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. 2020 Aug 8;12(8):868. doi: 10.3390/v12080868

Figure 1.

Figure 1

Schematic model for T-cell receptor signaling. Engagement of the T-cell receptor (TCR)/CD3 complex by the peptide-MHC complex requires the stabilization of the TCR-peptide/MHC complex interaction by CD4 or CD8 molecules, resulting in the activation of the p56 leukocyte kinase (Lck) which phosphorylates the immunoreceptor tyrosine-based activation motifs (ITAMS) within the cytoplasmic tails of CD3-zeta (not shown), resulting in the generation and transmission of the TCR signals. Engagement of the CD28 co-receptor (not shown) present on the surface of T-cells by B7 ligands on antigen-presenting cells is required for full TCR activation. Following full TCR activation, the zeta associated protein 70 (ZAP-70) and linker of activated T-cells (LAT) are activated. Activation of ZAP-70 and LAT results in the induction of three main signal pathways, namely: the calcium–calcineurin pathway which induces nuclear factor of activated T-cells (NFAT); the protein kinase C pathway which induces nuclear factor-kappa beta (NF-κB) and the MAP kinase/ extracellular signal-regulated kinase (ERK) pathway which induces activator protein 1 (AP-1) and positive transcription elongation factor b (P-TEFb). All these transcription factors translocate into the nucleus to regulate human immunodeficiency virus (HIV) transcription.