TAGRA 2025

This microscopic study aims to characterize the structural organization of secondary encapsulated immune organs, specifically the spleen and lymph nodes, in the gray marmot (Marmota baibacina). The gray marmot serves as a principal reservoir in Central Asian plague foci and plays a critical role in zoonotic pathogen dynamics; however, its lymphoid anatomy remains poorly characterized. Previous ecological studies underscore the epidemiological significance of this species. Using light microscopy on fixed tissue samples from wild M. baibacina, the splenic parenchyma was observed to be organized into distinct white and red pulp compartments, consistent with typical mammalian secondary lymphoid architecture. The white pulp contains periarteriolar lymphoid sheaths and scattered lymphoid follicles, indicating active sites of antigen-driven lymphocyte proliferation. In contrast, the red pulp comprises a dense network of reticular cells and sinusoidal capillaries, facilitating blood filtration and immune cell trafficking. This structural organization closely parallels that observed in other mammalian species. Lymph nodes exhibit classical histoarchitecture, being encapsulated by dense connective tissue and comprising cortical regions with B-cell follicles and germinal centers, as well as paracortical T-cell zones. The reticular stromal framework supports lymphocyte compartmentalization and likely facilitates antigen presentation. Considering the relatively large body size of M. baibacina, it is inferred that lymph nodes are relatively few in number but well-developed, reflecting scaling patterns of adaptive immune responses across mammals. These morphological insights provide a foundational understanding of the gray marmot’s immune system. Further immunohistochemical and functional investigations are warranted to delineate lymphocyte subpopulations, activation states, and immunological implications for plague ecology in this species.