Our study provides interesting observations about the clinical course, outcomes, and cost of the H1N1 influenza pandemic. Although patients with severe pulmonary complications of pandemic influenza infection have poor oxygenation and require significant ventilatory support and rescue therapies, their younger age and tendency to have fewer comorbid medical conditions contribute to their improved prognosis compared with patients with ALI from other causes. Both groups of patients consume enormous amounts of hospital resources, and physicians and policy makers must be aware of this when future pandemics arise. Identification of a Conserved B-cell Epitope on Reticuloendotheliosis Virus Envelope Protein by Screening a Phage-displayed Random Peptide Library BACKGROUND: The gp90 protein of avian reticuloendotheliosis-associated virus (REV-A) is an important envelope glycoprotein, which is responsible for inducing protective antibody immune responses in animals. B-cell epitopes on the gp90 protein of REV have not been well studied and reported. METHODS AND RESULTS: This study describes the identification of a linear B-cell epitope on the gp90 protein by screening a phage-displayed 12-mer random peptide library with the neutralizing monoclonal antibody (mAb) A9E8 directed against the gp90. The mAb A9E8 recognized phages displaying peptides with the consensus motif SVQYHPL. Amino acid sequence of the motif exactly matched (213)SVQYHPL(219) of the gp90. Further identification of the displayed B cell epitope was conducted using a set of truncated peptides expressed as GST fusion proteins and the Western blot results indicated that (213)SVQYHPL(219) was the minimal determinant of the linear B cell epitope recognized by the mAb A9E8. Moreover, an eight amino acid peptide SVQYHPLA was proven to be the minimal unit of the epitope with the maximal binding activity to mAb A9E8. The REV-A-positive chicken serum reacted with the minimal linear epitopes in Western blot, revealing the importance of the eight amino acids of the epitope in antibody-epitope binding activity. Furthermore, we found that the epitope is a common motif shared among REV-A and other members of REV group. CONCLUSIONS AND SIGNIFICANCE: We identified (213)SVQYHPL(219) as a gp90-specific linear B-cell epitope recognized by the neutralizing mAb A9E8. The results in this study may have potential applications in development of diagnostic techniques and epitope-based marker vaccines against REV-A and other viruses of the REV group. Reticuloendotheliosis viruses (REVs) are a group of viruses in the family Retroviridae, specifically gammaretroviruses in the same genus as mammalian C-type retroviruses [1] . The REV group includes defective REV-T [2, 3] , non-defective REV-A [4, 5] , chick syncytial virus (CSV) [6] , duck infectious anemia virus [7] , and spleen necrosis virus (SNV) [8] . Except for the defective REV-T, all isolated REV strains belong to a single serotype [5] and their genetic sequences show little variation [9] .