AUTHOR=Pereira Suelen Bastos , Mattos Débora Passos de , Gonzalez Marcelo Salabert , Mello Cicero Brasileiro , Azambuja Patrícia , Castro Daniele Pereira de , Vieira Cecília Stahl 

TITLE=Immune signaling pathways in Rhodnius prolixus in the context of Trypanosoma rangeli infection: cellular and humoral immune responses and microbiota modulation

JOURNAL=Frontiers in Physiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2024.1435447

DOI=10.3389/fphys.2024.1435447

ISSN=1664-042X

ABSTRACT=<sec><title>Introduction</title><p><italic>Rhodnius prolixus</italic> is a hematophagous insect and one of the main vectors for <italic>Trypanosoma cruzi</italic> and <italic>Trypanosoma rangeli</italic> parasites in Latin America. Gut microbiota and insect immune responses affect <italic>T. cruzi</italic> and <italic>T. rangeli</italic> infection within triatomines. Particularly the Toll and IMD signaling pathways activations and how they orchestrate the antimicrobial peptides (AMPs) expressions in <italic>R. prolixus</italic>, especially when infected by <italic>T. rangeli</italic>.</p></sec><sec><title>Objectives</title><p>Examine how <italic>T. rangeli</italic> infection modulates <italic>R. prolixus</italic> cellular and humoral immunity and its impacts on insect microbiota.</p></sec><sec><title>Methods</title><p><italic>R. prolixus</italic> was fed on blood containing epimastigotes of <italic>T. rangeli</italic>, and infection was quantified in insect tissues. The gene expression of <italic>dorsal</italic>, <italic>cactus</italic>, <italic>relish</italic>, <italic>PGRP</italic>, and AMPs was examined in the midgut, fat body, and salivary glands by quantitative real-time PCR. Microbiota composition was analyzed using RT-q PCR targeting specific bacterial species. Hemocyte numbers and phenoloxidase activity were quantified to assess cellular immune responses.</p></sec><sec><title>Results</title><p><italic>T. rangeli</italic> infection modulated triatomine immunity in midgut and hemocoel, activating the expression of the NF-kB gene <italic>dorsal</italic>, associated with the Toll pathway; increasing expression of the gene encoding <italic>PGRP</italic> receptor, a component involved in the IMD pathway, both in the intestine and fat body; repressing the expression of the <italic>relish</italic> transcription factor, mainly in salivary glands. Among the <italic>R. prolixus</italic> AMPs studied, <italic>T. rangeli</italic> infection repressed all AMP gene expression, other than <italic>defensin C</italic> which increased mRNA levels. The PO activity was enhanced in the hemolymph of infected insects. <italic>T. rangeli</italic> infection did not induce hemocyte number alterations compared to control insects. However, an increase in hemocyte microaggregation was detected in infected insects.</p></sec><sec><title>Discussion</title><p><italic>R. prolixus</italic> recognizes <italic>T. rangeli</italic> infection and triggers humoral and cellular immune responses involving Toll pathway activation, <italic>defensin C</italic> synthesis, increased phenoloxidase activity, and enhanced hemocyte aggregation. On the other hand, <italic>T. rangeli</italic> infection suppressed some IMD pathway components, suggesting that, in <italic>R. prolixus</italic>, this pathway is involved in <italic>defensins A</italic> and <italic>B</italic> gene regulation. Importantly, these immune responses altered the bacterial microbiota composition, potentially favoring <italic>T. rangeli</italic> establishment in the insect vector.</p></sec>