P3-S1.35 Systemic and mucosal IgG and IgA antibody responses in genital Chlamydia trachomatis infection

Background Chlamydia trachomatis (CT) is the most common sexually transmitted infection in the UK. Screening and treatment programmes do not appear to have reduced the population levels of Chlamydia. Ideally a vaccine stimulating both humoural and T-cell responses against CT should be developed. We therefore wished to further study the humoural immune response to chlamydial infection both systemically and mucosally in the female genital tract in natural infection. Methods Cervical secretions (obtained with Weck-Cel spears, Medtronic) and serum from twenty-six women diagnosed chlamydia-positive were assessed for Chlamydia-specific IgA and IgG responses (Anilab systems, Finland) at baseline and at 4 months follow-up. Samples from thirty chlamydia-negative women were used as controls. The Mann–Whitney non-parametric test was used to compare groups. Results There was a significant difference between CT+ve and CT−ve IgG in serum samples (IgG median absorbance values p=0.006, median CT-ve samples 0, +ve samples 0.255) and IgA serum values (p=0.005, CT+ve median 0.491, CT−ve 0.119). There was no significant difference between cervical IgG and IgA levels between CT+ve and CT−ve women (IgG median absorbance values, CT+ve samples 0.012, 0 CT−ve; IgA CT−ve 0.202, CT+ve, 0.032), although there was a trend towards raised cervical IgG in CT+ve samples (p=0.08). There was no significant difference between antibody levels at baseline and 4 months for the 10 CT+ve women who have returned so far. Discussion Our data suggests that the local and systemic antibody responses to genital chlamydial infection are highly variable. No CT+ve samples studied display positive absorbance levels in all four tested parameters. However, serum IgG and IgA responses are significantly raised in CT+ve individuals, and these values remain high at 4 months follow-up. This is in contrast to local responses which are not significantly different between CT+ve and CT−ve individuals, although there is a trend towards raised cervical IgG in CT+ve samples. The results of this study so far indicate that local immune responses, in comparison to systemic responses, are not well-defined. This may have implications both for chlamydial vaccine development, and mucosal assessment of candidate vaccines.