Two key features of the immune system are the clonal expansion of B cells and T cells in response to antigens, and the potentiation of future immune responses by long-lived memory cells. CD4 expressing T cells require costimulatory signals along with antigen stimulation to mount an effective immune response. CD28 has been widely characterized as a costimulatory receptor for CD4+ T cells. OX40, also called CD134, is another transmembrane receptor protein expressed by CD4 T cells that provides a costimulatory signal for T cell activation by antigen. The OX40L ligand for OX40 is expressed as a transmembrane protein by antigen-presenting cells, and is required for function of antigen-presenting cells. The T cell costimulatory signal provided by the OX40/OX40L interaction increases the clonal amplification of antigen-specific T cells and the survival of memory T cells that respond to this antigen.

Contributor: Glenn Croston, PhD.

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