Monitoring of blood vessels and tissues by a population of monocytes with patrolling behavior.

The cellular immune response to tissue damage and infection requires the recruitment of blood leukocytes. This process is mediated through a classical multistep mechanism, which involves transient rolling on the endothelium and recognition of inflammation followed by extravasation. We have shown, by direct examination of blood monocyte functions in vivo, that a subset of monocytes patrols healthy tissues through long-range crawling on the resting endothelium. This patrolling behavior depended on the integrin LFA-1 and the chemokine receptor CX(3)CR1 and was required for rapid tissue invasion at the site of an infection by this "resident" monocyte population, which initiated an early immune response and differentiated into macrophages.

Secretory cytotoxic granule maturation and exocytosis require the effector protein hMunc13-4.

Cytotoxic T lymphocytes and natural killer cells exert their cytotoxic activity through the polarized secretion of cytotoxic granules at the immunological synapse. Rab27a and hMunc13-4 are critical effectors of the exocytosis of cytotoxic granules. Here we show that the cytotoxic function of lymphocytes requires the cooperation of two types of organelles: the lysosomal cytotoxic granule and the endosomal 'exocytic vesicle'. Independently of Rab27a, hMunc13-4 mediated the assembly of Rab11(+) recycling and Rab27(+) late endosomal vesicles, constituting a pool of vesicles destined for regulated exocytosis. It also primed cytotoxic granule fusion, possibly through interaction with active Rab27a. Cytotoxic T lymphocyte-target cell recognition induced rapid polarization of both types of organelles, which coalesced near the cell-cell contact area. Our data provide insight into the regulation of the generation and release of cytotoxic granules by effector cytotoxic T lymphocytes and natural killer cells.

X-linked susceptibility to mycobacteria is caused by mutations in NEMO impairing CD40-dependent IL-12 production.

Germline mutations in five autosomal genes involved in interleukin (IL)-12-dependent, interferon (IFN)-gamma-mediated immunity cause Mendelian susceptibility to mycobacterial diseases (MSMD). The molecular basis of X-linked recessive (XR)-MSMD remains unknown. We report here mutations in the leucine zipper (LZ) domain of the NF-kappaB essential modulator (NEMO) gene in three unrelated kindreds with XR-MSMD. The mutant proteins were produced in normal amounts in blood and fibroblastic cells. However, the patients' monocytes presented an intrinsic defect in T cell-dependent IL-12 production, resulting in defective IFN-gamma secretion by T cells. IL-12 production was also impaired as the result of a specific defect in NEMO- and NF-kappaB/c-Rel-mediated CD40 signaling after the stimulation of monocytes and dendritic cells by CD40L-expressing T cells and fibroblasts, respectively. However, the CD40-dependent up-regulation of costimulatory molecules of dendritic cells and the proliferation and immunoglobulin class switch of B cells were normal. Moreover, the patients' blood and fibroblastic cells responded to other NF-kappaB activators, such as tumor necrosis factor-alpha, IL-1beta, and lipopolysaccharide. These two mutations in the NEMO LZ domain provide the first genetic etiology of XR-MSMD. They also demonstrate the importance of the T cell- and CD40L-triggered, CD40-, and NEMO/NF-kappaB/c-Rel-mediated induction of IL-12 by monocyte-derived cells for protective immunity to mycobacteria in humans.