Reduced invasion of cultured cells pretreated with a monoclonal antibody elicited against refractile body antigens of avian coccidial sporozoites

The effect of a monoclonal antibody (1209-C2) elicited against sporozoite refractile-body antigen on invasion of cultured baby hamster kidney cells by avian Eimeria species was examined in vitro. Pretreatment of sporozoites with 1209-C2 for 45 min before inoculation into cultures or simultaneous introduction of sporozoites and 1209-C2 into cultures had no significant effect on invasion. However, pretreatment of cultures for 45 min with 1209-C2 (also with media from other cloned 1209 cell lines) significantly inhibited invasion by sporozoites of Eimeria tenella and E. adenoeides. Pretreatment of cultures with 2 unrelated monoclonal antibodies with the same isotype as 1209-C2 did not inhibit invasion by E. tenella. There was a significant correlation between time of exposure of the cultures to 1209-C2 and invasion (r = -0.80924; p = 0.0001), with inhibition of invasion occurring after 20 min exposure, but not after 10 min. There was also a significant correlation between the titer of 1209-C2 and invasion (r = 0.62291; p = 0.0305). Monoclonal antibody 1209-C2 cross-reacted with epitopes of baby hamster kidney cells by both immunofluorescence and Western blot. The fluorescent labeling of the cells differed according to the fixative that was used. In formalin-fixed cultures labeled with 1209-C2, fluorescent foci were distributed over the entire cell; after methanol fixation, 1209-C2 reacted with only discrete foci in the nucleus. On Western blots of sporozoites, 1209-C2 reacted with antigens having molecular sizes of similar to 8, 17, 23, 30, and 45-60 KDa, and with several minor bands. On baby hamster kidney cells, the antibody reacted primarily with bands of similar to 30, 45-60, and slightly with other bands. The data suggest that interactions among similar molecules in the sporozoites and host cells may play a role in cellular invasion.