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J. Exp. Med.,
Volume 188, Number 1, July 1, 1998 145-155
By



From the * Institute of Experimental Immunology, Department of Pathology, University Hospital,
CH-8091 Zürich, Switzerland; and the Coligation of CD19, a molecule expressed during all stages of B cell development except plasmacytes, lowers the threshold for B cell activation with anti-IgM by a factor of 100. The cytoplasmic tail of CD19 contains nine tyrosine residues as possible phosphorylation sites and is
postulated to function as the signal transducing element for complement receptor (CR)2. Generation and analysis of CD19 gene-targeted mice revealed that T cell-dependent (TD) antibody responses to proteinaceous antigens were impaired, whereas those to T cell-independent
(TI) type 2 antigens were normal or even augmented. These results are compatible with earlier
complement depletion studies and the postulated function of CD19. To analyze the role of
CD19 in antiviral antibody responses, we immunized CD19
Institute for Genetics, University of Cologne, D-50931
Cologne, Germany
/
mice with viral antigens of TI-1,
TI-2, and TD type. The effect of CD19 on TI responses was more dependent on antigen dose
and replicative capacity than on antigen type. CR blocking experiments confirmed the role of
CD19 as B cell signal transducer for complement. In contrast to immunization with protein
antigens, infection of CD19
/
mice with replicating virus led to generation of specific germinal centers, which persisted for >100 d, whereas maintenance of memory antibody titers as
well as circulating memory B cells was fully dependent on CD19. Thus, our study confirms a
costimulatory role of CD19 on B cells under limiting antigen conditions and indicates an important role for B cell memory.
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