The innate immune system has been shown to play an important pathologic role in systemic lupus erythematosus (SLE). TLR2, a PRR, recognizes exogenous PAMPs, and endogenous damage-associated molecular patterns and has been implicated in the initiation and maintenance of the perpetuated inflammatory reactions in autoimmune diseases. Here, we report increased expression of TLR2 in CD4+ and CD8 + T cells, CD19 + B cells, and CD14 + monocytes from SLE patients. Conventional treatment, such as hydroxychloroquine and corticosteroids, showed no effect on TLR2 expression in CD4 + T cells from SLE patients. In vitro stimulation of TLR2 in CD4 + T cells from SLE patients increased CD40L and CD70 expression, as well as secretion of IL-6, IL-17A, IL-17F, and TNF-α, while Foxp3 transcription decreased. This effect was reversed by TLR2 siRNA. Moreover, TLR2 activation upregulated H3K4 tri-methylation and H4 acetylation levels while downregulated H3K9 tri-methylation level in the IL-17A promoter region. In addition, it also increased H4 acetylation levels and decreased H3K9 tri-methylation levels in the IL-17F promoter region. In summary, our findings demonstrate that increased expression of TLR2 contributes to immune reactivity and promotes IL-17A and IL-17F expression through histone modifications in SLE.Keywords: Histone modification r IL-17 r Systemic lupus erythematosus r T cells r TLR2
IntroductionSystemic lupus erythematosus (SLE) is a prototypical systemic autoimmune disease that results in multiple organ damage and diverse clinical manifestations [1]. SLE is characterized by T-cell hyperactivity and B-cell overstimulation. Uncontrolled T-cell activation results in increased secretion of inflammatory cytokines, production of autoantibodies, and aberrant inflamCorrespondence: Prof. Qianjin Lu e-mail: qianlu5860@gmail.com matory response, which contribute to the development of SLE [2]. How T cells become hyperactive during SLE remains to be determined. However, both genetic background and environmental factors are believed to contribute to the development of SLE [3]. A number of epidemiological studies have suggested that onset and flares of SLE are associated with infection [4]. One of the mechanisms whereby invasive microorganisms disrupt host immune system is through the interaction with TLRs, as demonstrated in experimental lupus [5,6]. * These authors contributed equally to this work. Eur. J. Immunol. 2015. 45: 2683-2693 TLRs are membrane-bound proteins referred to as pathogenassociated molecular patterns that belong to innate immune system. Each TLR can recognize a specific set of microbes bearing PAMPs and endogenous damage-associated molecular patterns (DAMPs) [7]. Activation of TLRs can trigger intracellularsignaling cascades and upregulate the expression of inflammatory cytokines [8]. TLR2 is a cell-surface TLR with extracellular recognition domain that can bind with exogenous ligands including lipoproteins, peptidoglycan, lipoteichoic acid, and endogenous DAMPs, such as HSP70 and high mobility group box protei...