Two large protein families with roles in the immune system were the subject of this thesis. In part one of the thesis, TRIM proteins were studied, which are part of an ancient intracellular immune system. In mammals, TRIM proteins were recently found to play an important role in the antiviral immune response as they can restrict multiple viruses. To better understand the evolution of the TRIM protein family, TRIM proteins were investigated in teleost fish, which emerged early during vertebrate evolution. A detailed description of the entire TRIM gene family in fish was made and it was discovered that certain TRIM genes have undergone a radical expansion, giving rise to three multigene families. Experimental studies indicated a role for trout TRIM proteins in antiviral immunity and demonstrated that they have E3 ubiquitin ligase activity. As it recently became evident that ubiquitination is an important mode to control the activity of proteins of innate immune pathways, possibly TRIM proteins in fish have a similar activity. In part two of this thesis, inflammatory CXC chemokines were studied, for which limited functional data was available in fish at the start of the thesis project. CXC chemokines are specialized cytokines that direct leukocyte migration during inflammation. In zebrafish and carp, two CXC lineages were identified that resemble mammalian CXCL8, a similar diversification was observed for chemokines that resemble mammalian CXCL9, CXCL10, CXCL11chemokines. A characterization of the functions for cyprinid CXCL8-like and CXCL9-11-like (named CXCb) chemokines was made by in vitro and in vivo gene expression studies. By preparation of recombinant proteins it was demonstrated that carp chemokines of the CXCL8-like and CXCb subsets are both chemotactic for fish leukocytes. Chemokines of the CXCL8-like and CXCb subsets appeared to be functionally distinct, as they have a different effect on phagocyte activation and act during different phases of the inflammatory response. These results indicate that CXC chemokines have already specialized functions in fish.