Regulation of cytoplasmic, surface and soluble forms of CD40 ligand in mouse B cells.
CD40 and CD40 ligand (CD40L) form one of most important receptor-ligand pairs that dock during T-B cell interactions as part of T-dependent antibody responses. It has been reported that among other cell types, B cells can express CD40L. Here we show that a large proportion of mouse B cells express CD40L in their cytoplasm, but not on the surface and that this is readily released as a soluble molecule. Thus, in their resting state up to 50% of mouse B cells express CD40L within their cytoplasm and both the proportion of cells expressing and the amount of CD40L is increased by signaling through immunoglobulin (Ig) or CD38. In contrast, T cell-derived signals such as CD40L (anti-CD40) or Th2-type cytokines cause a decrease in CD40L expression that is related to a release of a soluble form of the molecule from the cell. Supernatants from B cells activated with anti-Ig and anti-CD40 contain CD40L in a variety of forms (18 kDa, 33 kDa and 66 kDa) that are readily detectable by immunoprecipitation with CD40-Fc gamma fusion protein (CD40-Ig) followed by Western blotting with anti-CD40L antibody (MR1). The 33-kDa species is distinct from the 39-kDa membrane-bound molecule found in activated T cells or in resting B cells and appears to be a novel soluble form of CD40L. Inhibition of T cell-independent in vitro stimulation of B cells with CD40-Ig or anti-CD40L suggests that the B cell-derived soluble CD40L or CD40L expressed on the B cell surface can play a positive role in B cell proliferation.
Wykes
M
M
Department of Immunology, Imperial College School of Medicine, Hammersmith Hospital, London, GB.
Poudrier
J
J
Lindstedt
R
R
Gray
D
D
D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D019013:CD40 Antigens / Q000276:immunology / Q000378:metabolism*; D023201:CD40 Ligand; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism*; D005260:Female; D007424:Intracellular Fluid / Q000276:immunology / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008811:Mice, Inbred DBA; D011993:Recombinant Fusion Proteins / Q000276:immunology / Q000494:pharmacology; D012995:Solubility
D019138:Antibodies, Blocking; D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; D008024:Ligands; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D023201:CD40 Ligand