Impaired Ca²⁺ mobilization by X-linked agammaglobulinaemia (XLA) B cells in response to ligation of the B cell receptor (BCR)

Abstract

XLA bone marrow samples were shown to contain B cells expressing IgM, and pre-B cells that express the μ-surrogate light chain (μψLC) complex, albeit at a reduced frequency to that found in normal bone marrow. Antibody ligation of μ heavy chain on these cells and an XLA B cell line did not induce a Ca²⁺ flux, whereas ligation of μ heavy chain on normal bone marrow cells, μψLC⁺ pre-B cell lines and an IgM⁺ B cell line did. The block in XLA B cells was not due to a defect in the basic mechanism of Ca²⁺ flux generation, as the cells responded well to thapsigargin. In addition, the defect did not affect T cells, which were shown to respond to CD3 antibody with a Ca²⁺ flux. Ligation of μ heavy chain on XLA bone marrow cells did, however, activate tyrosine kinases, resulting in tyrosine phosphorylation of a cellular protein with a molecular weight of approximately 115 kD. These results indicate that Btk may be necessary for the generation of the Ca²⁺ flux in response to ligation of μ heavy chain on B cells and μψLC⁺ pre-B.

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