CD22 ligation inhibits downstream B cell receptor signaling and Ca(2+) flux upon activation

Arthritis Rheum. 2013 Mar;65(3):770-9. doi: 10.1002/art.37818.


Objective: CD22 is a surface molecule exclusively expressed on B cells that regulates adhesion and B cell receptor (BCR) signaling as an inhibitory coreceptor of the BCR. Central downstream signaling molecules that are activated upon BCR engagement include spleen tyrosine kinase (Syk) and, subsequently, phospholipase Cγ2 (PLCγ2), which results in calcium (Ca(2+)) mobilization. The humanized anti-CD22 monoclonal antibody epratuzumab is currently being tested in clinical trials. This study was undertaken to determine the potential mechanism by which this drug regulates B cell activation.

Methods: Purified B cells were preincubated with epratuzumab, and the colocalization of CD22 and CD79α, without BCR engagement, was assessed by confocal microscopy. The phosphorylation of Syk (Y348, Y352) and PLCγ2 (Y759) as well as the Ca(2+) flux in the cells were analyzed by flow cytometry upon stimulation of the BCR and/or Toll-like receptor 9 (TLR-9). The influence of CD22 ligation on BCR signaling was assessed by pretreating the cells with epratuzumab or F(ab')(2) fragment of epratuzumab, in comparison with control cells (medium alone or isotype-matched IgG1).

Results: Epratuzumab induced colocalization of CD22 and components of the BCR independent of BCR engagement, and also reduced intracellular Ca(2+) mobilization and diminished the phosphorylation of Syk and PLCγ2 after BCR stimulation in vitro. Inhibition of kinase phosphorylation was demonstrated in both CD27- and CD27+ B cells, and this appeared to be independent of Fc receptor signaling. Preactivation of the cells via the stimulation of TLR-9 did not circumvent the inhibitory effect of epratuzumab on BCR signaling.

Conclusion: These findings are consistent with the concept of targeting CD22 to raise the threshold of BCR activation, which could offer therapeutic benefit in patients with autoimmune diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Antibodies, Monoclonal, Humanized / pharmacology*
  • Autoimmune Diseases / drug therapy*
  • Autoimmune Diseases / immunology
  • Autoimmune Diseases / metabolism
  • B-Lymphocytes / cytology
  • B-Lymphocytes / drug effects*
  • B-Lymphocytes / metabolism
  • CD79 Antigens / immunology
  • CD79 Antigens / metabolism
  • Calcium / metabolism*
  • Dose-Response Relationship, Immunologic
  • Female
  • Humans
  • Immunoglobulin Fab Fragments / pharmacology
  • Immunoglobulin G / pharmacology
  • Male
  • Middle Aged
  • Phospholipase C gamma / metabolism
  • Phosphorylation / drug effects
  • Phosphorylation / immunology
  • Receptor Protein-Tyrosine Kinases / metabolism
  • Sialic Acid Binding Ig-like Lectin 2 / antagonists & inhibitors*
  • Sialic Acid Binding Ig-like Lectin 2 / immunology
  • Sialic Acid Binding Ig-like Lectin 2 / metabolism
  • Signal Transduction / drug effects*
  • Signal Transduction / immunology
  • Toll-Like Receptor 9 / metabolism
  • Young Adult


  • Antibodies, Monoclonal, Humanized
  • CD22 protein, human
  • CD79 Antigens
  • CD79A protein, human
  • Immunoglobulin Fab Fragments
  • Immunoglobulin G
  • Sialic Acid Binding Ig-like Lectin 2
  • TLR9 protein, human
  • Toll-Like Receptor 9
  • epratuzumab
  • Receptor Protein-Tyrosine Kinases
  • TYRO3 protein, human
  • Phospholipase C gamma
  • Calcium