Characterization of antibodies to nerve growth factor: assay-dependent variability in the cross-reactivity with other neurotrophins.

The neurotrophin family of growth factors consists of proteins sharing a sizable degree of amino acid sequence and structural homology. These similarities greatly increase the probability that antibodies directed against any single neurotrophin may cross-react with other family-members. Various investigators have documented such cross-reactivity can occur under experimental conditions, although the extent of cross-reactivity reported in different studies has varied greatly. Although the use of different antibody preparations may have contributed to the differing degrees of cross-reactivity observed, it is important to note that different assay conditions were also used to evaluate cross-reactivity in the various studies. Little information is currently known about how antibody-antigen interactions vary as a function of the assay conditions used for the evaluation. The present study addressed this question by evaluating the cross-reactivity occurring between various neurotrophins and a single preparation of antibodies directed against purified mouse nerve growth factor-beta (beta-NGF) in a wide variety of immunological assay systems. Our results indicate that cross-reactivity between NGF antibodies and related neurotrophins can vary greatly depending upon the assay system chosen for the evaluation. These data strongly argue against transferring cross-reactivity data across various assay systems.