Immunology – Block III – Lecture Notes

Types of APCs:o Antigen Presenting Cells (APCs): present foreign antigen to the

naïve T Cell to elicit an immune response.o Professional APCs: Express MHC Class I and Class II molecules.

Co-Stimulation Molecules: Signal 2: Binding to CD80/CD86 oto the CD28 on the T-Cell.

T Cells recognize Linear Peptides MHC I and MHC II

o CD4+ sees MHC II – Antigen from Extracellular Exogenous Acid Proteases Invariant Chain: prevents early binding of peptides until it

reaches Extracellular Area and directs the MHC II to acidic vesicle after leaving the Golgi, leaving CLIP.

HLA-DM: Exchanges the CLIP for the Peptide that you want in the Peptide Binding Groove.

o CD8+ sees MHC I – Antigen from Intracellular (cytosolic) Endogenous Usually Viruses use this pathway. Misfolded proteins Polyubiquinated Proteosome

Peptides to go the ER MHC I binds the Peptide while inside of the rER (MHC I must pick up the peptide before it is allowed to leave and go to the Plasma Membrane)

These MHCs have an open groove. We always have Proteosome, but Immunoproteosomes

can be induced by IFN-y. This changes the subunits of the Proteosome so that the peptides that are cut fit well in the MHC Class I groove. The Immunoproteosome has a PA28 Cap.

Uses Calnexin and Calretiulin. TAP1/TAP2 transports the peptides from the Cytosol to

the ER. ERAP: Protease in the ER that breaks down the peptides

further while in the Binding Groove until its perfect for the MHC Molecule.

** Even though Viruses go through MHC class I (CD8) because it is replicated inside of the cell, the Virus must still bind to the outside of the cell first, meaning that it ALSO activates as MHC class II response (CD8)

DENDRITIC CELLS ARE THE ESCEPTION, YOU CAN HAVE CROSS PRESENTATION – THE DETAILS ARE UNKNOWN.

CD1 Molecules: Present lipid antigens (LPS for Gram -) to NKT Cells. o Requires Endosome Acidification.

o MHC I-Like________________________________________________________________________________________

CLP Thymus (cortex) Pro-T-Cell Pre-T-Cell (γ δ OR α β)

o γ δ (Mature, Double negative)o α β (Mature, CD4+)o α β (Mature, CD8+)

Steps:1. CLP enters the Cortex of the Thymus2. They encounter Thymic Epithelial Cells (TEC)

a. Signals:i. CLP: Notch and C-Kit

ii. TEC: Notch Ligand and SCF1. Commit to T-Cell Lineage2. CLP Thymocyte

3. This will cause more signals.i. Thymocyte: IL-7R

ii. TEC: IL-71. TCR Gene Rearrangement

4. This initiates TCR Gene Rearrangement.5. TCR Gene Rearrangement:

a. γ , ,δ and all rearrange together and race to finish.βb. If γ , rearranges first δ DN γ ,δc. If rearranges first, it becomes a Pre-TCR.β

i. Signaling through the Pre-TCR Receptor 1. Induction of A-Chain Rearrangement2. Allelic Exclusion3. CD4 AND CD8 (DP)

6. Enter Selection:a. Positive Selection: you must bind an MHC Molecule to survive.

i. CD4 or CD8 (SP)b. Negative Selection:

i. If cell has a TCR that binds to Self-Peptide tightly diesii. If cell has a TCR that binds to Self-Peptide weakly

livesiii. If cell has a TCR that binds to Self-Peptide

intermediately CD4+ CD25+FoxP3+Treg Cells CD4 Cells: Helper T-Cells

o Th1: Cell-Mediated Immune Responseo Th2: Humoral Immune Response o Treg: Suppress Immune Responses

CD8 Cells: Cytotoxic T-Cells (CTLs) NKT Cells:

o Express CD3 and NK Marker with limited TCR Diversity.o Recognize Glycopeptides and Glycolipids presented by CD1d

AIRE:o Autoimmune Regulatoro Transcription Factoro Activates Ectopic Gene Expression

Expression of genes in a tissue that does not normally express those genes.

o Allows developing Thymocytes to be exposed to, and therefore selected against, antigens that are not normally expressed in the Thymus.

o Expressed by mTEC in the Thymus APECED:

o Autoimmune Polyendocrinopathy Candidiasis-Ectodermal Dystrophyo Caused by a mutation in AIRE.o Autoimmune attack on multiple endocrine tissues.o Failure to delete auto-reactive Thymocytes during Negative Selection

Tolerance:o Central Tolerance:

Acquired during Lymphocyte Development in the Bone Marrow and Thymus.

Not 100% Efficient Process of Negative Selection AIRE

o Peripheral Tolerance: Suppression from Regulatory T-Cells

CD4+CD25+Foxp3+ Anergy: Cells rendered non-responsive to stimulation. Signal 1: MHC Presentation to TCR, CD3 Signal Signal 2: CD80/86 binding to CD 28 on T-Cell IL-2 Secreted

o IL-2 binding to IL-2R is Autocrine TCR: Receive Signal 1, but not Signal 2 = Anergy TCR: Receive Signal 2, but not Signal 2 = Nothing

Happens Signal 3: The cytokines that stimulate differentiation Immune Privileged Sites

Sites where suppression of Immune Responses is normal Leukocyte Entry:

o Rolling: L-Selectin (T-Cell) loosely binds to GlyCAM-1 or CD34 (adressin on

HEV)o Adhesion:

LFA-1 (T-Cell) tightly binds to ICAM-1 (on HEV) Markers:

o CD28 (T-Cell) binds to CD86/CD80 (APC) = Signal 2o CTLA-4 (T-Cell) binds to CD86/CD80 (APC) = Suppression

CD80=B7 (different names)o CD-2 (PanT-Cell) binds to LFA-3 (APC) = Cell Adhesiono LFA-1 (T-Cell) binds to ICAM-1 = Cell Adhesiono CD45: Signal Transductiono CD40L (T-Cells) binds to CD40 (B-Cells) = Activation

T-Cell Activation by Antigens:o Clonal Selection: binding of APC by an Antigen specific T-Cell in

Peripheral Lymph Organs Signal 1: APCs present MCH+Peptide to TCR on CD4+ T-Cells Signal 2: APCs present co-stimulatory molecules to CD28 on T-

Cell, leading to IL-2 production and IL-2 expression.o Clonal Expansion:

T-Cells are now receptive to Autocrine (CD4+T) and Paracrine (CD8+T) stiulation by IL-2 Proliferation.

First Checkpoint: preTCRo B has been rearranged.o Surrogate A chain.

Second Checkpoint: TCRo Both chains are rearranged.o Postiive Selectiono Negative Selection

Two Types of TCR:o γ δ TCR o α β TCR

Hypervariable Regions:o CDR3: Binds the peptide. – Most Variableo CDR 1/2: Binds MHC Molecules

Enzymes needed for TCR Gene Rearrangement:o RAG-1, RAG-2o TdT

Co-Receptors:o CD4: binds to B2 Domain on MHC IIo CD8: binds to a3 Domain on MHC I

Antibody Dependent Cell-Mediated Killing (ADCC)o Bypassing KAR Activation (Killing Activating Receptor of NK Cells).o Solely dependent on the specificity of the antibody.o Antibody binds to Antigen on infected cell.so NK Cells bind to Antibody Fc portion of Antibody:

IgGo Eosinophils bind to Antibody Fc portion of Antibody:

IgE Parasites

Th1 CD4+ T Cells Th2 CD4+ T CellsIL-12, IFN-y Induce Differentiation IL-4 Induces Differentiation

Transcription Factor: T-Bet Transcription Factor: GATA-3Cytokine Production:

Interferon y – Prevents Th2Secretes: IL-2

Cytokine Production:IL-4, IL-10. – Prevents Th1Secretes: IL-5, IL-10, IL-13

Intracellular Pathogens ExtracellularMacrophage Activation B-Cell Activation

IgE Eosinophil ResponseDelayed Type Hypersensitivity Immediate Type HypersensitivityIFN-y comes from INKT Cells. IL-4 comes from iNKT Cells.

Th0 Cells:o Have CD40L, which binds to CD40 on the MHC.o Have CD28, which binds to B7 on the MHCo Differentiation into either Th1 or Th2

Signal 3 TGF-B TGF-BIL-6

Transcription Factor FoxP3, AIRE RORyTSecretes TGF-B

IL-10IL-17

Effector CD4+CD25+Foxp3+Treg Cells

Secrete TFG-B and IL-10

Th17 CellsPro-Inflammatory

Secrete IL-17 and IL-22 TGF-B and IL-10

o Can shut down the expression of T-Cells (regulation)o Can inhibit proliferationo Can inhibit Macrophage activation.

IL-17o IL-6, IL-8 Inflammation

_________________________________________________________________________________________________

CD 8 Cells Th1 Cells Th2 CellsCell-Cell

InteractionCD8

Infected CellTh1

Macrophage Containing Bacteria

Th2 B-Cell Presenting Specific Antigen

MHC Required MHC Type I MHC Type II MHC Type IIBonds formed Fas Ligand (CD8)

Fas (Infected Cell)LFA/ICAM

CD40L (Th1)CD40 (Macrophage)

CD40L (Th2)CD40 (B-Cell)

Cytokines IFN-y IFN-y IL-4

TNF-aIF-2

IL-5IL-10IL-13

Cytotoxins PerforinGranzymesGranulysin

- -

Th1 Independent:o Signal is strong enough for CD8 to synthesize it’s own IL-2,

which drives its own proliferation and differentiation.o Has to be an extremely strong signal.

Th1 Dependent:o Dendritic cell activates Th1 to secrete IL-2 and IFN-y

Tthe CD8 is activated to present receptors to these.o IL-2 from the Th1 drives the proliferation and differentiation

of CD8 Cells. CD8 Killing Mechanism:

o Perforin: forms pore o Granzyme: Activate Caspace Cascade Caspace3 Apoptosiso Fas Ligand (CD8) binds to Fas (infected cell) activation of

Caspace 8 Apoptosis CD95/CD95L

INFECTION AND IMMUNITY I

Skin:o Large surface area.o Keratinized, stratified epithelial barrier.o Specialized Cells: All express PRR to find PAMPS

Keratinocytes: keratin/cytokine production, defensins IL-1 and TNF-a

Langerhans Cell: Sampling of antigen in the Epidermis. APC Induced to leave Epidermic by IL-1 and TNF-a Present Ag to Memory T-Cells or migrate to

Lymph Node DC Subsets: Sampling of antigen in the Dermis.

APC Promote Th1 or Th2 Responses

GI Tract:o Large surface area.o Lots of Lymphoid Tissue (MALT: Tonsils, Peyer’s Patches)o Commensal Flora

Anti-microbial Peptides are secreted. Inhibit pro-inflammatory cytokines against the

commensals. Commensal-Specific IgA prevent overgrowth.

o Specialized Cells: Intestinal Epithelial Cells: mucus secretion M Cells: sampling of antigen from lumen.

At the top of Peyer’s Patches sIgA: neutralization of luminal microbes, dimer. DC Subsets: sampling of antigen from lumen: immune

activation or tolerance induction. Induce To Treg Because they secrete TGF-B

TLR: Th17 Pro-inflammatory cytokines (NKT,

innate lymphocytes, and γ δ) Secrete IL-17 and IL-22 promote inflammation

o Organized Lymphoid Tissue: Similar Structures MALT: Mucosa

Diffuse MALT – Lamina Propria Organized MALT: OMALT Peyer’s Patches Mesenteric Lymph Node

GALT: Gut BALT: Bronchus NALT: Nasal

o Secretory IgA There is much more IgA than IgG Directly blocks entry of pathogens and neutralizes

pathogens before entering gut/adhering to epithelium M Cell transcytoses pathogen to Peyer’s Patch B Cells

Dendritic Cells secrete TGF-B Class-Switch to IgA IgA goes to Lamina Propria Dimerized IgA is secreted (Poly-iG receptor is cleaved)

o Mucosal T-Cells Th17 secrete IL-22 Inhibiting colonization of

pathogenic bacteria._________________________________________________________________________________________

Bacteria: Innate:

o Complement – Opsonization MAC Lysis can happen to Gram-Negative Bacteria Lysozyme can degrade Gram-Positive Bacteria

o Inflammation (Neutrophils and Macrophages) Neutrophils: Oxidative Killing Mechanism (Respiratory

Burst) and Non-Oxidative Killingo These are stimulated by PAMPS:

Lipoteichoic Acid: Gram + and Fungi TLR2:TLR6 LPS: Gram - TLR4 Flagella TLR 5 TLR3: DS RNA TLR7/8: SS RNA TLR 9: DNA, Bacteria

Adaptive Response:o Intracellular:

Th1 IFN-y Macrophages DTH – Delayed Type Hypersensitivity CTLs ADCC

o Resolution: Th1 (DTH) Opsonizing Antibodies for Extracellular Phase

o Prevention: BCG Vaccination (blocking antibodies) Th1 Response Granuloma

o Example: Mycobacterium Tuberculosis: Intracellular, Acid-Fast – No enzymes or toxins

Activating Macrophages by Th1: IFN-y and CD40L (T-Cell)

o Extracellular: Th2 Opsonization Phagocytosis Complement via Classical Pathway ADCC

Can bring in Neutrophils, Eosinophils, Basophils due to Fc Receptors

Neutralizing Antibodieso These responses are stimulated by:

Lipoteichoic Acid O-Antigen (LPS)

Porins Adhesins Pilin/Fimbrin Capsules (T-Dependent) Exotoxins

o Prevention: Antibody

o Resolution: Antibody

o Example: Strep. Pneumoniae: Extracellular, GraM +, Capsule

Anti-Phagocytic – PspA prevents opsonization Opsonized by Antibody

Opsonizing: Capsule Neutralizing: Enzymes

Viruses: Innate: curtails spread of the virus

o IFN-a, IFN-B, TNF-a, IL-12o NK Cells activatedo Complement Opsonization (MAC?)

Adaptive:o NK Cells IFN-y Macrophages o APCs IL-12o Causes Th1 Responseo Neutralizing Antibodies for the Extracellular Phaseo CTLs for Intracellular Phase

IFN-y IgG1o If Mucosal IgAo Enveloped (Budding):

CTLs (CD8) Antibody (for outside components)

o Naked (Lytic) CTLs not as important Antibody

Prevention:o Neutralizing Antibody

Peplomers Resolution:

o CTLs can act before the progeny viruses have been assembledo Antibody