Differential Kinetics of Antigen Dependency of CD4+ and CD8+ T Cells

Ag recognition via the TCR is necessary for the expansion of specific T cells that then contribute to adaptive immunity as effector and memory cells. Because CD4+ and CD8+ T cells differ in terms of their priming APCs and MHC ligands we compared their requirements of Ag persistence during their expansion phase side by side. Proliferation and effector differentiation of TCR transgenic and polyclonal mouse T cells were thus analyzed after transient and continuous TCR signals. Following equally strong stimulation, CD4+ T cell proliferation depended on prolonged Ag presence, whereas CD8+ T cells were able to divide and differentiate into effector cells despite discontinued Ag presentation. CD4+ T cell proliferation was neither affected by Th lineage or memory differentiation nor blocked by coinhibitory signals or missing inflammatory stimuli. Continued CD8+ T cell proliferation was truly independent of self-peptide/MHC-derived signals. The subset divergence was also illustrated by surprisingly broad transcriptional differences supporting a stronger propensity of CD8+ T cells to programmed expansion. These T cell data indicate an intrinsic difference between CD4+ and CD8+ T cells regarding the processing of TCR signals for proliferation. We also found that the presentation of a MHC class II–restricted peptide is more efficiently prolonged by dendritic cell activation in vivo than a class I bound one. In summary, our data demonstrate that CD4+ T cells require continuous stimulation for clonal expansion, whereas CD8+ T cells can divide following a much shorter TCR signal. Samples 1-12: Analysis on day 2. Purified CD4+ AND-TCR transgenic cells and CD8+ OT1-TCR transgenic cells were separately stimulated with anti-CD3 and anti-CD28 antibodies. 48 hours later, the cells were sorted again to a purity of >99 %. Extracted total RNA was amplified twice and hybridized on Affymetrix Mouse 430A2 microarrays. First, we analysed the changes of the CD4+ and CD8+ T cells after stimulation. Second, we compared the differences of the changes between the two cell types after stimulation. For each of the four groups (CD4+ and CD8+, stimulated and unstimulated), we analysed three independent biological replicates. Samples 13-28: Analysis on day 5. AND and OT1 TCR-transgenic T cells were prepared as described before, but transferred into mice that do not or do present their respective antigens. 72 hours later, the cells were FACS-sorted twice to >99 % purity, directly into Trizol. For each of the six groups (CD4+ and CD8+, unstimulated, transient (2 days) and continuous (5 days) stimulation), three independent biological replicates were analyzed, except for CD4+ unstimulated and CD4+ transient, with two replicates each.