Cross-reactions between 2, 4-dinitrophenyl and menadione (vitamin K3) and the general problem of antibody specificity.

Early and late antisera to 2, 4-dinitrophenyl (DNP) and to menadione (K3)4 were compared for reactivity with diverse DNP and K3 ligands. Late antisera were generally more reactive (higher affinity) than early antibodies. Nevertheless, the early antibodies had higher affinity for homologous ligands than late antibodies had for heterologous ligands; the exception, a small (ca. 5%) and possibly heteroclitic subset from late anti-DNP sera, had higher affinity for K3-butyrate than for DNP-lysine. Early antisera appeared to be more specific than late antisera by one criterion (the precipitin reaction), but less specific by a more fundamental criterion (KO/KX, the ratio of intrinsic affinities for homologous and cross-reacting ligands). By several methods (precipitation, binding to heterologous immunoadsorbants) 25 to 75% of the antibodies in both anti-DNP and anti-K3 sera were cross-reactive; even more cross-reactivity was evident by equilibrium dialysis, where it appeared that virtually all anti-DNP antibodies can bind K3 and that virtually all anti-K3 can bind DNP. This extreme level of cross-reaction is not as "strange" as was once thought, it seems unwarranted to regard this cross-reaction as support for the view that antibodies in general are multispecific.