Immune Tolerance in Mytilus galloprovincialis Hemocytes After Repeated Contact With Vibrio splendidus

Abstract

Mediterranean mussels ( Mytilus galloprovincialis ) are sessile filter feeders that live in close contact with numerous marine microorganisms. As is the case in all invertebrates, mussels lack an adaptive immune system, but they respond to pathogens, injuries or environmental stress in a very efficient manner. However, it is not known if they are able to modify their immune response when they reencounter the same pathogen. In this work, we studied the transcriptomic response of mussel hemocytes before and after two consecutive sublethal challenges with Vibrio splendidus . The first exposure significantly regulated genes related to inflammation, migration and response to bacteria. However, after the second exposure, the differentially expressed genes were related to the control and inhibition of ROS production and the resolution of the inflammatory response. Our results also show that the second injection with V. splendidus led to changes at the transcriptional (control of the expression of pro-inflammatory transcripts), cellular (shift in the hemocyte population distribution), and functional levels (inhibition of ROS production). These results suggest that a modified immune response after the second challenge allowed the mussels to tolerate rather than fight the infection, which minimized tissue damage.

Shift in Immune Parameters After Repeated Exposure to Nanoplastics in the Marine Bivalve Mytilus

“…In the mussel M. galloprovincialis, increased bactericidal activity was observed after in vivo and subsequent in vitro challenge with Vibrio anguillarum (26). Recent transcriptomics data obtained in M. galloprovincialis hemocytes after repeated challenge with Vibrio splendidus demonstrated a shift from a pro-inflammatory response to an anti-inflammatory and probably regenerative phenotype, indicating the existence of a secondary immune response in mussels oriented to tolerate infection (56).…”

Hemocytes released in seawater act as Trojan horses for spreading of bacterial infections in mussels

“…This possibility leads us to consider that mussel beds have their own immune repertoire and can develop some kind of a “herd immunity”. On the other hand, it may also be involved in the development of immune tolerance against specific bacteria, a form of immune memory of the innate response that has been highlighted following a secondary exposure of Mytilus galloprovincialis to Vibrio splendidus 40 . Such tolerance would favor systemic homeostasis with the goal of preserving energy, as suggested by studies in corrals 41 .…”

Vibrio–bivalve interactions in health and disease

“…In agreement, in M . galloprovincialis infected with LGP32, hemocytes show an altered expression of genes involved in innate immune response, inflammatory response, cell migration and defence responses to bacteria (Rey‐Campos et al ., 2019). Although less documented, cellular interactions of LGP32 with M .…”

“…Expression of Vibrio diseases depends on host factors, essentially host genetics (species, population), life stage (larval, juvenile or adult form) and life‐history traits, e.g. co‐infection by other pathogens (viruses as for example), the weakening of immune capacity due to environmental stressors (Zannella et al ., 2017), or immune priming following the previous encounter with vibrios (Zhang et al ., 2014; Rey‐Campos et al ., 2019).…”