Identification of Antigenic Targets for Immunodetection of Balamuthia mandrillaris Infection

The free-living amoebaBalamuthia mandrillariscauses granulomatous amoebic encephalitis (GAE) in humans. Rapid identification of balamuthiasis is critical for effective therapeutic intervention and case management. In the present study we identified target antigens for the development of a serological assay forB. mandrillarisinfection. We demonstrated by silver staining that protein profiles for all eight isolates ofB. mandrillaris, independent of human or animal origin or geographic origin, appeared to be similar except for some minor differences, indicating the molecular homogeneity of these strains. The profiles of all isolates, which ranged from 200 to 10 kDa, were similar, with a prominent protein visible around 30 kDa; all appeared considerably different from protein profiles of the control E6 cells andAcanthamoeba castellaniiandNaegleria fowleriisolates. Western blot analysis with rabbit hyperimmune serum identified the major immunodominant antigens of 25, 50, 75, and 80 kDa; positive human sera reacted strongly with proteins around 25, 40, 50, and 75 kDa. Proteins around 40 kDa detected by human serum were not recognized by hyperimmune rabbit serum. None of the target proteins were detected by uninfected control sera. Reactivities of five patients' sera with 4 different isolates ofB. mandrillaris(2 strains of human and 2 strains of animal origins) revealed that patients' sera reacted slightly differently with differentB. mandrillarisisolates, although major proteins of approximately 25, 50, and 75 kDa were present in all extracts.