T Cell ActivationFunction Ned Braunstein MD nedbraunsteinmerck com

T Cell Activation/Function Ned Braunstein, MD ned_braunstein@merck. com nsb 2@columbia. edu

The Major T Cell Subsets CD 4+ T cells p 56 lck z z g d e Ca Cb CD 4 Va CD 8+ T cells p 56 lck Vb MHC II z z g d e CD 3 TCR peptide (1) Interacts with MHC class II expressing cells (B cells, macrophages) (2) Induce(help) B cells to synthesize antibody (3) Induce and activate macrophages (4) Secretes lymphokines CD 8 Ca Cb Va Vb MHC I CD 3 TCR peptide (1) Interacts with MHC class I expressing cells (all nucleated cells) (2) Kill MHC class I expressing target cells (3) Suppress immune responses (4) Secretes lymphokines

Naïve T cells are activated by antigen in LNs where they mature into effector cells (1) Naive T cells home continuously from the blood to lymph nodes and other secondary lymphoid tissues. Homing to lymph nodes occurs in high endothelial venules (HEV), which express molecules for the constitutive recruitment of lymphocytes. (2) Lymph fluid percolates through the lymph nodes; the fluid is channeled to them from peripheral tissues, where dendritic cells collect antigenic material. In inflamed tissues, dendritic cells are mobilized to carry antigen to lymph nodes, where they stimulate antigen-specific T cells. On stimulation, T cells proliferate by clonal expansion and differentiate into effector cells, which express receptors that enable them to migrate to sites of inflammation. (3) Although most effector cells are short-lived, a few antigen-experienced cells survive for a long time. These memory cells are subdivided into two populations on the basis of their migratory ability: the effector memory cells migrate to peripheral tissues, whereas central memory cells express a repertoire of homing molecules similar to that of naive T cells and migrate preferentially to lymphoid organs.

The Biology of Dendritic Cells: Antigen capture and presentation to T cells Antigens are captured by DCs in peripheral tissues and processed to form MHC-peptide complexes. As a consequence of antigen deposition and inflammation, DCs begin to mature, expressing molecules that will lead to binding and stimulation of T cells in the Tcell areas of lymphoid tissues. If the antigen has also been bound by B cells, then both B and T cells can cluster with DCs. After activation, B blasts move to the lining of the intestine, the bone marrow, and other parts of the lymphoid tissue with some becoming antibody-secreting plasma cells. T blasts leave the blood at the original site of antigen deposition, recognizing changes in the inflamed blood vessels and responding vigorously to cells that are presenting antigen. This limits the T-cell response to the site of microbial infection. Banchereau, J. and Steinman, R. Nature 392, 245 - 252 (1998)

The T cell activation cycle Minutes Hours Days IL-2 R P P Ca++ IP 3 DAG Antigen recognition c- fos c- jun c- myc NF-KB NF-AT Immediate events IL-2 etc. Cytokine production and autocrine stimulation Effector functions: Help DTH Killing (CTL) regulation Proliferation

MHC + Ag ICAM-1 (CD 54) CD 80 LFA-1 (CD 11 a/CD 18) CD 4 CD 3 CD 45 CD 28 lck fyn ZAP-70 PTK Cytoplasm IL 2 R RAS PLC PIP 2 PKC DAG IP 3 MAPkinase Ca Nucleus NF-AT NF-KB OTF 1 IL-2

MHC + Ag CD 80 ICAM-1 (CD 54) LFA-1 (CD 11 a/CD 18) CD 4 CD 3 CD 45 CD 28 lck fyn ZAP-70 PTK Cytoplasm IL 2 R RAS PLC DAG PKC PIP 2 IP 3 Ca 2+ I-k. B P NF-k. B Nucleus NF-AT NF-k. B OTF 1 IL-2 MAP kinase

MHC + Ag CD 80 ICAM-1 (CD 54) LFA-1 (CD 11 a/CD 18) CD 4 CD 3 CD 45 fyn CD 28 ZAP-70 IL 2 R lck PTK Cytoplasm PLC PKC DAG CNB PIP 2 IP 3 Ca 2+ CNA Calmodulin P NF-AT Nucleus Jun Fos P NF-AT NF-k. B OTF 1 IL-2

The T cell activation cycle Minutes Hours Days IL-2 R P P Ca 2+ IP 3 DAG Antigen recognition c- fos c- jun c- myc NF-k. B NF-AT Immediate events IL-2 etc. Cytokine production and autocrine stimulation Effector functions: Help DTH Killing (CTL) regulation Proliferation

Key molecular interactions between T cells and APCs CD 3 TCR MHC class II/ autopeptide CD 40 CD 80 Activated T cell CD 40 L CD 28 CD 40 CD 80 MHC class II (1) induction of cytokines/chemokines (IL-8, IL-12, TNF-a, MIP-1 a) (2) stimulation of CD 80 and CD 86 expression and co-stimulatory function with activation of T cell growth (3) augmentation of antigen-presenting function

Naïve CD 4+ T cells differentiate into Th 1 and Th 2 subsets Th 1 Cells IL-2 , g IFN Antigen + APC Resting CD 4+ cell “p. Th” IL IFN-g (–) Activated CD 4+ cell IL 4 IL-2 IFN-g TNF -12 IL-4 IL -10 (–) IL-4 IL -5 IL-6 IL-10 , IL -13 Th 2 Cells

Functions of Th subsets Functions of Th 1 subsets Th 1 Cells IL-2 IFN-g TNF IFN-g (–) IL-4 IL -10 (–) IL-4 IL -5 IL-6 IL-10 Th 2 Cells • Activate macrophages/dendritic cells augment antigen presentation • induce delayed type hypersensitivity (DTH) responses important in eradicating intracellular pathogens (TB, leprosy, listeria • mediate Th 1 diseases (ie; rheumatoid arthritis, multiple sclerosis and type I diabetes Functions of Th 2 subsets • Help B cells and induce humoral immunity • mediate allergic and immediate hypersensitivity responses • involved in antibody mediated immune diseases like SLE and ITP

Major Functions of T Lymphocytes (1) Induction and Activation of B cells (Help)required for most antibody responses (2) Delayed Type Hypersensitivity (DTH) - important in elimination of intracellular pathogens (virus, fungi and mycobacteria) (3) Cell mediated Cytotoxicity (Killer function)important in the immune response to virus infected cells and cancer cells (4) Suppressor Cell Functionregulates the cell mediated antibody responses

The Induction and Activation of B cells (Helper Function) Antigen binds specifically to Sm. Ig, is internalized into vesicles and cleaved into peptides which displace CLIP and bind to MHC class II molecules in the endocytic compartment. The peptide/MHC complex is then transported to the surface membrane. The CD 4+ T cell a, b TCR/CD 4 complex binds to the MHC class II/peptide complex on the surface of B cells. The CD 4+ Th 2 cells are triggered to secrete IL-2, IL-4, IL-5, IL -6 and IL-10 and begin to express CD 40 L. These lymphokine and contact dependent signals (CD 40 L) induce B cells to proliferate, class switch and differentiate into antibody (Ig. M, Ig. G, Ig. A and Ig. E) secreting B cells and plasma cells.

Antigen Processing and Presentation by B cells ANTIGEN BCR (Sm. Ig) MHC Class ll B cell Peptide Antigenic peptides Bind to MHC class II molecules Internalization of antigen/Ig Antigen binds specifically to BCR (surface membrane Ig), is internalized into vesicles and cleaved into peptides which displace and bind to MHC class II molecules. The peptide/MHC complex is then transported to the surface membrane.

Antigen Presentation by B cells BCR (Sm. Ig) hapten Antigen MHC class II carrier protein MHC class II/ carrier peptide complex B cell carrier peptides Antigen binds specifically to Sm. Ig, is internalized into vesicles and cleaved into peptides which displace and bind to MHC class II molecules. The peptide/MHC complex is then transported to the surface membrane.

Expression of Membrane Proteins Following Antigen Specific Activation of T and B Cells BCR (Sm. Ig) TCR MHC class II CD 4 Resting B cell BCR (Sm. Ig) Resting Effector T cell CD 23 IL-2 R MHC class II Activated B cell CD 40 CD 86 CD 40 L TCR CD 4 MHC class II Activated Effector T cell

CONSEQUENCES OF CD 40 L/CD 40 INTERACTIONS DURING T-B CELL INTERACTIONS CD 23 CD 40 L Sm Ig CD 40 Activated B Cell TCR CD 4 Activated Effector T cell Triggering of B cell proliferation Rescue from apoptosis Induction of Ig isotype class switching Up-regulation of CD 80 and CD 86 Germinal center formation Up-regulation of CD 23 Downregulation of CD 40 L expression

Final Phases of B cell Differentiation are Mediated by Contact T cell signals (CD 40 L/CD 40) and Lymphokines CD 23 CD 40 L TCR Sm. Ig CD 40 Activated Effector T cell Activated B cell Lymphokines IL-2, IL-4, IL-5, IL-6, IFN-g, TGFb Ig. G Ig. A Ig. E Plasma Cell

The Hyper Ig. M Syndrome (HIM) is an X chromosome-linked Ig deficiency characterized by low serum levels of Ig. G, Ig. A and Ig. E with normal numbers of circulating Ig. M expressing mature B cells. Germinal centers and splenic follicles due not develop. Affected patients (usually males) are susceptible to pyogenic infections, autoimmune disease and lymphoproliferative disease. In addition, patients are also susceptible to Pneumocystis carini infections. The genetic defect in the majority of HIM patients is associated with mutations in the gene encoding CD 40 L and can be corrected functionally by soluble CD 40 ligand, in vitro. A few HIM patients have normal CD 40 L but defects in CD 40 signaling.

Major Functions of T Lymphocytes (1) Induction and Activation of B cells (Help)required for most antibody responses (2) Delayed Type Hypersensitivity (DTH) - important in elimination of intracellular pathogens (virus, fungi and mycobacteria) (3) Cell mediated Cytotoxicity (Killer function)important in the immune response to virus infected cells and cancer cells (4) Suppressor Cell Functionregulates the cell mediated antibody responses

Delayed Type Hypersensitivity (DTH) a. DTH is initiated principally by CD 4+ Th 1 cells and is the primary defense mechanism against intracellular parasites including the mycobacteria (TB), fungi and intracellular bacteria (listeriae monocytogenes). b. The cognitive phase of DTH involves CD 4+ T cell macrophage/dendritic cell (MHC class II/peptide) interaction resulting in the local secretion of lymphokines. c. The effector phase of DTH is effected by lymphokines which activate macrophages to secrete lysozyme, TNF, IL 1 and IL-12 as well as chemotactic and migration inhibitory factors restricting granulocytes, macrophages and eosinophils to the site of inflammation.

DTH Pathway of Contact Hypersensitivity

Th 1 CD 4+ T Cells Induce Inflammation and DTH APC Activated CD 4+ Th 1 cell CD 4 TCR CD 4+ Th 1 cell CD 40 L CD 40 dendritic cell Macrophage/ mesenchymal cell Inflammation inducing CD 40 L/CD 40 interactions Activated macrophages, mesenchymal cells and endothelial cells activated dendritic cell Proinflammatory molecules Chemokines (IL-8, SDF-1) Lymphokines (IL-1, GM-CSF, TGFb IFNb, IL-12, IL-6 NO, proteolytic enzymes, PGE 2

T Cell- Macrophage Interactions Fc receptor TCR a, b MHC class II CD 3 CD 4 Th 1 Cell CD 4 CD 28 Macrophage B 7 (CD 80) IL-2 IL-12 CD 40 L CD 80 TCR a, b CD 4 IL-2 Receptor MHC II IFN-g CD 28 Activated Th 1 Cell CD 80 IL-1 IL-6 IL-12 TNF TGF-b cytotoxic granules Activated Macrophage

Physiology of the DTH Response CD 2 MHC II/peptide Antigen/Ig. G TCR a, b CD 4+ TH 1 T Cell IL-2 R Phagocytosis killing Fc Receptor CD 4 IL-12 Macrophage/ Dendritic cell TCR a, b IL-1, TNF, IL-6 IFN-g CD 4 fibroblasts endothelial cell hypothalamus granulocytes IL-3, IL-8 Mast Cell Eosinophil IL-3, IL-4, IL-5 fever

Functions of Th subsets Functions of Th 1 subsets Th 1 Cells IL-2 IFN-g TNF IFN-g (–) IL-4 IL -10 (–) IL-4 IL -5 IL-6 IL-10 Th 2 Cells • Activate macrophages/dendritic cells augment antigen presentation • induce delayed type hypersensitivity (DTH) responses important in eradicating intracellular pathogens (TB, leprosy, listeria • mediate Th 1 diseases (ie; rheumatoid arthritis, multiple sclerosis and type I diabetes Functions of Th 2 subsets • Help B cells and induce humoral immunity • mediate allergic and immediate hypersensitivity responses • involved in antibody mediated immune diseases like SLE and ITP