Lung histopathological findings in fatal pandemic influenza A (H1N1)

Abstract

Objective: To describe the lung pathological changes in influenza A (H1N1) viral pneumonia. We studied morphological changes, nitro-oxidative stress and the presence of viral proteins in lung tissue. Methods and patients: Light microscopy was used to examine lung tissue from 6 fatal cases of pandemic influenza A (H1N1) viral pneumonia. Fluorescence for oxidized dihydroethydium, nitrotyrosine, inducible NO synthase (NOS2) and human influenza A nucleoprotein (NP) (for analysis under confocal microscopy) was also studied in lung tissue specimens. Results: Age ranged from 15 to 50 years. Three patients were women, and 5 had preexisting medical conditions. Diffuse alveolar damage (DAD) was present in 5 cases (as evidenced by hyaline membrane formation, alveolo-capillary wall thickening and PMN infiltrates), and interstitial fibrosis in one case. In the fluorescence studies there were signs of oxygen radical generation, increased NOS2 protein and protein nitration in lung tissue samples, regardless of the duration of ICU admission. Viral NP was found in lung tissue samples from three patients. Type I pneumocytes and macrophages harbored viral NP, as evidenced by confocal immunofluorescence microscopy. Resultados histopatológicos pulmonares en la gripe A (H1N1) pandémica letalResumen Objetivo: Describir la histopatología pulmonar de pacientes que fallecieron con neumonía por virus de la influenza A (H1N1), el tipo celular infectado por el virus y la presencia de stress oxidativo y nitrosativo. Métodos: Hemos examinado tejido pulmonar de 6 pacientes fallecidos en la UCI con el diagnós-tico de infección por el virus influenza A (H1N1) (15---50 años de edad) mediante (i) microscopía óptica, (ii) microscopia confocal con tinciones específicas para diferentes tipos celulares (aquoporina 5, factor Von Willebrand, proteína D del surfactante), (iii) inmunofluorescencia (IF) para sonda de dihidroetidio oxidado, óxido nítrico sintasa inducible (NOS2), anti-3-nitrotirosina y nucleoproteína (NP) del virus de la influenza A (H1N1). Resultados: (1) En 5 casos se encontró daño alveolar difuso (DAD), evidenciado mediante la observación de membranas hialinas, engrosamiento de la pared alveolo-capilar e infiltración de PMN, asociado con hemorragia intensa en un paciente. Un caso presentó fibrosis intersticial.(2) Se demostró en todos los casos aumento de la inmuno-reactividad para DHE oxidado, NOS2 y 3-nitrotirosina independientemente de la duración de la estancia en la UCI. (3) Se encontró NP viral en tres pacientes. (4) El virus se localiza en los neumocitos tipo I y en macrófagos alveolares. Conclusiones: El tejido pulmonar de pacientes fallecidos con neumonía por virus de la influenza A (H1N1) evidencia hallazgos histológicos compatibles con DAD. El estrés nitro-oxidativo prolongado está presente a pesar del tratamiento antiviral. Las proteínas virales pueden permanecer en el tejido pulmonar durante períodos prolongados de tiempo, albergándose en los macrófagos y neumocitos tipo I.

Metabolic host response and therapeutic approaches to influenza infection

“…In a survey by Nin et al on pandemic A/H1N1 influenza infection, all cases showed increased levels of iNOS protein, tyrosine nitration, and oxygen free radicals, indicating the production of peroxynitrite. Their results revealed the involvement of oxidative and nitrative stress in the pathogenesis of H1N1 influenza virus-induced acute respiratory distress syndrome (ARDS) [15]. Influenza-induced cytokines such as IFNγ stimulate NO release from human airway epithelial cells [150][151][152].…”

“…In people with influenza infection, increased levels of DNA, lipid, and protein oxidation products are found in plasma and urine [12][13][14]. Also, increased levels of ROS and inducible nitric oxide synthase (iNOS) have been observed as markers of oxidative stress in the lungs of people who died due to pandemic influenza infection [15]. ROS-producing enzymes induced by influenza infection mainly include NADPH oxidase (Nox) and xanthine oxidase, upregulation of which causes the impaired defensive function of antioxidants [16].…”

Clinicopathological Findings of Four Cases of Pure Influenza Virus A Pneumonia

“…They also reported a 24-year-old woman who died after a 21-day illness who used ECMO from day seven onward, and the main pathological finding was organized DAD (21). In addition, Nin et al described six autopsied cases and found that granulation tissue was present in four (8,16,36, and 45 days mechanical ventilation) (22). The patient with the longest time from diagnosis to death (45 days mechanical ventilation) had residual fibrosis with intense granulation tissue repair and interstitial inflammation.…”

“…The patient with the longest time from diagnosis to death (45 days mechanical ventilation) had residual fibrosis with intense granulation tissue repair and interstitial inflammation. They concluded that signs of DAD evolved over time from exudative to proliferative and fibrotic changes according to the duration of mechanical ventilation (22).…”

Pulmonary function in patients with pandemic H1N1

“…The research of Marchiori et al (9) and Nin et al (10) showed pulmonary histopathology in patients contaminated with H1N1 after death. In general they presented diffuse alveolar exudative damage, varying degrees of hemorrhage and alveolar edema, necrosis and sloughing of the epithelium of the bronchioles, atelectasis of the alveoli and records of thrombus.…”