Immune signaling pathways in in the context of infection: cellular and humoral immune responses and microbiota modulation.

Introduction: is a hematophagous insect and one of the main vectors for and parasites in Latin America. Gut microbiota and insect immune responses affect and infection within triatomines. Particularly the Toll and IMD signaling pathways activations and how they orchestrate the antimicrobial peptides (AMPs) expressions in , especially when infected by .

Objectives: Examine how infection modulates cellular and humoral immunity and its impacts on insect microbiota.

Methods: was fed on blood containing epimastigotes of , and infection was quantified in insect tissues. The gene expression of , , , , 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.

Results: infection modulated triatomine immunity in midgut and hemocoel, activating the expression of the NF-kB gene , associated with the Toll pathway; increasing expression of the gene encoding receptor, a component involved in the IMD pathway, both in the intestine and fat body; repressing the expression of the transcription factor, mainly in salivary glands. Among the AMPs studied, infection repressed all AMP gene expression, other than which increased mRNA levels. The PO activity was enhanced in the hemolymph of infected insects. infection did not induce hemocyte number alterations compared to control insects. However, an increase in hemocyte microaggregation was detected in infected insects.

Discussion: recognizes infection and triggers humoral and cellular immune responses involving Toll pathway activation, synthesis, increased phenoloxidase activity, and enhanced hemocyte aggregation. On the other hand, infection suppressed some IMD pathway components, suggesting that, in , this pathway is involved in and gene regulation. Importantly, these immune responses altered the bacterial microbiota composition, potentially favoring establishment in the insect vector.