We investigated the expression of a calcium-binding protein, the S100 prote
in, in Eimeria tenella. Cecal paraffin sections from experimentally infecte
d chickens were treated with anti-alpha-S100 (anti-alpha subunit of S100 pr
otein) and anti-beta-S100 (anti-beta subunit of S100 protein) monoclonal an
tibodies and anti-S100 whole molecule polyclonal antibody. The avidin-bioti
n peroxidase method was used for immunocytochemical staining. Our results d
emonstrated a positive immunoreaction within the schizonts, macrogametes, a
nd oocysts. These stages were all beta subunit and S100 whole-molecule posi
tive. Immunoblot studies of the total proteins of E. tenella merozoites and
sporozoites of the original strain and 2 precocious lines have demonstrate
d that precocious attenuation produced different S100 protein isotypes.