Western immunoblots showing recognition of native DT by antiserum obtained from mice immunized with heat-killed recombinant S. gordonii. DT (1 μg) was separated on an SDS-10% PAGE gel. Mouse antisera: lane 1, S. gordonii DTA; lane 2, S. gordonii DTA2; lane 3, S. gordonii DTA3. P, preimmune serum; I, immune serum; +, anti-DT antiserum; M, prestained protein size markers (sizes shown in kilodaltons).