Tracking human antigen-specific memory B cells: a sensitive and generalized ELISPOT system

In the interest of better understanding the role of human memory B cells in protection against disease, we developed an assay to quantitate antigen-specific memory B cells in human blood. This assay utilizes a 6-day polyclonal stimulation of PBMC followed by an antigen-specific ELISPOT for the detection of memory B cells that have differentiated into antibody secreting cells (ASC) in vitro. We have used this assay to demonstrate that the anthrax vaccine (AVA; BioThrax) elicits a substantial population of protective-antigen (PA) specific memory B cells, and these B cells satisfy the canonical surface phenotype of human memory B cells: CD19 + CD20 + Ig + CD27 + . These anti-PA antigen-specific memory B cells are IgG + and represent up to 2% of circulating IgG + B cells. Furthermore, these results confirm that vaccine-elicited memory B cells reside in the CD27 + B cell population. This ELISPOT-based system has been designed in a generalized manner, such that the assay can be rapidly adapted to detect human antigen-specific memory B cells of any given specificity. This method should be useful for quantitatively assessing the potency of vaccines and the longevity of B cell immunological memory to various vaccines or infectious diseases. D 2004 Elsevier B.V. All rights reserved.