Immunohistochemical and in situ hybridization studies of influenza A virusinfection in human lungs

Influenza viruses are responsible for acute febrile respiratory disease. Wh en deaths occur, definitive diagnosis requires viral isolation because no c haracteristic viral inclusions are seen. We examined the distribution of in fluenza A virus in tissues from 8 patients with fatal infection using 2 imm unohistochemical assays (monoclonal antibodies to nucleoprotein [NP] and he magglutinin [HA]) and 2 in situ hybridization (ISH) assays (digoxigenin-lab eled probes that hybridized to HA and NP genes). Five patients had prominen t bronchitis; by immunohistochemical assay, influenza A staining was presen t focally in the epithelium of larger bronchi (intact and detached necrotic cells) and in rare interstitial cells. The anti-NP antibody stained primar ily cell nuclei, and the anti-HA antibody stained mainly the cytoplasm. In 4 of these cases, nucleic acids (ISH) were identified in the same areas. Th ree patients had lymphohistiocytic alveolitis and showed no immunohistochem ical or ISH staining. Both techniques were useful for detection of influenz a virus antigens and nucleic acids in formalin-fixed paraffin-embedded tiss ues and can enable further understanding of fatal influenza A virus infecti ons in humans.