Among the many advantages of studying ocular infection are the unambiguous phenotype, which can be easily determined by everting the upper eyelid, and the ability to study immune responses at the site of infection in the conjunctival

epithelium. Tear fluid or sera from children with trachoma can neutralise homologous ocular isolates of Ct if incubated with them before inoculation into the owl monkey eye [40]. Serovar-specific neutralising epitopes have been mapped to the MOMP [41]. However, cohort studies in trachoma endemic communities found no evidence that local anti-chlamydial IgG antibodies in ocular secretions were associated with a reduced incidence Adriamycin of infection. Indeed, the presence of anti-chlamydial IgG in ocular secretions was associated with an increased incidence of active trachoma in this study. The incidence was lower in subjects with anti-chlamydia IgA antibodies in ocular secretions, but the difference was not statistically significant [42]. In NHPs reduction in shedding and clearance of Ct infection was associated Venetoclax mouse with antibody responses to a limited

number of native proteins (MOMP, PmpD, Hsp60, CPAF, pgp3 and 3 as yet unidentified polypeptides) which were slowly acquired as the B cell immune response matured [43]. Children who spontaneously resolved ocular Ct infection had higher peripheral blood mononuclear cell (PBMC) proliferative responses to chlamydial antigens than children with persistent infection and disease [44], whereas increased conjunctival expression of IL-10

and FOXP3 were associated with longer episodes of infection [45]. Conjunctival gene expression profiling showed that T-helper 1 (Th1) (IFNγ, IL12) cytokine expression was increased the in children with active trachoma and Ct infection [46] and [47]. One study showed that the expression of FOXP3, a marker for T-regulatory cells, was increased in children with clinical signs of trachoma in whom infection had resolved [48]. The expression of IL17A is significantly increased in active trachoma [49] and [50]. IL17A is the signature cytokine of Th17 cells, a CD4+ T-cell population which act in an antigen-specific manner [51], but is also produced by other cell types such as γδ T-cells, NK cells, macrophages, neutrophils [52] and [53]. IL17A is pro-inflammatory and plays an important role in host immunity to extracellular and some intracellular pathogens.