TLR-2, TLR-4 and dectin-1 expression in human monocytes and neutrophils stimulated by Paracoccidioides brasiliensis

Paracoccidioidomycosis (PCM) is an endemic mycosis in Latin America caused by the dimorphic fungus Paracoccidioides brasiliensis. The pattern of the immune responses to P. brasiliensis determines the disease progression and clinical outcome. Innate immune response is mediated by phagocytic cells, such as macrophage and neutrophils, which ingest and kill invading pathogens and then trigger the adaptive immune system through the secretion of cytokines and chemokines. The C-type like lectin receptors (CLR) and Toll-like receptors (TLRs) are the two main pattern recognition receptors in phagocytic cells that recognize fungal components. Therefore, the purpose of the present study was to evaluate the expression of TLR-1, TLR-2, TLR-4 and dectin-1 (CLR) in monocytes and neutrophils from healthy individuals after stimulation with Pb18 (high virulence) and Pb265 (low virulence) yeasts of P. brasiliensis. As positive controls we used specific ligands to TLR-4 (LPS), TLR-2 and dectin-1 (zymosan). Our results demonstrated a decreased of TLRs and dectin-1 expression mainly on monocytes as opposes on neutrophils, as soon as 30 minutes after yeast cells stimulation. This decrease was similar to the one caused by zymosan stimulation and indicates that up binding the complexes are rapidly internalized. There was a tendency towards an increased TLR2 and dectin-1 mRNA expression in response to fungal cells, mainly to Pb265. P. brasiliensis yeast cells induced the production of pro-inflammatory and anti-inflammatory cytokines, but the low ratio between TNF-alpha and IL-10 in response to zymosan and Pb265 indicates a balanced production of IL-10 and TNF-alpha, while Pb18 predominantly induced TNF-alpha secretion. Fungal cells also induced an elevated production of PGE(2) by monocytes and neutrophils showing their potential to provoke an intense inflammatory response. Altogether our results suggest the participation of TLR2, TLR-4 and dectin-1 in P. brasiliensis recognition, internalization and consequent activation of the immune response against the fungus. Moreover, the preferential recognition of zymosan and Pb265 by TLR-2 and dectin-1 would result in the production of adequate concentration of IL-10, which would be able to counterbalance the excessive inflammatory response mediated by TNF-alpha and PGE2. With these attributes the low virulence strain of P. brasiliensis would induce a controlled immune response beneficial to the host.