07/22/2024
By Irma Silva

The Kennedy College of Sciences, Department of Biological Sciences, invites you to attend a Ph.D. Dissertation Defense in Applied Biology by Saraswathy Vaidyanathan entitled: "The teleost melanomacrophage center response to antigens and environmental pollutant."

Candidate: Saraswathy Vaidyanathan
Date: Tuesday, July 23, 2024
Time: 11 a.m. – 1 p.m.
Location: Ball Hall 206 (updated location) and via Zoom: Those interested in attending the defense via zoom should email student saraswathy_pv@student.uml.edu at least 24 hours prior to the defense to request access to the meeting.

Committee:

  • Advisor: Natalie Steinel, Assistant Professor, Biological Sciences, University of Massachusetts Lowell
  • Peter Gaines, Chair & Professor, Biological Sciences, University of Massachusetts Lowell
  • Frédéric chain, Associate Professor, Biological Sciences, University of Massachusetts Lowell
  • Irene Salinas, Associate Chair & Professor, Biology, University of New Mexico

Title: The teleost melanomacrophage center response to antigens and environmental pollutant

Brief Abstract: Non-mouse models such as fish have the potential to expand our understanding of vertebrate immunity and also reveal the evolutionary origins of vertebrate immunity. In addition, understanding fish immunity can aid in better fish vaccines for use in aquaculture, and fish are an important source of protein for humans. However, our understanding of the fish immune system is limited compared to mice and human immune systems. Following exposure to antigen, B cells are activated through the germinal center response or extrafollicular response. Germinal center (GC) response is mediated by T-dependent protein antigens. GCs are specialized microstructures that form within secondary lymphoid organs in mammals. GCs increase in size in response to infection/immunization and within these specialized structures, high affinity antibodies, plasma cells and memory cells are generated. Furthermore, GCs have a discernible histologic organization that involves organized zones of B and T cells. On the other hand, extrafollicular (EF) response is mediated by T-independent polysaccharide antigens. However antibodies generated by EF response are low affinity and no memory cells are produced. Further there is no discernible histologic organization seen in this response. While extensive experimentation in endotherms have illuminated the complex processes that occur within GC, we are only beginning to understand whether ectothermic counterparts have similar processes or spatial organization. Fish lack GCs; instead they possess melanomacrophage centers (MMCs). MMCs are aggregates of pigmented phagocytes that have been demonstrated to function like GCs in fish. MMCs increase in size in response to infection/immunization like GCs. In addition MMCs also increase in response to various stressors like pollutants, metals etc. However, considering the diverse roles MMCs perform in function, it is unclear whether MMCs are specialized structures like GC that respond only to protein (TD) antigens or are generalist structures that could respond to both protein and polysaccharide antigens. In addition, we do not know the spatial organization of adaptive immune cells around MMCs. To fill these gaps in knowledge, we used an emerging immunologic model organism, the threespine stickleback fish. We found that MMC responses vary between species and within populations of the same species. Furthermore, we did not find a significant difference in MMC response between protein and polysaccharide antigen stimulation, suggesting that MMCs could be generalist cell type that performs multiple roles. We also found that the density of B cells but not T cells increased upon stimulation with protein antigen compared to polysaccharide antigen, suggesting B cell aggregation near MMCs is T-dependent. Overall, these results suggest that MMCs are generalist tissue structures, and the adaptive immune response may not depend on MMCs. Apart from antigen, this work also studied the effect of a common aquatic pollutant, copper (Cu) on MMC and stickleback splenic architecture. We found that the fraction of spleen occupied by MMCs is reduced upon dietary Cu exposure, however there was no change in MMC density/size or the red pulp/white pulp ratio. This work expands our current knowledge of stickleback immunobiology, characterizing MMCs and splenic lymphocyte organization in response to diverse antigens and environmental toxicants. Furthermore, the results in stickleback highlight the immunological diversity in fish and underscore the importance of studying immunity in diverse species.