Coelomocyte populations in the sea urchin, Strongylocentrotus purpuratus, undergo dynamic changes in response to immune challenge

Abstract

The sea urchin, Strongylocentrotus purpuratus has seven described populations of distinct coelomocytes in the coelomic fluid that are defined by morphology, size, and for some types, by known functions. Of these subtypes, the large phagocytes are thought to be key to the sea urchin cellular innate immune response. The concentration of total coelomocytes in the coelomic fluid increases in response to pathogen challenge. However, there is no quantitative analysis of how the respective coelomocyte populations change over time in response to immune challenge. Accordingly, coelomocytes collected from immunoquiescent, healthy sea urchins were evaluated by flow cytometry for responses to injury and to challenge with either heat-killed Vibrio diazotrophicus, zymosan A, or artificial coelomic fluid, which served as the vehicle control. Responses to the initial injury of coelomic fluid collection or to injection of V. diazotrophicus show significant increases in the concentration of large phagocytes, small phagocytes, and red spherule cells after one day. Responses to zymosan A show decreases in the concentration of large phagocytes and increases in the concentration of small phagocytes. In contrast, responses to injections of vehicle result in decreased concentration of large phagocytes. When these changes in coelomocytes are evaluated based on proportions rather than concentration, the respective coelomocyte proportions are generally maintained in response to injection with V. diazotrophicus and vehicle. However, this is not observed in response to zymosan A and this lack of correspondence between proportions and concentrations may be an outcome of clearing these large particles by the large phagocytes. Variations in coelomocyte populations are also noted for individual sea urchins evaluated at different times for their responses to immune challenge compared to the vehicle. Together, these results demonstrate that the cell populations in sea urchin immune cell populations undergo dynamic changes in vivo in response to distinct immune stimuli and to injury and that these changes are driven by the responses of the large phagocyte populations.

Recombinant SpTransformer proteins are functionally diverse for binding and phagocytosis by three subtypes of sea urchin phagocytes

“…The results presented here suggest new and noteworthy information regarding the three types phagocytes and their capacities to interact with the different rSpTrf proteins cross-linked to beads. i) Polygonal phagocytes have been noted with more than 70 associated beads and are the major phagocytic cell in sea urchins, in agreement with a previous report ( 75 ). They show specificity for binding and phagocytosis for a subset of rSpTrf proteins cross-linked to beads, which infers specificity for binding specific natSpTrf proteins in the CF.…”

“…The large phagocytes in S. purpuratus are the major types of coelomocytes in the CF, making up 40% to 80% of the cells (reviewed in ( 64 )). These cells respond to immune challenges and have been characterized as the cells that govern cellular immune responses in the purple sea urchin ( 75 ). The polygonal and discoidal phagocytes are distinct cell types with different cytoskeletal morphologies ( 61 ).…”

“…Of the four classes of sea urchin phagocytes, the polygonal and discoidal cells – or the large phagocytes – have generally been evaluated together and considered as a group as the major immune response cells in S. purpuratus ( 75 ). However, the activities of the large phagocytes presented here clearly differentiates the functions of these two types of cells.…”

Temperature influences immune cell development and body length in purple sea urchin larvae

“…Similar to the S. purpuratus larval stage, the adult purple sea urchin has a complex immune system that responsive to environmental change and is mediated by a heterogeneous suite of coelomocytes (Barela Hudgell et al, 2022; Matranga et al, 2000, 2005; Rast et al, 2006; L. C. Smith et al, 2006). In response to temperature stress, coelomocytes increase in concentration (particularly red sphere cells and phagocytes) (Branco et al, 2012) and upregulate heat shock proteins (Matranga et al, 2000).…”

Stable germline transgenesis using theMinosTc1/marinerelement in the sea urchin,Lytechinus pictus

“…Examples include the discovery of cyclins (1), which ultimately led to currently approved drugs targeting metastatic cancers (2), and the first descriptions of gene regulatory networks (3,4), which have become a foundational framework for understanding development (5)(6)(7). Sea urchins remain favorites for study across diverse fields including gene regulation of development (8)(9)(10), innate immunity (11)(12)(13)(14)(15)(16), biomineralization (17)(18)(19)(20)(21), nervous system development (22)(23)(24), reproduction (25)(26)(27), and developmental physiology (28)(29)(30).…”