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Syk Tyrosine Kinase and B Cell Antigen Receptor (BCR) Immunoglobulin-α Subunit Determine BCR-mediated Major Histocompatibility Complex Class II–restricted Antigen Presentation

1998; Rockefeller University Press; Volume: 188; Issue: 5 Linguagem: Inglês

10.1084/jem.188.5.819

1540-9538

Danielle Lankar, Volker Briken, Kristin Adler, Peter Weiser, Sylvanie Cassard, Ulrich Blank, Mireille Viguier, Christian Bonnerot,

Immune Cell Function and Interaction

Stimulation of CD4+ helper T lymphocytes by antigen-presenting cells requires the degradation of exogenous antigens into antigenic peptides which associate with major histocompatibility complex (MHC) class II molecules in endosomal or lysosomal compartments. B lymphocytes mediate efficient antigen presentation first by capturing soluble antigens through clonally distributed antigen receptors (BCRs), composed of membrane immunoglobulin (Ig) associated with Ig-α/Ig-β heterodimers which, second, target antigens to MHC class II–containing compartments. We report that antigen internalization and antigen targeting through the BCR or its Ig-α–associated subunit to newly synthesized class II lead to the presentation of a large spectrum of T cell epitopes, including some cryptic T cell epitopes. To further characterize the intracellular mechanisms of BCR-mediated antigen presentation, we used two complementary experimental approaches: mutational analysis of the Ig-α cytoplasmic tail, and overexpression in B cells of dominant negative syk mutants. Thus, we found that the syk tyrosine kinase, an effector of the BCR signal transduction pathway, is involved in the presentation of peptide– MHC class II complexes through antigen targeting by BCR subunits.