comparing different immunoglobulin Flashcards
Introduce the two polymeric antibody and where they locate and functions
- IgM: pentamer & 2. IgA: dimer-tetramer
Both are linked by J-chain
Poly-Ig receptor (pIgR)
- basolateral surface of most mucosal epithelia (e.g. the lining of the digestive, respiratory, and genital tracts) and on glandular epithelia in the mammary, salivary, and lacrimal glands
- interacts with the J (joining) chain of both polymeric IgA & IgM
Secretory component (SC):
- masks sites susceptible to protease cleavage in the hinge region of secretory Ig (sIg)
Compare the half-life of the Igs
longer: IgG>IgA>IgM>IgD>IGE
Which one is not found in blood, and where it is located?
IgD
It is membrane immuoglobin only found on the surface of B-cell
Which one found in blood in highest amount? Does it occur in mucous membrane?
IgG
No
It can activate complement活化母體
What is the role of IgE?
IgE appears in monomer form, acting on peripheral nervous system, and causing allergy on the pheripheral tissues.
Compare how ruminants, primates, dog/cats and other non-ruminants fetus acquire maternal antibody.
How is antibody absorption be enhanced for newborns?
- Low level of protease activity in digestive tract + reduced by trypsin inhibitors in colostrum
- Colostral Igs binds FcRn
- special FcRs found on the intestinal epithelial cells of newborns
- distributed across intestinal epithlium à facilitate endocytosis of Ig which is then transported towards the whole body
- 一般Fc receptor分佈在吞噬細胞上面，嬰兒有此種情況是為了吸收抗體。
- 細胞間排列較疏鬆 –> Highest permeability of epithelium à nutrient absortion enhanced
- FcRn(+ve) intestinal epithelial cells gradually replaced by FcRn(-ve) cells after 6hr
- Permeability falls as a result –> antibody absorption falls
- 初乳內的抗體（IgG）可跑到全身提供全身性免疫；而母乳(milk)內的抗體只能跑到腸道提供腸道免疫
What is anaphylaxis?
serious allergic reaction happened rapidly and may cause death
What is IgY
- Evolutionary ancestor of IgG和IgE in mammals
- 所以可以發現IgY介於兩者的特性中。
- IgE:多了一個domain，且能媒介一些過敏反應
- IgG: Complement fixation, carbohydrate content and distribution, major systemic antibody (maternally derived)
- 可在鳥類、爬蟲類(reptiles)、兩生類(amphilbia)體內發現（圖十五）
- 分子量為180 kD(即在constant region多一個domain，共四個，構型像IgE)
- 雞只產生IgY
what is the use of IgY(triangle Fc)
- Incomplete IgY(120 kD)à truncated protein (lack of Fc)
- Able to recognise antigen, without causing immune response / complement activation / 調理作用(opsonization) / anaphylaxis
- 可在雁形鳥類aniseriform birds(鴨、鵝)、爬蟲類(特別是烏龜)、肺魚中發現
- 在某些雁形鳥類及烏龜身上可同時存在IgY及IgY (△Fc)
- 可調控宿主的免疫反應，避免過強的免疫反應傷害宿主，因為免疫力太好，會對我們造成傷害。（少了CH3、CH4）
How are antibodies distributed in eggs?
IgY is secreted by epithelial cells of oviducts and stored in yolk –> absorbed by chick into blood stream
IgA stored in albumin ingested by chick –> protects intestines
What is C3b?
An opsonin participating in opsonisation
- 調理反應(opsonization)：
- Opsonin: any molecule that targets an Ag for an immune response and acts as a binding enhancer for the process of phagocytosis
- Both Ab and complements can act as opsonin
- Ag bound by Ab à Ab then binds to FcR pf phagocyte
- Complement activation: Ag bound by complement, C3b à C3b binds to CR1
- Princle: both phagocytes and Ag are -ve chargedàelectrostatic repulsionàhard for phagocyte to get close to Ag ; 當opsonin與抗原結合，會屏蔽其表面負電，幫助吞噬作用的進行
What is C1?
Complement.
- Activation of complement 補體的活化 (打洞器!)
(1) 當immune complex (IgG或IgM binding tp Ag) binds to C1 (complement) àC1 complex à Trigger the classical pathway
(2) 因IgM為pentamer，一個即可活化補體；而IgG為monomer，故須多個才可活化補體。
Which Igs can cause complement activation?
- Activation of complement 補體的活化 (打洞器!)
(1) 當immune complex (IgG或IgM binding to Ag) binds to C1 (complement) àC1 complex à Trigger the classical pathway
(2) 因IgM為pentamer，一個即可活化補體；而IgG為monomer，故須多個才可活化補體。
What is ADCC
Immune complex所引發的細胞毒殺作用(Ab-dependent cell-mediated cytotoxicity or Ab- dependent cellular cytotoxicity ＝ADCC)
(1) Immune complex binds via FcR on immune effector cell吞噬細胞(macrophages, neutrophils, eosinophils或natural killer cells)
–> triggers release of lethal cellular products from the bound immune effector cells(細胞致死物)，或是打洞使之滲透壓內外失衡。
Examples：lytic enzymes, perforins（打洞的）, granzymes（進入細胞內導致凋亡，與前者合作）, tumor necrosis factor（接在細胞膜上面，不用進入細胞內讓細胞凋亡）, oxidants, etc)
Isotypic determinants
- 抗體在不同物種間，會有不同的heavy-chain class and subclass, and light-chain type and subtype，如：鳥類有IgY，人類沒有
* Determined by C regions
Allotypic determinants
抗體在同種不同individuals之間，constant region的genetic sequence不相同(除非是雙胞胎) –> subtle amino acid differences
idiotypic determinants
- 在同一個體內，不同抗體間variable region的序列不相同。
* Antigenic determinants of the V region
how’s signal 2 produced?
- T-cell’s CD40L (CD154)與B cell’s CD40 binding
- T cell’s CD28與B cell’s CD86 binding
Clonal selection theory
The Ag-mediated activation and proliferation of members of a clone of B cells that have receptors for the Ag (or for complexes of MHC and peptides derived from the Ag, in the case of T cells)
What is IL-4?
Interleukin-4 (cytokines secreted by T cells)
- stimulating T-cell proliferation
- a key regulator in humoral and adaptive immunity. IL-4 induces B-cell class switching to IgE (and IgG1, IgA),
- Up-regulates MHC class II production.
- IL-4 binds to IL-4R on the suface of B-cells, producing signal 3 --> proliferation and differentiation into plasma cell and production antibody are all activated.
- Also stimulating class swithcing IgG1, IgE, IgA
What are involved in signal 2? (B-cell activation and proliferation)
After Ag-Ab complex formed,
1. T-cell’s CD40L (CD154) binds B cell’s CD40
2. T cell’s CD28 binds B cell’s CD86
Anergy of B cells
Unable of B cell to produce antibody
- When more than 5% of mIgM molecules are occupied by monomeric soluble因為B cell認為有可能是自自身的抗原，故抑制免疫反應，推測是抗原的量太多，會被視為自己的antigen。
- Absence of T-cell help à lack of signal 2，稱為免疫耐受性(immune tolerance)
- Unresponsiveness to antigenic stimulation (即便有T細胞的幫忙也不會製造抗體)
What is CD154?
=CD40L, receptor found on the suface of Th cells, responsible for binding to CD40 ligand present in APC (B-cell, dendritic cell, macrophages)
Their corresponding activations are as follows
Which antibody rises greatly in second exposure to the same Ag?
IgG
Showing that IgG should be the real protector of the adaptive immune system. In reality, if high level of IgM is detected–> chronic infection
If high level of IgG is detected, indicating previous experience of infection
What class of mIg present on the surface of naive B-cells? What is the sequence of class switching?
How does class switching change affinity and specificity?
In naive B-cells, only mIgD and mIgM are present.
Sequence:
mIgD/mIgM –> IgG –> mIgE –> mIgA
Thats why IgE causing allergy only happens after second time of exposure to the allergin
Affinity is improved, specificity is unchanged
mIg present on suface of memory cell
mIgG, mIgE and mIgA
IFN-g
cytokine signal produced by T cell acting on B cell for class swithcing
–>IgG3, IgG2a
IL-5, transforming growth factor B
- IgG2b, IgA(黏膜上皮細胞主要cytokine為TGF-β，故較多IgA分布於黏膜)～（cytokine的幫忙，可超車，直接從IgM變成IgA）
Bcl-2
Anti-apoptotic proteins expressed on B cells.
When continued stimulating signals (cytokines/Th cell/Ag) is stopped, expression of Bcl-2 falls, leading to apoptosis of B cells.
bax oppose bcl-2, promoting apoptosis
Idiotypic regulation
There is idiotype-specific Ab present: can recognize the Ag-sepcific lymphocytes –> anti-idiotypic response
- Anti-idiotypic T cells: can also recognize idiotypic determinants of the mIg on B cells MHCII
- A steady state in the immune system is maintained by the network of reciprocal idiotypes and anti-idiotypes.
- The introduction of Ag perturbs that balance and leads to detectable immune responses
CD22
Inhibitory B-cell coreceptor
- CD22上的免疫受器immoreceptor tyrosine phosphate inhibitory motif (ITIM)與SHP-1(tyrosine phosphate磷酸水解酶)結合
- dephosphorylating tyrosines of BCR
- B cell的signal I被抑制
- Igα/Igβ上有免疫受器tyrosine-based activation motifs (ITAM)
CD19
負責傳遞訊息，attracting kinase –> phosphorylation –>活化B 細胞製造抗體
Phagocytosis
Complement activation
Phagocytosis: IgG only (IgM unknown)
CA : both IgG and Ig M can do
SHP-1
Recruited by CD22 on B cells, so as to remove phosphates on Iga/Igb of the CD79 (accessory molecules for BCR)
--> inhibitory
Antibody that B cells must contain on its surface
mIgM, mIgD
What are the two classes of globulin
Ƴ globulin
Most antibodies except IgM
beta globulin: IgM :
What determines the class of the Ig?
sequence of constant region on the heavy chain
note: light chain sequence is irrelavent
Hinge on the antibody
- 一段胺基酸序列 (amino acid sequence)
- 2 heterodimers are connected by disulphide bond
- 有proline, 使抗體具有靈活度，可轉動、開張與抗原結合，不同抗體種類間hinge不同，彈性(flexibility)也不同
- IgE、IgM沒有hinge的構造
Which Ig has subclasses
- IgG: 4 subclasses in humans, and 2 in canine
- IgA: 2 subclasses
compare the three types of digestion
- pepsin digestion
- papin digestion
3.
Mercaptoethanol reduction
1. pepsin
- cleavage under hinge, just separating the Fab and Fc regions
no breakage of disulphide bind，辨識能力較papain digestion處理後的強
- papain digestion*
- cleavage at the hinge: turning Fc separates from Fab, Fabs also separates into two heterodimers. No breaking between heavy chain and light chain, so still remains antigen recognition function
3.mercatoethanol
- breaking all disulphide bond –> the Ig is cleaved into 4 units
CD79
- accessory membrane protein of the BCR, help signal transdcution (tell b cells to produce Ig)
- 2 groups of CD79 are available next to BCR, and each contains a α and β group
for Igα/Igβ
- α較深，β較淺，均是往下傳遞訊息的東西
- b cell上重要的marker，例如要判別是T cell還是B cell來源的腫瘤，可以從CD79有無來判斷
Which antibodies got one more constant domain?
IgM and IgE: got CH1, CH2, CH3 and CH4(多出來的）
hinge of these two are absent, connected by only one S-S bond
binding forces of Ag-Ig
Ionic, hydrophobic, VDW
BUT NO COVALENT BINDING
CD21
Complement receptor for C3d
- expressed strongly on mature B-cell
- complement activation
- enhance the ability of B-cell for antigen as it interact with CD19 (co-receptor)
CD81
- present on both B-cell and T-cell
- co-stimulatory molecules of their activation
