Pre-induction of Hsp70 expression to protect the grooved carpet shell clam, Ruditapes decussatus, against Micrococcus luteus: A trained immunity strategy

Abstract

Bacterial pathogens cause disease-associated mortality in Ruditapes decussatus, a model bivalve for aquaculture in Egypt. In this study, it was hypothesized that trained immunity could be achieved to enhance disease resistance against Micrococcus luteus by pre-inducing Hsp70 expression. Clams were challenged via a seawater bath with M. luteus at various concentrations (2.5 × 104, 5.0 × 104, and 7.5 × 104 CFU/ml), gill Hsp70 was quantified using ELISA and infected clams were compared to controls in two experiments (with one 17-day and two 17-day infection periods separated by a 7-day depuration period for recovery, respectively). Infection with M. luteus significantly altered Hsp70 expression compared to the control levels. Downregulation occurred at low concentrations and upregulation at the two higher concentrations. When used in the trained immunity trial, Hsp70 upregulation occurred in infected clams during the first infection and persisted during the 7-day recovery. Re-infection led to the increase of Hsp70 levels, which reached maximum values, and enhanced survival. The results confirmed that Hsp70 is involved in the immune response and disease resistance by protecting R. decussatus against re-infection with M. luteus. These results suggested the use of trained immunity as disease control strategy.