HPV antibody detection by ELISA with capsid protein L1 fused to glutathione S-transferase.

An alternative enzyme linked immunosorbent assay (ELISA) system was developed to analyze antibodies to human papillomavirus capsid antigens. The assay uses glutathione crosslinked to casein to capture the major capsid protein L1 from human papillomavirus (HPV) types 6b, 16 and 18 fused to glutathione S-transferase (GST) as antigen. The method allows efficient one-step purification of L1 fusion protein from crude bacterial lysates on ELISA plates coated with glutathione casein. The GST-L1 capture ELISA detected HPV 16 antibodies with high type specificity. Comparison with the current "gold-standard" for L1-serology that uses virus-like particles (VLP) as antigen demonstrated similar assay sensitivity. Pairwise comparison of the absorbance values of 105 human sera obtained in the two ELISA formats for HPV 16 showed a R(2) value of linear regression of 0.68. Conformity of the two ELISAs in classification of sera as HPV 16 L1 antibody-positive or -negative was verified with Cohen's kappa test, yielding a value of 0.62. These data indicate that the GST-L1 capture ELISA is similar in performance to the VLP ELISA. The ease of antigen production and purification in the GST-based ELISA will be advantageous to screen large sample numbers in vaccine trials or epidemiological studies examining immune responses to many HPV types in parallel.