Evidence for an important interaction between a complement-derived CD21 ligand on follicular dendritic cells and CD21 on B cells in the initiation of IgG responses

J Immunol. 1998 Nov 1;161(9):4549-54.


The addition of Ags to mononuclear leukocyte cultures typically elicits modest Ab responses, implying that cosignals beyond those provided by T cells and macrophages may be needed. Recently, we reported that Ab responses could be dramatically enhanced (10-1000-fold) by the addition of follicular dendritic cells (FDC), suggesting that FDC may provide an important costimulatory signal. This result prompted a study of molecules involved in FDC-mediated enhancement of Ab responses stimulated by specific Ag with memory T and B cells or nonspecifically by the addition of LPS. In this study, we report evidence supporting the concept that FDC bear a ligand that engages complement receptor II (CR2 or CD21) on B cells and provides a critical cosignal for both Ag-specific and polyclonal responses. A blockade of the CR2 ligand on FDC by the use of soluble CR2 or a blockade of CR2 on B cells by use of CR2 knockout mice (or B cells with CR2 blocked) reduced Ab responses from the microg/ml to the ng/ml range (10-1000-fold reductions). FDC from C3 knockout mice, which cannot generate the CR2-binding fragments (iC3b, C3d, and C3dg), were unable to provide costimulatory activity, suggesting the CR2 ligand on FDC consists of C3 fragments. FDC trap complement-activating Ag-Ab complexes, and it appears that FDC present B cells with both specific Ag to engage B cell receptors and a CR2 ligand to engage B cell-CR2. In short, optimal induction of specific Ab responses appears to require the combination of specific Ag and costimulatory molecules from both T cells and FDC.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antibody Formation*
  • B-Lymphocytes / immunology*
  • Complement C3 / deficiency
  • Complement C3 / genetics
  • Complement C3 / pharmacology
  • Complement C3 / physiology*
  • Complement System Proteins / immunology*
  • Dendritic Cells / immunology*
  • Female
  • Immunoglobulin G / biosynthesis*
  • Lymphocyte Activation
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Receptors, Complement 3d / immunology*


  • Complement C3
  • Immunoglobulin G
  • Receptors, Complement 3d
  • Complement System Proteins