Antibodies to parvovirus B19 non-structural protein are associated with chronic but not acute arthritis following B19 infection

Objective. To determine the incidence and significance of antibodies to the parvovirus B19 non-structural (NS1) protein in B19-infected persons during acute infection and convalescence. Methods. The B19 NS1 protein was expressed in SF9 cells using the baculovir us expression system and was used to prepare immunofluorescence slides. The se were used in a fluorescent antibody test to determine anti-B19 NS1 IgG i n a well-characterized cohort of 53 persons at the time of acute B19 infect ion and again after a follow-up period of 26-85 months. Results were examin ed for statistical significance by the use of Fisher's exact test. Results. NS1 antibodies were detected in five of 32 persons with acute B19 infection (four with arthritis) and 10 of 53 persons with past B19 infectio n (six with chronic arthritis and two with chronic arthritis and chronic fa tigue syndrome). Regarding the correlation of NS1 antibodies and arthritis, at the time of acute infection four of 24 per sons with arthritis had NS1 antibodies detected compared with one of eight persons with any other sympt oms (P = 1). During convalescence, eight of 20 persons with chronic arthrit is had NS1 antibodies compared with two of 33 with symptoms of any other ca tegory tall except one were asymptomatic) (P = 0.007). All 10 patients with NS1 antibodies during convalescence had arthritis during acute infection. which persisted in eight persons until the time of follow-up. Conclusion. Antibodies to parvovirus B19 NS1 protein are associated with ch ronic but not with acute arthritis after B19 infection.