Determination and distribution of two types of hepatitis-associated antigen.

Two types of hepatitis-associated antigen (HAA), AB and AC, and the corresponding antibodies were distinguished by immunodiffusion, blocking of antigens with type-specific antibodies, and absorption of antibodies by saturation with heterotypic antigens. Both determinants of each antigen were carried on one particle. Blocking of antigens with type-specific antibodies was used for distinguishing a mixed infection with two types of antigens from combinations of determinants on one particle. Monkey antisera to both types were suitable reagents for type differentiation. Rabbit antisera had anti-A but little or no anti-B or anti-C reactivity, and thus, although suitable for screening, were unsatisfactory for type differentiation. Carriers of the two types were found in separate dialysis units, consistent with the concept of two independent infectious agents. Sera of staff members who contracted hepatitis in these units contained the type circulating in the unit concerned.