Soluble extracellular antigen-specific T cell immunoproteins

Some T cells release proteins that bind specifically to antigens that have not been processed by antigen-presenting cells. These soluble immunoproteins induce or effect antigen-specific T cell functions in immunoregulation and/or hypersensitivity. After certain immunization regimens, T cell immunoproteins specific for the immunogen rise in serum, and therefore may be an antigen-specific, humoral manifestation of the activation of some T cells during an immune response. Although non-MHC (major histocompatibility complex)-associated antigen is bound, soluble antigen-specific T cell immunoproteins share variable and constant region epitopes and some amino acid sequence with the T cell receptor for antigen alpha or beta chains, and their expression depends on T cell receptor structural genes. Herein, the properties of extracellular antigen-specific T cell immunoproteins are reviewed and it is suggested that these molecules are a soluble analogue of the T cell receptor for antigen and provide an amplifying element for some T cell functions.