Immunoglobulin A responses to Puumala hantavirus.

Puumala hantavirus (PUUV) causes nephropathia epidemica (NE), a form of haemorrhagic fever with renal syndrome that occurs in northern and central Europe. The immunoglobulin A (IgA) response in NE patients was studied. The levels of total serum IgA in acute-phase samples from NE patients were found to be significantly elevated when compared with the levels in healthy controls. ELISAs for detection of the IgA1 and IgA2 responses against each PUUV structural protein (N, G1 and G2) were developed and evaluated. Sequential sera from NE patients (acute, convalescent, 2-year) and 10-20 year NE-convalescent sera were examined. Most patients developed detectable levels of IgA1 against N and G2, while the G1 responses were low or undetectable. Seven of nine 10-20 year sera contained virus-specific IgA1, which may indicate the prolonged presence of viral antigens after the initial infection. PEPSCAN analysis revealed several IgA-reactive antigenic regions in the N protein. Serum IgA and IgG was purified by affinity chromatography and examined by a virus-neutralization assay. Three of five sera from acute-phase NE patients contained neutralizing IgA1. The diagnostic potential of the PUUV-specific IgA1 response was evaluated. The N and G2 assays showed specificities of 100% with sensitivities of 91 and 84%, respectively, compared with an IgM mu-capture ELISA. Several NE patients, clinically diagnosed for acute PUUV infection, with borderline or undetectable levels of PUUV-specific IgM, were found to be highly positive for the presence of PUUV N-specific serum IgA1, proving the diagnostic value of IgA analysis as a complement to detection of IgM.