Synthetic peptides based on Chlamydia trachomatis antigens identify cytotoxic T lymphocyte responses in subjects from a trachoma-endemic population

Abstract

SUMMARYCD8 + cytotoxic T lymphocytes (CTL) recognize peptide antigens in the context of class I MHC antigen molecules. To identify peptides capable of eliciting anti-Chlamydia trachomatis CTL responses, 13 synthetic peptides conforming to human leucocyte antigen (HLA)-B8-or -B35-predicted binding motifs were synthesized using sequences based on C. trachomatis major outer membrane protein (MOMP) and heat shock protein 60 (hsp60). Two of 11 HLA-B35-predicted binding peptides were able to stabilize HLA-B35 in an in vitro binding assay. All peptides were tested in CTL assays using peripheral blood mononuclear cells (PBMC) isolated from 26 HLA-B8 or -B35 individuals resident in a trachomaendemic community. Responses to MOMP and hsp60 peptides were identified in a minority of both HLA-B8 and -B35 individuals. Two of 12 HLA-B8 subjects responded to MOMP and 1/13 to hsp60 peptides. Responses in HLA-B35 subjects were similar, 1/13 subjects responding to MOMP and 2/13 to hsp60 peptides. CTL responses were observed only in children resolving current infection and in adults without scarring of the conjunctiva. These results suggest that anti-chlamydial CTL occur at low levels in peripheral blood, but may be important in the resolution of naturally acquired human ocular chlamydial infection.

Human CD8+ T Cells Recognize the 60-kDa Cysteine-Rich Outer Membrane Protein fromChlamydia trachomatis

“…For example, the structure and function of OmpA (MOMP) of Chlamydia vary dramatically between a highly disulfide-linked form in EBs (that functions possibly in adhesion) and a completely reduced form in RBs that functions (only in the non-cross-linked state) as a porin for ATP (44). Coincidently, MOMP has also been shown to be presented by MHC class I molecules (15)(16)(17), and consistent with MHC class I processing of this Ag, extrainclusionary, cytosolic distribution of MOMP in infected cells has been recently demonstrated, where it is found associated with inclusion membrane protein A-laden filaments (45). Whether OmcB protein also directly localizes to the cytosol or has a cytosolic function in addition to its hypothesized membrane cross-linking function is unknown.…”

“…Chlamydia-reactive, peptide-specific CD8 ϩ T cells are elicited during human infection and are detected in children resolving infection, in adults without scarring of the conjunctiva in a trachomaendemic population (15), and in individuals who have acquired a genital tract infection (16,17). The limitation of these studies is that these responses are specific to predicted class I binding peptides derived from the major outer membrane protein (MOMP) or the heat shock protein 60.…”

Chlamydia trachomatis-Specific Human CD8+T Cells Show Two Patterns of Antigen Recognition

“…Both of these antigens have been shown to be associated with the chlamydia inclusion membrane. As noted previously, human CD8 ϩ T cells able to recognize C. trachomatis MOMP or hsp60 have been generated from infected individuals by using synthetic peptides (18,(24)(25)(26). The identity of the antigen(s) recognized by HLArestricted T cells isolated in our laboratory is as yet unknown but can be revealed by approaches such as expression library screening, as recently described for the identification of Cap1 and CrpA and C. trachomatis antigens recognized by CD4 ϩ T cells (15).…”

“…In contrast, much less is known about the antigenic specificity and roles of CD8 ϩ T cells during human C. trachomatis infection. In recent years human CD8 ϩ T cells which are able to recognize MOMP (18,24,25) or hsp60 (18,26) have been isolated from infected humans, but the approach in each case was to identify peptides in C. trachomatis proteins which would be predicted to bind to common class I HLA alleles and to determine whether infected subjects had CD8 ϩ T cells able to recognize these peptides. T-cell lines and clones were isolated by stimulation with synthetic peptides.…”

Functional Characterization of Class Ia- and Non-Class Ia-RestrictedChlamydia-Reactive CD8+ T Cell Responses in Humans

“…These peptides have been derived from the major outer membrane protein (MOMP) 3 using algorithms that predict binding to MHC class Ia molecules. MOMP-specific CTL responses have been preferentially found in children resolving infection or in adults, without scarring of the conjunctiva in a trachoma-endemic population (10), as well as in subjects who have acquired a genital tract infection (11,12). Furthermore, these MOMP-specific T cells have been shown to lyse C. trachomatis-infected epithelial cells.…”