Cloning and expression of Taenia ovis antigens in Escherichia coli

Double stranded DNA complementary to poly(A)+ mRNA from the tapeworm Taenia ovis was cut with Sau 3A to an average length of about 300 bp and inserted into the Bam HI site of the expression plasmids pEX1, pEX2 and pEX3. These plasmids express a hybrid protein derived from a fusion of the cro gene with the lac Z gene (truncated at its 5' end by 53 bp) of phage lambda. Cloning sites lie downstream from the gene fusion. Escherichia coli infected with another plasmid (pCI857) bearing the temperature sensitive repressor of phage lambda was transformed with the pEX plasmids into which T. ovis DNA had been inserted; recombinants were selected by growth at 30 degrees C in the presence of ampicillin at 100 micrograms ml-1. Replicas were made and hybrid protein expression induced in recombinants by transferring them to 42 degrees C. Several recombinants expressing antigenic determinants of T. ovis were detected with T. ovis infected sheep serum that had been absorbed to remove antibodies to E. coli. Of five selected for further study, three expressed hybrid proteins of between 165 and 170 kDa of which the T. ovis component contributed between 48 and 55 kDa; in the other two, the tapeworm contribution was between 0.5 and 1.5 kDa. These antigenic determinants may be of some interest with respect to vaccine development since they are expressed during the normal course of T. ovis infection in sheep, and they are also present in the oncosphere - the infective larva of the parasite which stimulates immunity in sheep. The native antigens in adult worms and oncospheres that correspond to the antigenic determinants produced by the recombinant clones comprise a number of species ranging from 92.5 to 180 kDa. Tests with affinity purified antibodies indicate that the expressed products of the clones represent different epitopes on the same subset of polypeptides in both adult worms and oncospheres.