Detection of alpha-interferon in nasopharyngeal secretions and sera in children infected with respiratory syncytial virus.

We investigated the relationship between respiratory syncytial virus (RSV) antigen and interferon (IFN) in nasopharyngeal secretions (NPS) and sera obtained from 252 patients infected with RSV. A total of 146 (57.9%) of 252 patients had IFN in NPS with a mean titer of 28 units/ml and IFN was detected in 164 (71.6%) of 229 patients in the acute stage sera with a mean titer of 28 units/ml. IFN activities were neutralized with antiserum to IFN-alpha. RSV antigen in NPS decreased on Day 5 and later in parallel with the change of mean titer of IFN in NPS. IFN in NPS was detected in 40 to 60% of the samples with some fluctuation in the acute stage. Within 4 days IFN was detected in more than 70% of the sera whereas on Day 5 and later the IFN positivity rate decreased in sera. RSV antigen in NPS decreased in the older patient groups. No significant change of positive rate of IFN in NPS was observed in different age groups and the mean titer of IFN in NPS and sera did not vary with age, except in those younger than 3 months and older than 3 years of age.