Serotypes of hepatitis B antigen (HBs Ag): the problem of "new" determinants, as exemplified by "t"

The principal antigenic determinants of hepatitis-B surface antigen (HBs Ag) are specified by distinct genotypes of hepatitis-B virus (HBV). This hypothesis still stands undisproven. These specificities include the common antigen(s), called a, and two pairs of subdeterminants, d/y and w/r. The members of each pair are in general mutually exclusive, resulting in four "primary" phentoypes of HBs Ag: adw, adr, ayw, and ayr. The newer "a(w) subcategories" probably also reflect differences in viral genotype; if so, the number of "subtypes" rises to eight. Further subdivision into independent strains of HBV may eventually become feasible on the basis of one or more of the following "new" HBs Ag reactivities, once these have been shown to be virus-coded: g, n, q, x, and t. The requirements for accepting new reactivities as HBV-specific, and for comparing them among themselves, are discussed, using t as an example. A peculiar feature of t is its variable physical behaviour: "overt" t reactivity is correlated with the adw phenotype; "cryptic" [t], with ayw; while adr and ayr have so far been t-negative. Pending the indispensable tests of experimental transmission, this uneven distribution would seem to suggest that expression of t is regulated by the HBV genome.