Heat stress increases immune cell function in Hexacorallia

Abstract

Climate change induced heat stress has increased coral bleaching events worldwide. Differentially regulated immune genes are one of the primary responses to heat stress suggesting that immune activation is critical. However, the cellular immune mechanisms of coral bleaching is currently unknown, and it is still not known if the immune response documented during heat stress is a consequence of bleaching or is directly caused by the heat stress itself. To address this question, we have used two model system sea anemones (Order: Actiniaria): Exaiptasia diaphana and Nematostella vectensis. E. diaphana is an established sea anemone model for algal symbiont interaction, while N. vectensis is an established sea anemone model that lacks the algal symbiont. Here, we examined the effect of increased temperature on phagocytic activity, as an indication of immune function. Our data shows that immune cell activity increases during heat stress, while small molecule pinocytosis remains unaffected. We observed an increase in cellular production of reactive oxygen species with increasing temperatures. We also found that the cellular immune activity was not affected by the presence of the Symbiodiniaceae. Our results suggest that the immune activity observed in heat-stress induced bleaching in corals is a fundamental and basic response independent of the bleaching effect. These results establish a foundation for improving our understanding of hexacorallian immune cell biology, and its potential role in coral bleaching.

Short-Term Thermal Stress Affects Immune Cell Features in the Sea Urchin Paracentrotus lividus

“…Phagocytosis, encapsulation, and the production of ROS and RNS are the most widespread mechanisms by which the immune cells of invertebrates react under conditions of defense against pathogens and stressors [ 42 ]. In the sea anemones Exaiptasia diaphana and Nematostella vectensis , overnight exposure to 30 °C (moderate HS) increased phagocytic activity and immune gene expression together with cellular ROS production compared to the ambient temperature (18 °C) [ 43 ]. In the present study, we focused on the production of ROS and on the effects related to it, such as lipid peroxidation.…”

Starvation differentially affects gene expression, immunity and pathogen susceptibility across symbiotic states in a model cnidarian

“…Like Aiptasia, the facultatively symbiotic coral O. arbuscula shows an upregulation of immune response pathways under starvation. Moreover, thermal challenges have been shown to upregulate NF-κB transcripts in symbiotic anemones [39,46] and in multiple species of symbiotic coral [47,48]. Thus, it appears that NF-κB has different roles in cnidarians existing with versus without symbionts.…”

Nutrient deprivation differentially affects gene expression, immunity, and pathogen susceptibility across symbiotic states in a model cnidarian

“…Similar to Aiptasia, the facultative coral O. arbuscula also shows an upregulation of immune response pathways in starved conditions. Moreover, thermal challenges, which have been well-documented to induce symbiont cell loss 8,23,61,62 , have been shown to upregulate NF-κB transcripts in not only symbiotic anemones 51,63 , but also in multiple species of symbiotic coral 64,65,66,67 . Thus, it appears that NF-κB has different biological roles in cnidarians that normally exist with vs. without symbionts.…”