ACCURATE DETERMINATION OF ADJUVANT-ASSOCIATED PROTEIN OR PEPTIDE BY NINHYDRIN ASSAY

Modern peptide and subunit vaccines are increasingly having to rely on the use of immunological adjuvants to achieve effective immunity. How ever, the only, adjuvant currently approved use in humans is aluminium hydroxide, although many adjuvants are currently under preclinical de velopment. Determining immunogen concentration in the presence of adju vants such as aluminium hydroxide gel, liposomes or NISV has proved to be problematic. One approach has been to use radiolabelled antigens t o extrapolate concentration to a preparation using native immunogen. H owever, the use of a colorimetric assay would allow greater flexibilit y in terms of immunogen used and would reduce costs and remove safety problems. Of the colorimetric methods we have examined thus far, only the manual ninhydrin assay has produced consistent results with detect ion of microgram quantities of protein or peptide in the presence of N ISV or Alhydrogel, but not liposomes. As the assay relies on the detec tion of free amino groups after protein hydrolysis, peptides as well a s proteins may be effectively determined irrespective of amino acid co mposition, a considerable advantage over other colorimetric assay syst ems.