Immune defence mechanisms of triatomines against bacteria, viruses, fungi and parasites

Abstract

Triatomines are vectors that transmit the protozoan haemoflagellate Trypanosoma cruzi, the causative agent of Chagas disease. The aim of the current review is to provide a synthesis of the immune mechanisms of triatomines against bacteria, viruses, fungi and parasites to provide clues for areas of further research including biological control. Regarding bacteria, the triatomine immune response includes antimicrobial peptides (AMPs) such as defensins, lysozymes, attacins and cecropins, whose sites of synthesis are principally the fat body and haemocytes. These peptides are used against pathogenic bacteria (especially during ecdysis and feeding), and also attack symbiotic bacteria. In relation to viruses, Triatoma virus is the only one known to attack and kill triatomines. Although the immune response to this virus is unknown, we hypothesize that haemocytes, phenoloxidase (PO) and nitric oxide (NO) could be activated. Different fungal species have been described in a few triatomines and some immune components against these pathogens are PO and proPO. In relation to parasites, triatomines respond with AMPs, including PO, NO and lectin. In the case of T. cruzi this may be effective, but Trypanosoma rangeli seems to evade and suppress PO response. Although it is clear that three parasite-killing processes are used by triatomines - phagocytosis, nodule formation and encapsulation - the precise immune mechanisms of triatomines against invading agents, including trypanosomes, are as yet unknown. The signalling processes used in triatomine immune response are IMD, Toll and Jak-STAT. Based on the information compiled, we propose some lines of research that include strategic approaches of biological control.

Humoral and cellular immune responses induced by the urease-derived peptide Jaburetox in the model organism Rhodnius prolixus

“…Cecropin-like and lysozyme activities are humoral responses that occur mainly upon bacterial challenge, although lysozyme activity is also related to other types of pathogens (parasites for example, reviewed in [ 67 ]). As shown in Fig.…”

Estudio de componentes hemolinfáticos de Rhodnius prolixus y Triatoma maculata alimentados con diferentes fuentes sanguíneas

“…En una revisión reciente se destaca que es escasa la información acerca de la respuesta inmune de los triatominos a patógenos, tanto en términos cualitativos de la descripción de la maquinaria de defensa de estos insectos ante sus agentes patógenos, o cuantitativos, al conocerse apenas información en no más de 10 especies 44 de las aproximadamente 148 especies de triatominos descritas 45,46 . Aunque son abundantes los estudios sobre cómo afecta la fuente de alimentación sobre parámetros biodemográficos en triatominos, como lo muestran Rabinovich, et al 47 en una revisión extensa sobre los patrones ecológicos y las fuentes de alimentación, no se ha reportado información acerca de cómo inciden las fuentes de alimentación sobre el sistema inmune, pese a ser éste un componente importante de la competencia vectorial.…”

Redox Balance Keepers and Possible Cell Functions Managed by Redox Homeostasis in Trypanosoma cruzi

“…Other enzymes, namely dual oxidase (DUOX) and NADPH oxidase (NOX), produce superoxide radical (O 2 • − ), and the latter can dismutate to hydrogen peroxide (H 2 O 2 ) or react with nitric oxide (NO) to produce peroxynitrite (ONOO − ) (Ha et al, 2005;Azambuja et al, 2016). The phenoloxidase (PO) cascade, a hallmark immune component of insects, is also present in triatomines leading to the production of toxic quinones, melanin, and some intermediates of reactive oxygen species (ROS) and reactive nitrogen species (RNS) to encapsulate and kill the pathogens (reviewed in Flores-Villegas et al, 2015). PO activity was increased after vector infection with T. cruzi Dm28c strain though it had no effect on parasite viability (Castro et al, 2012), and therefore, its function as a driver of innate immunity against T. cruzi was not established.…”