Lymphocyte recognition of human parvovirus B19 non-structural (NS1) protein: associations with occurrence of acute and chronic arthropathy?

Immune recognition of recombinant parvovirus B19 non-structural (rNS1) prot ein was studied by immunoblot and lymphoproliferative assays in blood from the following B19 seropositive groups: B19 infected (n = 14), B19 exposed b ut non-infected (n = 16), other illness with rash (n = 3), chronic arthropa thy of unknown aetiology (n = 4) and healthy controls (n = 7), Sera from 11 B19 seronegative subjects were also studied. Sera collected at initial dia gnosis or at the time of accidental B19 exposure in pregnancy were tested f or NS1 antibody and evidence of B19 DNA by nested PCR, Follow-up specimens were obtained 3-12 months later for serological, PCR and proliferation stud ies. B19 DNA was detected sporadically in early specimens and in one follow -up specimen from a subject who developed chronic arthropathy after B19 inf ection. There was no correlation with development of arthropathy, NS1-speci fic Ige was detected in early sera from B19-infected and exposed subjects b ut to a lesser degree in follow-up specimens, and in only one healthy contr ol serum. No correlation with the presence of NS1-specific antibodies was f ound with development of acute or chronic arthropathy. Although lymphocyte proliferation in response to stimulation with rNS1 in vitro occurred at a h igher frequency in patients who developed acute and chronic joint manifesta tions after B19 infection, suggesting an association with this outcome, NS1 -reactive lymphocytes were also found in three B19 seronegative patients, t wo of whom had recently been exposed to B19 but had no illness. Hence, immu ne recognition of NS1 may be more indicative of recent infection with, or e xposure to, parvovirus B19 than associated with development of arthropathy as previously reported.