Nitrocellulose immunoblotting for identification and molecular gene cloning of Eimeria maxima antigens that stimulate lymphocyte proliferation.

An immunoblotting technique was used to identify lymphostimulatory antigens within sized polypeptide fractions of Eimeria maxima sporozoites. Six fractions contained polypeptides that specifically stimulated the proliferation of immune lymphocytes in an in vitro assay, and polyclonal antisera were made in rabbits against these fractions. cDNA clones, isolated with antisera against a lymphostimulatory fraction of around 70 kDa, were found to encode four different antigens including a classical hsp70, a molecule homologous to an endoplasmic reticulum chaperonin (BiP/GRP), and a calcium-dependent serine/threonine protein kinase that appears homologous to a recently described molecule from Plasmodium falciparum. The protein kinase cDNA clone was overexpressed in Escherichia coli, and the recombinant antigen was found to induce both antibody and lymphoproliferative responses in chickens when administered subcutaneously. Thus, immunoblotting, in combination with in vitro lymphoproliferation assays, can be used as an initial screen for the identification of lymphostimulatory antigens from a complex pool of polypeptides, and a combination of cDNA cloning, expression, and immunization allows assessment of the lymphostimulatory activity of individual polypeptides. These studies should facilitate further evaluation of antigens that are potential candidates for inclusion in a recombinant vaccine against poultry coccidiosis.