Altered expression of the TCR signaling related genes CD3 and FcεRIγ in patients with aplastic anemia

<p>Abstract</p> <p>Background</p> <p>Aplastic anemia (AA) is characterized by pancytopenia and bone marrow hypoplasia, which results from immune-mediated hematopoiesis suppression. Understanding the pathophysiology of the immune system, particularly T cells immunity, has led to improved AA treatment over the past decades. However, primary and secondary failure after immunosuppressive therapy is frequent. Thus, knowledge of the immune mechanisms leading to AA is crucial to fundamentally understand the disease.</p> <p>Findings</p> <p>To elucidate the T cell receptor (TCR) signal transduction features in AA, the expression levels of CD3γ, δ, ε and ζ chain and FcεRIγ genes, which are involved in TCR signal transduction, and the negative correlation of the expression levels between the CD3ζ and FcεRIγ genes in T cells from peripheral blood mononuclear cells (PBMCs) were analyzed. Real-time RT-PCR using the SYBR Green method was used to detect the expression level of these genes in PBMCs from 18 patients with AA and 14 healthy individuals. The β2microglobulin gene (β2M) was used as an endogenous reference. The expression levels of the CD3γ, CD3δ, CD3ε and CD3ζ genes in patients with AA were significantly increased compared to a healthy control group, whereas the FcεRIγ gene expression level was significantly decreased in patients with AA in comparison with the healthy control group. Moreover, the negative correlation of the expression levels between the CD3ζ and FcεRIγ genes was lost.</p> <p>Conclusions</p> <p>To our knowledge, this is the first report of the CD3γ, CD3δ, CD3ε, CD3ζ and FcεRIγ gene expression in patients with AA. The abnormally expressed TCR signaling related genes may relate to T cells dysfunction in AA.</p

HIV-infected T cells are migratory vehicles for viral dissemination

After host entry through mucosal surfaces, HIV-1 disseminates to lymphoid tissues to establish a generalized infection of the immune system. The mechanisms by which this virus spreads among permissive target cells locally during early stages of transmission, and systemically during subsequent dissemination are not known1. In vitro studies suggest that formation of virological synapses (VSs) during stable contacts between infected and uninfected T cells greatly increases the efficiency of viral transfer2. It is unclear, however, if T cell contacts are sufficiently stable in vivo to allow for functional synapse formation under the conditions of perpetual cell motility in epithelial3 and lymphoid tissues4. Here, using multiphoton intravital microscopy (MP-IVM), we examined the dynamic behavior of HIV-infected T cells in lymph nodes (LNs) of humanized mice. We found that most productively infected T cells migrated robustly, resulting in their even distribution throughout the LN cortex. A subset of infected cells formed multinucleated syncytia through HIV envelope (Env)-dependent cell fusion. Both uncoordinated motility of syncytia as well as adhesion to CD4+ LN cells led to the formation of long membrane tethers, increasing cell lengths to up to 10 times that of migrating uninfected T cells. Blocking the egress of migratory T cells from LNs into efferent lymph, and thus interrupting T cell recirculation, limited HIV dissemination and strongly reduced plasma viremia. Thus, we have found that HIV-infected T cells are motile, form syncytia, and establish tethering interactions that may facilitate cell-to-cell transmission through VSs. While their migration in LNs spreads infection locally, T cell recirculation through tissues is important for efficient systemic viral spread, suggesting new molecular targets to antagonize HIV infection

Systems model of T cell receptor proximal signaling reveals emergent ultrasensitivity

Receptor phosphorylation is thought to be tightly regulated because phosphorylated receptors initiate signaling cascades leading to cellular activation. The T cell antigen receptor (TCR) on the surface of T cells is phosphorylated by the kinase Lck and dephosphorylated by the phosphatase CD45 on multiple immunoreceptor tyrosine-based activation motifs (ITAMs). Intriguingly, Lck sequentially phosphorylates ITAMs and ZAP-70, a cytosolic kinase, binds to phosphorylated ITAMs with differential affinities. The purpose of multiple ITAMs, their sequential phosphorylation, and the differential ZAP-70 affinities are unknown. Here, we use a systems model to show that this signaling architecture produces emergent ultrasensitivity resulting in switch-like responses at the scale of individual TCRs. Importantly, this switch-like response is an emergent property, so that removal of multiple ITAMs, sequential phosphorylation, or differential affinities abolishes the switch. We propose that highly regulated TCR phosphorylation is achieved by an emergent switch-like response and use the systems model to design novel chimeric antigen receptors for therapy

Memory CD8(+) T cells require CD8 coreceptor engagement for calcium mobilization and proliferation, but not cytokine production

Memory T-cell responses are faster and more robust than those of their naïve counterparts. The mechanisms by which memory T cells respond better to subsequent antigenic exposure remain unresolved. A portion of the more rapid response is undoubtedly the result of the increased frequency of antigen-specific cells. In addition, there are also differences in the cells themselves with respect to their requirements for costimulation and the apparent avidity of the T cells. We used major histocompatibility complex (MHC) class I tetramers to stimulate T cells to focus on the interaction of T-cell receptor (TCR)/MHC and CD8 in the absence of other molecules that are present on cell surfaces and so contribute to the activation of T cells by undefined mechanisms. Mutated MHC class I tetramers that are unable to engage CD8 were used to investigate the role of CD8 engagement in memory cell activation. Either wild-type tetramers or tetramers carrying the mutation were used to stimulate both memory and naïve TCR transgenic T cells in vitro. Surprisingly, like naïve cells, memory CD8(+) T cells required CD8 engagement for calcium mobilization and optimum proliferation. In contrast, the requirements for cytokine production differed. Unlike naive cells, memory cells were able to produce cytokine in the absence of CD8 engagement. This suggests both a CD8-dependent pathway for early events and a CD8-independent pathway for cytokine production in memory cells

Efficient T cell activation requires an optimal dwell-time of interaction between the TCR and the pMHC complex.

Cytotoxic T cell (CTL) activation by antigen requires the specific detection of peptide-major histocompatibility class I (pMHC) molecules on the target-cell surface by the T cell receptor (TCR). We examined the effect of mutations in the antigen-binding site of a Kb-restricted TCR on T cell activation, antigen binding and dissociation from antigen.These parameters were also examined for variants derived from a Kd-restricted peptide that was recognized by a CTL clone. Using these two independent systems, we show that T cell activation can be impaired by mutations that either decrease or increase the binding half-life of the TCR-pMHC interaction. Our data indicate that efficient T cell activation occurs within an optimal dwell-time range of TCR-pMHC interaction. This restricted dwell-time range is consistent with the exclusion of either extremely low or high affinity T cells from the expanded population during immune responses