The smallpox vaccine induces an early neutralizing IgM response

Area of Science:

• Immunology
• Virology
• Vaccinology

Background:

• Antibody responses following vaccinia virus (VacV) immunization protect against VacV and smallpox.
• While long-term anti-VacV antibody production is documented in humans, the early antibody response kinetics and protective role remain unclear.

Purpose of the Study:

• To investigate the kinetics and function of the early antibody response after VacV immunization.
• To determine the role of early IgM antibodies in neutralizing VacV and their contribution to host protection.

Main Methods:

• Induction of VacV infection in C57BL/6 mice.
• Analysis of T cell dependency and germinal center involvement in IgM production.
• Neutralization assays using infectious forms of VacV (MV, IMV, EV, EEV).
• Examination of anti-VacV antibodies in human subjects post-vaccination.

Main Results:

• VacV-neutralizing IgM antibodies were identified as early as 4 days post-infection in mice.
• IgM production was largely T cell-dependent but independent of the germinal center reaction.
• The identified IgM neutralized both mature intracellular virions (MIV) and extracellular enveloped virions (EEV).
• In humans, VacV IgM neutralizing antibodies were detected in a subset of individuals (IgG(lo) group) early after immunization.

Conclusions:

• An early neutralizing IgM antibody response occurs after VacV immunization in both mice and humans.
• This early IgM response likely plays a significant role in controlling VacV infection before a substantial IgG response develops.