Figure 4.

CD8⁺ and CD4⁺ T cell dependency of IFN-γ responses. Frozen PBMCs from (a) volunteer BJ11 (needle i.m.) or (b) volunteer BJ7 (Biojector i.m.) collected 2 weeks after the second immunization or 6 weeks after the third immunization, respectively, were either untreated or selectively depleted of CD4⁺, CD8⁺, both CD4⁺ and CD8⁺ T cells, or CD45RO⁺ cells immediately before culture with peptide A2.386 or peptide DR.375. Alternatively, frozen PBMCs from the same volunteer were either untreated (whole PBMCs), or selectively enriched for CD8⁺ T cells, CD4⁺ T cells, or CD8⁺ plus APCs or CD4⁺ plus APCs immediately before culture with peptides A2.386 or DR.375. Two distinct patterns are presented. Pattern 1: (a) IFN-γ induced against both A2.386 and DR.375 peptides depended on CD4⁺, CD8⁺, and CD45RO⁺ T cells. (c) Either positively selected CD8⁺ or CD4⁺ T cells, with or without APCs, failed to reconstitute the effector response. Pattern 2: (b) IFN-γ induced against peptides A2.386 and DR.375 depended on CD8⁺ and CD45RO⁺ T cells, but not CD4⁺ T cells. (d) Positively selected CD4⁺ cells with or without APCs, or of CD8⁺ cells without APCs, failed to reconstitute the effector response. Positively selected CD8⁺ T cells with APCs completely restored the effector response to the class I peptide A2.386 and partially restored the response to the class II peptide, which contains a nested class I epitope.