The role of soluble and transmembrame TNFa on macrophage polarization during infection and sterile inflammation

Tumor necrosis factor alpha (TNFa) is apleiotropic citokine that can be expressed in a soluble (s) or transmembrane (tm) form. Wile sTNFa is generally associated with inflammation, the role of tmTNF is not well understood. Numerous studies describe how a tight regulation of this cytokine is required to control inflammation and infec-tions, but the relative contribution of STNFa and tmTNFa to inflammation is currently not understood. This project will investigate the function of STNFa and tmTNFa in vivo, during inflammation induced by injury or infections in zebrafish, with special focus on macrophage polarization. The zebrafish model has several advantages, including: 1) transparency of the embryos or larvae enabling real-time in vivo tracking of cells, 2) availability of a well-annotated genome for gene manipulation, 3) availability of trans-genic lines fluorescently marking innate immune cells and TNFa-expressing cells. Zebrafish possesses two TNFa homologues, namely tnfoa and tnfob. In a preliminary study from our group, amino acid substitutions in the hinge region of tnfoa and tnfob allowed for the constitutive expression of their transmembrane form. This information, combined with the zebrafish model, will enable the generation of new transgenic lines expressing Tnfoa or Tnfob in either soluble or transmembrane form and the use of tnfa knockout lines. In a similar manner, also the expression of both Tnf receptors can be manipulated. Altogether, this project will unravel I) the relative role of sTNFa and tmTNFa during injury and infection; II) through which receptors they exert their activities, with special focus on macrophage polarization.