Passive immunization does not provide protection against experimental infection with Mycoplasma haemofelis

Sugiarto, Sarah; Spiri, Andrea M.; Riond, Barbara; Novacco, Marilisa; Oestmann, Angelina; de Miranda, Luisa H. Monteiro; Meli, Marina L.; Boretti, Felicitas S.; Hofmann-Lehmann, Regina; Willi, Barbara

Infection enhancement, i.e. earlier onset of bacteremia and anemia, was recently documented in cats that had recovered from CMt infection and were re-challenged with Mhf [15] . All CMt-recovered cats were serologically positive before Mhf inoculation. The study suggested that the pre-existing antibodies against CMt might have had enhanced infection kinetics in the CMt-recovered cats [15] . Although infection kinetics were not different between the passively immunized and control cats in this study, our results still suggest that the transfer of antibodies from Mhf-recovered cats could potentially be harmful. The passively immunized cats showed a significant increase in RBC OF during the course of infection. This effect was not observed in the control cats, indicating that the increase was not simply due to a non-specific effect of plasma transfusion on RBC fragility. It can be hypothesized that the antibodies bound to the Mhf organisms attached to RBCs. RBC-bound antibodies have been found after primary Mhf infection [16, 39, 40] and can induce receptor-mediated RBC phagocytosis or the activation of the complement system [41] . In the present study, RBCbound antibodies were not detected in the cats by Coombs test, but the sensitivity of this assay may be limited [42] .