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

The cats in both groups tested negative in the DnaK ELISA (defined as an OD 415 ≤ 0.33) prior to the plasma transfusion (Figures 2A and B) . After passive immunization and subsequent infection, group A cats showed slightly but significantly higher DnaK ELISA OD 415 values at days 3, 7 and 14 pi compared with the OD 415 values of cats in group B (p MWU < 0.05; Figure 2C ). From day 21 until day 100 pi, no significant difference in the DnaK ELISA OD 415 values was evident between the two groups. When cat JHW3 was excluded from the analyses, the anti-DnaK antibody level in cats in group A was still significantly higher early after passive immunization (days 3 and 7 pi, P MWU < 0.05), but not at day 14 pi and thereafter until day 100 pi when compared to cats in group B. There was no significant difference in the time of seroconversion (OD 415 > 0.33) between the two groups; cats in both groups, A and B, seroconverted between days 21 and 49 pi, with the exception of cat JHW3 (group B), which did not develop anti-Mhf DnaK antibodies throughout the study ( Figure 2B ). Two other cats (JHW2, group A, and JHV1, group B) were seronegative (OD 415 ≤ 0.33) by the end of the experiment ( Figure 2B ); one of these cats (JHW2) was treated with doxycycline between days 28 to 42 pi because of a pronounced decrease in packed cell volume (PCV) to 21% (day 28 pi, see below).