Abstract
The capability of normal equine, bovine and rabbit sera to combine with poliovirus was investigated in a cell-free system, using the precipitation test in agar gel. Two active factors were found by the test : one was D precipitin which caused precipitation by reacting with D antigen of poliovirus, and the other was C precipitin causing precipitation with C antigen of the virus. The frequency of detection of D precipitin was the highest in equine serum, while C precipitin was detectable with the highest frequency in bovine serum. The serum containing D precipitin demonstrated a distinct virus-neutralizing activity. However, the number of serum with D precipitin was small, even in those sera with the highest virus-neutralizing activity. The relationship between C precipitin and virus-neutralizing factor differed depending upon the animal species. In bovine serum, the precipitin was detectable with increased frequency in sera demonstrating higher virus-neutralizing activity. In equine serum, no noticeable relationship was observed between the two.
The identity of D precipitin with virus-neutralizing factor was proven more convincingly by the study using a poliovirus mutant insensitive to a certain inhibitory equine serum. The study demonstrated, at the same time, that the structure of combining sites of the inhibitor for the virus may differ from that of the type-specific antibody.
Immunoelectrophoretic examinations revealed that D precipitins of equine serum were located mostly in the β globulin region, while C precipitins of two equine sera were in the γ regions. In contrast, both D and C precipitins of bovine serum and D precipitin of a single rabbit serum were located invariably in the γ globulin regions.
