1. Immune system 1.Component of immune system
center immune organs: bone marrow, thymus
Immune organs
peripheral immune organs: spleen, lymph nodes, skin，
mucous membrane
Immunocytes: T lymphocyte, B lymphocyte, macrophage, natural killer etc
immune molecules: antibody, cytokines (tumor necrosis factor, interferon
interleukin etc), complement（补体）

2. 2. Antigen
2.1 Definition: An antigen is any substance that causes your immune system to produce antibodies against it. An antigen may be a foreign substance from the environment such as chemicals, bacteria, viruses, or pollen. An antigen may also be formed within the body, as with bacterial toxins or tissue cells
2.2 What kind of substances can be identified as antigen by immune system?
① Foreign substance
② Large molecules with certain chemical composition and structure.
③ Integrity

3. 2.3 Complete antigen and hapten
Complete antigen: an antigen capable of stimulating immune system to produce antibody and binding with the antibiody.
Hapten: a hapten is a small molecule which can elicit an immune response(to stimulate the production of antibody) only when it is attached to a larger carrier such as a protein.
2.4 Antigen determinant: The site on the surface of an antigen molecule which binds to an antibody. Different antigen has different antigenic determinant and can stimulate the production of different antibody.

4. 3.Antibody
3.1 Definition: Antibodies are immune system-related immunoglobulins that are found in blood or other bodily fluids of vertebrates, and are used to identify and neutralize foreign objects, such as bacteria and viruses. Antibodies can bind very tightly to their targets (antigen) to inactivate them.

5. 3.2 structure

7. 3.3 Production
Antibodies are made
by a class of white blood cells, called B lymphocytes. Each resting B cell carries different membrane bound receptors to recognize a specific antigen. When antigen binds to this receptor, the B cell is stimulated to divide into plasma cells
（浆细胞） which is capable of producing large amount of the same antibody in a soluble form.

8. B cells can also form memory cells that remember the same pathogen for faster antibody production in future infections.

9. 4. Important immunocytes
4.1 T lymphocyte: T cells originate in the bone marrow, mature in the thymus, and travel in the blood to other lymphoid tissues, such as the spleen, tonsils, and lymph nodes. Through receptor molecules on their surfaces, T cells directly attack invaders (antigens) by binding to them and helping remove them from the body .

10. 4.2 Macrophage: Macrophages are white blood cells that crawl around in the extracellular fluids of your body and gobble up microbes and other foreign material. They ingest these microbes by phagocytosis ("cell eating").
a. Ingestion,a phagosome is formed b. The fusion of lysosomes with the phagosome, the pathogen is broken down by enzymes c. Waste material is expelled or assimilated Parts: 1. Pathogens 2. Phagosome 3. Lysosomes（溶酶体）4. Waste material 5. Cytoplasm6. Cell membrane

11. 4.3 Natural killer cell
NK cells are cytotoxic; small granules in their cytoplasm contain proteins such as perforin(穿孔素) and proteases known as granzymes（粒酶）. Upon release in close proximity to a cell slated for killing, perforin forms pores in the cell membrane of the target cell, creating an aqueous channel through which the granzymes and associated molecules can enter, inducing either apoptosis（凋亡） or cell lysis（溶解）。

12. 5.Pathology 5.1 autoantibody & autoimmune disease:
Antibodies are normally produced in response to a foreign protein or substance within the body, typically a pathogen (infectious organism). Normally, the immune system is able to recognize and ignore the body's own cells.
Sometimes, however, the immune system ceases to recognize one or more of the body‘s normal constituents as “self,” leading to production of autoantibodies. These autoantibodies attack the body’s own cells, tissues, and/or organs, causing inflammation and damage。

13. 5.2 Immunodeficiency disorders are a group of disorders in which part of the immune system is missing or defective. Therefore, the body's ability to fight infections is impaired.
primary immunodeficiency disorders: caused by inherited defects in the cells and other components of our immune system.
secondary (acquired) immunodeficiency disorders :caused by particular external processes or diseases, such as malnutrition, aging, particular medications and chronic infection.

14. immun/o: immune
Immunology， Immunodeficiency disease
Immunoglobin
lymph/o: lymph
splen/o: spleen
tonsill/o: tonsil
plasm/o: plasma
neoplasma : tumor
cytoplasm

15. thym/o：thymus
phag/o: eat, engulf
hapt/o: attach, touch
haptics: sense of touch