Innate immune cells must be able to distinguish between direct binding to microbes and detection of components shed from the surface of microbes located at a distance. Dectin-1 is a pattern recognition receptor expressed by myeloid phagocytes (macrophages, dendritic cells and neutrophils) that detects β-glucans in fungal cell walls and triggers direct cellular anti-microbial activity, including phagocytosis and production of reactive oxygen species1, 2. In contrast to inflammatory responses stimulated upon detection of soluble ligands by other pattern recognition receptors, such as Toll-like receptors (TLRs), these responses are only useful when a cell comes into direct contact with a microbe and must not be spuriously activated by soluble stimuli. In this study we show that despite its ability to bind both soluble and particulate β-glucan polymers, Dectin-1 signalling is only activated by particulate β-glucans, which cluster the receptor in synapse-like structures from which regulatory tyrosine phosphatases CD45 and CD148 are excluded (Supplementary Figure 1). The “phagocytic synapse” now provides a model mechanism by which innate immune receptors can distinguish direct microbial contact from detection of microbes at a distance, thereby initiating direct cellular anti-microbial responses only when they are required.

Chemokines regulate the homeostatic trafficking of lymphocytes and lymphocyte influx into sites of injury and inflammation. The signaling pathways by which chemokine receptors regulate lymphocyte migration remain incompletely characterized. We demonstrate that Jurkat T cells lacking the ZAP-70 tyrosine kinase exhibit reduced migration in response to the CXCR4 ligand CXCL12 when compared with wild-type Jurkat T cells. Expression of wild-type, but not kinase-inactive, ZAP-70 resulted in enhanced migration of ZAP-70-deficient Jurkat T cells. The tyrosine residue at position 292 in the interdomain B region of ZAP-70 exerts a negative regulatory effect on ZAP-70-dependent migration. Stimulation of Jurkat T cells with CXCL12 also resulted in ZAP-70-dependent tyrosine phosphorylation of the Src homology 2 domain-containing leukocyte protein of 76 kDa (SLP-76) adapter protein. Although CXCL12-dependent migration of SLP-76-deficient Jurkat T cells was impaired, re-expression of SLP-76 did not enhance migration. These results suggest a novel function for ZAP-70, but not SLP-76, in CXCR4 chemokine receptor signaling in human T cells.

IntroductionDendritic cells (DCs) are professional antigen-presenting cells (APCs) that display an extraordinary capacity to stimulate naive T cells and to initiate primary immune responses. 1 Recent studies suggest that DCs also play critical roles in the induction of peripheral immunologic tolerance, regulate the types of T-cell immune responses, and function as effector cells in innate immunity against microbes. 2,3 The diverse functions of DCs in immune regulation depend on the functional plasticity of DCs at the immature stage and the diversity of DC subsets and lineages. 2 Progress in understanding the molecular regulation of DC development from hematopoietic progenitor cells (HPCs) has led to the development of in vitro culture systems for the generation of large numbers of myeloid DCs from CD34 ϩ HPCs with granulocyte macrophage-colony-stimulating factor (GM-CSF) and tumor necrosis factor ␣ (TNF-␣) 4 or peripheral blood monocytes with GM-CSF and interleukin-4 (IL-4). 5,6 These culture systems not only permit detailed studies of DC biology, they allow the development of DC-based cancer vaccines. 7 Type 1 interferon-producing cells (IPCs), or plasmacytoid DC precursors, are distinct from myeloid-derived DC types. IPCs appear to be lymphoid-related because they express antigens or mRNA transcript related to lymphocytes (CD2, CD5, CD7, pre-Tcell receptor-␣ [TCR␣], immunoglobulin germline J chain, immunoglobulin-like 14.2, and Spi-B), and they display neither common myeloid antigens (CD11b, CD13, CD33) nor macrophage function or differentiation potential. IPCs express a set of microbial pattern recognition receptors (Toll-like receptors 7 and 9) different from that expressed by myeloid DCs (Toll-like receptors 2-6). 8 In antimicrobial innate immune responses, though monocytes or immature myeloid DCs play a critical role in phagocytoses of bacteria and parasites, IPCs play a major role in antiviral immunity by rapidly producing large amounts of type 1 interferon after viral infection. The critical role of IPCs in human antiviral immunity is suggested by the observation that the loss of IPCs correlates with disease progression to AIDS in HIV-infected patients. 9 In patients of systemic lupus erythematosus (SLE), constitutive activation of IPCs by dsDNA and anti-dsDNA antibody complexes appears to contribute to the pathogenesis of SLE. 10 In allogeneic bone marrow transplantation, increasing evidence indicates that IPCs may play an important role in immune responses after hematopoietic stem cell transplantation (HSCT) to facilitate engraftment and to prevent graft-versus-host disease (GVHD). [11][12][13] Understanding the molecular mechanisms underlying IPC development from HPCs may provide a novel therapy for viral [16][17][18][19][20] Studies also show that FLT3-L treatment increases the numbers of CD11c ϩ myeloid DCs and CD4 ϩ CD123 high CD11c Ϫ IPCs in the peripheral blood of human donors by 13-fold and 48-fold, respectively. 21,22 These findings suggest that FLT3-L directly induces the differentiation of C...