Pkl_files

The cellular components and defense mechanisms of innate immunity have diversified alongside the evolution from invertebrates to vertebrates to adapt to a rapidly changing environment. It remains unclear how immune functions and corresponding molecules are conserved or have diverged during evolution. Here, we generated invertebrate hemolymph and vertebrate blood single cell transcriptome landscapes across six species at different taxonomic nodes and combined them with public data to construct a comprehensive cross-species cellular hierarchy. We defined distinctive phagocytic-like cells (PLCs) within various invertebrates that share homologous transcriptional programs with vertebrate myeloid cells. Through cross-species comparisons, we identified a variety of functional molecules and transcription factors shared by phagocytic cells in invertebrates and myeloid cells in vertebrates, which are the core regulatory programs for the inheritance of phagocytic capabilities. Remarkably, we combined the latest Stereo-Cell technology to define specific hemocyte subtypes in invertebrates as potential ancestors of thrombocytes through the expression of coagulation-related factors in clots. Our study elucidates the ancient and conserved aspects of phagocytosis in immune system evolution and provides the first specific definition for the origin of thrombocytes.