Upon recognizing cognate antigen, B cells mobilize multiple cellular apparatuses to propagate an optimal response

Upon recognizing cognate antigen, B cells mobilize multiple cellular apparatuses to propagate an optimal response. immune system complexes colligate the BCR and FcRIIB, which leads to the activation of SHIP (26). SHIP converts phosphatidylinositol-3,4,5-triphosphate [PtdIn(3,4,5)P3] to PtdIn(3,4)P2, which eliminates lipid raft-docking sites for PLC2, Akt, and Btk, consequently inhibiting their activation (27). BCR activation by antigen binding also induces SHIP activation. SHIP has been shown to bind BCR ITAMs with only one of the two tyrosines phosphorylated in anergic B cells, which is critical for keeping B cells in the anergic state (28). The downregulation of BCR signaling mediated by these inhibitory phosphatases is critical for maintaining B-cell self-tolerance and controlling B-cell-mediated autoimmunity (8, 29). Dynamic organization of surface BCRs Recent advances in high resolution live cell imaging techniques have enabled us to reveal molecular details of receptor activation at the cell surface in real time. Upon interacting with antigen, particularly membrane-associated antigen, BCRs at the B-cell surface briefly increase their lateral mobility (30, 31). This is followed by immobilization of surface BCRs and concurrent formation of BCR microclusters (32). While the microclusters interact with lipid rafts and lipid raft-associated Lyn, tyrosine GSK744 (S/GSK1265744) phosphorylation in the microclusters increases and Syk is recruited to the microclusters (18, 22, 33). Many additional signaling molecules are subsequently recruited to BCR microclusters, such as CD19, PLC2, and Btk (34, 35), indicating that these microclusters function as signalosomes. Over a timescale of a few minutes, BCR microclusters grow by recruiting more receptors into the clusters while simultaneously moving towards one pole of the cells. In B cells interacting with membrane-associated antigen, BCR microclusters move towards the center of the contact surface between the B cell and the antigen-presenting GSK744 (S/GSK1265744) membrane (B-cell contact zone). GSK744 (S/GSK1265744) While moving centripetally, BCR microclusters merge into one another, forming a central cluster, a molecular complex similar to the immunological synapse formed between T cells and antigen-presenting cells (9, 36, 37). While most of these results were obtained by studies of B cells activated by membrane-associated or immobilized antigen, our recent studies show that multi-valent soluble antigen is capable of inducing similar receptor cluster dynamics and formation of a central cluster. However, the BCR central cluster induced by soluble antigen is more dynamic GSK744 (S/GSK1265744) and less stable compared to that induced by membrane-associated antigen (38). It has also been shown that dynamic clusters of surface BCRs are targets for disruption by inhibitory signaling molecules. Colligation of the BCR with FcRIIB by immune complexes inhibits the interaction of the BCR with lipid rafts and the formation of BCR microclusters and central clusters (39, 40). These results additional support the look at that molecular dynamics and reorganization of BCRs in the B-cell surface area are key occasions aswell as regulatory focuses on during BCR-mediated B-cell activation. Although it has been obviously proven that antigen-induced receptor clustering Rabbit polyclonal to LRRC15 is necessary for BCR signaling activation (9, 36, 41), latest studies show that surface area BCRs can be found as clusters in the nanoscale in the lack of antigen binding. This is demonstrated by solitary molecule imaging using immediate stochastic optical reconstruction microscopy (dSTORM) (42) and molecular discussion measurements using Forster resonance energy transfer (43). These BCR clusters are smaller than those induced by antigen, as they are not detectable using traditional confocal fluorescence microscopy. In addition to their size, BCR conformation and BCR-BCR interactions within these nano-clusters are likely different from those within antigen-induced clusters. The lateral mobility of these BCR nano-clusters has been implicated in regulating tonic signaling in resting B cells (42). BCRs within these nano-clusters have been postulated to be in an inhibitory conformation (43, 44). The physical constraints associated with antigen binding by BCRs have been shown to cause conformational changes in the receptor (10, 18, 32). BCR conformational changes may alter the ways in which BCRs in clusters interact with each.

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