Methylation on RNA: A Potential Mechanism Related to Immune Priming within But Not across Generations

Abstract

Recent evidence suggests that invertebrates have properties that resemble vertebrate immune memory (Contreras-Garduño et al., 2016; Milutinović and Kurtz, 2016). The process has been termed immune priming, and it refers to enhanced protection (i.e., resistance, immune response, and survival) to a pathogen or parasite in a second encounter after a first specific exposure (Kurtz and Franz, 2003; Little and Kraaijeveld, 2004; Kurtz, 2005). This phenomenon has been reported in ctenophores, sponges, mollusks, crustaceans and insects, among others (Milutinović and Kurtz, 2016). Within generations, immune priming is strain or species specific (Roth et al., 2009) and long lasting (it can persist across different life developmental stages; Thomas and Rudolf, 2010). In addition, immune priming not only occurs within generations but also across generations: parents can protect their offspring against the same parasites or pathogens that they confronted (Sadd and Schmid-Hempel, 2007). In bumble bees (Bombus terrestris), when the parental colony was either injected with lipopolysaccharides diluted in Ringer’s solution (primed group) or injected with Ringer’s solution (Control group); the male offspring derived from the primed group exhibited more phenoloxidase activity than the control group offspring (Moret and Schmid-Hempel, 2001). In another study, female bumblebees that were challenged with heat-killed bacteria produced eggs with more antimicrobial activity than eggs of non-challenged control females (Sadd and Schmid-Hempel, 2007). Immune priming across generations has been documented in both wild and laboratory populations (Tate and Graham, 2015) and such changes can be transmitted by either insect mothers or fathers (Roth et al., 2009). This suggests that some information is passed from parents to offspring but the mechanism remains understood.