Phổ biến các tính năng của MHC lớp I và II glycoprotein • đa dạng allelic • kháng nguyên trình bày các đặc điểm Lớp tôi phân tử MHC khác nhau: • thể hiện trên tất cả các tế bào nucleated • kích hoạt T-tế bào mang các phân tử bề mặt tế bào CD8 (CD8 +) loại II MHC phân tử: • thể hiện trên đuôi gai các tế bào | 6 Liver Transplantation 2 Figure 1. Schematic structure of MHC class I and class II. Figure 2. Antigen processing and presentation. The antigen presenting cell presents exogenous protein bound to class II molecules to CD4 T-cells and also processes intracellular protein and presents it with MHC class I to CD8 T-cells. The T-cell receptors recognize peptide bound to MHC. The Allograft Immune Response 7 Table 1. Characteristics of MHC molecules Common features of MHC Class I and II glycoproteins allelic diversity antigen presentation Differing characteristics Class I MHC molecules expressed on all nucleated cells activate T-cells bearing the CD8 surface molecule CD8 Class II MHC molecules expressed on dendritic cells B-cells and macrophages activate T-cells bearing the CD4 antigen CD4 2 cell. T-cell recognition is associated with the initation of complex intracellular signaling pathways that result in activation and proliferation of the T-cell Fig. 3 . There are two classes of T-cells based on the surface expression of CD4 or CD8 molecules. CD4 and CD8 molecules bind to the same MHC on the antigen presenting cell as the T-cell receptor. CD4 cells are known as helper cells and play an important role in initiating and directing the immune response Fig. 4 . CD8 cells also known as cytotoxic T-cells are responsible for cell directed cytotoxicity. Whether a T-cell whose receptor has bound the MHC-peptide displayed on the antigen presenting cell becomes activated depends on a receiving a second set of signals co-stimulation from the antigen presenting cell. These costimulatory interactions act directly through cell surface receptor-ligand interactions and soluble cytokines that are linked to intracellular signaling pathways Fig. 4 . CD4 T-cells are the dominant phenotype initiating acute cellular allograft rejection. Once activated the CD4 T-cells undergo clonal expansion and differentiation. In doing so they secrete cytokines that attract other leukocytes to activate .
