Serological expression cloning of novel immunoreactive antigens of Babesiamicroti

Increased recognition of the prevalence of human babesiosis in the United S tates, together with rising concern about the potential for transmission of this infection by blood transfusion, has provided motivation to develop de finitive serologic and molecular tests for the causative agent, Babesia mic roti. To develop more sensitive and specific assays for B. microti, we scre ened a genomic expression library with patient serum pools. This screening resulted in the identification of three classes of novel genes and an addit ional two novel, unrelated genes, which together encode a total of 17 uniqu e B. microti antigens. The first class (BMN1-2 family) of genes encodes sev en closely related antigens with a degenerate six-amino-acid repeat that sh ows limited homology to Plasmodium sp, merozoite and sporozoite surface ant igens. A second class (BMN1-8 family) of genes encodes six related antigens , and the third class (BMN1-17 family) of genes encodes two related antigen s, The two remaining genes code for novel and unrelated sequences. Among th e three classes of antigens and remaining novel sequences, five were chosen to code for the most immunodominant antigens (BMN1-2, -9, -15, and -17 and MN-10). Western blot analysis with the resulting recombinant proteins indi cated that these antigens were targets of humoral immune responses during B . microti infection in humans.