EPITOPE DIVERSITY OF F-STRAIN MYCOPLASMA-GALLISEPTICUM DETECTED BY FLOW-CYTOMETRY

A culture of F strain Mycoplasma gallisepticum (F-MG) that exhibited a n epitope identified by monoclonal antibody (MAb) 6F10 was used to ino culate leghorn hens in two different trials. In Trial 1, mature hens c hronically infected with F-MG were swabbed at intervals from 230 to 34 5 days postinoculation (PI). The F-MG isolates were tested with an aga r place fluorescent antibody (APFA) method that used a polyclonal anti body and with a flow cytometry (FC) technique that used MAb 6F10. Prim ary cultures of swabs taken at 258, 272, 293, 318, and 345 days PI wer e all identified as positive by APFA, whereas FC identified 23%-41% as positive. Subsequently, MAb 6B11 was found, which reacted positively with isolates negative to MAb 6F10. Both 6F10 and 6B11 were used in th e second trial, which was designed to identify F-MG isolates that were negative to 6F10. In Trial 2, naive birds were inoculated with F-MG w hen they were 9 wk old and were sampled at six intervals from 13 to 15 4 days PI. The APFA method was used to identify primary isolation (PO) cultures, and FC was performed on PO cultures and the same cultures a fter they had been passed three times (third serial passage [P3] cultu res). The APFA rest identified 100% of the PO cultures as F-MG. The FC results on PO cultures showed 34.5% as 6F10 positive and 85.1% as 6B1 1 positive. Results for FC on P3 cultures showed 92.3% 6F10 positive a nd 96.3% 6B11 positive. These results suggest that the microenvironmen t of the colonization site in the hen induced an epitope diversity in F-MG, as evidenced by the loss in the expression of MAb 6F10-defined e pitope. Isolation of the organism from hens and propagation for severa l in vitro passages resulted in the re-expression of the epitope defin ed by MAb 6F10.