Ronment. CD4+ T cell clones that populate the Th1 effector pool do not compete equally for entry into the memory compartment. Following infection with lymphocytic choriomeningitis virus (LCMV), small numbers of adoptively transferred SMARTA TCR transgenic T cells, which are specific for a LCMV glycoprotein epitope (GP61?0), responded in a manner that mirrored the functionality, kinetics, effector differentiation, and memory development of polyclonal endogenous CD4+ responders to the same peptide in the same host. Conversely, following infection with a Listeria monocytogenes engineered to secrete the LCMV GP61?0 epitope (Lm-gp61), SMARTA cells developed sub-optimal effector function as compared to polyclonal endogenous CD4+ T cell responders to the same epitope in the same host, Of important pathologies, the body needs approximately 1 mg of iron per exemplified by decreased antigen sensitivity and lower cytokine production, and failed to populate the memory pool [14]. Lmgp61 itself is not defective in its ability to stimulate Th1 memory, as endogenous primary and secondary Th1 memory cells are readily detectable up to a year post-infection [14,15]. Specifically, it was the SMARTA TCR transgenic T cells that are defective in their ability to enter the memory pool in the context of the Lmgp61 infection. Our previous findings have found that SMARTABim Shapes the Functional CD4+ Memory Poolcells display defective functional avidity prior to their disappearance, and our extensive analysis of both primary and secondary CD4 memory development has found a strong correlation between functional avidity [14], as calculated by measuring IFNc production in response to decreasing concentrations of peptide during ex vivo restimulation, and the likelihood of entering the memory pool. These observations have led us to seek to determine the Lycerol, and centrifugation at 12000g for 15 minutes before ultracentrifugation at 33000 rpm mechanisms regulating the elimination of SMARTA cells in this setting. Because SMARTA cells are monoclonal, we hypothesized that quality and duration of signaling during the primary response may play a role in the specification of CD4+ memory T cell fate [14]. The downstream molecular pathways that link signal strength during the primary response to survival into the CD4+ T cell memory pool are not well understood. We observed that SMARTA effector cells exhibited increased expression of Bim mRNA transcripts at the peak of the 23148522 response to Lm-gp61, as compared to SMARTA effector cells induced by LCMV. Bim is a pro-apoptotic BH3-only Bcl-2 family member that promotes apoptosis by directly or indirectly inhibiting anti-apoptotic Bcl-2 [16]. Bim regulates T cell survival during several stages of T cell development and differentiation [17,18]. The relative balance of Bim and Bcl-2 activity in any given T cell is thought to be a key determinant of survival during thymic selection and in mature peripheral T cells [19]. Of particular relevance, Bim has been shown to mediate the loss of effector CD4+ and CD8+ T cells following antigen clearance during the contraction phase of the T cell response to several pathogenic infections [20?4]. However, the extrinsic and intrinsic signals that regulate Bim activity during the acute response to infection have not been well defined. Due to its known role in contraction, we hypothesized that increased Bim activity during the primary response accounted for the elimination of SMARTA cells following infection with Lmgp61. To address this problem experimentally, we crossed SMARTA mice to a Bim-deficient (bim2/2) background and cotransferred small numbers of wildtyp.Ronment. CD4+ T cell clones that populate the Th1 effector pool do not compete equally for entry into the memory compartment. Following infection with lymphocytic choriomeningitis virus (LCMV), small numbers of adoptively transferred SMARTA TCR transgenic T cells, which are specific for a LCMV glycoprotein epitope (GP61?0), responded in a manner that mirrored the functionality, kinetics, effector differentiation, and memory development of polyclonal endogenous CD4+ responders to the same peptide in the same host. Conversely, following infection with a Listeria monocytogenes engineered to secrete the LCMV GP61?0 epitope (Lm-gp61), SMARTA cells developed sub-optimal effector function as compared to polyclonal endogenous CD4+ T cell responders to the same epitope in the same host, exemplified by decreased antigen sensitivity and lower cytokine production, and failed to populate the memory pool [14]. Lmgp61 itself is not defective in its ability to stimulate Th1 memory, as endogenous primary and secondary Th1 memory cells are readily detectable up to a year post-infection [14,15]. Specifically, it was the SMARTA TCR transgenic T cells that are defective in their ability to enter the memory pool in the context of the Lmgp61 infection. Our previous findings have found that SMARTABim Shapes the Functional CD4+ Memory Poolcells display defective functional avidity prior to their disappearance, and our extensive analysis of both primary and secondary CD4 memory development has found a strong correlation between functional avidity [14], as calculated by measuring IFNc production in response to decreasing concentrations of peptide during ex vivo restimulation, and the likelihood of entering the memory pool. These observations have led us to seek to determine the mechanisms regulating the elimination of SMARTA cells in this setting. Because SMARTA cells are monoclonal, we hypothesized that quality and duration of signaling during the primary response may play a role in the specification of CD4+ memory T cell fate [14]. The downstream molecular pathways that link signal strength during the primary response to survival into the CD4+ T cell memory pool are not well understood. We observed that SMARTA effector cells exhibited increased expression of Bim mRNA transcripts at the peak of the 23148522 response to Lm-gp61, as compared to SMARTA effector cells induced by LCMV. Bim is a pro-apoptotic BH3-only Bcl-2 family member that promotes apoptosis by directly or indirectly inhibiting anti-apoptotic Bcl-2 [16]. Bim regulates T cell survival during several stages of T cell development and differentiation [17,18]. The relative balance of Bim and Bcl-2 activity in any given T cell is thought to be a key determinant of survival during thymic selection and in mature peripheral T cells [19]. Of particular relevance, Bim has been shown to mediate the loss of effector CD4+ and CD8+ T cells following antigen clearance during the contraction phase of the T cell response to several pathogenic infections [20?4]. However, the extrinsic and intrinsic signals that regulate Bim activity during the acute response to infection have not been well defined. Due to its known role in contraction, we hypothesized that increased Bim activity during the primary response accounted for the elimination of SMARTA cells following infection with Lmgp61. To address this problem experimentally, we crossed SMARTA mice to a Bim-deficient (bim2/2) background and cotransferred small numbers of wildtyp.