Humoral immune response to a recombinant hemoplasma antigen in experimental 'Candidatus Mycoplasma turicensis' infection

'Candidatus Mycoplasma turicensis' is a feline hemoplasma species that was isolated in a cat with hemolytic anemia. PCR has been widely used to investigate and diagnose 'Candidatus Mycoplasma turicensis' infection, but so far, little is known about the humoral immune response in infected cats. Recently, enzyme-linked immunosorbent assays (ELISA) were developed to monitor anti-feline hemoplasma antibodies. The aim of the present study was to investigate the humoral immune response in cats experimentally infected with 'Candidatus Mycoplasma turicensis' and to monitor the influence of the pre-administration of methylprednisolone and subsequent antibiotic treatment. Serum and plasma samples from 15 specified pathogen-free cats infected with 'Candidatus Mycoplasma turicensis' were analyzed by ELISA. Seroconversion was demonstrated in all cats, and the antibodies remained detectable until the end of the study (up to 100 weeks post-exposure). In some cats, the ELISA seemed more sensitive and better able to demonstrate exposure to 'Candidatus Mycoplasma turicensis' than PCR. The peak antibody level occurred after the peak of the bacterial blood loads. The methylprednisolone administrations were associated with increased antibody levels, while antibiotic treatment, particularly with doxycycline, resulted in a decrease in antibody levels. Additionally, preliminary data indicated that three of four seropositive cats were protected from bacteremia after a subsequent challenge. In conclusion, the ELISA was found to be a useful tool to investigate the humoral immune response in hemoplasma-infected cats and a desirable addition to PCR to study the pathogenesis of hemoplasma infections.