Identification of CT521 as a frequent target of Th1 cells in patients with urogenital Chlamydia trachomatis infection

Abstract

Background. The human immune response to a Chlamydia trachomatis serovar D lysate was investigated in patients with urogenital C. trachomatis infection, to identify novel T cell targets. Methods. A C. trachomatis lysate was fractionated on the basis of molecular mass, and each fraction was used to stimulate peripheral-blood mononuclear cells from patients with C. trachomatis infection. In frequently recognized fractions, proteins were identified by mass spectrometry, recombinantly expressed, and tested for T cell recognition. Results. T cell recognition of the fractions was highly heterogeneous in patients with C. trachomatis infection (n = 16). Four patients exhibited responses that were strongly targeted to antigens of 16-20-kDa molecular mass. Three proteins were identified in this fraction: CT043, CT511, and CT521. The T cell response to the individual recombinant proteins were investigated, and CT521 was found to induce the highest level of interferon (IFN)-γ. The recognition of CT521 was investigated in a larger study population (n = 41), and a positive IFN-γ response was measured in 83% of the patients. Several T cell epitopes were identified in CT521; in particular, peptide 5 in the central part of the protein was frequently recognized by T cells (63%). Conclusion. We have identified a novel C. trachomatis antigen, CT521, that is frequently recognized in patients with urogenital C. trachomatis infection. © 2006 by the Infectious Diseases Society of America. All rights reserved.