LACK OF DETECTABLE ENHANCED PULMONARY HISTOPATHOLOGY IN COTTON RATS IMMUNIZED WITH PURIFIED F-GLYCOPROTEIN OF RESPIRATORY SYNCYTIAL VIRUS (RSV) WHEN CHALLENGED AT 3-6 MONTHS AFTER IMMUNIZATION

The cotton rat model has been used to evaluate the potential for immun ogens to induce respiratory syncytial virus (RSV)-enhanced pulmonary h istopathology. A recent study evaluated purified F protein in this mod el when animals were challenged intranasally with RSV 3 or 6 months af ter immunization. The authors concluded that the purified F protein wa s associated with the same level of histopathological changes as obser ved with the positive control, a formalin-inactivated RSV immunogen. T hree pathologists have independently evaluated the lung sections from the animals of this study and the results are reported in this article . In contrast to the previously published data, we have found that F p rotein was associated with a substantially milder and qualitatively di fferent response to that observed with the formalin-inactivated RSV va ccine. We concluded that the minimal histological changes observed and lack of clinical disease make it very difficult to assess the issue o f enhanced pulmonary RSV disease with the cotton rat model.