The local antibody response to R.S. virus infection in the respiratory tract.

Nasopharyngeal secretions were taken during the acute phase of illness from 66 infants and children admitted to hospital with lower respiratory tract infections. Second secretions were taken, after an interval of 7 days, from 33 of these patients. A significant increase in neutralizing activity to R.S. virus was demonstrated in the nasopharyngeal secretions of patients in response to severe R.S. virus infection. Seventeen out of 25 patients (68%) with R.S. virus infections developed a rise in secretory neutralizing titre, compared with only 1 out of 8 patients (13%) with respiratory infections not involving R.S. virus.A high titre of secretory neutralizing activity was found more often in the acute phase of illness in patients with R.S. virus infections, especially bronchiolitis, than in patients with respiratory infections not involving R.S. virus. Fifteen out of 34 patients (44%) with R.S. virus bronchiolitis were found to possess a neutralizing titre of (1/4) or more in their first secretions, compared with 4 out of 12 patients (33%) with R.S. virus infections other than bronchiolitis and 3 out of 20 patients (15%) with respiratory infections not involving R.S. virus.A quantitative analysis of the immunoglobulins present in the secretions indicated that IgA was the only immunoglobulin consistently present at a detectable concentration. The geometric mean values of IgA, IgM and IgG in the secretions examined were found to be 22.3, 4.3 and 5.3 mg./100 ml. respectively.The neutralizing activity against R.S. virus, present in the secretions, was shown to be due to specific IgA antibody. This was accomplished by removing the neutralizing activity in two secretions by absorption with anti-IgA serum.