Characterization of humoral immune responses to chlamydial HSP60, CPAF, and CT795 in inflammatory and severe trachoma

Abstract

Purpose: Chlamydia trachomatis (Ct) remains the leading global cause of preventable blindness. There are limited data on humoral immune responses in trachoma. Evaluating these responses is important for understanding host-pathogen interactions and informing vaccine design. Antibodies to chlamydial heat shock protein 60 (cHSP60) have been associated with infertility and trachomatous scarring. Other proteins, including chlamydial protease-associated factor (CPAF) and a hypothetical protein unique to the family Chlamydiaceae, CT795, elicit strong immune responses in urogenital infections, but their role in trachomatous disease is unknown.

Methods: This study was conducted to expand on previous cHSP60 findings and evaluate the association of CPAF and CT795 antibodies with ocular Ct infection and disease. Clinical trachoma grading was performed, and conjunctival samples were obtained from individuals with trachomatous trichiasis (TT; one or more inturned eyelashes) or inflammatory trachoma without trichiasis and control subjects without disease, all of whom resided in trachoma-endemic regions of Nepal. Ct infection was determined using commercial PCR. IgG and IgA tear antibodies against cHSP60, CT795, and CPAF fusion proteins were measured by quantitative ELISA.

Results: Significantly higher IgG antibody levels were found against cHSP60, CPAF, and CT795 in the inflammatory cases compared with levels in the controls (P < 0.005 for all three). Ct infection was independently associated with IgG antibodies against all three immunogens in the inflammatory cases but not in the controls (P = 0.025, P = 0.03 and P = 0.017, respectively). Only IgG antibodies against CPAF were significantly elevated among the TT cases (P = 0.013).

Conclusions: Among individuals with trachoma, IgG antibody responses to CPAF are likely to be both a marker and risk factor for inflammatory trachoma and severe trachomatous disease.

Figure 1.

Tear IgG and IgA antibodies against cHSP60, CT795, and CPAF fusion proteins in the TF/TI cases compared with levels in the age-matched controls. Preabsorbed tear samples were measured by ELISA for IgG (A) and IgA (B) antibody titers specific for the chlamydial proteins cHSP60, CT795, and CPAF. (A, B) Data represent antibody titers based on the chlamydial gene/GST ratio in the TF/TI cases (n = 65) or the age-matched controls (n = 65). Horizontal lines: geometric means. (C, D) Frequency of tear IgG and IgA antibodies, respectively, against cHSP60, CT795, and CPAF (ratios of chlamydial gene/GST ≥ 2) in the TF/TI cases compared with that in the age-matched controls. Significant differences between the TF/TI cases and controls were determined by multiple logistic regression adjusted for sex and Ct infection. *P < 0.005; **P < 0.05.

Figure 2.

Tear IgG and IgA antibodies against cHSP60, CT795, and CPAF fusion proteins in the TT cases compared with levels in age-matched controls. Preabsorbed tear samples were measured by an ELISA for IgG (A) and IgA (B) antibody titers specific for the chlamydial proteins cHSP60, CT795, and CPAF. (A, B) Data represent antibody titers based on the chlamydial gene/GST ratio in the TT cases (n = 59) or the age-matched controls (n = 65). Horizontal lines: geometric means. (C, D) Frequency of tear IgG and IgA antibodies, respectively, against cHSP60, CT795, and CPAF (ratios of chlamydial gene/GST ≥ 2) for the TT cases compared with the age-matched controls. Significant differences between TT and control groups were determined by using multiple logistic regression adjusted for sex and Ct infection. *P < 0.05; **P = 0.013.