Myeloid-Specific Deletion of Mcl-1 Yields Severely Neutropenic Mice That Survive and Breed in Homozygous Form.

Mouse strains with specific deficiency of given hematopoietic lineages provide invaluable tools for understanding blood cell function in health and disease. Whereas neutrophils are dominant leukocytes in humans and mice, there are no widely useful genetic models of neutrophil deficiency in mice. In this study, we show that myeloid-specific deletion of the Mcl-1 antiapoptotic protein in Lyz2 Cre/Cre Mcl1 flox/flox (Mcl1 ΔMyelo) mice leads to dramatic reduction of circulating and tissue neutrophil counts without affecting circulating lymphocyte, monocyte, or eosinophil numbers. Surprisingly, Mcl1 ΔMyelo mice appeared normally, and their survival was mostly normal both under specific pathogen-free and conventional housing conditions. Mcl1 ΔMyelo mice were also able to breed in homozygous form, making them highly useful for in vivo experimental studies. The functional relevance of neutropenia was confirmed by the complete protection of Mcl1 ΔMyelo mice from arthritis development in the K/B×N serum-transfer model and from skin inflammation in an autoantibody-induced mouse model of epidermolysis bullosa acquisita. Mcl1 ΔMyelo mice were also highly susceptible to systemic Staphylococcus aureus or Candida albicans infection, due to defective clearance of the invading pathogens. Although neutrophil-specific deletion of Mcl-1 in MRP8-CreMcl1 flox/flox (Mcl1 ΔPMN) mice also led to severe neutropenia, those mice showed an overt wasting phenotype and strongly reduced survival and breeding, limiting their use as an experimental model of neutrophil deficiency. Taken together, our results with the Mcl1 ΔMyelo mice indicate that severe neutropenia does not abrogate the viability and fertility of mice, and they provide a useful genetic mouse model for the analysis of the role of neutrophils in health and disease.

Inflammatory signal induced IL-10 production of marginal zone B-cells depends on CREB.

IL-10 is a suppressive cytokine that has been implicated in the pathophysiology of autoimmune disorders and can be produced by different cell types such as regulatory B-cells. Our previous work showed that under inflammatory condition MZ B-cells differentiated into IL-10 producing cells and contributed to the downregulation of collagen-induced arthritis, while follicular B-cells failed to do so. Based on these observations, we aimed to investigate how inflammatory signals mediated through the BCR, TLR9 and IFN-γ receptors trigger IL-10 production in MZ B-cells but leave FO B-cells unresponsive. We particularly focused on the CREB transcription factor as it is involved in all three signalling cascades and analysed its contribution to IL-10 production. Our results demonstrate that the IL-10 production of MZ B-cells induced by the BCR, TLR9 and IFN-γ receptors is mediated by CREB. We showed that the activation of CREB is prolonged in MZ B-cells while the transcription factor only transiently phosphorylated in FO B-cells. The sustained phosphorylation of CREB is clearly associated with its prolonged binding to molecular partner CBP, whereas inhibition of their association decreased IL-10 production. We assume that sustained activation of CREB is required for IL-10 production by B-cells under inflammatory conditions.