Figure 4.

DC proteases can generate immunodominant peptide fragment. (A and B) Generation of HEL48–62 peptide antigen from intact HEL protein by conditioned medium from splenic DC (●) but not from B cells (BC) (■). Cell-free supernatants from 4-hr DC or B cell cultures were incubated with intact HEL protein before addition to (A) fixed B cells or (B) DC for presentation to an IA^k-restricted and HEL48–62-specific T cell hybridoma. T cell activation was measured by using an IL-2 secretion assay (21). (C) The I-A^k-HEL complex detected by using the complex specific antibody Aw3.1 instead of the T-cell hybridoma. (D) Same as for A but using intact β-casein antigen and an I-A^s-restricted, casein-specific T cell line, with T cell activation determined by using a proliferation assay (21).