Innate immune recognition of Bartonella bacilliformis: TLR2/TLR4 expression and cytokine modulation

BackgroundConsider this Carrion's disease (CD) is a biphasic illness-comprising acute and chronic phases-endemic to Peru and caused by Bartonella bacilliformis, a bacterium transmitted by sandflies. Despite its clinical relevance, the mechanisms underlying innate immune activation in response to B. bacilliformis remain poorly understood. Toll-like receptors (TLRs) play a central role in recognizing conserved molecular patterns present in pathogens, thereby initiating innate immune responses. The present study aimed to describe the expression patterns of TLR2 and TLR4, along with cytokine secretion profiles, during peripheral blood mononuclear cells (PBMCs) exposure to B. bacilliformis.MethodsPeripheral blood mononuclear cells (PBMCs) from healthy donors were stimulated with heat-inactivated B. bacilliformis (ATCC 35685 strain), zymosan (TLR2 control), or E. coli LPS (TLR4 control). TLR2 and TLR4 gene expression was quantified by RT-qPCR at 0, 12, 24, 36, and 48 h. Cytokines were measured using a 17-plex panel. Analyses were descriptive, using non-parametric statistics.ResultsResults elicited measurable changes in the transcriptional expression of TLR2 and TLR4 during stimulation, with peak activation typically observed at 12 h, although in one case the maximal response was delayed to 24 h. These expression changes coincided with significant modulation of multiple cytokines, including pro-inflammatory mediators (TNF-α, IL-17, IL-12p70), Th1/Th2 cytokines (IFN-γ, IL-2, IL-5, IL-13), regulatory cytokines (IL-10), and growth factors (GM-CSF, IL-7).ConclusionsThis exploratory study describes the transcriptional expression patterns of TLR2 and TLR4 and the accompanying cytokine responses in PBMCs exposed to B. bacilliformis. These profiles expand current knowledge of the early innate immune signature elicited by this neglected pathogen and provide a foundation for future studies using receptor-specific functional assays. Importantly, these patterns likely reflect early innate immune response signatures rather than definitive evidence of functional receptor activation.