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

Abstract

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 , 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.immune memory | signal transduction | linker-adapter T he enhanced functional and survival properties of memory T cells enable them to provide long-lasting secondary responses to recall antigens. Memory T cells are generated following antigen activation of naive T cells (1) and differ from naive T cells in their rapid production of effector cytokines following antigenic stimulation through the T cell receptor (TCR). The TCR-coupled signaling pathways for naive T cell activation have been well defined (2) and include an initial phosphorylation of TCR/CD3 components, leading to activation of the ZAP-70 proximal kinase, and the coupling of proximal phosphorylation events to distal signaling through linker-adapter molecules such as the SH2-containing phosphoprotein of 76 kDa (SLP-76) and linker for activated T cells (LAT) (3). The specific TCR-coupled signaling events important for promoting memory T cell development and persistence remain undefined.Once generated, memory T cells have variable requirements for TCR engagement for their maintenance. Whereas memory CD8 T cells can persist and maintain recall function in the absence of MHC class I expression (4), memory CD4 T cells exhibit impaired functional responses when maintained in the absence of MHC class II expression (5, 6), although they can survive in MHC class II-deficient hosts (5,7,8). In addition, the presence of MHC class II or TCR signaling is associated with improved memory CD4 T cell survival and homeostasis (9-11), suggesting that memory CD4 T cells may depend on TCR signals during their long-term maintenance. Cytokine...

T-cell receptor signals direct the composition and function of the memory CD8+ T-cell pool

“…This is consistent with recent studies showing that deletion of SLP-76 in CD4 ϩ T cells following priming results in the generation of phenotypic effector and memory cells that cannot produce cytokine in response to TCR ligation. 50 While the surface phenotype of KI T-cell populations may suggest a memory bias, the failure of KI T cells to produce IL-2 following MHC:peptide stimulation suggests otherwise. However, when primary or secondary effector cells were stimulated with PMA plus ionomycin to bypass the proximal TCR signaling machinery, KI cells were fully capable of IL-2 production, suggesting that their differentiation was intact.…”

Human memory T cells: generation, compartmentalization and homeostasis

“…In mouse models, the long-term requirements for T cell maintenance and homeostasis have been defined using mice deficient for various cytokines and cytokine receptors, for MHC molecules and/or for components of the TCR signalling cascade (for a review, see 126 ). These studies established that virus-specific memory CD8 + T cells do not require antigen or MHC for their maintenance, but rely on IL-15 for homeostasis and IL-7 for survival, whereas memory CD4 + T cells require TCR signalling and/or MHC class II molecules for their functional maintenance and homeostasis 127–129 .…”

CD4 T-Cell Memory Generation and Maintenance

“…The mechanisms have not been fully elucidated, but it has been reported that TCR signaling blockade during memory decreases responsiveness to IL-7 signaling. 119,120 IL-7 is required during the transition from CD4 T-cell effector to memory in the SLOs and target tissues, and again for long-term maintenance of CD4 memory. 93,114,118,121,122 Similar to memory CD8 T cells, memory CD4 T cells require IL-15 for long-term maintenance, and the relative strengths of IL-7 and IL-15 signaling may significantly alter the rate of homeostatic turnover of memory CD4 T cells and influence the proliferation of secondary responses.…”