BAFF-secreting neutrophils drive plasma cell responses during emergency granulopoiesis.

Prolonged infections or adjuvant usage can trigger emergency granulopoiesis (EG), leading to dysregulation in neutrophil blood counts. However, the impact of EG on T and B cell function remains largely unknown. In this study, to address this question, we used a mouse model of neutropenia and studied immune activation after adjuvant administration. The initial neutropenic state fostered an environment of increased dendritic cell activation and T cell-derived IL-17 production. Interestingly, neutropenic lysozyme 2-diphtheria toxin A mice exhibited striking EG and amplified neutrophil recruitment to the lymph nodes (LNs) that was dependent on IL-17-induced prostaglandin activity. The recruited neutrophils secreted a B cell-activating factor that highly accelerated plasma cell generation and antigen-specific antibody production. Reduction of neutrophil functions via granulocyte colony-stimulating factor neutralization significantly diminished plasma cell formation, directly linking EG with the humoral immune response. We conclude that neutrophils are capable of directly regulating T cell-dependent B cell responses in the LN.

Variability in C-type lectin receptors regulates neuropathic pain-like behavior after peripheral nerve injury.

INTRODUCTION: Neuropathic pain is believed to be influenced in part by inflammatory processes. In this study we examined the effect of variability in the C-type lectin gene cluster (Aplec) on the development of neuropathic pain-like behavior after ligation of the L5 spinal nerve in the inbred DA and the congenic Aplec strains, which carries seven C-type lectin genes originating from the PVG strain. RESULTS: While both strains displayed neuropathic pain behavior early after injury, the Aplec strain remained sensitive throughout the whole study period. Analyses of several mRNA transcripts revealed that the expression of Interleukin-1ß, Substance P and Cathepsin S were more up-regulated in the dorsal part of the spinal cord of Aplec rats compared to DA, indicating a stronger inflammatory response. This notion was supported by flow cytometric analysis revealing increased infiltration of activated macrophages into the spinal cord. In addition, macrophages from the Aplec strain stimulated in vitro displayed higher expression of inflammatory cytokines compared to DA cells. Finally, we bred a recombinant congenic strain (R11R6) comprising only four of the seven Aplec genes, which displayed similar clinical and immune phenotypes as the Aplec strain. CONCLUSION: We here for the first time demonstrate that C-type lectins, a family of innate immune receptors with largely unknown functions in the nervous system, are involved in regulation of inflammation and development of neuropathic pain behavior after nerve injury. Further experimental and clinical studies are needed to dissect the underlying mechanisms more in detail as well as any possible relevance for human conditions.