Evolution of Innate Immune Protein Complexes, Toll-like Receptor 4 and Calprotectin, in Early Vertebrates and Zebrafish
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Date
2024-08-07
Authors
Orlandi, Kona
Journal Title
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Publisher
University of Oregon
Abstract
The innate immune system is our first line of defense against pathogens as well as our interface with our commensal microbiota. Toll-like receptor 4 (TLR4) and calprotectin are two innate immune proteins that are tightly associated with inflammatory disorders. Zebrafish (Danio rerio) has been successfully used to model the human innate immune system, but TLR4 and calprotectin models have not been developed because of their significant divergence in humans and zebrafish. Here, we set out to reveal the evolutionary and functional relationships between human and zebrafish TLR4 and calprotectin. We used phylogenetic analyses to define the evolutionary relationships between homologous proteins and characterized their immune functions in cell-based assays. We found that an antagonist of human TLR4 is a potent agonist for zebrafish TLR4, but when tested in live fish there was no difference in immune stimulation. We further investigated the evolutionary origin of this change in ligand specificity and determine that TLR4 in the cyprinid order of fish likely convergently evolved sensitivity to LPS. Our characterization of zebrafish proteins homologous to human calprotectin also suggest that the zebrafish proteins do not share functional similarities to calprotectin during the immune response. We conclude that although humans and zebrafish share many immune system characteristics, the TLR4 and calprotectin immune responses are not directly comparable.
This dissertation includes previously published and unpublished co-authored material. Supplement files are multiple sequence alignments and phylogenetic trees for TLR4 and MD-2.
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Keywords
Ancestral Sequence Reconstruction, Biochemistry, Calprotectin, Immunology, Protein Evolution, Toll-like receptor 4