Polyclonal antisera species-specific

Antibodies to one protein antigen will often react (cross-react) with a wide variety of similar proteins from other species. For example, 15% of the antibody in a polyclonal antiserum to bovine serum albumin will react with human serum albumin. The molecular basis for this cross-reaction is not clearly understood, but cross-reactivity is believed to be caused by the presence of a configuration of amino acid side chains on another protein molecule that has a sufficient overall similarity to the specific configuration on the original antigen that induced antibody formation. 

Lynch et al. (47) made use of such an antiserum to isolate vWf mRNA from polysomes of cultured endothelial cells. From the enriched mRNA, single-stranded cDNA probes were derived. A cDNA library made from endothelial cell mRNA larger than 28S rRNA was screened with this probe. Nine clones out of 3000 were positive and appeared to share a common region. The longest clone of 2.4 kbp hybridized to an endothelial cell mRNA species that was about 9.5 kb in size. When mRNA from this partial cDNA clone was prepared with the SP6 RNA polymerase system and translated in a rabbit reticulocyte lysate, several polypeptides were produced that reacted with a specific polyclonal rabbit antibody against vWf, and also with four out of a collection of 30 monoclonal antibodies raised against vWf. Final proof that the cDNA clone isolated by Lynch et al. was an authentic vWF cDNA clone was obtained by comparing the sequence of the 3 end of the clone with the sequence of the carboxy-terminal 10 amino acids (270). 

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