Capping of Immune Complexes by Sporozoites of Eimeria tenella

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Abstract
Sporozoites of D. tenella were incubated for 10, 20, or 30 min with parasite-specific monoclonal IgG antibody 3D3II from mice and then rinsed in a Tris-buffered glucose saline solution (TBGS). Some sporozoites were then incubated for 10, 20, or 30 min with ferritin- or colloidal gold-conjugated goat anti-mouse IgG antibody and then fixed in 2.5% glutaraldehyde and prepared for transmission (TEM) or scanning (SEM) electron microscopy. Sporozoites previously exposed to monoclonal antibody were prefixed with 0.25% glutaradehyde, incubated with ferritin- or colloidal gold-conjugated anti-mouse IgG antibody and then fixed and prepared for TEM or SEM. Control preparations consisted of sporozoites exposed only to TBGS, monoclonal antibody 3D3IIor to ferritin- or colloidal gold-conjugated anti-mouse IgG antibody. Capping of immune complexes occurred only on the surface of those sporozoites exposed to monoclonal antibody 3D3II followed by ferritin- or gold-conjugated antibody. Immune complexes moved laterally and posteriorly on the outer surface of the parasite plasma membrane to form a cap at the posterior end of the sporozoite. Capping did not occur in TBGS controls nor in sporozoites treated with monoclonal antibody 3D3II and prefixed in 0.25% glutaraldehyde before exposure to ferritin- or gold-conjugated antibody. Capping of surface antigens did not occur in the presence of monoclonal 3D3II antibody only, whereas specimens exposed to both monoclonal and ferritin- or colloidal gold-conjugated antibodies were able to cap immune complexes.