Antigen Recognition by B-cell and T-cell Receptors 第 4 章 Outlines: Antibody, TCR, and MHC 1. The structures and functions of antibodies, including variable and constant domains, antigen binding sites. 2. The structures of T-cell receptors, CD4 and CD8. 3. Difference between the Ag-recognition by Ab and TCR. 4. The structures and presented peptides of MHC I and MHC II. (4.13-4.16) by Dr. Lin.
免疫的種類 以免疫力來源分 : 天然免疫 (nature), 遺傳而得 後天性免疫 (acquired), 獲得免疫 - 被動免疫 (passive) - 主動免疫 (active) 以免疫反應分 : 非專一性免疫 (innate, nonspecific immunity) 專一性免疫 (adaptive, specific immunity) - 體液性免疫 (humoral) - 細胞性免疫 (cellular)
免疫系統的器官 初級 (primary): Thymus + Bone marrow 次級 (secondary): Peripheral lymphoid organs ( 淋巴球主要活化 / 複製處 )
Blood cells 特異性辨識 (CD19) (CD3) (CD16/56) (CD14) CD: clusters of differentiation
Clonal selection (expansion) 每一個 (T or B) 細胞只能表現一種辨識分子 一種 放大對特定抗原的辨識能力
抗體是什麼? What are antibodies (immunoglobulin, Ig)?
(5 isotypes)
The Y-shaped Ab molecule can be dissected by partial digestion with proteases Single chain Fv: V L + V H
epitope Antigenic determinants: different between Ab and TCR 抗原決定部位 (antigenic determinant) 抗原真正與抗體結合的部分, 是發生抗原抗體反應的部分 此部份通常只佔原分子的一小部份, 具有專一性, 是能被免疫系統辨認的部位, 故又稱頂位 (epitope)
Epitopes are sites within Ags to which Ag receptors ( 即 Ab) bind ( 構型 )) Epitope 可以是不連續的胺基酸序列
TCRs bind a complex of an Ag fragment and a self molecules (MHC) ( 線型 )) Epitope 是連續的胺基酸序列
Ab: conformational or discontinuous epitopes TCR: linear or continuous epitopes + MHC
The noncovalent forces that hold together the antigen:antibody complex
high vs. low affinity
Ags can bind in pockets, grooves, on extended, or protruding surfaces in the binding sites of Abs Ferrocene hapten HIV peptide Egg-white lysozyme gp120 結合CD4
CDR (HV) Complementaritydetermining region (CDR) Framework region (FR) 4+3 in C 4+5 in V 2 -sheets form barrel a disulfide bridge
There discrete regions of hypervariability in V domains
The hypervariable regions lie in discrete loops of the folded structures
Subclasses (isotytes) of Igs (human) Mouse 4 IgG subclasses: IgG1, IgG2a, IgG2b, and IgG3
Ab-mediated effector functions Promote opsonization Activate complement ADCC (Ab-dependent cell-mediated cytotoxicity) Transcytosis (cross epithelial layers)
Immunoglobulin superfamily Ig-like domains (page 143-144)
T-cell receptor Antigen recognition by T cells TCR resembles a membrane-bound Fab fragment. TCR 由 2 peptide chains 構成 : 成人體內主要是 - 胚胎或是成人腸胃道 -
Structure of the TCR
21-22 aa 5-12 aa
V-C: 147 vs. 111
The crystal structures of an : TCR
The crystal structures of an : TCR Assist the binding between C and C
The crystal structures of an : TCR HV4 不與抗原直接接觸
Differences in the recognition of HEL by Ab and TCR Surface: for Ab Core of the protein: for TCR
T 細胞抗原辨識 主要組織相容性複合體 (MHC) (major histocompatibility complex) 人類的 MHC 稱 HLA (human leukocyte antigen) - Class I: A, B, C - Class II: DP, DQ, DR 小鼠的 MHC 常以 H-2 表示 - Class I: K, D, L - Class II: I-A, I-E
T 細胞抗原辨識
Professional antigen-presenting cells (APC)
Self-MHC restriction of the TCR
The expression of MNC molecules differs between tissues MHC I: all nucleated cells Activated human T, not mice MHC II: mainly APCs Liver for transplantation Malaria (Plasmodium) in RBC - as an immune privileged site Except microglia
The TCR binds to MHC:peptide complex CDR3 center of peptide CDR1,CDR2 MHC + peptide
The TCR interacts with MHC class I and II molecules in a similar fashion
CD3:
Co-receptor of TCR: CD4 & CD8
The binding sites for CD4 and CD8 on MHC I and MHC II molecules lie in the Ig-like domain D1 of CD4 to 2 (MHC II) CD8 to 3 (MHC I)
CD4 and TCR bind to distinct regions of the MHC class II molecule CD8 binds to a site on MHC I molecules distant from that to which the TCR binds
Binding affinity Dissociation constant
Costimulatory signals B7-1 (CD80) B7-2 (CD86)
Clonal angery - blocks of costimulatory signals
Clonal activation - the presence of costimulatory signals
Annu Rev Immunol 2003,21:659
(cytotoxic T-lymphocyte antigen 4) (programmed death 1) (inducible costimulator) (B and T lymphocyte attenuator) Annu Rev Immunol 2005,23:515
Co-stimulatory signals and tissue transplantation Soluble CTLA4 in RA clinical trial
有許多反而出現於腫瘤細胞上 Annu Rev Immunol 2005,23:515
Summary of B7 family ligands and their receptors 具免疫抑制功能 Clin Cancer Res 2007,13:5271
Pathways: regulate T cell activation and tolerance B7-1/B7-2:CD28/CTLA-4 - CD28: constitutively on T cells; CTLA-4: upregulated following T cell activation - B7-1: inducibly expressed later than B7-2 - B7-2: constitutively expressed at low levels and rapidly upregulated - CD28:B7 interactions are needed for the development and maintenance of CD4 + CD25 + Treg cells - B7-2 expressed on some resting T cells and interact with CTLA-4, caused GVHD - B7 may not only engage CTLA-4 on T cells, but also deliver signals into the T cells DC through IFN- production and induce IDO (indoleamine 2,3-dioxygenase) to inhibit T cell proliferation - B7-1 in kidney might serve as an inducible regulator of the glomerular filtration apparatus - B7-1 and B7-2 are the receptors for adenovirus serotype 3
Pathways: regulate T cell activation and tolerance - ICOSL:ICOS ICOS expressed on Th1 and Th2 cells, but persist at higher levels on Th2 cells ICOS engagement selectively produces high levels of IL-10 and IL-4 CD28 appears to have a predominant role in priming T cells, whereas ICOS regulates effector T cell responses CD28 and ICOS pathways have synergistic role in promoting antimicrobial immunity and long-term survival of allografts - PD-1L:PD-1 Broader expression of PD-1 than CD28 family members PD-L1 is expressed on CD4 + CD25 + Treg cells PD-L1 expressed on nonhematopoietic cells prevent potentially self-reactive lymphocytes from causing tissue injury - B7-H3:? B7-H3 mrna expression is stimulated in mouse DC by IFN-, but suppressed by IL-4 B7-H3 binds to activated but not resting CD4 + and CD8 + T cells B7-H3 negatively regulates T cell responses that occur under Th1 polarizing conditions
Pathways: regulate T cell activation and tolerance B7-H4 (B7x):? is a negative regulator of T cell responses is highly expressed in lung and ovarian tumors -(HVEM):BTLA selectively expressed on Th1 cells may specifically downregulated Th-1 mediated inflammatory responses BTLA -/- mice spontaneously develop signs of autoimmune disease PD-1 and BTLA may have redundant inhibitory functions directed toward maintaining peripheral tolerance and attenuating inflammatory responses
The Tang Prize provides each a cash rewards of NT$ 40 million, and the research projects proposed by the laureates will also receive a grant of up to NT$ 10 million. Profs James P Allison and Tasuku Honjo for the discoveries of CTLA-4 and PD-1. (2014) 抑制腫瘤新藥 anti-pd-1 Immunology blockade
The production of monoclonal antibodies 特性 : 1. 1 個 clone 只產出一種 MoAb 2. 即每種 MoAb 僅結合 1 特定 epitope 並也只有 1 種 isotope
單株抗體與融合瘤製造
HAT medium
單株抗體與融合瘤製造
Antibody engineering Humanized antibody