The rap GTPases regulate B cell morphology, immune-synapse formation, and signaling by particulate B cell receptor ligands

Immunity. 2008 Jan;28(1):75-87. doi: 10.1016/j.immuni.2007.11.019.


B lymphocytes spread and extend membrane processes when searching for antigens and form immune synapses upon contacting cells that display antigens on their surface. Although these dynamic morphological changes facilitate B cell activation, the signaling pathways underlying these processes are not fully understood. We found that activation of the Rap GTPases was essential for these changes in B cell morphology. Rap activation was important for B cell receptor (BCR)- and lymphocyte-function-associated antigen-1 (LFA-1)-induced spreading, for BCR-induced immune-synapse formation, and for particulate BCR ligands to induce localized F-actin assembly and membrane-process extension. Rap activation and F-actin assembly were also required for optimal BCR signaling in response to particulate antigens but not soluble antigens. Thus by controlling B cell morphology and cytoskeletal organization, Rap might play a key role in the activation of B cells by particulate and cell-associated antigens.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Animals
  • Antigen Presentation / immunology
  • B-Lymphocytes / enzymology*
  • B-Lymphocytes / immunology
  • B-Lymphocytes / ultrastructure*
  • Cell Line
  • Enzyme Activation / physiology
  • Humans
  • Lymphocyte Activation / immunology*
  • Mice
  • Microscopy, Confocal
  • Microscopy, Electron, Scanning
  • Receptors, Antigen, B-Cell / immunology*
  • Receptors, Antigen, B-Cell / metabolism
  • Signal Transduction / immunology*
  • rap GTP-Binding Proteins / immunology
  • rap GTP-Binding Proteins / metabolism*


  • Actins
  • Receptors, Antigen, B-Cell
  • rap GTP-Binding Proteins