Systemic effector and regulatory immune responses to chlamydial antigens in Trachomatous Trichiasis

Original Research Article published: 10 February 2011 doi: 10.3389/fmicb.2011.00010 Systemic effector and regulatory immune responses to chlamydial antigens in trachomatous trichiasis Alevtina Gall 1, Amir Horowitz 2, Hassan Joof 1, Angels Natividad 3, Kevin Tetteh4, Eleanor Riley 2, Robin L. Bailey 3, David C. W. Mabey 3 and Martin J. Holland 1,3* Viral Diseases Programme, Medical Research Council Laboratories, Banjul, The Gambia Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, UK 3 Department of Clinical Research, London School of Hygiene and Tropical Medicine, London, UK 4 Department of Pathogen Molecular Biology, London School of Hygiene and Tropical Medicine, London, UK 1 2 Edited by: Rey Carabeo, Imperial College London, UK Reviewed by: Kathleen Kelly, University of California at Los Angeles, USA Toni Darville, University of Pittsburgh Medical Center, USA *Correspondence: Martin J. Holland, Department of Clinical Research, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK. e-mail: Trachomatous trichiasis (TT) caused by repeated or chronic ocular infection with Chlamydia trachomatis is the result of a pro-fibrotic ocular immune response. At the conjunctiva, the increased expression of both inflammatory (IL1B, TNF) and regulatory cytokines (IL10) have been associated with adverse clinical outcomes. We measured in vitro immune responses of peripheral blood to a number of chlamydial antigens. Peripheral blood effector cells (CD4, CD69, IFNγ, IL-10) and regulatory cells (CD4, CD25, FOXP3, CTLA4/GITR) were readily stimulated by C. trachomatis antigens but neither the magnitude (frequency or stimulation index) or the breadth and amount of cytokines produced in vitro [IL-5, IL-10, IL-12 (p70), IL-13, IFNγ, and TNFα] were significantly different between TT cases and their non-diseased controls. Interestingly we observed that CD4+ T cells account for <50% of the IFNγ positive cells induced following stimulation. Further investigation in individuals selected from communities where exposure to ocular infection with C. trachomatis is endemic indicated that CD3−CD56+ (classical natural killer cells) were a major early source of IFNγ production in response to C. trachomatis elementary body stimulation and that the magnitude of this response increased with age. Future efforts to unravel the contribution of the adaptive immune response to conjunctival fibrosis should focus on the early events following infection and the interaction with innate immune mediated mechanisms of inflammation in the conjunctiva. Keywords: Chlamydia trachomatis, trachoma, immune response, Tregs, NK cells, interferon-gamma Introduction Chlamydia trachomatis is the leading infectious cause of blindness worldwide. Persistent infection or recurrent infection with C. trachomatis, can stimulate a fibrotic immune response that leads to deposition of scar tissue on the upper tarsal conjunctiva and the development of a dry eye syndrome. The progressive development of scar tissue can lead to entropion and trachomatous trichiasis (TT), which if left untreated may result in damage to the cornea causing opacity, low vision, and blindness (Mabey et al., 2003). There are an estimated eight million individuals currently suffering from TT with about 1.3 million irreversibly blind as a result (Mariotti et al., 2009). Chlamydia trachomatis is also the most common bacterial sexually transmitted infection. It is frequently asymptomatic, especially in women and can lead to sub-fertility, chronic pelvic inflammatory disease, ectopic pregnancy, and sterility (WHO, 2007). Although both ocular and genital chlamydial infections are treatable with antibiotics, persistent, and recurring infection is common. A licensed vaccine against C. trachomatis for use in the human population is not yet available despite continued efforts since the 1960s. Recent developments (reviewed by Rockey et al., 2009) have yielded encouraging results in some animal models; however, the development of an effective vaccine requires further understanding of the basic features of the human immune response to C. trachomatis www.frontiersin.org infection. Indeed work in mice has suggested that chlamydial vaccine induced immunity without pathology can be achieved and this is distinct from immunity induced by infection that results in pathology (Igietseme et al., 2009). However in naturally exposed populations only a minority develops the pathological sequelae of infection, suggesting that the immunological features of naturally immune individuals may be equally distinct. In animal models of infection it is well established that CD4+ T helper type 1 (Th1) cells are essential for the clearance of primary chlamydial infection (Igietseme et al., 2009). In particular, IFNγ plays an important role in the clearance of chlamydial infection. In mice and in humans its production is associated with protection from re-infection (Wang et al., 1999; Cohen et al., 2005). However, uncontrolled inflammatory responses, in part driven by IFNγ production, result in pathology. Regulatory T cells (Tregs), induction of regulatory cytokines such as IL-10 or the activation of type 2 (Th2) responses counteract the inflammatory environment and contribute to restoring homeostasis (Yang et al., 1999; Wang et al., 2005). Conversely unchecked type 2 responses are frequently associated with chronic inflammation and infection (Wynn, 2004) and hampering Th2 responses have been implicated in chlamydial infections and induced disease (Holland et al., 1993, 1996; Gondek et al., 2009). In addition some immune mediated fibrotic diseases, such as schistosomula induced hepatic fibrosis, February 2011 | Volume 2 | Article 10 | 1 Gall et al. are also dominated by Th2-cytokine responses (Chiaramonte et al., 2003). The pathogenic changes observed at the site of infection in chlamydial genital and ocular disease are also due to development of fibrotic tissue yet convincing evidence of a significant role for polar CD4+ Th2 responses or alternative macrophage activation are lacking (Holland et al., 2010; Natividad et al., 2010). Many groups have now demonstrated the important role of immunoregulatory subsets of CD4+ T cells in preventing immune damage during viral, bacterial, and parasitic infections, and specifically in persistent infections at mucosal surfaces (Maloy and Powrie, 2001; Belkaid and Tarbell, 2009) but these have not been extensively studied in human chlamydial disease. One subset of CD4+ T cells that has key functions in immune homeostasis are Tregs (CD4+CD25+FOXP3+). The regulatory function of these natural and adaptive Tregs may be mediated by production of TGF-β and IL-10 or by cognate interaction (Hori et al., 2003; Fontenot et al., 2005). Antigen-specific IL-10 secreting type-1 T regulatory cells (TR1) which do not express FOXP3 have also been described in vivo following chronic antigenic stimulation (Vieira et (...truncated)