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J. Exp. Med.,
Volume 188, Number 9, November 2, 1998 1691-1703
By
From the Department of Immunobiology, DNAX Research Institute of Molecular and Cellular
Biology, Palo Alto, California 94304
Memory B cells isolated from human tonsils are characterized by an activated cell surface phenotype, localization to mucosal epithelium, expression of somatically mutated immunoglobulin
(Ig) variable (V) region genes, and a preferential differentiation into plasma cells in vitro. In
spleens of both humans and rodents, a subset of memory B cells is believed to reside in the
marginal zone of the white pulp. Similar to tonsil-derived memory B cells, splenic marginal
zone B cells can be distinguished from naive follicular B cells by a distinct cell surface phenotype and by the presence of somatic mutations in their Ig V region genes. Although differences
exist between human naive and memory B cells, no cell surface molecules have been identified
that positively identify all memory B cells. In this study, we have examined the expression of
the receptor-type protein tyrosine phosphatase CD148 on human B cells. CD148+ B cells
present in human spleen exhibited characteristics typical of memory B cells. These included an
activated phenotype, localization to the marginal zone, the expression of somatically mutated
Ig V region genes, and the preferential differentiation into plasma cells. In contrast, CD148
B
cells appeared to be naive B cells due to localization to the mantle zone, the expression of surface antigens typical of unstimulated B cells, and the expression of unmutated Ig V region
genes. Interestingly, CD148+ B cells also coexpressed CD27, whereas CD148
B cells were
CD27
. These results identify CD148 and CD27 as markers which positively identify memory
B cells present in human spleen. Thus, assessing expression of these molecules may be a convenient way to monitor the development of memory B cell responses in immunocompromised individuals or in vaccine trials.
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