Long-lived antigen-induced IgM plasma cells demonstrate somatic mutations and contribute to long-term protection.

Long-lived plasma cells are critical to humoral immunity as a lifelong source of protective antibodies. Antigen-activated B cells-with T-cell help-undergo affinity maturation within germinal centres and persist as long-lived IgG plasma cells in the bone marrow. Here we show that antigen-specific, induced IgM plasma cells also persist for a lifetime.

Influenza virus-specific neutralizing IgM antibodies persist for a lifetime.

Detection of immunoglobulin M (IgM) antibodies has long been used as an important diagnostic tool for identifying active viral infections, but their relevance in later stages has not been clearly defined in vivo. In this study, we followed the kinetics, longevity, and function of influenza virus-specific IgM antibodies for 2 years following sublethal infection of mice with live mouse-adapted A/PR/8/34 virus or immunization with formalin-inactivated virus. These groups mounted robust protective immune responses and survived lethal challenges with 50 × 50% lethal dose (LD50) mouse-adapted A/PR/8/34 virus 600 days after the primary exposure.

Immunity to pre-1950 H1N1 influenza viruses confers cross-protection against the pandemic swine-origin 2009 A (H1N1) influenza virus.

The 2009 H1N1 influenza virus outbreak is the first pandemic of the twenty-first century. Epidemiological data reveal that of all the people afflicted with H1N1 virus, <5% are over 51 y of age. Interestingly, in the uninfected population, 33% of those >60 y old have pre-existing neutralizing Abs against the 2009 H1N1 virus.