Investigations on the Function of Immune-like Cell Clusters in the Larval Lake Sturgeon Brain

Immune-like cells were observed within the brain ventricles of larval lake sturgeon (Acipenser fulvescens). Morphologically these cells appear to be dendritic and pigmented macrophage cell clusters, moving freely within the cerebrospinal fluid (CSF). Sturgeon hatch as eleutheroembryos with few differentiated organ systems, however these cell clusters are present at hatching in every lake sturgeon population we have examined. They appear to mimic melanomacrophage aggregate centers (MMC’s) observed in vertebrate liver, kidney and spleen tissue, where they function as an immune system component. MMC’s normally present with infection and encapsulate the pathogen. However, our aggregates of immune cells are being found in healthy populations from relatively pristine tributaries in the upper Great Lakes. We are continuing to characterize the molecular identity of these cell clusters to better understand their function. In early larval stages these clusters are freely moving in the CSF, but older specimens suggest an association with the hypothalamus, a region that integrates endocrine and nervous systems. Possibly this region could be “educating” the acquired immune system. Larval teleost fish have previously been used to investigate the origins of vertebrate immune system. Given that sturgeon are a more ancestral taxonomic group, they may yield significant information on this question.