Life and Health Sciences Research Institute, ICVS, School of Health Sciences, University of Minho, Braga, Portugal.
PLoS Negl Trop Dis. 2013 Jul 25;7(7):e2317. doi: 10.1371/journal.pntd.0002317. Print 2013.
Paracoccidioides brasiliensis causes paracoccidioidomycosis, one of the most prevalent systemic mycosis in Latin America. Thus, understanding the characteristics of the protective immune response to P. brasiliensis is of interest, as it may reveal targets for disease control. The initiation of the immune response relies on the activation of pattern recognition receptors, among which are TLRs. Both TLR2 and TLR4 have been implicated in the recognition of P. brasiliensis and regulation of the immune response. However, the role of TLR9 during the infection by this fungus remains unclear.
METHODOLOGY/PRINCIPAL FINDINGS: We used in vitro and in vivo models of infection by P. brasiliensis, comparing wild type and TLR9 deficient ((-/-)) mice, to assess the contribution of TLR9 on cytokine induction, phagocytosis and outcome of infection. We show that TLR9 recognizes either the yeast form or DNA from P. brasiliensis by stimulating the expression/production of pro-inflammatory cytokines by bone marrow derived macrophages, also increasing their phagocytic ability. We further show that TLR9 plays a protective role early after intravenous infection with P. brasiliensis, as infected TLR9(-/-) mice died at higher rate during the first 48 hours post infection than wild type mice. Moreover, TLR9(-/-) mice presented tissue damage and increased expression of several cytokines, such as TNF-α and IL-6. The increased pattern of cytokine expression was also observed during intraperitoneal infection of TLR9(-/-) mice, with enhanced recruitment of neutrophils. The phenotype of TLR9(-/-) hosts observed during the early stages of P. brasiliensis infection was reverted upon a transient, 48 hours post-infection, neutrophil depletion.
CONCLUSIONS/SIGNIFICANCE: Our results suggest that TLR9 activation plays an early protective role against P. brasiliensis, by avoiding a deregulated type of inflammatory response associated to neutrophils that may lead to tissue damage. Thus modulation of TLR9 may be of interest to potentiate the host response against this pathogen.
巴西副球孢子菌引起副球孢子菌病，是拉丁美洲最常见的系统性真菌病之一。因此，了解巴西副球孢子菌保护性免疫反应的特征很有意义，因为这可能揭示疾病控制的靶点。免疫反应的启动依赖于模式识别受体的激活，其中包括 TLRs。TLR2 和 TLR4 都被认为参与了巴西副球孢子菌的识别和免疫反应的调节。然而，TLR9 在该真菌感染过程中的作用尚不清楚。
方法/主要发现：我们使用巴西副球孢子菌的体外和体内感染模型，比较野生型和 TLR9 缺陷型（(-/-)）小鼠，以评估 TLR9 对细胞因子诱导、吞噬作用和感染结果的贡献。我们表明，TLR9 通过刺激骨髓来源的巨噬细胞表达/产生促炎细胞因子，也增加其吞噬能力，从而识别酵母形式或来自巴西副球孢子菌的 DNA。我们进一步表明，TLR9 在巴西副球孢子菌静脉感染后早期发挥保护作用，因为感染 TLR9(-/-)的小鼠在感染后前 48 小时内的死亡率高于野生型小鼠。此外，TLR9(-/-)小鼠表现出组织损伤和几种细胞因子（如 TNF-α和 IL-6）表达增加。在 TLR9(-/-)小鼠的腹腔内感染中也观察到细胞因子表达模式增加，中性粒细胞募集增加。在巴西副球孢子菌感染后 48 小时短暂耗尽中性粒细胞后，TLR9(-/-)宿主的表型得到逆转。
结论/意义：我们的结果表明，TLR9 的激活在巴西副球孢子菌感染早期发挥了保护作用，避免了与中性粒细胞相关的失调性炎症反应，从而可能导致组织损伤。因此，TLR9 的调节可能对增强宿主对这种病原体的反应具有重要意义。
