《Immunology》Lecture 3：B
Cell and Antibody
Feng Zhang (Ph.D)
Office：Biological Building Room 402
Email：zhangfeng@imau.edu.cn
3.1 B Cell
• Born in the bone marrow
• 1 billion B cell per day per guy
• Early stage: select gene coding 2 kinds of BCR
proteins and relocate to B cell surface.
• BCR v.s. Antibody
– Very simillar
– Antibody lack anchor sequence
3.1.1 BCR
• Components: 2H + 2L
• Gene localized on Chromosome 14
3.1.2 How BCR transfer signal
• Homologous /cognate antigen
• Epitope
3.1.3 B Cell activation
With Th help:
• Without Th help:
– Repeat epitopes  BCR
– Mitogens (error activation)
• BCR crosslinking + ?  activation
• BCR crosslinking  proliferation but no
antibodies secreted!
• Only with 2nd signal: from innate Immune sys
(such as IFN- γ)
• Other reason: T cell only recognize proteins,
so with Th help, only for proteins, but not for
other molecules like lipid or saccharides..
3.1.4 Class Switching
3.2 Antibody
3.2.1 IgM
3.2.2 IgG
• Subtype: IgG1, 2,3
• ADCC (antibody dependent cellular
cytotoxicity)
• Neutralize virues
• Penetrate blood-placenta barrier
• Half life: about 3 weeks (v.s. IgM 1 day)
3.2.3 IgA
3.2.4 IgE
3.3 SOMATIC HYPERMUTATION
• Normal: single base mutation rate:
1/100million
• In V, D, J region: 1/1000
• Increase the high affinity to antigen-
optimization!
• Affinity mutation
• Only for B cell activated by Th.
3.4 B CELLS MAKE A CAREER CHOICE
Plasma cells are antibody
factories.
Memory B cells are not produced
when B cells are activated
without T cell help.
SUMMARY
FIGURE
Questions
1. B cells are produced according to the principle of clonal selection.
Exactly what does this mean?
2. Describe what happens during T cell-dependent activation of B cells.
3. Describe “fail-safe” systems that are involved in B cell activation.
4. How can B cells be activated without T cell help?
5. Why is T cell-independent activation of B cells important in defending
us against certain pathogens?
6. Describe the main attributes of IgM, IgG, IgA, and IgE antibodies.
7. Why do class switching and somatic hypermutation produce B cells
that are better able to defend against invaders?
8. Why do most mast cells wait until their second exposure to an
allergen before they degranulate? Hint: Think about the timing.
• 1， B细胞是通过克隆选择理论产生的，这是什么意
思？
• 2， 请详述T细胞依赖的B细胞活化。
• 3， 请详述在B细胞活化过程中的两个保险体系。
• 4， 请详述在没有T细胞辅助的情况下B细胞是如何
被激活的。
• 5， 为什么非依赖T细胞的B细胞活化对于我们防御
特定病原体是如此重要？
• 6， 详述IgM、IgG和IgA的主要作用。
• 7， 为什么经过类型转换和体细胞高突变产生的B细
胞可以更好地防御入侵者？