Notes on Humoral Effector Mechanism Generator

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Humoral Immunity:

• Antibody-mediated.

• Mediated by B cells.

• First signal for B-cell activation: antigen binds to, and cross-links the idiotypes of B-cell membrane receptors.

Thymus-Dependent Antigens:

• More common.

• Response to these requires contact of B cells with TH cells and their cytokines.

• Then, they are endocytosed, digested, and processed via the exogenous pathway to generate MHC II conjugates, which are then inserted in the membrane of the B-cell.

• Upregulated B7 molecule on B cells presents antigens to TH cells.

• TH cell becomes TH2 cell after seeing antigen on MHC II.

• CD40L molecule on TH2 cell interacts with CD40 molecule on B cell, again activating B cells, which proliferate.

• TH2 releases cytokines that activate B cells.

• There is immunologic memory.

Thymus-Independent Antigens:

• Directly stimulate B-cells without TH cell or cytokine intervention.

• These include LPS from Gram - cell envelope bacteria.

• T cells only recognize processed antigens, not free floating antigens.

• These antigens are called thymus-independent antigens.

• Act as B cell mitogen.

• Weaker response; secretion of IgM only.

• No memory.

Cytokines Induce B Cell:

• Differentiation, memory, class switching.


• First antibody produced by B cells without T-cell intervention.

• Pentamer.

• Valence of 10.

• Traps free antigen.

• Low affinity (?) but high avidity.

• Effective in activating complement.

• Primary immune response.

X-linked Hyper-IgM syndrome:

Respiratory infections in children.


• Activates complement, acts as an opsonin, and mediates ADCC.

• Second major Ab after IgM.

• 4 types.

• Crosses placenta.


• Dimer.

• Defense of mucosal surfaces of body.


• Binds to mast cells and basophils.

• Works in helminth parasitic infections and allergic responses.


• Proteins produced in the liver.

• Innate response, but overlapping functionality with adaptive response.

• Two pathways.


• More primitive; bacterial cell envelope initiates it.


• Activated by antigen-antibody complexes; activated by IgM and IgG.

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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