Different B Cell Populations Mediate Early and Late Memory During an Endogenous Immune Response

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Science  10 Feb 2011:
DOI: 10.1126/science.1201730


Memory B cells formed in response to microbial antigens provide immunity to later infections; however, the inability to detect rare endogenous antigen-specific cells limits current understanding of this process. Using an antigen-based technique to enrich these cells, we found that immunization with a model protein generated B memory cells that expressed isotype-switched immunoglobulins (swIg) or retained IgM. The more numerous IgM+ cells were longer-lived than the swIg+ cells. However, swIg+ memory cells dominated the secondary response due to the capacity to become activated in the presence of neutralizing serum Ig. Thus, we propose that memory relies on swIg+ cells until they disappear and serum Ig falls to a low level, in which case memory resides with durable IgM+ reserves.