A plethora of work implicates important effects of the Vitamin A derivative, retinoic acid (RA), in myeloid differentiation, while fewer studies explore the role of RA on lymphoid cells. accompanied by an enhanced memory precursor phenotype at the effector (increased CD127hi, IL-2+) and contraction phase (increased CD127hi, IL-2+, eomesoderminhi) of the CD8 response in the absence of RA signaling. The lack of RA also increased the proportion of central memory CD8s. Collectively; these results introduce RA in a new role in CD8 T cell activation and differentiation. This may have significant implication in optimal vaccine design where Vitamin A supplementation is used to LDE225 augment effector responses, but this may be to the detriment of the long-term central memory response. Introduction The morphogenic role of all trans retinoic acid (RA), a vitamin A derivative, in development and differentiation was confirmed by White et al. in 2007, using a zebra fish model to confirm RA patterning the hindbrain (1). However, immunologists have studied it in various contexts of immune cell differentiation as early as the 1980s. Amongst myeloid cells RA has been shown to allow for differentiation into mature macrophage or antigen presenting cells (2). This RA mediated differentiation of dendritic cells (DCs) has been shown to skew them towards IL-12 producing DCs (3). RA also regulates isotype switching and plasma cell formation by B cells (4C6). In the adaptive immune compartment RA has been shown to promote regulatory CD4 LDE225 T and CD8 T cell differentiation and stabilization (7C9). Further, RA has been shown to enhance inflammatory effector responses by CD4 helper T cells (10, 11). In CD8 T cells, an early study showed that increased expression of RA receptor gamma increased the number of CD8 T cells (12). To our knowledge, no previous studies have looked at the cell LDE225 intrinsic role of RA signaling in CD8 T cell effector and memory formation in the context of virus infection. Paramount to eliciting optimal protective immunity to infections is the generation of high quality memory cells. Superior memory generation is a key component of vaccine design, as NOS2A these cells can elicit optimal protection. In response to an acute viral insult, CD8 T cell responses go through three phases: the primary acute expansion phase to resolve the infection; the contraction phase to eliminate potentially harmful cytotoxic effectors and a memory phase, where self-renewing antigen (Ag) specific cells are maintained at low frequencies for extended periods of time (13). Upon activation in mice and humans after infection, CD8 T cells form highly differentiated short-lived effector cell (SLEC) and a memory-precursor effector cell (MPEC) populations (14C16). The SLEC population is driven by inflammatory cytokines like LDE225 IL-12 or type-I interferons and characterized by high T-bet expression, compared to MPEC, which have high eomesodermin expression, recently shown to be driven by Forkhead Box Protein 01 (FOX01) expression (17C23). SLECs are identified by surface expression of high killer cell lectin-like receptor subfamily G member 1 (KLRG1) and low IL-7R (CD127) while MPECs are identified by the expression of low KLRG1 and high IL-7R (17). The terminally differentiated SLEC population is the desired population to resolve a viral infection with its high cytotoxic potential, while the MPEC population is thought to differentiate into the long-lived memory population (24). Amongst the memory population, central memory cells (Tcm) are the most long-lived, and are characterized by robust recall potential, capacity for homeostatic proliferation and homing to lymphoid organs. Effector-memory cells (Tem) are characterized by homing to peripheral sites and lower homeostatic turnover, while being the first to respond after re-exposure to infection (16, 25C27). Acknowledging the role of RA in differentiation as seen by studies in development and in other immune cell types, we hypothesized LDE225 that RA would promote the differentiation of CD8 T cells to their terminally differentiated phenotype, SLECs. To test this hypothesis, we used a mouse model expressing a dominant negative RA receptor alpha (RARDN) in the T cell compartment, and mixed bone marrow (BM) chimeric mice to measure CD8 T cell intrinsic effects. To determine the effect of the absence of RA signaling in CD8 T cell differentiation, mice were infected with vaccinia virus, which.