Comparison of the kinetics of Puumala virus specific IgM and IgG antibody responses in nephropathia epidemica as measured by a recombinant antigen-based enzyme-linked immunosorbent assay and an immunofluorescence test.

Immunoglobulin M and G (IgM and IgG) responses were followed up to 6 months in patients with nephropathia epidemica (NE) by an enzyme-linked immunosorbent assay (ELISA) using a recombinant Puumala virus (PUU) nucleocapsid protein as antigen and an immunofluorescence test (IF) using PUU infected, acetone-treated cells as antigen. The recombinant protein was produced by cloning and expressing the nucleocapsid encoding gene of PUU as a polyhistidine fusion protein in Escherichia coli. The product was purified over a metal chelating ion affinity column. On admission, all 17 patients had an IgM response by both methods. The IgM titers decreased significantly by both methods 3 months after onset (ELISA P < 0.05 and IF P < 0.05). Four of six still had detectable IgM, however at low levels, after 6 months. Presence of specific IgG differed significantly on admission between the two methods: by ELISA 8 of 17 had detectable specific IgG, whereas by IF 15 of 17 had specific IgG (P < 0.02). There were 10 significant titer rises between acute and convalescent serum samples in the same patients by both methods. It is concluded that the IgG antibody response differs in the early phase of NE as measured by a method using a recombinant PUU nucleocapsid protein and a method using PUU infected acetone-treated cells as antigens. Furthermore, the results suggest that it is of importance to rely on specific IgM for serodiagnosis of NE during the acute phase.