We have demonstrated that natural monoclonal antibodies (NmAbs) prepared from the spleens of either adult or neonatal non-immunized mice are polyspecific, i.e., they react with various self or non-self antigens. In the present study the polyspecificity of several NmAbs is analyzed in terms of dissociation constants (KDs) using a recently published sandwich-type immunoassay (Friguet et al. 1985). We calculated the NmAb KDs for various croos-reacting self (actin, myosin, tubulin, DNA) or non-self (spectrin, DNP-lysine, TNP-protein) antigens, and we compared the values obtained with those of experimentally-induced antibodies derived from immunized animals. The results show the NmAb KDs for macromolecule range between 10(-5) and 10(-10)M and, for a given antigen they are often of the same order of magnitude as those of induced monoclonal or polyclonal antibodies. On this basis, it appears that antibody specificity and affinity do not always correlate. In contrast to those of induced antibodies, the KDs for free hapten are high, whereas they are low when the same hapten is complexed to a macromolecule. Thus, it seems that although NmAbs and induced antibodies exhibit similar "functional affinities" for a macromolecule, they differ in their "intrinsic affinities" for a given epitope (hapten). Although the NmAbs examined exhibit similar broad reactivities for several antigens, their fine specificities for these antigens, as defined by the measurement of their KDs, are different. Thus, it appears that each NmAb can be considered unique.

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endoplasmic reticulum, and the Golgi apparatus complex. In i Supported by a USPHS Grant NS 05572 and a Fulbright Grant to Materials and Methods Preparation of Immunoreagents and Fixation.

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