Deciphering the function of the atypical inhibitor of NF-kB, IkBNS/Nfkbid, in macrophages and neutrophils

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The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) is the paradigm of an inducible transcription factor, being regulated by inhibitor of kB (IkB) proteins. In addition to the cytosolic IkB proteins, another class of nuclear (or atypical) IkB proteins exists that modulates the transcriptional activity of NF-kB. IkBNS, which is encoded by the Nfkbid gene, is one of these atypical IkB proteins and we previously demonstrated that it is crucial for the development of regulatory T cells and the differentiation of Th1 and Th17 effector cells. Despite its role in T cells, crucial functions in B cells and macrophages have been described for IkBNS. Using a novel reporter mouse that expresses lacZ under the control of the endogenous Nfkbid promoter, we screened for promoter activity of the Nfkbid gene in different cell types. We confirmed expression in macrophages and detected high promoter activity in neutrophils. To investigate the function of IkBNS in these myeloid cells, we generated conditional knockout mice lacking IkBNS expression either in both cell types or specifically in neutrophils. Moreover, we generated Hoxb8-transduced progenitor cells from wildtype and IkBNS-deficient bone marrow cells, which can be differentiated into macrophages or neutrophils. Using these systems, we will analyze the function of IkBNS in macrophages and neutrophils with respect to phagocytosis, polarization into subsets, antigen presentation, degranulation, NET formation, generation of reactive oxygen species, and bacterial killing in vitro and in vivo. We will use Staphylococcus aureus, an opportunistic pathogen that is the leading cause of nosocomial infections and often multidrug-resistant, as an infectious agent. The immune response against these bacteria crucially depends on neutrophils and macrophages with S. aureus being a prime stimulus of NET formation in neutrophils. Thus, this pathogen is perfectly suited to decipher the functions of IkBNS in neutrophils and macrophages.