Monoclonal Antibody Specific for Activated Form of Holospora obtusa, a Macronucleus-Specific Bacterium of Paramecium caudatum

Summary

Two monoclonal antibodies (mAb IR-4–2 arid mAb AF-1) were developed by injecting sonicated debris of the activated forms of Holospora obtusa into mice. Indirect immunofluorescence microscopy showed that the antigen of mAb IR-4–2 was located inside the cell and that ther amount increases in the activated form. On the other hand, the antigen of mAb AF-1 appears only in the activated form, and is present inside the cell. The immunoblot showed that the molecular weights of the antigen of mAb AF-1 are 58.8 and 22.9 kDa. These results show that new antigens appear when the infectious forms transform the activated forms in early infection. We found that the AF-1 antigens were inducible in vitro if the infectious forms were treated with a buffer of low pH (pH 3–4) for 15–20 min. This strongly suggests that a trigger for the appearance of the AF-1 antigens in activated forms is low pH in the host digestive vacuoles.