Purified HLA class II peptide complexes can induce adherence and activation of peptide-specific human T cell clones

An initial event in T cell activation is the specific adherence of T cells via their T cell receptor to the MHC peptide complex. We have studied this adherence by incubating T cells with preformed HLA DR4Dw4 peptide complexes attached to a solid support. Adherence of sodium 51Cr-labeled T cell clones specific for the influenza hemagglutinin peptide, HA 307-319, was maximal after 15 min and was specific for the HLA DR4Dw4-HA 307-319 complex. The binding was temperature dependent and could be blocked with azide or protein kinase C inhibitors, indicating that for adherence the T cells need to be metabolically active and have a functioning protein kinase C pathway. The adherence could be blocked with CD4- or CD3-reactive murine mAb, suggesting that the TCR and CD4 molecules work in concert to induce strong adherence to the HLA DR4Dw4-HA 307-319 complex. A subsequent event in T cell activation is proliferation, which is thought to need additional proteins such as IL-1 or other adhesion molecules. MHC peptide complexes coated on microtiter plates also induced proliferation in the human T cell clones. Removal of any monocytes by treatment of human T cell clones with anti-CD14 in conjunction with C, followed by purification over a nylon wool column, did not abrogate proliferation. After prolonged culture of the T cell clones in plates coated with peptide-pulsed HLA DR4Dw4 in the presence of IL-2, the T cell clones continued to proliferate in response to peptide. These results suggest that human T cell clones do not require a second signal from a monocyte or other APC to proliferate.