Figure 1.
The Dynamics of the Coreceptor-LCK Coupling Predicts Self-Reactivity
(A) Mature T cells or DP thymocytes were lysed and incubated with beads coated with antibodies to CD4 (RM4-4) or CD8β (53-5.8). Beads were probed with PE-conjugated antibodies to LCK (3a5), CD8α (53-5.7), or CD4 (H129.19) and analyzed by flow cytometry. Calculated CD4-LCK or CD8-LCK stoichiometry for thymocytes and mature T cells is shown. Mean + SEM; n = 3–5 mice in 3–4 independent experiments.
(B and C) CD4 (H129.19) or CD8β (53-5.8) were immunoprecipitated from lysates of thymocytes or enriched peripheral CD8+ and CD4+ T cells from WT mice, followed by immunoblotting using anti-CD4 (D7D2Z), anti-CD8α (D4W2Z). and anti-LCK (3a5) antibodies. (B) Representative experiments for CD8β and CD4 immunoprecipitation. CD8α' truncated isoform is marked with an asterisk. (C) Ratio of LCK-coupled coreceptors (periphery/thymus). Mean + SEM; n = 3–5 samples (pooled 2–3 mice) in 3–4 independent experiments.
(D) TCR signal intensity predicted by the “LCK come&stay/signal duration model” (Stepanek et al., 2014) induced by strong cognate or suboptimal antigens (at the threshold for negative selection) in MHCI- or MHCII-restricted DP or mature T cells. The TCR signal intensity corresponds to the number of signaling TCRs and is shown as a function of antigen density. The input data correspond to the parameters obtained from monoclonal OT-I and B3K508 T cells (Stepanek et al., 2014).
(E) Schematic illustration of the prediction of the mathematical model applied to the process of T cell selection. The coreceptor-LCK coupling in the thymocytes sets the self-antigen affinity window of the positively selected T cell, resulting in higher affinity to self-antigens in the MHCI-restricted than in the MHCII-restricted T cells. Increased CD8-LCK, but not CD4-LCK, coupling frequency in mature T cells leads to the increased sensitivity of peripheral CD8 T cells to suboptimal antigens. Altogether, mature CD8+ T cells have, on average, higher level of self-reactivity than CD4+ T cells.