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Original Article |
Immunoreceptor Tyrosine–Based Activation Motif (Itam) Phosphorylation Modulates or Blocks B Cell Development, Depending on the Availability of an Igβ Cytoplasmic Tail
kraus{at}cbr.med.harvard.edu
To determine the function of immunoglobulin (Ig)
immunoreceptor tyrosine–based activation motif (ITAM) phosphorylation, we generated mice in which Ig
ITAM tyrosines were replaced by phenylalanines (Ig
FF/FF). Ig
FF/FFmice had a specific reduction of B1 and marginal zone B cells, whereas B2 cell development appeared to be normal, except that
1 light chain usage was increased. The mutants responded less efficiently to T cell–dependent antigens, whereas T cell–independent responses were unaffected. Upon B cell receptor ligation, the cells exhibited heightened calcium flux, weaker Lyn and Syk tyrosine phosphorylation, and phosphorylation of Ig
non-ITAM tyrosines. Strikingly, when the Ig
ITAM mutation was combined with a truncation of Igβ, B cell development was completely blocked at the pro-B cell stage, indicating a crucial role of ITAM phosphorylation in B cell development.
Key Words: mb-1 protein B cell antigen receptor ITAM B cell subsets gene targeting
Abbreviations used in this paper: BCR, B cell receptor; BM, bone marrow; ES, embryonic stem; ITAM, immunoreceptor tyrosine–based activation motif; MZ, marginal zone; PTK, protein tyrosine kinase; RT, room temperature; SH2, Src homology 2; TD, T cell–dependent; TI, T cell–independent.
© 2001 The Rockefeller University Press
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