected individuals compared with noninfected controls. As IL-7 levels are often elevated in lymphopenic individuals in association with increased Fas expression, we analyzed whether IL-7 would influence Fas-mediated proliferative signals in T cells. We show that IL-7 is able to increase the efficacy of Fas to induce proliferation of suboptimally activated T cells. Thus, high IL-7 levels associated with lymphopenic conditions may simultaneously induce sensitivity to Fas-mediated apoptosis in nonactivated T cells and increase Fas-induced costimulatory signals in T cells recognizing low-affinity antigens.     

IL-15 mimics T cell receptor crosslinking in the induction of cellular proliferation, gene expression, and cytotoxicity in CD8+ memory T cells

Generation of CD8(+) memory T cells requires antigenic stimulation through T cell receptor (TCR); however, maintenance of CD8(+) memory T cells seems to be mediated by cytokines, such as IL-15, in a TCR-independent manner. Compared with the TCR-induced activation, less is known about the mechanisms of IL-15 action. We report here a comparative and kinetic analysis of the responses of memory phenotype CD8(+) T cells to IL-15 or TCR (anti-CD3) stimulation in vitro. These two stimuli induce highly similar responses in memory phenotype CD8(+) T cells as measured by cellular proliferation, gene expression changes, synthesis of effector molecules (IFNgamma, tumor necrosis factor beta, granzyme B, and perforin), and induction of cytotoxicity. From 189 genes/expressed sequence tags (ESTs) whose expression changed in CD8(+) memory T cells after IL-15 and anti-CD3 stimulation identified by cDNA microarray analysis, 77% of the genes/ESTs exhibit a highly similar pattern of expression between IL-15 and anti-CD3-treated cells, and only 16% and 7% of the genes/ESTs are differentially expressed in response to IL-15 and anti-CD3 treatments, respectively. These results show that IL-15 and anti-CD3 stimulation induced remarkably similar gene expression and effector function. Thus, IL-15 acts not only as a crucial growth factor but also as an antigen-independent activator of effector functions for CD8(+) memory T cells.     

白介素23受体在支气管哮喘小鼠脾源性CD4+T细胞中的表达及意义

目的 探讨急性支气管哮喘(简称哮喘)小鼠CD4+T细胞表面白介素23受体(IL-23R)的表达及在哮喘发病中的作用.方法 建立急性哮喘小鼠模型,免疫磁珠分离小鼠脾源性CD4+T细胞,培养24 h后,检测CD4+T细胞表面IL-23R的表达、Th17细胞的阳性率及细胞培养上清液中的IL-17水平.结果 哮喘小鼠脾脏CD4+T细胞表面IL-23R的表达明显高于正常组(P＜0.01);哮喘小鼠脾脏CD4+T细胞中Th17细胞的阳性率明显高于正常组(P＜0.01);哮喘小鼠脾脏CD4+T细胞分泌IL-17浓度明显高于正常组(P＜0.01);小鼠脾脏CD4+T细胞表面IL-23R的表达与Th17细胞的阳性率和IL-17的浓度呈正相关.结论 IL-23R在急性哮喘的发病机制中可能起重要作用.     

UV irradiation can induce in vitro clonal anergy in alloreactive cytotoxic T lymphocytes

The alloreactive cytotoxic T lymphocytes (CTL) were generated by coculturing peripheral blood mononuclear cells (PBMC) with allogeneic Sa cells (an Epstein-Barr virus [EBV]-transformed B-cell line). The CTL did not proliferate in response to UV-B-irradiated Sa cells unless exogenous interleukin-2 (IL-2) was present, although they could kill the UV-B-irradiated Sa cells. The results indicate that UV-B-irradiated Sa cells do not provide sufficient signals for the proliferation of the CTL while they can be recognized by CTL and induce high-affinity IL-2 receptor (IL-2R) expression on them. The alloreactive CTL could be rendered anergic by previous exposure to UV-B-irradiated Sa cells. The alloreactive CTL previously stimulated with UV-B-irradiated Sa cells failed to proliferate in response to nontreated Sa cells. Proliferation of the anergic CTL could not be restored by Sa cells and exogenous IL-2 but by the combination of phorbol 12-myristate 13-acetate (PMA) and calcium ionophore (A23187). The anergic CTL showed a considerably low cytotoxic activity against Sa target cells. The expression of TCR on the anergic CTL was downregulated while expression of high-affinity IL- 2R was upregulated. Their CD28 and CD8 expression were unchanged. In addition, the proliferative response and cytotoxicity of the anergic CTL to Sa cells could be restored after the cells had been rested for 7 days to allow reexpression of TCR. These results suggest that downregulation of T-cell receptor (TCR) and impairment in the post-IL- 2/IL-2R signaling pathway are relevant to the clonal anergy induced in the alloreactive CTL by stimulation of UV-B-irradiated Sa cells.     

Loss of IL-7 receptor alpha-chain (CD127) expression in acute HCV infection associated with viral persistence

Interleukin-7 (IL-7) is required for the establishment and maintenance of memory CD4(+) and CD8(+) T lymphocytes, and cells lacking IL-7Ralpha (CD127) demonstrate impaired IL-2 secretion and have a short life-span. Chronic HCV is characterized by T cells that are functionally impaired and exhibit an immature phenotype. To investigate the potential role of IL-7/IL-7Ralpha in the outcome of HCV infection, we used multiparameter flow cytometry to characterize patients with acute infection (n = 24), long-term chronic infection (12) and normal subjects (13). HCV infection per se resulted in downregulation of CD127 on total CD4(+) and CD8(+) T lymphocytes as compared to normal controls. Total expression was lowest in those patients who subsequently developed persistence and intermediate in those patients with acute-resolving infection. This reduction affected both na?ve and effector/memory T cells. CD127 correlated phenotypically with upregulation of chemokine receptors CCR7 and CXCR4, expression of the anti-apoptotic molecule B cell leukemia/lymphoma 2 (Bcl-2), and enhanced IL-2 production. In six HLA A2-positive patients, we longitudinally tracked tetramer responses to HCV and CMV epitopes; at baseline, reflecting the expression of CD127 on whole T cell populations, viral-specific CTLs in patients who became chronic demonstrated lower CD127. In conclusion, CD127 is a useful marker of functional CD4(+) and CD8(+) T cells and its expression correlates with virologic outcome of acute HCV. These data provide a mechanistic basis for the observation that CTLs generated in early infection rapidly decline as chronicity is established; CD127 expression should be considered in the design of novel immunotherapeutic approaches.     

Phorbol ester induces interleukin-2 receptor on the cell surface of precursor thymocyte leukemia with no rearrangement of T cell receptor beta and gamma genes

The early event of thymocyte maturation has been analyzed using acute lymphoblastic leukemia (ALL) cells. A group of ALL cells whose cell surface phenotype was CD2 (SRBC receptor) negative and CD7 (T cell antigen) positive has been considered as precursor thymocyte ALL (pre-T- ALL). No rearrangements of the T cell receptor beta-gene (TCR beta) and gamma-gene (TCR gamma) were found in three of four pre-T-ALL patients. Stimulation of these pre-T-ALL cells with 12-0-tetradecanoylphorbol-13- acetate (TPA) induced only CD25 (Tac) antigen but no other T cell antigens. These findings suggest that the activation pathway of interleukin 2 (IL-2) receptor already exists in the most immature precursor thymocytes. Pre-T-ALL cells from the fourth patients showed the expression of CD3 antigen, and both TCR beta and TCR gamma rearrangement. TPA induced the differentiation of the more mature pre-T- ALL cells of this case in vitro, and not only CD25 (Tac) antigen but also CD4 and CD8 antigens appeared on the cell surface. The low affinity binding of 125I-IL-2 to TPA-stimulated leukemia cells was observed in the three cases of pre-T-ALL tested, and the addition of recombinant IL-2 to TPA-stimulated cells showed no effect on cell proliferation.     

Activated human B lymphocytes express three CTLA-4 counterreceptors that costimulate T-cell activation.

Signaling via the T-cell receptor complex is necessary but not sufficient to induce antigen-specific T lymphocytes to expand clonally. To proliferate, T cells must receive one or more costimulatory signals provided by antigen presenting cells (APCs). One such critical costimulatory signal is delivered by the CD28/CTLA-4 counterreceptor, B7, expressed on APCs. B7 costimulation induces CD28 signaling, resulting in interleukin 2 (IL-2) secretion, and T-cell proliferation. Conversely, T-cell receptor signaling in the absence of B7 costimulation results in induction of antigen-specific tolerance. Here, we show that activated human B lymphocytes express two additional CTLA-4 counterreceptors also capable of providing T-cell costimulation. At 24 hr postactivation, B cells express a CTLA-4 counterreceptor not recognized by anti-B7 or -BB-1 monoclonal antibodies (mAbs), which induces detectable IL-2 secretion and T-cell proliferation. At 48 and 72 hr postactivation, B cells express both B7 and a third CTLA-4 counterreceptor identified by the anti-BB-1 mAb. BB-1 appears to be a molecule distinct from B7 by its expression on B7- cells and its capacity to induce T cells to proliferate without significant accumulation of IL-2. As observed for B7, costimulatory signals mediated by these alternative CTLA-4/CD28 counterreceptors are likely to be essential for generation of an immune response and their absence may result in antigen-specific tolerance. We propose the following terminology for these CTLA-4 counterreceptors: (i) B7, B7-1; (ii) early CTLA-4 binding counterreceptor, B7-2; and (iii) BB-1, B7-3.     

Altered IL-7Ralpha expression with aging and the potential implications of IL-7 therapy on CD8+ T-cell immune responses

We investigated the effects of aging on the IL-7-mediated CD8+ T-cell survival pathway and of IL-7 therapy on T-cell immunity. Cells expressing IL-7 receptor (IL-7R) alphahigh and alphalow were identified in a CD45RA+ effector memory (EM(CD45RA+), CD45RA+CCR7-) CD8+ T-cell subset. Elderly subjects (65 years and older) had an increased frequency of EM(CD45RA+) IL-7Ralphalow) CD8+ T cells, leading to decreased STAT5 phosphorylation and survival responses to IL-7 compared with young subjects (40 years and younger). These EM(CD45RA+) IL-7Ralphalow cells were largely antigen experienced (CD27-CD28-), replicatively senescent (CD57+), and perforinhigh CD8+ T cells that had decreased IL-7Ralpha mRNA, independent of guanine and adenine binding protein alpha (GABPalpha) and growth factor independence-1 (GFI1) expression. In measuring T-cell receptor (TCR) repertoires of EM(CD45RA+) CD8+ T cells, the elderly had a limited repertoire in IL-7Ralphahigh and IL-7Ralphalow cells, whereas the young had a diverse repertoire in IL-7Ralphahigh but not in IL-7Ralphalow cells. These findings suggest that aging affects IL-7Ralpha expression by EM(CD45RA+) CD8+ T cells, leading to impaired signaling and survival responses to IL-7, and that IL-7 therapy may improve the survival of EM(CD45RA+) CD8+ T cells with a diverse TCR repertoire in the young but not in the elderly.     

Reconstitution of deficient T cell receptor zeta chain restores T cell signaling and augments T cell receptor/CD3-induced interleukin-2 production in patients with systemic lupus erythematosus

OBJECTIVE: T cells from a majority of patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain, a subunit of the TCR/CD3 complex. This study was undertaken to explore the possibility that forced expression of TCR zeta chain may reverse the known signaling abnormalities and defective interleukin-2 (IL-2) production in SLE T cells. METHODS: Freshly isolated SLE T cells were transfected with TCR zeta chain construct in a eukaryotic expression vector at high efficiency, by a recently developed nucleoporation technique. Restoration of TCR/CD3-mediated signaling was studied in the zeta chain-transfected cells. RESULTS: In SLE T cells transfected with TCR zeta chain, surface expression of TCR chain was increased and the TCR/CD3-induced increased free intracytoplasmic calcium concentration response was normalized, as was hyperphosphorylation of cellular substrates. Simultaneously, the previously noted increased expression of the Fc receptor gamma chain was diminished in SLE T cells transfected with the zeta chain expression vector, and the surface membrane clusters of cell signaling molecules were redistributed to a more continuous pattern. TCR zeta chain replacement also augmented the expression of diminished TCR/CD3-mediated IL-2 production in SLE T cells, associated with increased expression of the p65 subunit of nuclear factor kappaB in the nuclear fractions of these T cells. CONCLUSION: These results suggest that reconstitution of deficient TCR zeta chain can reverse the TCR/CD3-mediated signaling abnormalities as well as the defective IL-2 production in T cells of patients with SLE.     

IL-15 availability conditions homeostasis of peripheral natural killer T cells

Steady-state numbers of peripheral lymphocyte are tightly controlled. For conventional T cells, signals delivered through the interaction of the T cell receptor (TCR) with antigen-loaded MHC molecules are required for the peripheral survival of naive T cells and for their homeostatic expansion in lymphopenic hosts. Cytokines, including IL-7, are also essential for survival of peripheral naive T cells. CD1d-restricted, V alpha 14(+) natural killer (NK)-T cells are a specialized autoreactive T subset with immunoregulatory activity. The relative roles of TCR engagement and cytokine signaling in the peripheral homeostasis of V alpha 14(+) NK-T cells were investigated. After adoptive transfer, the survival and expansion of peripheral V alpha 14(+) NK-T cells was independent of CD1d expression in the host. In contrast, IL-15 (but not IL-7) was required for maintenance of peripheral CD1d-reactive V alpha 14(+) T cells. Comparison of V alpha 14(+) T cell transfers into NK-proficient vs. deficient hosts suggests that NK-T cells and NK cells compete for peripheral resources. Our results indicate that IL-15 maintains the homeostasis of peripheral V alpha 14(+) NK-T cells. In contrast, TCR "tickling" of NK-T cells, if it occurs under steady-state conditions, does not by itself provide a sufficient signal for their peripheral survival.     

Identification of a murine CD28 dileucine motif that suppresses single-chain chimeric T-cell receptor expression and function

Recent preclinical and clinical trials have demonstrated the therapeutic potential of T lymphocytes redirected with genetically engineered T-cell receptor (TCR) surrogates against infected, cancerous, or autoreactive cells. These surrogate TCRs link a ligand-recognition domain to signaling regions from the TCR. We previously compared the function of surrogate TCRs that include TCR or TCR and CD28 signaling regions. We found that primary murine T cells modified to specifically target Kb-restricted CD8+ T cells using either Kb-zeta or Kb-CD28-zeta receptors had similar functional activities, although the CD28-zeta receptor showed a 2-fold to 4-fold decreased expression. We have now identified a previously unrecognized dileucine motif in the murine CD28 signaling domain that accounts for this reduced expression. Inactivation of this motif increased chimeric receptor surface expression 2- to 5-fold. T cells expressing the dileucine-mutated CD28-zeta chimeric receptor demonstrated enhanced proliferation, cytokine production, and cytolytic activities. Further, cells expressing this dileucine-mutated receptor were highly effective in eliminating antigen-specific CD8+ T lymphocytes in vivo. These results therefore identify a critical motif limiting the function of receptor-modified T lymphocytes, demonstrate that inactivation of this motif enhances chimeric receptor function, and illustrate a potential novel application of receptor-modified T lymphocytes in the induction of immune tolerance.     

T cell receptor (TCR) clustering in the immunological synapse integrates TCR and costimulatory signaling in selected T cells

During T cell activation, T cell receptors (TCR) cluster at the center of the T cell/antigen-presenting cell interface forming a key component of the immunological synapse. The function of this TCR clustering is still unresolved. A comprehensive search for such a function yielded a very limited and specific result. A micrometer-scale receptor clustering integrated the TCR and CD28 signals required for IL-2 secretion in primary 5C.C7 T cells, a low-affinity/avidity TCR system. 5C.C7 TCR signaling itself was not affected. In addition, central TCR accumulation was not required for any T cell effector function tested in three other TCR transgenic models. Central TCR accumulation thus had a specific role in signaling integration in low-affinity T cells.     

Ablation of SLP-76 signaling after T cell priming generates memory CD4 T cells impaired in steady-state and cytokine-driven homeostasis

The intracellular signaling mechanisms regulating the generation and long-term persistence of memory T cells in vivo remain unclear. In this study, we used mouse models with conditional deletion of the key T cell receptor (TCR)-coupled adaptor molecule SH2-domain-containing phosphoprotein of 76 kDa (SLP-76), to analyze signaling mechanisms for memory CD4 T cell generation, maintenance, and homeostasis. We found that ablation of SLP-76 expression after T cell priming did not inhibit generation of phenotypic effector or memory CD4 T cells; however, the resultant SLP-76–deficient memory CD4 T cells could not produce recall cytokines in response to TCR-mediated stimulation and showed decreased persistence in vivo. In addition, SLP-76–deficient memory CD4 T cells exhibited reduced steady-state homeostasis and were impaired in their ability to homeostatically expand in vivo in response to the γ_c cytokine IL-7, despite intact proximal signaling through the IL-7R–coupled JAK3/STAT5 pathway. Direct in vivo deletion of SLP-76 in polyclonal memory CD4 T cells likewise led to impaired steady-state homeostasis as well as impaired homeostatic responses to IL-7. Our findings demonstrate a dominant role for SLP-76–dependent TCR signals in regulating turnover and perpetuation of memory CD4 T cells and their responses to homeostatic cytokines, with implications for the selective survival of memory CD4 T cells following pathogen exposure, vaccination, and aging.