MOLECULAR DRIVERS OF LYMPHOCYTIC ORGANIZATION AT VERTEBRATE MUCOSAL SITES
Irene Salinas, University of New Mexico
RYAN HEIMROTH, IRENE SALINAS
Department of Biology, University of New Mexico, Albuquerque
The aggregation and organization of lymphocytes at mucosal lymphoid tissues in structures such as Peyer’s patches (PP) and tonsils is thought to be a unique feature of the mucosal immune system of endotherms. However, cold-blooded vertebrates also have lymphocyte aggregates at mucosal sites, albeit less organized. This progressive organization of the mucosal immune system has been attributed to the expansion and diversification of members of the tumor necrosis factor superfamily (TNFSF). This hypothesis is based on mammalian studies using different mouse knock-outs in which organized mucosa-associated lymphoid structures (O-MALT) or lymph nodes are missing. However, an unbiased search of molecular drivers of O-MALT formation across vertebrate groups has not been conducted thus far. Revisiting the TNFSF hypothesis indicated a lack of support for the progressive diversification of TNFSF from bony fish to mammals based on BLAST and HMM searches of all available genomes and transcriptomes. We next performed RNA-Seq from the interbranchial lymphoid tissue of rainbow trout, the nasal lymphoid aggregates of African lungfish, avian ceacal tonsils and mouse PP and LN. After subtracting genes expressed in non-O-MALT negative control tissues from each species, we identified unique and shared suites of genes in the different O-MALT structures. Specifically, we identified that genes with predicted neuroactive ligand-receptor functions are enriched in all vertebrate O-MALT transcriptomes and that lungfish and mouse OMALT are enriched in olfactory receptors genes. Our results provide a new theoretical framework for understanding the molecules required for the formation and organization of lymphocytic structures at vertebrate mucosal tissues.