Biochemical analysis of CTLA-4 immunoreactive material from human blood

BMC Immunol. 2009 Sep 22;10:51. doi: 10.1186/1471-2172-10-51.

Abstract

Background: CTLA-4 was initially described as a membrane-bound molecule that inhibited lymphocyte activation by interacting with B7.1 and B7.2 molecules on antigen presenting cells. Alternative splicing of mRNA encoding the CTLA-4 receptor leads to the production of a molecule (sCTLA-4) that lacks a membrane anchor and is therefore secreted into the extracellular space. Despite studies finding that people with autoimmune disease more frequently express high levels of sCTLA-4 in their blood than apparently healthy people, the significance of these findings is unclear.

Methods: Molecules isolated from blood using CTLA-4 specific antibodies were analyzed with ligand binding assays, mass spectroscopy, and biochemical fractionation in an effort to increase our understanding of CTLA-4 immunoreactive material.

Results: Mass spectroscopy analysis of the molecules recognized by multiple CTLA-4-specific antibodies failed to identify any CTLA-4 protein. Even though these molecules bind to the CTLA-4 receptors B7.1 and B7.2, they also exhibit properties common to immunoglobulins.

Conclusion: We have identified molecules in blood that are recognized by CTLA-4 specific antibodies but also exhibit properties of immunoglobulins. Our data indicates that what has been called sCTLA-4 is not a direct product of the CTLA-4 gene, and that the CTLA-4 protein is not part of this molecule. These results may explain why the relationship of sCTLA-4 to immune system activity has been difficult to elucidate.

MeSH terms

  • Antibodies, Monoclonal / immunology
  • Antigen-Antibody Complex / blood
  • Antigen-Antibody Complex / chemistry
  • Antigen-Antibody Complex / immunology*
  • Antigens, CD / blood
  • Antigens, CD / chemistry
  • Antigens, CD / immunology
  • Antigens, CD / metabolism*
  • B7-1 Antigen / immunology
  • B7-1 Antigen / metabolism
  • B7-2 Antigen / immunology
  • B7-2 Antigen / metabolism
  • Blood Proteins / chemistry
  • Blood Proteins / immunology
  • Blood Proteins / metabolism*
  • CTLA-4 Antigen
  • Chemical Fractionation
  • Humans
  • Immunomodulation
  • Mass Spectrometry
  • Myasthenia Gravis / blood
  • Myasthenia Gravis / immunology*
  • Protein Binding

Substances

  • Antibodies, Monoclonal
  • Antigen-Antibody Complex
  • Antigens, CD
  • B7-1 Antigen
  • B7-2 Antigen
  • Blood Proteins
  • CTLA-4 Antigen
  • CTLA4 protein, human