Key immune proteins in cat eye infection by Chlamydophila felis

Abstract

Chlamydophila felis is a common cause of conjunctivitis in cats. Greater understanding of C. felis infection and immunity and identification of protective antigens will facilitate improved vaccine design. Chlamydial polymorphic membrane proteins (Pmps) represent a family of homologous proteins of likely importance in chlamydial infection and immunity. To identify immunogenic C. felis Pmps, we generated recombinant C. felis Pmps (rPmps) and used these to detect serum antibody reactivity against Pmps arising during C. felis infection in cats. Sequencing of Pmp genes 1, 7, 13, 18, 19 and 20 from 3 laboratory strains of C. felis (K2487, 1497V and Cello) and alignment with the Fe/C-56 genome revealed high genetic identity in Pmp genes between strains. PCR products lacking the predicted N-terminal signal sequence peptide and C-terminal domain were generated, cloned and expressed in Escherichia coli prior to purification by nickel-agarose affinity chromatography. Serum samples from 4 cats collected up to 55 days post-inoculation with C. felis (K2487) were analysed by western blotting and rPmp-specific ELISAs for evidence of serum antibody reactivity against each rPmp. Strong serum antibody reactivity against rPmps 1 and 7, and weak heterogeneous serum immunoreactivity against rPmps 13, 19 and 20, were detected from 14 to 21 days post-infection (dpi), peaking at 28-35 dpi and tending to plateau thereafter. No significant serum antibody reactivity was detected against rPmp18. This study provides the first evidence that C. felis Pmps 1 and 7 are likely to represent immunodominant proteins and recommends investigation of their potential as serodiagnostic antigens and novel vaccine candidates.