Polyreactivity as an acquired artefact, rather than a physiologic property, of antibodies: evidence that monoreactive antibodies may gain the ability to bind to multiple antigens after exposure to low pH.

Evidence is presented that monoreactive antibodies exposed to low pH may acquire the ability to bind to multiple antigens. M11, a murine, monoclonal, IgM(K) anti-goat IgG (GIgG) was purified from a hybridoma supernatant by elution at low pH from an anti-mu-Sepharose 4B affinity column. By measuring the specific antiGIgG activities and the affinity constants for the interactions of M11, pre- and post-affinity-purification, with GIgG, M11 was shown to be monoreactive before purification. Quite unexpectedly, however, the affinity-purified M11 reacted extensively with size-fractionated liver proteins when tested in an immunoblot, clearly indicating that it was polyreactive. It was concluded that the exposure to low pH had altered the M11 binding-site so as to allow it to bind to many different proteins. This phenomena provides an alternative basis for interpreting the polyreactivity observed following affinity-purification.