The two strains of Eimeria maxima, Guelph and Florida, used in this study were previously shown to only partially cross-protect immunologically with respect to lesion scores, weight gains and feed conversions after heterologous challenge. In this paper, we provide evidence that this partial lack of cross-protection is manifested at the level of sporozoite transport. In birds immunized and challenged with the homologous strain, sporozoites accumulated in the lamina propria and were blocked from further movement into the crypts by 72 h post-challenge, unlike the situation observed in naive birds. Fewer than 5% of sporozoites were found in the crypts by 72 h post-challenge. In immunized birds challenged with the heterologous strain, fewer sporozoites reached the crypts than in naive birds but at least four times as many sporozoites successfully migrated to the crypts, when compared with birds challenged with the homologous strain. The degree of cross-protection afforded by the heterologous strain as measured by sporozoite transport success was not equally reciprocal.
The phenotype of cells transporting sporozoites of Eimeria necatrix during a primary infection was determined using a panel of six monoclonal antibodies to various chicken lymphocyte surface markers. Sporozoites and cells harboring them were examined at 8, 12 and 18 h postinfection using two-color immunoflorescence and confocal microscopy. The majority of parasites observed within lymphocytes were found in CD 8 + (15%) or CD 3+ (13-22%) cells at all time periods examined. Smaller numbers were found within deltagamma TCR+ (5%) and alphabeta TCR+ (5%) lymphocytes. No sporozoites were found within CD 4+ or IgM+ lymphocytes at any of the time periods.
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