Synthetic positive controls for ELISA test kits for detection of IgA and IgM antibodies to Chlamydia trachomatis

Abstract

The enzyme-linked immunosorbent assay (ELISA) is the most informative and versatile method of serological diagnostics. The possibility of detecting by ELISA specific antibodies of different classes allow to differentiate primary infectious process and its remission, exacerbation and chronic disease (holding of differential diagnosis). This approach is implemented in the methodology for evaluation of patients for presence of humoral immune response against the causative agent of urogenital chlamydiosis. As with other infections immediately after Chlamydia trachomatis infection the specific IgM antibodies are formed, and subsequently basic projective antibodies of IgG class are synthesized. However, at exacerbation of chronic urogenital chlamydiosis specific IgA antibodies can be synthesized. That is why comprehensive evaluation of patients for presence of humoral immune response to Ch. trachomatis involves plasma testing of specific antibodies of all three classes. The essential problem in the production of ELISA diagnostic kits is obtaining of positive control. The classic version of positive control is human blood plasma containing specific antibodies. But specific IgM- and IgA-positive sera are deficit raw materials. This fact can significantly limit the production of diagnostic kits, especially in case of large-scale manufacture. We have suggested methodological approach to use of synthetic positive controls in indirect ELISA kits based on conjugate of normal human IgM (IgA) and monoclonal antibodies against major outer membrane protein of Ch. trachomatis. It was found that it’s possible to realize such task by means of NHS ester-maleimide-mediated conjugation (by sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate) and reductive amination-mediated conjugation (by sodium periodate). It was found that synthetic positive controls obtained by different methods are characterized by higher titer compared to IgM- and IgA-positive high-titer serum. However, positive control obtained by NHS ester-mediated maleimide conjugation has the best titration profile characteristics, at the release time and after one-week storage at37 °C.