Evolution of innate lymphoid cells in lampreys 4415

Description Innate lymphoid cells (ILCs) are early responders to potential pathogens at barrier surfaces, modulate development and function of antigen-specific T and B cells and facilitate wound healing by reaction to tissue injury. To determine when the ILCs evolved, we FACS-sorted the antigen receptor-positive and -negative lymphocytes in lampreys, a jawless vertebrate representative, and examined their expression of genes orthologous to those shown to be important for ILC development and function in mammals. We first compared the gene expression profiles for 4 sorted lymphocyte populations: variable lymphocyte receptor (VLR) A+, VLRB+, VLRC+ and VLR-null lymphocytes by quantitative RT-PCR analysis. We next divided the VLR-null lymphocytes into two subpopulations by using LysoTracker to identify cells rich in acidic intracellular vesicles such as lysosomes. The lysosome-positive (Lyso+) VLR-null lymphocytes preferentially expressed CD56, IL-23R, Runx2 and granzyme orthologues, whereas the Lyso- VLR-null lymphocytes expressed PLZF, Id2, GATA3 and RORα. By staining with a lamprey TLR5-specific antibody, we found that Lyso+ VLR-null lymphocytes expressed high levels of TLR5. Electron microscopic analysis of the TLR5high/Lyso+/VLR-null cells indicated their morphological similarity to mammalian NK cells. Our composite findings suggest that the basic genetic programs for NK-like, ILC2-like, T-like and B-like cells were already present in a common vertebrate ancestor ∼500 million years ago. Funding Sources Supported by NIH R01AI072435; NIH R35GM122591; NIH R35GM108838; NSF 1755418; NSF 1655163 Topic Categories Veterinary and Comparative Immunology (VET)