Development and Evaluation of an Isospora Suis Sporozoite Neutralizing Antibody Assay in Swine Testicular Cells

Abstract

An in vitro Isospora suis sporozoite neutralizing antibody assay has been developed in swine testicular (ST) cells. This assay measures the titer of neutralizing antibodies present in sera, milk and monoclonal antibody culture fluids by determining both the amount of intracellular sporozoites by immunofluorescence and the cytopathic effect in ST cells. A monoclonal antibody against the apical complex of I. suis sporozoites inhibited the infection of sporozoites in vitro. Hyperimmune sera produced in goats and guinea pigs inhibited sporozoite infection in ST cells. Milk samples from gilts vaccinated with I. suis contained neutralizing antibodies, however the titers did not correlate with protection observed in nursing pigs after challenge.