Activity of a monoclonal antibody against Besnoitia besnoiti endozoites.

Besnoitia besnoiti multiplication in vitro was inhibited by a specific organelle complex-directed monoclonal antibody (MoAb) raised against the endozoite stage. Multiplication rates in antibody-treated cultures were lower at parasite/cell ratios of 1:1, 1:2 and 1:10, than in untreated cultures, after 4 or 8 d of incubation. At 1:100 ratio, there was no difference between test and control cultures irrespective of the incubation period. In in vivo experiments, the anti-B besnoiti MoAb had no neutralizing effect on the infectivity of endozoites. Inoculation of gerbils with antibody-preincubated endozoites, followed by treatment with these MoAb through 5 successive days ultimately failed to prevent death in any of them. In Western blots the specific anti-B besnoiti MoAb of the IgG1 subclass recognized a 70 kDa endozoite protein in the cytosolic and the insoluble membrane fraction of endozoites.