Identification of the gene repertoire of the IMD pathway and expression of AMP genes in several tissues and hemolymph of the cockroach Blattella germanica

An essential component of the immune system in the German cockroach Blattella germanica is the expression of antimicrobial peptide genes, which besides its role killing pathogenic bacteria could be involved in the control of the symbiotic system that coexist in the insect (endosymbiont and microbiota). Their expression is triggered by several signaling pathways, being immune deficiency the most relevant. The immune deficiency pathway was active in the adult female transcriptomes of six tissues and hemolymph, which contains immune cells called hemocytes. The total expression of antimicrobial peptide genes was also analyzed, finding that it was very high in hemolymph and salivary glands and much lower in foregut, midgut, hindgut, Malpighian tubules and fat body. The expression of antimicrobial peptide genes in salivary glands could help control pathogens ingested with food and even determine the composition of the gut microbiota. Furthermore, this would explain the low expression levels in midgut and hindgut, probably related with the presence of beneficial microbiota. On the other hand, the low expression of antimicrobial peptide genes in fat body could be related with the presence of the bacterial endosymbiont Blattabacterium cuenoti, which is harbored inside specialized cells called bacteriocytes.