Ectothermic vertebrates evolved gut-associated germinal center-like structures

The constant exposure to foodborne pathogens drives the evolutionary selection for potent gut mucosal immune defenses in vertebrate species. Despite retaining ancestral ectothermic traits including underdeveloped lymph nodes, teleost fish have evolved specialized gut-associated lymphoid tissue capable of generating robust antigen-specific immune responses.

How and where ectothermic vertebrates initiate adaptive immunity in the gut remains enigmatic. Through single-cell RNA sequencing (scRNA-seq), we comprehensively mapped the dynamic immune landscape of common carp (Cyprinus carpio) in the gut and head kidney (HK) following Spring Viremia of Carp Virus (SVCV) challenge. Strikingly, lymphocytes within gut exhibited pronounced upregulation of memory-related genes upon secondary viral exposure, oncomitant with robust expression of canonical GC markers in B cells.