Antigenic characterisation of monoclonal antibodies against Sarcocystis muris by western blotting and immuno-electron microscopy.

The antigenic specificities of 13 monoclonal antibodies (mAbs) raised against Sarcocystis muris cystozoites were examined by Western blotting and immuno-electron microscopy against homologous S. muris and heterologous S. gigantea, S. tenella, S. arieticanis, S. capracanis, S. miescheriana and Toxoplasma gondii antigens. Four mAbs reacted in Western blots against S. muris antigens: SM-4 and -17 recognized single antigenic bands (31,000 and 34,000 MW, respectively) and SM-2 and -3 reacted against multiple bands (ranging from 12,500-30,000 and 13,000-50,000 MW, respectively). Similar antigens were also recognized by polyclonal immune sera from chronically infected mice. None of the mAbs cross-reacted with heterologous Sarcocystis spp. or T. gondii. Ultrastructural studies performed with colloidal-gold conjugates demonstrated that three mAbs reacted with specific antigenic elements in S. muris cystozoites: SM-3 and -4 labelled pellicular determinants and SM-19 labelled micronemes. None of the mAbs cross-reacted with heterologous Sarcocystis spp., whereas polyclonal immune sera from chronically infected sheep, goats and pigs cross-reacted with a variety of antigens in all Sarcocystis spp. except the primary cyst-wall determinants.