Notes on Selection of Lymphocytes

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What are Primary Lymphoid Organs?

• Bone marrow and Thymus.

What are Secondary Lymphoid Organs?

• Spleen, lymph nodes, MALT.

B and T Cell Selection Process:

• Rigorous T/B cell selection process helps prevent autoimmunity.

• Done by exposing developing T cells to MHC antigens.

• MHC found on chromosome 6.

Two MHC Classes:


• HLA-A, HLA-B, HLA-C; expressed on all nucleated cells, even platelets; small groove on MHC I help present antigens to TCR.


• HLA-DP, HLA-DQ, HLA-DR; expressed on APCs; small groove on MHC II help present antigens to TCR.

Role of Thymus:

• In thymus, MHC products exposed to developing T-cells.

• Developing T-cells that bind to MHC products with low affinity receive signal to divide: positive selection.

• Developing T-cells that bind to MHC products with high affinity receive signal to die: negative selection.

CD4 and CD8 Receptors:

• Expressed on surface of T-cells; provide better linkage between TCR and MHC.

CD4+ T-cells:

• Those that recognize MHC II present on TH.

CD8+ T-cells:

• Those that recognize MHC I present on CTLs.

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

Related Topics

1. Histology of Lymphoid Tissue

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