Meeting Abstract
The sea cucumber Parastichopus californicus undergoes an annual cycle of visceral atrophy and regeneration. The trigger(s) of this process and evolutionary advantages are unknown. One hypothesis is that replacement of the gut may allow P. californicus to eliminate a dangerously high load of pathogenic bacteria, and permit repopulation by beneficial species. The ability to regenerate has been linked to the immune system in many species, including holothurians. However, the immune system of P. californicus has not been characterized during the cycle of visceral atrophy and regeneration. To better understand this species’ immune system, we collected coelomic fluid samples from adult animals during the summer (all viscera present), fall (viscera degenerated), and winter (viscera regenerating) to examine coelomocyte and immunoenzyme concentrations. Additionally, during the summer and fall, adult P. californicus were injected with citrated sheep red blood cells to elicit an immune response. We found that the concentration of coelomocytes and immunoenzymes is lower in this species than in other holothurians. The general immune response of P. californicus differs depending on the season/visceral regeneration state. Specifically, this species’ ability to respond to immune challenge in the fall appears to be stunted (lower coelomocyte concentrations for all subpopulations during this season) when compared to the response in summer. This immunosuppression could occur for two reasons. First, there is less energy available to put into the immune system because P. californicus has a reduction in metabolic rate when the viscera are atrophied. Second, coelomocytes make arise from the lumen of the respiratory trees and so this organ’s degeneration during the fall could inhibit the creation of new immune cells.
