Immunohistochemical and in situ hybridization studies of influenza A virus infection in human lungs

Influenza viruses are responsible for acute febrile respiratory disease. When deaths occur, definitive diagnosis requires viral isolation because no characteristic viral inclusions are seen. We examined the distribution of influenza A virus in tissues from 8 patients with fatal infection using 2 immunohistochemical assays (monoclonal antibodies to nucleoprotein [NP] and hemagglutinin [HA]) and 2 in situ hybridization (ISH) assays (digoxigenin-labeled probes that hybridized to HA and NP genes). Five patients had prominent bronchitis; by immunohistochemical assay, influenza A staining was present focally in the epithelium of larger bronchi (intact and detached necrotic cells) and in rare interstitial cells. The anti-NP antibody stained primarily 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. Three patients had lymphohistiocytic alveolitis and showed no immunohistochemical or ISH staining. Both techniques were useful for detection of influenza virus antigens and nucleic acids in formalin-fixed paraffin-embedded tissues and can enable further understanding of fatal influenza A virus infections in humans.

A novel immunohistochemical assay for the detection of Ebola virus in skin: implications for diagnosis, spread, and surveillance of Ebola hemorrhagic fever. Commission de Lutte contre les Epidémies à Kikwit

Laboratory diagnosis of Ebola hemorrhagic fever (EHF) is currently performed by virus isolation and serology and can be done only in a few high-containment laboratories worldwide. In 1995, during the EHF outbreak in the Democratic Republic of Congo, the possibility of using immunohistochemistry (IHC) testing of formalin-fixed postmortem skin specimens was investigated as an alternative diagnostic method for EHF. Fourteen of 19 cases of suspected EHF met the surveillance definition for EHF and were positive by IHC. IHC, serologic, and virus isolation results were concordant for all EHF and non-EHF cases. IHC and electron microscopic examination showed that endothelial cells, mononuclear phagocytes, and hepatocytes are main targets of infection, and IHC showed an association of cellular damage with viral infection. The finding of abundant viral antigens and particles in the skin of EHF patients suggests an epidemiologic role for contact transmission. IHC testing of formalin-fixed skin specimens is a safe, sensitive, and specific method for laboratory diagnosis of EHF and should be useful for EHF surveillance and prevention.

Congenital syphilis in a newborn: an immunopathologic study

A 3-week-old girl presented to the emergency room with respiratory distress and generalized maculopapular rash. The newborn was hospitalized with a presumptive diagnosis of congenital syphilis, but she died after 2 days of therapy. Tissue from the gastrointestinal tract, brain, liver, spleen, and lung was studied by using direct fluorescent antibody and immunohistochemical analysis (IHC) for Treponema pallidum. The inflammatory infiltrate was characterized by using IHC against CD3, CD20, CD68, and smooth muscle actin. The diagnosis of congenital syphilis was confirmed by demonstrating spirochetes in tissues with IHC and direct fluorescent antibody examination. IHC showed abundant treponemes in the small intestine and liver and occasional spirochetes in the meninges. Bacteria were seen as intact spirochetes, granular staining, or large extracellular collections of antigen. A constant pathologic feature throughout the tissues was concentric macrophage (CD68-positive) infiltrate around vessels, giving an onion-skin appearance. IHC identified the macrophages as the prime immune response in congenital syphilis.