Clinical Science Workshop 6 Viral opportunistic infections Chairpersons : T . Weber ( Hamburg , D ) B . Brew ( Darlinghurst , AUS ) 99 Evaluation of a JC virus - speci c immunoglobulin M enzyme linked immunosorbent assay

Objectives: Progressive multifocal leukoencephalopathy (PML) is caused by a reactivated infection with the human polyomavirus JC (JCV). Primary infection with JCV has not been linked to any disease in humans. Using recombinant viral protein 1 (VP1) of JCV as antigen, we developed an enzyme linked immunosorbent assay (ELISA) for the detection of VP1-speciŽc IgM. Methods: Two different direct ELISA methods, two capture ELISA methods and an indirect ELISA were evaluated. Only the indirect ELISA yielded reproducible results. As standard ten sera with known titers of IgM antibodies to JCV were used in each assay. Human sera negative for IgG antibodies to VP1 were used as negative controls. Results: Evaluating 24 JCV-IgG antibody negative human sera the cut-off was identiŽed at 5£ mean optical densities (OD). All sera with a reproducible OD above 563 mOD were deŽned as positive. Of the ten reference sera with known titers, three were reproducibly positive by ELISA. The serum 81/11455 yielding the highest OD was used as internal reference. In a cohort selected for age, i.e. with groups of 20 for each age group from 0–10 to 90–100 years, four of 383 sera (1.04%) were positive. Of these patients two suffered from infections of the genitourinary tract, one was pregnant and one was treated with systemic corticosteroids. Conclusion: Using recombinant VP1 in an indirect ELISA, human IgM antibodies to JCV-VP1 can be reliably measured. Interference with speciŽc IgG, rheumatoid factor or instability of IgM molecules appear not to be relevant in this test. Urinary tract infections, pregnancy and immunosuppression are also known to cause BKV infections. Given the known aminoacid similarities between JCV-VP1 and BKVVP1, crossreactions between these viruses may account for these positive results. As recombinant VP1 of BKV was not available for evaluation, this could not be determined at this time.