Chapter 1 and 2

1. Immunity
@ protective methods;
   - physical barriers
   - phagocyte cells in blood and tissues
   - lymphocytes
   - various blood-borne molecules

* Table 1-2
① innnate immunity
   -> are present prior to exposure
   -> not enhanced by exposure
   -> phagocytes (Macrophages , NK), complements

② adaptive immunity
   -> induced by exposure
   -> specific for distinct macromolecules
   -> remember (memory)
   -> amplify the innate immunity
   -> lymphocytes, antibody

 Table 1-2

2. Types of adaptive immunity (Fig 1-2)                                                                           

㉮ humoral: transfer by cell-free portion of blood (serum)
㉯ cell-mediated: transfer by cells from immmunized individuals

 Fig 1-2

3. Features of Adaptive Immune response

(table 1-3)

1) specificity; for antigens, depend on epitope (determinant)
2) diversity; discrimination of 10⁹ Ags
3) memory (Fig 1-4); 2' response is faster and more effective
4) self-limitation; IR is wane with time ---> basal state ; homeostasis
5) discrimination between self and non-self; tolerance/autoimmune disease

6) specialization; generate responses that are optimal for defense against different types of microbes

4. Phase of  adaptive immune response

   (Fig 1-6)
  ① recognition (cognitive); Ag recognition
  ② activation; proliferation (clonal expansion) and differentiation
  ③ effector; Ag elimination

  ④ homeostasis

  ⑤ memory

 Fig 1-6

5. How a diverse repertoire can be generated ?

   ① instruction theory
        -> by changing the conformation of Ag binding region
   ② clonal selection theory (Fig 1-7)
        -> each clone arise from a single precursor
        -> select and activate a specific pre-existing clone

 Fig 1-7

6. Cells of the immune system

(1) lymphocytes
     ① B lymphocytes; bird's bursa, bone marrow
     ② T lymphocytes; bone marrow -> thymus

      -- morphology (Fig 3-4)

  Table 3-1

(2) kinds of lymphocytes

Table 3-2

(3) Development of lymphocytes

 
- generative organs; lymphocytes arised and matured
- peripheral organs; mature lymphocytes recognize Ags

  (Fig 3-2)

(4) Activation of lymphocytes

   --- the phase of  lymphocyte activation;

        new protein synthesis (ex; cytokine) --> proliferation --> differentiation --> homeostasis

- morphological changes in activation
    larger: lymphoblast, G0->G1
    differentiated CTL; more granules
    plasma cells ; -> don't circulate in blood, no mitotic division
                                     -> only in lymphoid organs

     memory lymphocytes; -> survive for a long time
                                     -> surface marker

  (table 3-3)

  

Ag   ----->

                      -------->   normal immune response

Ag   ------->           irradiation

                              ----------->      X

lymphocytes ------->                 ----------->  normal immune response
             

(2) Antigen-presenting cells

   1) Mononuclear Phagocytes
   - development

  -- morphology

     - functions;
      1) in innate immunity
          -> phagocytosis
          -> produce cytokines and recruit infammatory cells
          -> produce growth factors and help the repair of injured tissues
      2) in adaptive immunity (ADCC)
          -> APC
          -> Fc receptor/ complement receptor and phagocytose

 2) Dendritic cells
    - spine-like projections
    - types; ① interdigitating dendritic cells
             -> from bone marrow
             -> interstitium of most organs
             -> a good APC
             -> related to phagocytes
             ② follicular dendritic cells (FDC)
             -> in germinal center of lymph node, spleen
             -> not from bone marrow     

      - plasmacytoid DC; early cellular responders to viral infection

                                       produce type 1 IFN

7. Lymphoid tissues

 1) bone marrow

- hematopoiesis ; generation of all blood cells

- hematopoietic cytokines; ① by stromal cells
                                           ② macrophages
                                           ③ T cells stimulated by Ags

 2) thymus

   morphology
  - cortex; dense T cells (CD4/CD8 double negative)

  - Hassall's corpuscles; epithelial cells

 3) lymph nodes
  - throughout the body
  - primary follicles (w/o germinal center) -> resting B not stimulated by Ags
    secondary follicles (w     "        ) -> B cells stimulated by Ags
  - T cell zone (paracortex); CD4 positive
  - Ag's pathway; by lymphatic
  - medulla; macrophages, dendritic cells, plasma cells
  - shape is flexible depend on Ag exposure; ex) germinal center within 1 week

   Fig

 4) spleen

           ① periarteriolar lymphoid sheath; T cells (2/3; CD4, 1/3; CD8)
white   ② marginal zone; both B and T cells, macrophages
 pulp    ③ germinal center; B cells
 

           ④ red pulp; erythrocyte, macrophages, dendritic cells, plasma cells

 8. Cutaneous immune system

 -- skin, lymphocytes and APCs

(Fig 3-12)

9. Mucosal immune system

 -- in gastrointestinal and respiratory tracts

 -- cells; lymphocytes and APCs

 -- each region has distinct lymphocytes; ex) intraepithelial (CD8+), lamina propia (CD4+), Peyer's patch (CD4+)

  -- M(membranous) cells --> delivering of antigen to Peyer,s patch

Fig. 3-13

10. Lymphocyte homing

Chapter 5   Antibodies and Antigens

                        
1. Antibody
 ① a related glycoprotein, no enzyme
 ② Ag binding (non-covalent), specific
 ③ BCR
 ④ other Ag recognizing molecules (MHC, TCR)  

2. Natural distribution of Ab
 -> fluid portion of blood
 -> cytoplasmic membrane-bound compartments (ER, Golgi)
 -> surface of B cells and other cells (phagocytes, NK, mast cells)
 -> interstitial fluid of tissues
 -> secretory fluids (mucus, milk)
                                                                                                                          

3. Structure of Ab
 ① all Abs are similar in overall structure
 ② 2 heavy + 2 light
    

    CDR (complementarity determining region, ~10 Aas); a hypervariable  region
    

 FW (Frame work region)

   1) H chain
     -> CDR3 is most variable
     -> hinge region; steric effect
     -> two forms (Fig 4-7); membrane and secreted form                                                                             

     -> tail pieces (Table 4-2); extended nonglobular seq. in secreted form
                                       intermolecular interactions (multimeric form)
                                       IgM(5), IgA(2)

      -> J chain; S-S bonding between tail pieces -> stabilization

 Table 4-2

    2) L chain
      ->   kappa and lamda  , (human 50:50; mouse 10 times in kappa  )
      -> CDR3 is most variable

③ isotype (table 4-2); A, D, E, G, M -> different effector functions

④ Fab and Fc
          --- Fab; Ag-binding
          --- Fc; crystalline
          --- Fab'; include hinge region

4. Maturation of B lymphocytes

1. pre-B lymphocytes; - only cytoplasmic  μ heavy chain
                        (associated with surrogate light chain (V_pre-B and λ₅): prevent the degradation of newly synthesized  μchain,  promote the Igs on the cell surface)
                        - bone marrow and fetal liver
                        - nonresponse to antigen

2. immature B lymphocytes; - synthesis of light chain
                           - membrane IgM
                           - not proliferate and differentiate by Ag
                             (self Ag - nonresponse; tolerance)
                           - bone marrow

3. mature B cells; - coexpress the IgM/IgD: same antigen specificity
                 - response to Ag, but can mature without Ag, however they will die (half life=3-4days)
                 - peripheral blood and lymphoid tissues

4. activated B cells; - Ag stimulated, and proliferate and differentiate (sIg>mIg)
                   - some: heavy chain class switching
                     others: keep the membrane form of Ig (memory B cells)

5. antibody secreting cells; - plasma cells

5. antigenic determinant (= epitope)

  -- features of biologic antigens

      1) conformational determinant

        2) linear determinant

        3) neoantigenic determinant

  -- structural and chemical basis of antigen binding

 6. changes of antibody structure after IR

Chapter 6  MHC (major histocompatibility complex) and Antigen processing

General features;
(1) major determinant of graft rejection (Fig 5-2)
(2) highly polymorphic, in various cells
(3) membrane-associated and not secreted
(4) involved in T cell development

1. kinds of MHC

1. Class I MHC molecules

- heterodimer ( α +  β₂ -microglobulin; non-covalent association)
  a)  α chain; by MHC genome, and highly polymorphic
                     heavy chain
                    5 domains (3 extracellular: α1,  α2, α 3; transmembrane; cytoplasmic)
                     N-linked glycosylation: human (1), mouse (2)

   b) β₂  microglobulin; by non-MHC genome

                                    non-attachment to the cells

2. Class II MHC molecules

- heterodimer ( α+ β)
  a) in overall structure,   α and  β chain are similar
  b) α> β ; due to the more glycosylation
  c)  α  and  β chain are encoded by MHC genome
  d)  α  and  β chain are polymorphic

2. Structure of MHC loci

General features:

A. in human and mouse

(1)  ~3500 kb DNA fragment  
(2) in class II; 2-3 funcional  β chains and 1 functional α chain -> more than two alleles
                     pseudo genes (DZ, DO, DX)
(3) in class III; complement (C2, C4)
(4) cytokines; TNF and LT
(5) class I; class I - like genes (some is pseudo genes; some is non-polymorphic proteins associated with  β₂-microglobulin),

                                            functions are unknown.

                                            called as class 1B proteins
                            ex: ① Tla (mouse thymocytes)
                                 ② Fc receptor-like protein; IgG transport across epithelial barrier
                                 ③ CD1; presenting of non-peptide antigens to unusual T cell populations                          

                                 ④ HLA-H; iron metabolism
            possible role; a repository for nucleic acid used for polymorphic sequence of class I (gene conversion -> new alleles)
           

B. in mouse
(1) smaller region
(2) class I - class II - class I                                                                                                                                

3. Expression of MHC molecules

1. regulatory sequences

  - target for DNA binding proteins
  - in class I; for cytokines (ex; interferon); A (enhancer A), ICS (interferon consensus sequence), B (enhancer B)
    in class II; S, X, Y box necessary for gene expression

2. expression
  - class I : CTL -- most cells
  - class II : T helper cells -- a few cells    

3. regulation of expression
  - 3 important features
    (1) transcriptional rate
    (2) coordinate regulation of transcription and expression
       class I; between α and β₂-microglobulin
       class II; between γ and α,β
    (3) cytokine modulation
       class I; induced by  γ-IFN, α,β-IFN, TNF, LT
       class II; induced by  γ-IFN, IL-4

 Fig 5-10

4. Biosynthesis of MHC
  - ribosome -> ER -> Golgi -> plasma membrane
  
(1) in class I
     a) within ER,    α and  β₂-microglobulin are associated
     b) role of β₂-microglobulin; transport
        evidence: Daudi B cells deficient β₂-microglobulin are transfected with β₂-microglobulin, and check the expression
                  or using cell fusion with β₂-microglobulin expressing cells

(i) class I MHC-restricted CD8+ T cell 에서의 antigen presentation
 1) 세포질내에서 단백질 항원의 합성 (예를들어 바이러스 단백질) 이나 세포질내로 단백질 항원의 전달
 2) ubiquitination을 통한 proteasome에 의해서 peptides로 분해
 3) TAP (transporter associated with antigen presentation) transport에 antigenic fragment (즉 분해되어진 peptides)의 결합 --> class 1 assembly and surface expression                                                       

 Fig 6-14
 4) ER에서 이미 생성되어 있는 class I MHC와 상호결합
 5) Golgi를 통하고 궁극적으로는 secretory vesicle의 세포막 융합에 의하여 발현되어지는 것이다.

 (2) in class II
     a) within ER,   α and  βchains are coordinately  associated
     b) γ(invariant) chain:
        - ~30 kDa, Ig superfamily, Type II protein
        - non-polymorphic, and not encoded by MHC loci
        - associated with a recently synthesized class II
        - separated from before class II expresses on surface
        functions:
        1) direct the trafficking
        2) prevent association of endogenously synthesized peptides with class II

(ii) class II MHC-restricted CD4+ T cell 에서의 antigen presentation

 - antigenic fragment 생성은 세포내 기관인 lysosome, endosome에서 일어난다.
 1) 항원으로써의 역할을 수행하는 단백질의 세포내로 흡입 (endocytosis)
 2) endosome, lysosome에서 단백질 항원의 분해, peptide 생성
 3) 한편 ER에서는 class II MHC가 생성되어지나 항원과의 상호결합은 없는 상태를 유지함, 이때 Ii (invariant chain)이 antigenic fragment 결합부위를 보호하고 있다.
4) Golgi를 통과한 class II MHC을 보유하고 있는 secretory vesicle 와 2)의 endosome의 융합, 따라서 Ii chain은 class II MHC으로부터 분리되고 대신에 endosome내의 peptide가 결합되어 진다.

  ** CLIP (class II-associated invariant chain peptide)

       HLA-DM (calss II like molecule) ---> binds the CLIP    

5. MHC restriction
  --> Fig 6-15 ; self-MHC and foreign Ags

-- MHC restriction of CTL

-->  - class I : CTL (CD8 positive)
       - class II : T helper cells (CD4 positive)

6. Antigen processing

-->  antigen features; recognized by T cells

  Table 6-1

 -->  Requirement of APC, not antigen itself, for T cell activation

 Fig 6-2

-->  Functions of different APCs

-->  Comparison of MHCI- and II-derived antigen presentation

Table 6-3

 -->  Antigen processing requires time and cellular metabolism (Fig 6-10)

Chapter 7 Antigen Receptors and Signal Transduction

 TCR and accessory molecules

-- Comparison of TCR and BCR signaling

Fig 7-2

** B cell antigen receptor (BCR) **

-- TCR and BCR

 table 7-1

- - TCR

1)   αβ TCR
       -> S-S bond
       ->  α chain; acidic,   β chain; basic and charged
       -> each C region; functional domains
       -> TM region; + charged (Lys, Arg)
       -> cytoplasmic tail; 5-12 Aas

    - differences between  α, βchains and Ig
       -> no isotype switching
       -> don't know the effector functions
               
     2)   γδTCR
      - in small subset of peripheral T cells
        in immature thymocytes and bowel mucosal
      - features;
       1) has a CD3 complex
       2) β = δ ,  α = γ 
       3) S-S bond and non-covalent binding
       4) γδrearrangement precedes those of  αβ 
       5) don't express CD4 or CD8
       6) no MHC restriction, non-specific cytolytic activity
       7) what  γδ TCR recognizes ?
           -> MHC I like proteins (CD1, Tla)
           -> heat shock proteins of Mycobacterium

     3) CD3 complex, table 6-1

       1) require for surface expression
         - evidence; ① coprecipitation
                     ② both endocytosis
                     ③ reconstitution of mutant cell line (TCR^-); (Fig 7-6)

Fig 7-6

       2) γδεζηchains
          - ζη(10%), ζζ(90%)
          - highly homologous, gene duplication
          - no polymorphism
          - TM; Asp(-)    

Accessory molecules of T cells

* Interaction between T cells and APC (Fig 7-7)

Fig 7-7

   CD4 and CD8                                                    
  

Fig 7-8

  - MHC restriction
  - Ig gene superfamily
  - not related each other, but similar functions
  - in peripheral T cells (CD4; 65%, CD8; 35%)
  
  1) CD4
  - as a monomer
  - functions; ① cell-cell adhesion   ② signaling
    evidences;
                                                            CD4

                                                             
             fibroblast                              fibroblast

                                         +

                           MHC II expressing cells

                                            
                            no-binding    binding

       (1) mAB against CD4 --> stimulatory or inhibitory
       (2) cytoplasmic tail --> phosphorylation

2) CD8
  - CD8 α and β, heterodimer and homodimer (αα)
  - functions; ① cell-cell adhesion   ② signaling
    evidences;
             (1) between fibroblast and MHC I expressing cells
             (2) mAB against CD8 --> stimulatory or inhibitory
             (3) cytoplasmic tail --> phosphorylation                                                                                                             

Adhesion molecules; integrin

-- role of integrin in T cell response

Chapter 8  Lymphocyte maturation & Antigen receptor gene rearrangement

 -- Stages of Lymphocyte maturation                                                                                

-- checkpoints of lymphocyte maturation (Fig 8-3)

    --> only cytoplasmic  μ heavy chain
          (associated with surrogate light chain (V_pre-B and λ₅): prevent the degradation of newly synthesized  μchain,  promote the Igs on the cell  surface)   

 Sequence of events in thymocyte maturation (Fig 8-20)

Fig 8-20

pre-Tα chain (pTα)
- analogous to surrogate light chain ( λ5)
- 3 important functions
  ① recombination at α chain locus; allelic exclusion of β chain
  ② stimulation of proliferation
  ③ transition from double-negative to double-positive cells; induction of CD4 and CD8

Ontogeny of T cells (Fig 8-21)

 - in thymus
     ① MHC; by non-lymphoid cells
     ② thymic hormone; by epithelial cells
     ③ IL-7; by stromal cells
   
   - positive and negative selection
     1) positive selection -- TCR binds self-MHC (low affinity) --> can survive
     2) negative selection -- TCR binds self-Ag (high affinity) --> can die (clonal deletion)
                                                                                            or can be inactivated (clonal anergy)

positive & negative selection

positive and negative selection in T cells  (Fig 8-24)

   Fig 8-24

-- Role of peptide in positive selection (Fig 8-26)

  Fig 8-26

 Formation of functional antigen receptor genes in B and T lymphocytes

 1. Genomic organization of Ig

1. V region; 300bp, 1000 to 2000kb long
             leader(=signal) peptide is 90bp of 5' of each V region, hydrophobic
             from ribosome to lumen of ER
             cleavage before complete translation
             duplication of a single V gene

2. C region; tandem array whose order is specific for each species
3. J region; 30-50bp long, 3'hypervariable region
4. D region; only in heavy chain, 3'hypervariable region
5. intron region; important role in the production of Ab
                - recognition seq for rearrangement, RNA splicing, regulation of transcription

2. Organization of TCR

3. Antigen receptor gene rearrangement

4. Sequence of Ig gene rearrangement (somatic recombination)

H chain:
1. DJ joining
  -- no-effect on 5' D and 3' J region
  -- before commitment of B precursors to B lineage cells
  
2. VDJ joining
  -- only in cells committed to become B cells
  -- not known whether all the C regions can be expressed in primary transcript

L chain:
1. VJ joining

5. Mechanism of Ig gene rearrangement

1. recombinases;
  - cell type specific (ex: B and T cells)
  - function at early stage of B cell development (pre-B cells)
  - multiple enzymatic activities (some are B cell specific, others are not; exonuclease and ligase)
  - RAG1/RAG2; genetic defect in SCID mice (no mature B and T cells)

** recognition sequence ;
   - located in 3' V, 5' J, and both side of D region
   - heptamer(CACAGTG)/nonamer(ACAAAAACC): conserved                                             
     12 and 23 spacers: non-conserved

2. accessibility of DNA to recombinase
  - chromatin; open in early B cell stage
    -> euchromatin (vs: heterochromatin)

3. programmed change or selection pressure by environmental antigens
  - in pre-B, proximal Vh region is preferred
  - in mature B, no bias in Vh usage

6. Antibody diversity (table 8-1)

1. mutiple germline genes
  - multiple germline V, D, J genes
2. combinational diversity: V X D X J
3. junctional diversity (Fig 8-13); more important in TCR diversity
  (a) imprecise DNA rearrangement: functional, nonfunctional(occasional compensation by  deletion of 1 or 2 nt)
  (b) N region diversification (addition) / P nucleotide addition
     - N sequence is not in germline
     - random process, by TdT(terminal deoxyribonucleotidyl transferase)

     - P nucleotide addition; by RAG1/2 and DNA polymerase

4. somatic mutations
5. combination between H and L chain           

 7. B cell maturation

** Roles of   heavy chain

1. inhibition of rearrangement on other chromosome (allelic exclusion)
  -- nonproductive; formation of stop codon by deletion, mutation, frame-shift
                            finally die (no response to Ag)

2. stimulation of L chain rearrangement
  -- k, and  λ chian rearrangement

** role of k light chain; allelic exclusion and light chain isotype exclusion
   (a) only k-producing B cells: lamda gene is a germline or unarranged
   (b) only λ-producing B cells: k gene is deleted or aberrantly recombined

 
** Coexpression of IgM and IgD
- in mature B cells
- same antigen specificity - same V region
- alternative RNA splicing

8. T cell maturation

-- T cell maturation in thymus (Fig 8-21)

-- TCR recombination; similar to Ig

-- positive and negative selection in thymus

Chapter 9  Activation of T lymphocytes

-- How T cells are activated ? (Fig 9-1)

  (a) effector function
     - T helper cells secrete cytokines
       --> (Fig 9-2)
     - CTL lyse the Ag-bearing target cells, and secrete cytokines
  (b) proliferation
     - autocrine pathway (by IL-2)
       -> clonal expansion and Ag-specific memory T cells

** T cell activation (Fig 9-8)

   - steps:
          1. early signal transduction
          2. transcriptional activation of a variety of genes
          3. expression of new cell surface molecules
          4. secretion of cytokines (ex; IL-2)
          5. induction of mitotic activity
   - two signal models
          1. by Ag-MHC and TCR
          2. costimulation by accessory molecules (ex; CD28): (Fig 9-6)

** Role of costimulators in T cell activation

Fig 9-6

 Ref; TCR and accessory molecules

  --->  Role of B7 and CD28 in T cell activation

-- Role of CD40 in T cell activation

Fig 10-11

-- T cell signal transduction
       

Fig 9-9

(1) tyrosine phosphorylation

Fig 9-10

 (2) Ras/MAP kinase pathway

Fig 9-12dmd

  (3) inositol lipid metabolism

Fig 9-13

(4) Activation of transcription factors in T cells

  Fig 9-14

Chapter 10   B cell activation and antibody production

General features of humoral immune response

     Fig 10-1                                                       

  (a) primary and secondary antibody response
     - cell cycle from G0 to G1
     - proliferation
     - Ig secretion
     - isotype switching

 (b) intracellular signal changes
     - Ca²⁺, DAG, PKC activation (within minutes)
     - c-fos and c-myc activation (within 30'-1hr)
     - size and cellular RNA increase (~12hr)
     - cytokine receptors and class II expression (within 12-24hr)

Fig 10-2

 Humoral immunity: mediated by antibodies

1. Antibody responses: Ag + resting B, IgM/IgD mature cells
                    -- proliferation (growth)
                    -- differentiation (Abs secretion)

2. Features of antibody responses:
  (a) presence of T cells; two signals (one from Ags, the other from T cells and their products)
  (b) in case of non-protein antigens; no need T cells
  (c) different primary and secondary responses: (Fig 10-2)
      

___________________________________________________________

             primary                                           secondary

___________________________________________________________
   10,000-1,000,000 fold                      1-100ng/ml of specific Ags
 macrophages/dendritic cells                 high affinity Igs on B cells
   (non-specific)                                  (only in T-dependent Ags)

____________________________________________________________

  (d) memory cell generation/heavy chain class switching/affinity maturation                               

Signal transduction by the BCR complex

Fig 10-4

Second signals for B cells provided by complement receptors

 Fig 10-5

Functional response of B cells to antigen recognition

Fig 10-6

Which effects are coming up when Ags are introduced into B cells ?

  (1) 2 types of responses :                        
                -- entry of resting B cells into the cell cycle
                -- antigen processing

 (2) functional aspects: -- phosphorylase C catabolization
                        -- c-fos and c-myc
                        -- size and cellular RNA increase
                        -- cytokine receptor/MHCII

  Antigens
 
  (a) thymus dependent and independent Ags

B-T cell interactions

 (a) How are T helper cells found to be involved in B cell activation ?
       ---> evidence

 (b) early and late phase after immune response in lymph node

Fig 10-7

참조 (Germinal Center): Fig 10-12

(c) B and T cell migration and interaction

Fig 10-8

(d) How B cells interact with T cells for immune response ?

Fig 10-9

 Role of CD40 in B cell activation

Fig 10-11

--> experimental evidence

 Secretion of Ig

- activation of mIg expressing B cells by antigen, in plasma cells
- more differentiation, more sIg
- mRNA splicing by choice of poly A sites

Fig 10-18

H chain class switching

- in IgM/IgD B cells by antigen stimulation
- mechanism: (Fig 10-14) -- switch recombination
                     switch region (5' each C region), ex; for IgE
                     - 1-10 kb long, numerous tandom repeat  of conserved seq (52bp)
- regulation: 1) by helper T cell and its cytokines  
                     2) by microenvironment
                    - opening the chromatin, and accessible to factors regulating rearrangement and transcription in switch region  
                    - sterile C transcript (not VDJ) in short time after treatment
                    examples: IL-4 (IgE), gamma-IFN (IgG2a), mucosal tissues (IgA)

Fig 10-14

Fig 10-13

Germinal Center Reaction: Late event in immune response

Fig 10-12

- Somatic mutations of Ig in germinal center

Fig 10-16

1. in antigen stimulation, occurrence in V (H and L) region, affinity maturation
2. characteristics;
  - number of mutations increase in IgG>IgM anibody, 3'>2' immunization, and with time after 1' immunization
  - hypervariable region of V exon is frequent (affinity maturation)
  - some mutations: loss of Ag binding activity - die
    other mutations: new Ag specificity
  - 1/1000 per base pair in V region
  - affinity maturation: in antibody response to helper T cell - dependent antigens

                                                                           T cell or T cell derived products                                                                    

 B cell selection in Germinal Center

  Fig 10-17

 Antibody feedback

definition: injection of Ag-specific antibody cause the reduction of Abs production
          in both humoral and cell-mediated response
          (ex: Rh disease) ---> ♂(Rh⁺)   ♀(Rh^-)  

How ? --> SHIP(SH2 domain containing inositol phosphatase) --> removal of PIP3

                   --> no signaling by BCR                      

  Fig 10-19