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To study the question when and where self peptides become associated with major histocompatibility complex class II molecules for tolerance induction, we recently developed a system in which the intracellular site(s) of antigen expression could be manipulated using gene cloning techniques. We previously constructed a truncated IgGa gene comprising a variable (V) domain and the CH3 domain (not including the membrane exons) from the IgG2ab heavy (H) chain. The secreted form of the V-CH3b protein was expressed at high levels under control of the Ig H chain enhancer in Ia+ B lymphoma cells and was efficiently recognized by class II-restricted IgG2ab-specific T cell hybrids. Here we describe a modified V-CH3b gene construct in which the sequences encoding the signal peptide were deleted. A strong argument can be made that the signal-less V-CH3b protein is predominantly expressed in the cytosol. We show that transfected L cell lines expressing the signal-less form of the V-CH3b protein can stimulate class II-restricted IgG2ab-specific T cells. Cell mixing experiments indicate that this response cannot be due to passive uptake of soluble antigenic peptides released into culture supernatants. These experiments demonstrate that a cytoplasmic protein having no obvious means of reaching the cell surface can be presented to class II-restricted T cells.

Original publication




Journal article


Eur J Immunol

Publication Date





1411 - 1417


Animals, Antigens, Genes, Immunoglobulin, Histocompatibility Antigens Class II, Immunoglobulin Constant Regions, Immunoglobulin G, Immunoglobulin Heavy Chains, Immunoglobulin Variable Region, L Cells (Cell Line), Lymphocyte Activation, Mice, Mice, Inbred C57BL, T-Lymphocytes, Transfection