Heat shock response of Babesia divergens and identification of the hsp70 as an immunodominant early antigen during ox, gerbil and human babesiosis

Summary— Using antisera (α‐R and α‐C7Ag) directed against the conserved Gly‐Gly‐Met‐Pro‐epitope of the hsp70 family, a single antigen was identified in the human Babesia divergens Rouen 1987 isolate by Western immunoblotting and immunoprecipitation experiments. This B divergens hsp70 is highly conserved as shown by the analysis of five other geographical B divergens isolates from different hosts (human and bovine). Indirect immunofluorescence assay performed on the asexual intraerythrocytic stages showed that the hsp70 is mainly cytoplasmic and stage‐independent. Heat‐shock experiments, with 20 min incubation at 40°C followed by a 10 to 50 min shift to 37°C in the presence of [35S]‐methionine, led to an increase of two hsp of 85 and 70 kDa while protein synthesis in general decreased within 10 min. Immunoprecipitations of [35S]‐methionine radiolabelled proteins with human, ox and gerbil antisera raised against various B divergens isolates, showed the presence of a B divergens 70 kDa protein which was demonstrated to be a hsp70 by coupling immunoblotting assays with α‐C7Ag serum on the same immunoprecipitated material. During human babesiosis, the B divergens hsp70 appears as an early antigen during the acute phase. These results are in agreement with the use of the B divergens hsp70 as an essential valence antigen in an anti‐babesiosis vaccine.