Associate professor University of Maryland School of Medicine Baltimore, Maryland, United States
Disclosure(s):
Helen Dooley, PhD: No financial relationships to disclose
Introduction/Rationale: Organized mucosal associated lymphoid tissue (O-MALT), such as Peyers Patches in the mammalian gut, play a critical role in immune protection by populating the mucosa with antigen-experienced B cells. Peyer’s Patches are also reported in the gut of birds, while organized lymphocyte aggregates have been described in the gut of both reptiles and amphibians. However, bony fishes appear to lack O-MALT, instead having a diffuse network of immune cells scattered throughout the gut mucosal epithelium and lamina propria. Thus, current data suggests an increase in gut lymphoid tissue organization in a common tetrapod ancestor.
Methods: To test this hypothesis, we used RNAscope in situ hybridization to study immune cell organization in the spiral valve (small intestine equivalent) of the nurse shark, a member of the oldest extant vertebrate lineage to possess antibody-based adaptive immunity, the cartilaginous fishes.
Results: We identified O-MALT in the form of AID+ T cells and AID+ B cell follicles with strikingly morphological similarity to mammalian Peyer’s Patches in the nurse shark spiral valve. We also mapped Ig bright (plasma) cells, T cells, and MHCII+ antigen presenting cells to the spiral valve lamina propria and villi. Finally, we detected antibody in spiral valve mucus and showed it coats the gut microbiota.
Conclusion: Together our data indicate that the emergence of O-MALT in gut occurred much earlier than previously thought, likely in a jawed vertebrate common ancestor.
