Evidence for a new antigen within the adenovirus capsid.

Complement-fixation and radioactive-agglutination tests were performed on purified preparations of adenovirus type 5 using specific antisera against capsid antigens and an antiserum which can detect an antigen (the P antigen) in infected cells which has many of the properties of the T antigen associated with infection by the oncogenic adenoviruscs. A serological reaction was detected between preparations containing intact virions and antihexon serum but not with antisera against fibres, penton bases and the P antigen. However, virus preparations which had been 'aged' at 4 ° , and in which electron microscopic examination revealed the presence of many broken capsids, did react in complement fixation and radioactive agglutination with all the antisera. It was concluded that within the adenovirus capsid there is a hitherto undescribed protein related to the P antigen.