Characterization of immune responses to bacterial stimulation in the Anopheles gambiae complex

Abstract

Anopheles arabiensis, An. merus and An. quadriannalatus are three zoophilic members of the An. gambiae complex that occur in southern Africa that differ in vector competence. They are considered as major, minor, and non-vector, respectively. This study aimed to characterise the molecular underpinnings of the immune responses in these species in response to bacterial challenges. Furthermore, it assessed whether the insecticide resistant phenotype affects these responses. This was achieved by assessing the global epigenetic landscape and the expression levels of transcripts for defensin-1 and gambicin antimicrobial peptide genes in response to Streptococcus pyogenes and Escherichia coli challenges. The epigenetic markers 5mC, 5hmC and m6A methylation levels were assessed by ELISA. Histone Acetyl Transferase activity was assessed calorimetrically. The transcript levels of defensin-1 and gambicin were assessed by qRT-PCR. Immune priming was examined in An. arabiensis. Species-specific differences in 5mC and m6A levels, as well as defensin-1 and gambicin transcript levels were observed, constitutively and post-immune stimulation. The minor/non-vectors had similar patterns that were different from major vectors. At the constitutive level, there were no differences in the epigenetic landscape and expression of antimicrobial peptide transcripts in insecticide resistant and susceptible An. arabiensis. Blood-borne immune priming was an efficient means of inducing immunological memory. Larval immune priming induced immunological memory in a species-specific manner, with a fitness cost in insecticide resistant An. arabiensis. Although larval immune priming effects induced transgenerational immunological memory, insecticide susceptible An. arabiensis maintained the immunological memory to a greater degree. This study highlights variation in immune responses in the members of the An. gambiae complex and the presence of immunological memory.