Immune history shapes human antibody responses to H5N1 influenza viruses.

Avian H5N1 influenza viruses are circulating widely in cattle and other mammals and pose a risk for a human pandemic. Previous studies suggest that older humans are more resistant to H5N1 infections due to childhood imprinting with other group 1 viruses (H1N1 and H2N2); however, the immunological basis for this is incompletely understood. Here we show that antibody titers to historical and recent H5N1 strains are highest in older individuals and correlate more strongly with year of birth than with age, consistent with immune imprinting.

Pathogenic determinants of disease.

is an emerging pediatric pathogen and is increasingly recognized as a leading etiology of septic arthritis, osteomyelitis, and bacteremia and an occasional cause of endocarditis in young children. The pathogenesis of disease begins with colonization of the upper respiratory tract followed by breach of the respiratory epithelial barrier and hematogenous spread to distant sites of infection, primarily the joints, bones, and endocardium. As recognition of as a pathogen has increased, interest in defining the molecular determinants of pathogenicity has grown.