Mitogenicity of anti-Thy-1 monoclonal antibodies attributable to an Fc-dependent mechanism

Eur J Immunol. 1993 Oct;23(10):2649-54. doi: 10.1002/eji.1830231039.

Abstract

We analyzed the mechanism by which certain anti-Thy-1 monoclonal antibodies (mAb) activate T cells directly without additional stimuli. Using a panel of rat anti-Thy-1 antibodies which included more than 30 IgG2c mAb, we found that only the IgG2c isotype was able to induce a strong proliferative response in both resting T cells and a T cell lymphoma, suggesting that this form of T cell activation is isotype restricted and might be a consequence of a unique physico-chemical property of the IgG2c heavy chain. Results from surface distribution studies of Thy-1 molecules, following specific interactions with anti-Thy-1 antibodies of different isotypes, again showed that only IgG2c mAb formed Thy-1 aggregates of high valence on the surface of a T cell lymphoma, and such clustering always evoked a biological response. This led us to propose that IgG2c mAb have the inherent tendency to self-associate, probably through homophilic Fc-Fc contacts, and that this feature renders anti-Thy-1 mAb mitogenic. To prove this, we set up cross-inhibition studies with randomly selected mitogenic (IgG2c) and nonmitogenic (IgG2b) anti-Thy-1 mAb. The results clearly demonstrated that IgG2c antibodies enhance their own binding, analogous to the new form of antibody binding that was recently demonstrated between murine IgG3 mAb and a multivalent antigen. Confirmation of this was also provided by IgG2c-derived F(ab')2 fragments, which were unable to cause proliferation. Furthermore, masking the Fc part of cell-bound IgG2c mAb with a monomeric and thus non-aggregating IgG-binding protein A-derived fragment cancelled their mitogenic ability. Finally, induction of T cell proliferation appeared to be independent of cross-linking via Fc gamma R. The results support a model in which noncovalent intermolecular homophilic contacts of the Fc regions of the IgG2c isotype bring about effective aggregation of Thy-1 molecules, thereby stimulating the mitotic apparatus of the cell.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal*
  • Antigens, Surface*
  • Cell Line
  • Cell Membrane / immunology
  • Hybridomas / immunology
  • Immunoglobulin Fc Fragments
  • Immunoglobulin G
  • Immunoglobulin Isotypes
  • Lymphocyte Activation
  • Membrane Glycoproteins*
  • Mice
  • Mitogens
  • Rats
  • T-Lymphocytes / immunology*
  • Thy-1 Antigens

Substances

  • Antibodies, Monoclonal
  • Antigens, Surface
  • Immunoglobulin Fc Fragments
  • Immunoglobulin G
  • Immunoglobulin Isotypes
  • Membrane Glycoproteins
  • Mitogens
  • Thy-1 Antigens