CLONING AND CHARACTERIZATION OF A 150 KDA MICROSPHERE ANTIGEN OF THEILERIA-PARVA THAT IS IMMUNOLOGICALLY CROSS-REACTIVE WITH THE POLYMORPHIC IMMUNODOMINANT MOLECULE (PIM)

To identify the genes encoding novel immunodominant antigens of Theile ria parva a lambda gt11 library of piroplasm genomic DNA was immunoscr eened with bovine recovery serum and a gene encoding a 150 kDa antigen (p150) was identified. The predicted polypeptide contains an N-termin al secretory signal sequence and a proline-rich region of repeated ami no acid motifs. The repeat region is polymorphic between stocks of T, parva in both copy number and sequence, and analysis of the repeat reg ion from 10 stocks of T. parva revealed 5 p150 variants. A monoclonal antibody (mAb) against the T. parva polymorphic immunodominant molecul e (PIM) cross-reacted with the recombinant p150. The p150 has sequence homology with a PIM peptide sequence containing the anti-PIM mAb epit ope. Immunoelectron microscopy demonstrated that the p150 antigen, lik e PIM, is located in the microspheres of the sporozoites and is exocyt osed following sporozoite invasion of the host lymphocyte. By immunoel ectron microscopy p150 was subsequently transiently detectable on the sporozoite surface and in the lymphocyte cytosol. Immunoblotting showe d that p150 is also expressed by the schizont stage, but at much lower levels compared to the sporozoite. These results suggest a major role for p150 in the early events of host-sporozoite interaction.