Trichophyton rubrum manipulates the innate immune functions of human keratinocytes

Abstract

Evasion or subversion of host immune responses have been shown for a variety of microorganisms, and this might be the case for Trichophyton rubrum, the most common pathogenic fungus causing chronic dermatophytosis in humans. Keratinocytes, the main epidermal cells, have important roles as a first defense against microbial challenges in local immune reactions. Epidermal keratinocytes express several Toll-like receptors and produce host defense peptides, cytokines and chemokines in response to various stimuli. We analyzed the expression of Toll-Like receptor TLR2, TLR4, TLR6, and Human Beta Defensin (HBD)-1, HBD-2, Interleukin IL-1b and IL-8 production, when exposing primary keratinocyte cultures to T. rubrum. We observed changes in size and granularity of keratinocytes stimulated with either whole conidia or conidial homogenates compared to other treatments. Intact conidia decreased keratinocytes’ TLR2 and TLR6 expression without affecting that of TLR4, while conidial homogenates increased the expression of these three receptors. Interestingly, whole conidia decreased HBD-1 and HBD-2 production, whereas conidial homogenate increased it. No changes were observed in IL-1b and IL-8 production after stimulation with conidia or conidial homogenate. CONCLUSIONS. Our results suggest that: 1) Keratinocytes can recognize and respond to cell wall components of T. rubrum; 2) Viable intact conidia inhibit TLR-2 and TLR6 expression and decrease HBD-1 and HBD-2 production; 3) Conidial homogenate from T. rubrum increases the expression of TLR2, TLR4 and TLR6 and induces HBD-1 and HBD-2 production; 4) Therefore, innate immune functions of keratinocytes as the first level of local skin immunity are apparently manipulated by T. rubrum, likely to ensure its establishment, persistence and survival.

Toll-Like Receptors (Tlr) 2 and 4 Expression of Keratinocytes From Patients With Localized and Disseminated Dermatophytosis

“…GARCÍA-MADRID et al (2011) showed that keratinocytes can recognize and respond to cell wall components of T. rubrum . Viable intact conidia inhibited TLR2 and TLR6 expression by cultured human keratinocytes while conidial homogenate from T. rubrum increased the expression of TLR2, TLR4 and TLR6 7 . Recently, YUKI et al 27 demonstrated that TLR2 activation enhances tight junctions among keratinocytes, a crucial step in maintaining the functional activity of epidermal barriers against infective agents, such as bacteria or fungi.…”

“…About 90% of chronic dermatophyte infections are caused by T. rubrum and T. mentagrophytes 8 , 9 , possibly because these organisms may suppress inflammation and cell-mediated immunity 7 .…”

“…Although it is known if certain elements of the fungal wall increase TLR expression upon recognition by these receptors, a previous in vitro study demonstrated that whole Trichophyton rubrum conidia could diminish TLR expression on a keratinocyte cell line 7 . However, there are few studies on human immune response to dermatophytes.…”

Extracellular Vesicles From the Dermatophyte Trichophyton interdigitale Modulate Macrophage and Keratinocyte Functions

“…Given that Trichophyton rubrum interacts with TLR2 and TLR4 on antigen-presenting cells and promotes cytokines production ( 30 ), we evaluated the relevance of TLR2 and TLR4 in the production of inflammatory mediators induced by T. interdigitale EVs. We stimulated BMDMs obtained from WT, TLR2 −/− , or TLR4 −/− mice with T. interdigitale EVs for 48 h and quantified the levels of TNF-α and IL-6 in the cell supernatants.…”

Análise da expressão dos receptores toll-like 2 e 4 nos queratinócitos dos doentes portadores de dermatofitoses localizadas e dermatofitoses extensas causadas por Trichophyton rubrum

“…Os TLRs 2 e 4 foram descritos na resposta imune às doenças fúngicas, participando da eliminação do patógeno e na imunomodulação da resposta de defesa do hospedeiro (Romani, 2004). Estudo recente em cultura de células mostrou que apesar de homogeneizados de parede fúngica serem capazes de aumentar a expressão de alguns TLRs, conídeos com parede íntegra falharam em fazê-lo (García-Madrid et al, 2011). Com intuito de verificar a expressão epidérmica destes receptores durante a infecção em indivíduos com dermatofitoses, desenhou-se este estudo.…”