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J. Exp. Med.,
Volume 186, Number 12, December 15, 1997 2013-2021
By


From the * National Institute for Medical Research, Mill Hill, London, NW7 1AA, United
Kingdom; and the The tyrosine kinase Syk has been implicated as a key signal transducer from the B cell antigen
receptor (BCR). We show here that mutation of the Syk gene completely blocks the maturation of immature B cells into recirculating cells and stops their entry into B cell follicles. Furthermore, using radiation chimeras we demonstrate that this developmental block is due to the
absence of Syk in the B cells themselves. Syk-deficient B cells are shown to have the life span of
normal immature B cells. If this is extended by over-expression of Bcl-2, they accumulate in
the T zone and red pulp of the spleen in increased numbers, but still fail to mature to become
recirculating follicular B cells. Despite this defect in maturation, Syk-deficient B cells were seen
to give rise to switched as well as nonswitched splenic plasma cells. Normally only a proportion
of immature B cells is recruited into the recirculating pool. Our results suggest that Syk transduces a BCR signal that is absolutely required for the positive selection of immature B cells
into the recirculating B cell pool.
Department of Immunology, University of Birmingham Medical School,
Birmingham, B15 2TT, United Kingdom
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