Neutrophils have long been viewed as the final effector cells of an acute inflammatory response, with a primary role in the clearance of extracellular pathogens. However, more recent evidence has extended the functions of these cells. The newly discovered repertoire of effector molecules in the neutrophil armamentarium includes a broad array of cytokines, extracellular traps and effector molecules of the humoral arm of the innate immune system. In addition, neutrophils are involved in the activation, regulation and effector functions of innate and adaptive immune cells. Accordingly, neutrophils have a crucial role in the pathogenesis of a broad range of diseases, including infections caused by intracellular pathogens, autoimmunity, chronic inflammation and cancer.

Alzheimer's disease is the most common cause of progressive intellectual failure. The lesions that develop, called senile plaques, are extracellular deposits principally composed of insoluble aggregates of beta-amyloid protein (A beta), infiltrated by reactive microglia and astrocytes. Although A beta, and a portion of it, the fragment 25-35 (A beta (25-35)), have been shown to exert a direct toxic effect on neurons, the role of microglia in such neuronal injury remains unclear. Here we report a synergistic effect between A beta and interferon-gamma (IFN-gamma) in triggering the production of reactive nitrogen intermediates and tumour-necrosis factor-alpha (TNF-alpha) from microglia. Furthermore, using co-culture experiments, we show that activation of microglia with IFN-gamma and A beta leads to neuronal cell injury in vitro. These findings suggest that A beta and IFN-gamma activate microglia to produce reactive nitrogen intermediates and TNF-alpha, and this may have a role in the pathogenesis of neuronal degeneration observed in ageing and Alzheimer's disease.

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer‐reviewed by leading experts in the field, making this an essential research companion.

Interleukin-17A (IL-17A) and IL-17F are 2 of several cytokines produced by T helper 17 cells (Th17), which are able to indirectly induce the recruitment of neutrophils. Recently, human Th17 cells have been phenotypically characterized and shown to express discrete chemokine receptors, including CCR2 and CCR6. Herein, we show that highly purified neutrophils cultured with interferon-␥ plus lipopolysaccharide produce the CCL2 and CCL20 chemokines, the known ligands of CCR2 and CCR6, respectively. Accordingly, supernatants from activated neutrophils induced chemotaxis of Th17 cells, which was greatly suppressed by anti-CCL20 and anti-CCL2 antibodies. We also discovered that activated Th17 cells could directly chemoattract neutrophils via the release of biologically active CXCL8. Consistent with this reciprocal recruitment, neutrophils and Th17 cells were found in gut tissue from Crohn disease and synovial fluid from rheumatoid arthritis patients. Finally, we report that, although human Th17 cells can directly interact with freshly isolated or preactivated neutrophils via granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-␣, and interferon-␥ release, these latter cells cannot be activated by IL-17A and IL-17F, because of their lack of IL-17RC expression. Collectively, our results reveal a novel chemokine-dependent reciprocal cross-talk between neutrophils and Th17 cells, which may represent a useful target for the treatment of chronic inflammatory diseases. (Blood. 2010;115:335-343)

Neutrophils are known to play an important role in inflammatory responses by virtue of their ability to perform a series of effector functions that collectively represent a major mechanism of innate immunity against injury and infection. In recent years, however, it has become obvious that the contribution of neutrophils to host defence and natural immunity extends well beyond their traditional role as professional phagocytes. Indeed, neutrophils can be induced to express a number of genes whose products lie at the core of inflammatory and immune responses. These include not only Fc receptors, complement components, cationic antimicrobial and NADPH oxidase proteins, but also a variety of cytokines (including tumour necrosis factor-alpha, interleukin (IL)-1beta, IL-1R alpha, IL-12 and vascular endothelial growth factor), and chemokines such as IL-8, growth-related gene product, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, interferon-gamma-inducible protein of 10 kDa and monokine induced by interferon-gamma. Because these chemokines are primarily chemotactic for neutrophils, monocytes, immature dendritic cells and T-lymphocyte subsets, a potential role for neutrophils in orchestrating the sequential recruitment of distinct leukocyte types to the inflamed tissue is likely to occur. The purpose of this review is to summarize the essential features of the production of chemokines by polymorphonuclear neutrophil leukocytes and the contribution that we have made to characterize some aspects of this newly discovered crucial function of neutrophils.

Inflammation involves a coordinated, sequential, and self limiting sequence of events controlled by positive and negative regulatory mechanisms. Recent studies have shown that microRNAs (miRNAs), an evolutionarily conserved class of endogenous 22-nucleotide noncoding RNAs, contribute to the regulation of inflammation by repressing gene expression at the posttranscriptional level. In this study, we characterize the profile of miRNAs induced by LPS in human polymorphonuclear neutrophils (PMN) and monocytes. In particular, we identify miR-9 as the only miRNA (among 365 analyzed) up-regulated in both cell types after TLR4 activation. miR-9 is also induced by TLR2 and TLR7/8 agonists and by the proinflammatory cytokines TNF-␣ and IL-1␤, but not by IFN␥. Among the 3 different genes encoding miR-9 precursors in humans, we show that LPS selectively induces the transcription of miR-9 -1 located in the CROC4 locus, in a MyD88-and NF-B-dependent manner. In PMN and monocytes, LPS regulates NFKB1 at both the transcriptional and posttranscriptional levels, and a conserved miR-9 seed sustained a miR-9-dependent inhibition of the NFKB1 transcript. Overall, these data suggest that TLR4-activated NF-B rapidly increases the expression of miR-9 that operates a feedback control of the NF-B-dependent responses by fine tuning the expression of a key member of the NF-B family.inflammation ͉ innate immunity ͉ Toll-like receptors ͉ cytokines ͉ NFKB1

The long pentraxin (PTX) 3 is produced by macrophages and myeloid dendritic cells in response to Toll-like receptor agonists and represents a nonredundant component of humoral innate immunity against selected pathogens. We report that, unexpectedly, PTX3 is stored in specific granules and undergoes release in response to microbial recognition and inflammatory signals. Released PTX3 can partially localize in neutrophil extracellular traps formed by extruded DNA. Eosinophils and basophils do not contain preformed PTX3. PTX3-deficient neutrophils have defective microbial recognition and phagocytosis, and PTX3 is nonredundant for neutrophil-mediated resistance against Aspergillus fumigatus. Thus, neutrophils serve as a reservoir, ready for rapid release, of the long PTX3, a key component of humoral innate immunity with opsonic activity.

Polymorphonuclear neutrophils, besides their involvement in primary defense against infections – mainly through phagocytosis, generation of toxic molecules, release of enzymes, and formation of extracellular traps – are also becoming increasingly important for their contribution to the fine regulation in development of inflammatory and immune responses. These latter functions of neutrophils occur, in part, via their de novo production and release of a large variety of cytokines, including chemotactic cytokines (chemokines). Accordingly, the improvement in technologies for molecular and functional cell analysis, along with concomitant advances in cell purification techniques, have allowed the identification of a continuously growing list of neutrophil-derived cytokines, as well as the characterization of their biological implications in vitro and/or in vivo. This short review summarizes crucial concepts regarding the modalities of expression, release, and regulation of neutrophil-derived cytokines. It also highlights examples illustrating the potential implications of neutrophil-derived cytokines according to recent observations made in humans and/or in experimental animal models.