Notes on Antigen Processing and Presentation

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Function of Antigen Presenting Cells:

APCs degrade antigens and load these particles into the grove of the class II MHC molecule to present to T cells, and this can be done using the exogenous pathway.

Similarly, MHC I molecules use the endogenous pathway.

Endosomal (exogenous) pathway:

• Small antigens are completely digested and degraded by macrophages.

• Antigen fragments are displayed in MHC II molecules to T-cells by APCs.

• Invariant chain on MHC II ensures normal cell fragments are not displayed, and only antigen is displayed.

• Recognized by CD4+.

Endogenous pathway:

• MHC I molecules express antigens digested endogenously, that is, proteins are degraded in cytoplasm by proteasomes.

• Recognized by CD8+.

First signal of T-cell activation:

• TCR-MHC II binding.

Role of CD4 and CD8:

• CD4 and CD8 activate T cells.

Cell Adhesion:

• Integrins: cell-cell adherence.

• IgCAMs: cell-cell adherence.

• CD28: cytokine transcription.


• Bacterial or viral protein: directly activate T-cells without intermediation of MHC II.

TH0 Differentiation:

TH0 differentiates into TH1:

• Due to strong innate response.

TH0 differentiates into TH2:

• By default.

Additional Readings:

Basic Immunology

1. Introduction to Immunology
2. Cells of Immunology
3. Selection of Lymphocytes
4. Primary Response to Antigen
5. Antigen Processing and Presentation
6. Humoral Effector Mechanism Generator
7. Cell-Mediated Effector Mechanism Generator
8. Vaccination and Immunotherapy
9. Immunodeficiency Diseases
10. Acquired Immunodeficiency Syndrome
11. Hypersensitivities and Autoimmunity Diseases
12. Immunology of Transplantation
13. Immunology of Cancer
14. Immunology Laboratory Technology
15. Acquired Immunity
16. Type II Hypersensitivity Reaction
17. Hypersensitivity Reactions
18. Primary Immunodeficiency
19. Secondary Immunodeficiency
20. Type III Hypersensitivity Reaction
21. Type IV Hypersensitivity Reaction
22. Type V Hypersensitivity Reaction
23. Tumor Immunology
24. Images of Antibodies
25. Th1 vs Th2 cells

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1. Histology of Lymphoid Tissue

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