title: Activation of an encephalitogenic T lymphocyte line with a cellfree supernatant containing basic protein and I region gene products.
abstract: Activation of antigen-specific T lymphocyte lines requires presentation of the relevant antigen by syngeneic accessory cells (AC) that express Class II MHC gene products. To determine if the T cell activation signal was AC associated or was shed into the medium, supernatants from rat thymic AC populations pulsed with guinea pig basic protein (GP-BP) or PPD were used to stimulate resting BP- or PPD-reactive T cell lines derived from Lewis or BN rats. Cellfree supernatants were found to stimulate the T cell lines in an antigen-specific, strain-restricted manner, reflecting the pattern of stimulation observed with intact AC used. The activity of the cellfree supernatant could be enhanced five to 20 times in the presence of activated T lymphocytes, the optimal production occurring over a 6-hr period. The cellfree T lymphocyte activation signal produced in the presence of activated T cell products contained both an antigen-specific, MHC-restricted component (85%) and an antigen-independent, mitogenic component (15%). Supernatants containing GP-BP but not bovine BP or PPD induced highly significant proliferation of the Lewis rat-derived BP-1 T lymphocyte line, and transfer of these supernatant-activated cells produced clinical signs of experimental autoimmune encephalomyelitis (EAE) and DTH reactions to GP-BP. The GP-BP component was not inhibited by either of two monoclonal antibodies directed at determinants on either side of the epitope(s) recognized by BP-1 cells. However, stimulation was inhibited by an anti-I-A but not an anti-I-E monoclonal antibody, suggesting the involvement of a Class II MHC gene product on the T cell activation signal. The supernatant activity could be separated by ultracentrifugation at 100,000 X G for 4 hr into a microsomal pellet and an ultrasupernatant, and both fractions had greatly reduced activity on resting T cells until they were reconstituted by vigorous mixing. These results suggest that T effector cells can be activated by AC-derived microsomal fragments bearing Class II antigens that associate noncovalently with processed antigen. This cellfree signal is sufficient to activate encephalitogenic T lymphocytes to transfer clinical EAE and DTH reactions without need for a direct T cell-AC interaction.
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D001688:Biological Products / Q000502:physiology; D016207:Cytokines; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000276:immunology*; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D006968:Hypersensitivity, Delayed / Q000276:immunology; D007116:Immunization, Passive; D008213:Lymphocyte Activation; D004676:Myelin Basic Protein / Q000276:immunology*; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D001688:Biological Products; D016207:Cytokines; D000949:Histocompatibility Antigens Class II; D004676:Myelin Basic Protein