The germinal center (GC) is a complex, highly dynamic microanatomical niche

The germinal center (GC) is a complex, highly dynamic microanatomical niche that allows the generation of high-affinity antibody-producing plasma cells and memory B cells. interaction. In the context of GCs, which contain large numbers of cells in a highly compacted structure, focused delivery of signals across the interacting cells becomes particularly important. Promiscuous or bystander delivery of positive selection signals could potentially lead to the appearance of long-lived self-reactive B cell clones. Cytokines, cytotoxic granules, and more recently neurotransmitters have been shown to be transferred from TFH to B cells upon cognate interactions. This review describes the current knowledge on immunological synapses occurring during GC responses Tgfb2 including the type of granules, their content, and function in TFH-mediated help to B cells. their TCRs, the TCRs become organized into structures of ~500?nm known as microclusters (MCs). These MCs are more efficient in the recruitment of kinases and adapters that Vandetanib enzyme inhibitor can initiate an activation signaling cascade (3). During formation of the immunological synapse, the TCR-MCs localize at the center of the interface between the T cells and the APC giving rise to the central supramolecular activation cluster (cSMAC) (4C7). This cSMAC is also called the bulls eye-type immunological synapse, due to its characteristic appearance, as first described by Kupfer (8). The immunological synapse between a T cell and an APC requires close juxtaposition of the membranes from the two different cell types. This is facilitated by a kinetic segregation of molecules that excludes negative regulatory phosphatases such as CD45 that relocates to the most external region or distal SMAC, and allows concentration of the key TCR signaling molecules at the center. This segregation process has been suggested to be an integral part of immune synapse function (9). Besides TCR signaling, integrins play a key role in T cell activation facilitating the formation of conjugates between T cells and APCs. Lymphocyte function-associated antigen-1 (LFA-1) is one of the most important integrins during the process of T cell activation. LFA-1 and its high-affinity ligand intercellular adhesion molecule 1 (ICAM-1), localize outside of the cSMAC, at the peripheral SMAC (pSMAC). The inside-out signal from TCR or chemokine stimulation elicits conformational changes in LFA-1 that increase affinity for its ligands and therefore adhesion between the interacting cells (10). Binding of LFA-1 by ICAM-1, then leads to what is known as outside-in signaling, which contributes to many aspects of T cell activation. Most membrane-proximal signaling molecules crucial for T cell activation such as ZAP70, LAT, SLP76, PLC-, etc., are recruited to TCR-MCs. Regulation of these large protein-complexes determines the outcome of T cell activation, not just in terms of TCR signaling strength but also with regards to the nature of the resulting effector cells (7, 11). It is still unclear how different activation, differentiation, and survival outcomes can derive from changes in the signal strength downstream of these signaling complexes. Together with T-cell antigen receptors and integrins, two additional groups of Vandetanib enzyme inhibitor receptors are located at the synapse: adhesion and costimulatory receptors. Adhesion is mediated by heterophilic interactions between the signaling lymphocyte activation molecules (SLAM) family members CD2 (expressed on T cells) and Vandetanib enzyme inhibitor CD58 (expressed on APCs). These CD2CCD58 interactions can contribute to TCR signaling processes even when direct TCR stimulation is absent (12). It has been known for over two decades that costimulatory receptors are poor in eliciting activation signals or inducing cell adhesion on their own, but when combined with signals from other receptors, most prominently the TCR, they can potently enhance T cell activation, adhesion, and differentiation (13C15). The typical T cell costimulator is CD28, a member of the Ig superfamily characterized by a homodimeric structure and a cytoplasmic domain. The cytoplasmic domain of CD28 recruits and activates Lck, which can then phosphorylate and activates protein kinase C (PKC)-. In T cells PKC-, a critical PKC isoform, contributes to the activation of NF-B transcription factors and promotes IL-2 production (16). Ligation of B7-1 (CD80) and B7-2 (CD86) on APCs and interaction within an immunological synapse regulate CD28 activity (17). Upregulation of CD80 and CD86 on DCs is.