DELIVERY OF THE P67 SPOROZOITE ANTIGEN OF THEILERIA-PARVA BY USING RECOMBINANT SALMONELLA-DUBLIN - SECRETION OF THE PRODUCT ENHANCES SPECIFIC ANTIBODY-RESPONSES IN CATTLE

The p67 sporozoite antigen of Theileria parva has been fused to the C- terminal secretion signal of Escherichia coil hemolysin and expressed in secreted form by attenuated Salmonella dublin aroA strain SL5631. T he recombinant p67 antigen was detected in the supernatant of transfor med bacterial cultures. Immunization trials in cattle revealed that SL 5631 secreting the antigen provoked a 10-hold-higher antibody response to p67 than recombinant SL5631 expressing but not secreting p67. Immu nized calves were challenged with a 80% lethal dose of T. parva sporoz oites and monitored for the development of infection, Two of three cal ves immunized intramuscularly with the p67-secreting SL5631 strain wer e found to be protected, whereas only one of three animals immunized w ith the nonsecreting p67-expressing SL5631 strain was protected. This is the first demonstration that complete eukaryotic antigens Fused to the C-terminal portion of E. coli hemolysin can be exported from atten uated Salmonella strains and that such exported antigens can protect c attle against subsequent parasite challenge.