Immunogenicity of three oocyst extracts of Cryptosporidium baileyi in experimentally infected chickens

The immunogenic properties of water-soluble and detergent-extracted components of Cryptosporidium baileyi oocysts were studied. Oocyst cytosol antigen (OCA) containing hydrophilic proteins was obtained by freeze-thaw cycles in liquid nitrogen. This was followed by Triton X-114 extraction of remaining oocyst fragments to dissolve membrane-bound proteins (TRE). The remainder of the pellet was solubilized with sodium dodecyl sulfate and treated with 2-mercaptoethanol to reduce disulfide-linked oocyst wall proteins (BME). The immune recognition of these three extracts was evaluated during the course of experimental cryptosporidiosis in chickens using ELISA, immunoblotting, and the lymphocyte stimulation test (LST). Four groups of chickens were infected at various times with different doses of C. baileyi and one group with the mammalian parasite C. parvum. Analysis of the data revealed that OCA proteins are well recognized by serum antibodies during the infection and to a limited extent by sera from chickens infected with C. parvum. Humoral responses of chicken groups to this antigen did not correlate well with the length of patency in contrast with its cellular recognition in LST. TRE gave lower values than OCA in both ELISA and LST, though it was still specifically recognized by samples from C. baileyi-infected chickens. Antibodies reacted aspecifically with BME, since only samples of birds which were immunocompetent at the time of their infection were able to recognize this extract as antigen. Immunoblotting revealed more specific components in OCA than in TRE or BME.