amino acids and more preferably of at least about 14 amino acids it is also preferable that these oligopeptides peptides or fragments are identical to a portion of the amino acid sequence of the natural protein and contain the entire amino acid sequence of a small naturally occurring molecule short stretches of antigen amino acids may be fused with those of another protein such as klh and antibodies to the chimeric molecule may be produced monoclonal antibodies to an antigen may be prepared using any technique that provides for the production of antibody molecules by continuous cell lines in culture these include but are not limited to the hybridoma technique the human b cell hybridoma technique and the ebv hybridoma technique see for example kohler et al 1975 nature 256 495 497 kozbor et al 1985 j immunol methods 81 31 42 cote et al 1983 proc natl acad sci 80 2026 2030 and cole et al 1984 mol cell biol 62 109 120 various methods such as scatchard analysis in conjunction with radioimmunoassay techniques may be used to assess the affinity of antibodies for an antigen affinity is expressed as an association constant k a which is defined as the molar concentration of antigen antibody complex divided by the molar concentrations of free antigen and free antibody under equilibrium conditions the k a determined for a preparation of polyclonal antibodies which are heterogeneous in their affinities for multiple antigen epitopes represents the average affinity or avidity.