Layered immunologic memory

Distinct populations of antibody-producing memory immune cells arise due to vaccination according to study published online this week in Nature Immunology.

Memory B cells ― the immune system's surveillance team with a 'memory' for specific microbes - can rapidly respond to subsequent infections by secreting pathogen-specific antibodies. Jean-Claude Weill and his colleagues devised a method in mice to 'visualize' these memory B cells by permanently marking the cells during immunization to express a fluorescent protein. The authors followed the immunized mice for over a year and identified several subsets of memory B cells existing in the spleen and bone marrow. These B cells had the ability make both IgM or IgG type antibodies ― which can recognize microbes in the same way but dictate differing immune responses that contribute to pathogen clearance.

Weill and colleagues found IgM memory cells can undergo further 'education,' which fine-tunes their antibody responses, in the body's germinal centers ― specialized areas necessary for generating immune responses. The scientists found that in the germinal centers, IgM can in fact switch to IgG-type memory cells. IgG memory cells, in contrast, do not re-enter germinal cells, and instead immediately commence secreting antibodies upon subsequent infection. Weill and colleagues found that IgM memory cells persist for a longer period, over the entire 12-month observation period, whereas IgG memory cells wane after 6 months.

These findings challenge the previous notions that IgM B cells were the early responders and that the IgG B cells represent long-term memory cells necessary for antibody production.