Complement-fixation analysis of four subtypes of foot-and-mouth disease virus type A.

Complement-fixation patterns were established for four subtypes of foot-and-mouth disease virus by block assays against homologous and heterologous antiserum. Inhibition of fixation by excess antigen was observed in most homologous systems but rarely in the heterologous systems. The heterologous antibody titers were, in all instances, considerably lower than those for the homologous systems. Although relatively high dilutions of antiserum may be desirable for subtyping, higher concentrations of antibody should be used for determining serological types.