Antibody responses after sendai virus infection and their role in upper and lower respiratory tract disease in rats

Background and Purpose: Sendai virus infection in rats is an excellent mode l for studying development and role of host defenses throughout the respira tory tract after this infection. Therefore, development of serum antibody r esponses and disease were studied. Methods: Forty-two anesthetized pathogen-free 3- to 4- week-old LEW/NCr rat s were inoculated intranasally with Sendai virus. At postinoculation days 0 , 2, 3, 5, 8, 10, and 14, rats were euthanized by administration of a pento barbital sodium overdose followed by exsanguination, Serum was obtained fro m all animals, and nasal wash and bronchoalveolar lavage specimens were col lected during selected experiments. An ELISPOT assay was used to measure nu mbers of Sendai virus-specific antibody-forming cells in respiratory tract lymphoid tissue. Results: Recovery from disease and clearance of virus from respiratory trac t tissues coincided with development of serum antibody responses, Upper res piratory tract lymph nodes were the initial and major sites of appearance o f antibody-forming cells. Immunoglobulin G was the predominant subtype of t hese cells during recovery from the infection and in rats resistant to infe ction. Passive transfer of antisera or specific IgG protected the lower but not the upper respiratory tract. Conclusions: Circulating components of immunity have a major role in resist ance and recovery from disease in the lower respiratory tract, whereas loca l responses are likely involved in protection of the upper respiratory trac t. Local lymphoid tissues are the major production sites of IgG, which cont ributes to resistance to and recovery from respiratory tract diseases.