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 α or β 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.