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General issues of Vaccine
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General issues of Tropical med.
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General issues of Travel med.
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Trematode (fluke, distoma)
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Immunoglobulin molecule
→免疫グロブリンとは#分子としての免疫グロブリン immunoglobulin
Immunoglobulin as B cell receptor
Primary and secondary responses of B cell
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Primary
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Secondary
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Type
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Naive B cell
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Memory B cell
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Lag time
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4-7 days
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1-3 days
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Peak
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7-10 days
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3-6 days
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Intensity
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Varies
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100-1000 times higher than primary
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Ig class
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IgM
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IgG
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Antigen
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T-cell independent
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T-cell dependent
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Affinity
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Low
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High
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B cell activation by cross-linking
- Cross-linking of multiple B cell receptors (immunoglobulins) by antigen is needed to activate B cell intracellular signaling
T cell independent antigens
- Antigen with repetitive structure (e.g., lipopolysaccharides) cross-link B cell receptors in wider ranges as well as non-BCR structures on B cell surface, resulting in activation of B cell without T cell (T cell independent antigen)
T cell dependent antigens
- Antigen of proteins cross-link B cell receptors but at the same time needs antigen presentation by TCR of CD4+ T cell onto pMHC class II on B cell via CD28 and/or CD40 co-stimulation
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T independent
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T dependent
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Antigen
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Repetitive structure
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Protein
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Ig class switching
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Little→IgM main
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Induce→IgG
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Affinity maturation
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Doesn't occur
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Occur
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B cell memory
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No
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Yes
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B cell longevity
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Long plasma cell
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Short plasma cell
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Affinity maturation at germinal center
- Somatic hypermutation at dark zone of lymph nodes
- Activation-induced cytidine deaminase (AID) induces random point mutations on V regions of both of heavy chain and light chain
- Affinity maturation at light zone of LN
- Follicular dendritic cells present antigens to select only B cells that randomly obtained affinitive BCR (Ig)