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

For the main experiment, the recipient cats were assigned to two groups: group A (n = 10, passive immunization, cats DHR1, DHR2, JHW1, JHW2, JHW4, JHW5, JHX1, JHX2, JHZ1 and JIC1) and group B (n = 5, control group, cats DHP1, DHT1, JHV1, JHW3 and JIC2). The cats of each group were housed together during and after the end of the study period. On day 0, plasma transfusion was performed, and the cats were experimentally inoculated with Mhf. For the passive immunization, each cat in group A was transfused with a 9 mL aliquot of plasma pool A. Each cat in group B was transfused with a 9 mL aliquot of plasma pool B. Ten minutes after the completion of the transfusion, all cats in groups A and B were inoculated with Mhf by a subcutaneous injection of 10 µL of 20% dimethyl sulfoxide (DMSO)-preserved blood containing 10 3 copies of Mhf diluted with 90 µL of phosphatebuffered saline (PBS), as previously described [22] . An aliquot of the same Mhf inoculum was used to infect the recipient cats in this study that had been used to infect the plasma donor cats (HBU2, HBZ2 and HCD2) in a previous study [28] . Clinical condition, body temperature and body weight were recorded, and blood samples collected prior to plasma transfusion and Mhf inoculation (day 0), twice weekly post inoculation (pi) until week 7 and weekly thereafter up to day 100 pi.; an additional blood collection to measure red blood cell (RBC) osmotic fragility (OF) was performed on day 179 pi because RBC OF was still increased compared with baseline values in several cats of group A and B at day 100 pi. All samples were collected without anesthesia, with the exception of the samples collected at day 0. Samples for PCR analysis and serology were stored at −80 °C until analysis. Flow cytometry, hematology, blood biochemistry, Coombs tests and RBC OF assays were carried out within 4 h of blood collection.