Induction of B cell autoimmunity by pristane

Type I interferon modulates monocyte recruitment and maturation in chronic inflammation

Chronic inflammation is characterized by continuous recruitment and activation of immune cells such as monocytes in response to a persistent stimulus. Production of proinflammatory mediators by monocytes leads to tissue damage and perpetuates the inflammatory response. However, the mechanism(s) responsible for the sustained influx of monocytes in chronic inflammation are not well defined. In chronic peritonitis induced by pristane, the persistent recruitment of Ly6C(hi) inflammatory monocytes into the peritoneum was abolished in type I interferon (IFN-I) receptor-deficient mice but was unaffected by the absence of IFN-gamma, tumor necrosis factor-alpha, interleukin-6, or interleukin-1. IFN-I signaling stimulated the production of chemokines (CCL2, CCL7, and CCL12) that recruited Ly6C(hi) monocytes via interactions with the chemokine receptor CCR2. Interestingly, after 2,6,10,14-tetramethylpentadecane treatment, the rapid turnover of inflammatory monocytes in the inflamed peritoneum was associated with a lack of differentiation into Ly6C(lo) monocytes/macrophages, a more mature subset with enhanced phagocytic capacity. In contrast, Ly6C(hi) monocytes differentiated normally into Ly6C(lo) cells in IFN-I receptor-deficient mice. The effects of IFN-I were specific for monocytes as granulocyte migration was unaffected in the absence of IFN-I signaling. Taken together, our findings reveal a novel role of IFN-I in promoting the recruitment of inflammatory monocytes via the chemokine receptor CCR2. Continuous monocyte recruitment and the lack of terminal differentiation induced by IFN-I may help sustain the chronic inflammatory response.

Effects of acute and chronic inflammation on B-cell development and differentiation

Recently, our understanding of hematopoiesis and the development of the immune system has fundamentally changed, leading to significant discoveries with important clinical relevance. Hematopoiesis, once described in terms of irreversible and discrete developmental branch points, is now understood to exist as a collection of alternative developmental pathways capable of generating functionally identical progeny. Developmental commitment to a particular blood-cell lineage is gradually acquired and reflects both cell intrinsic and extrinsic signals. Chief among the extrinsic factors are the environmental cues of hematopoietic microenvironments that comprise specific "developmental niches" that support hematopoietic stem and progenitor cells. Most of this new understanding comes from the study of normal, steady-state hematopoiesis, but there is ample reason to expect that special developmental and/or differentiative mechanisms operate in response to inflammation. For example, both stem and progenitor cells are now known to express Toll-like receptors that can influence hematopoietic cell fates in response to microbial products. Likewise, proinflammatory cytokines mobilize hematopoietic stem cells to peripheral tissues. In this Perspective, we review inflammation's effects on central and extramedullary B lymphopoiesis and discuss the potential consequences of peripheral B-cell development in the context of systemic autoimmune diseases.