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Lecture 3

ORIGINS AND MEANS OF THE IMMUNE RESPONSE

Jan Żeromski

2013/2014

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Points to be discussed• Rationale and phases of the immune response• The role of inflammation and tissue injury

• Cytokines and chemokines• Cell adhesion molecules• Leucocyte-endothelial cell interactions

• Origin and subsets of T and B cells• CD (Cluster Determinants) classification

• Intracellular biochemical events following Ag recognition

• Patterns and mechanisms of cell migration• Immunoglobulins and generation of diversity

Rationale of immune response• Recognition of foreign structure or organism

• Detection of its pathogenicity

• Prevention of its unwanted effects

• Destruction of invader

• Elimination it from the body

Phases of the immune response

• Induction phase – recognition of antigen

• Central (activation) phase – cell proliferation and differentiation into various subsets,

• Effector phase – engagement of various mechanisms and cells

Factors participating in particular phases of the immune response

• Induction phase: PRRs, MHC antigens, T and B cell receptors,

• Central ph: adhesion molecules, cytokines, antigen-presenting cells (APCs), macrophages

• Effector ph: cytotoxic T lymphocytes (CTLs),

immunoglobulins, activ. macrophages, NK cells

The role of inflammation• Inflammatory agent leads to activation of PRRs and results

in tissue injury

• Injury induces chemotaxis of various cells to the site of damage, such neutrophils, macrophages, APCs

• APCs ingest foreign antigens, process them to peptides suitable for the presentation to T cells

• Cytokines released by neutrophils, macrophages and other cells activate APCs and enhance them to migration to lymph nodes. Cytokines secreted by APC activate T cells responding to given antigen

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Main properties of some interleukins•IL-1 – proinflammatory, pleotropic•IL-2 – growth factor for T, B and NK cells•IL-4 –maturation and differentiation of B cells

•IL-5 – as above but of eosinophils•IL-6 – proinflammatory, differentiating agent for B cells,

•IL-7 – lymphocyte development in primary lymph organs ,•IL-10 – immunosuppressive

•IL-12 – strong activator of cellular immune response•IL-15 – maturation of NK cells in bone marrow

•IL-17 – proinflammatory, pleotropic•IL-18 – production of interferon gamma przez T and NK cells

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CELL ADHESION MOLECULES (CAM)

Integrins:adhesion to endothelium and extracellular matrix (VLA-1 to 6, LFA-1)

CAM of the immunoglobulin supergene family:various (ICAM-1-3, VCAM-1, PECAM-1, NCAM, CEA)

Selectins: molecules on leucocytes and endothelium which bind to carbohydrate (E, P, L-selectins, )

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CELL ADHESION MOLECULES (CAM)-2

Cadherins: bind to catenins, cytoskeleton elements in calcium dependent manner (E, N,T-cadherins)

CD44 and it variants:cell hyaluronate receptor involved in cell-to-cell and cell-to-matrix interactions

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LEUCOCYTE-ENDOTHELIAL CELL INTERACTIONS

• Leucocytes interact with the vessel wall in multistep fashion, using several leucocyte surface molecules that recognize their counter-receptors on endothelial cells

• The rolling and tethering of leucocytes on vessel wall is mediated by selectins (a subtype of cell adhesion molecules)

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LEUCOCYTE-ENDOTHELIAL CELL INTERACTIONS -2

• Chemokines and their receptors are needed to activate leucocyte integrins

• Only activated integrins are able to mediate firm adhesion between leucocytes and endothelium

• The transmigration of leucocytes into the tissues requires proteinases and repair mechanisms

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Subdivision of T lymphocytes

• T helper (CD4+)

• Th1

• Th2

• Treg (CD25, Foxp3)

• Th17

• T cytotoxic(CD8+)

• Tc1

• Tc2

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CD (CLUSTER DETERMINANTS) CLASSIFICATION

• Based on the identification of single epitopes by monoclonal antibodies

• Involves mainly differentiation antigens of cells and cell receptors, but also various proteins, enzymes

• Most, but not all, CD markers are at cell surface

• Actual number of CD markers is above 360.

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EXAMPLES OF CD MARKERS

• CD3 TCR signalling complex: T cells• CD4 MHC class II receptor: T cells• CD8 MHC class I receptor: T cells• CD10 neutral endopeptidase: ALL cells• CD19 co-receptor subunit: B cells• CD45 LCA (tyrosine phosphatase): leukocytes• CD62L L-selectin: T cells, mono-,

granulocytes• CD247 zeta chain of TCR : T cells, NK

cells

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CD4 Th1 and Th2 T cells: profile of produced cytokines

Th1Th2IL-2 IL-4IFN-gamma IL-5

TNF-beta IL-6 IL-10

IL-13

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T CELL ACTIVATION-EARLY STEPS

• Formation of immunological synapse – lymphocyte polarization, adhesion to APC, maturation of synapse

• Microdomains (lipid rafts) – regions of cell membranes rich in lipids: contain several proteins able for fast signal transduction, kinases from Src family, and other

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T CELL ACTIVATION-EARLY STEPS-2

• Lymphocyte activation leads to microdomain grouping- so called supramolecular activation clusters-SMAC

• First (Ag-TCR) and second signal (CD28-CD80, CD86, CD58-CD2) concept; naive lymphocytes need 2 signals, activated cells – only the first one

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• Involves transduction of signals from both T cell receptor and CD28

• CD4 bound lck kinases become activated by CD45 phosphatase

• ITAM (Immunoreceptor Tyrosine-based Activation Motif) domains of CD3 (zeta chains) become phosphorylated by lck

INTRACELLULAR SIGNALING

IN T CELL ACTIVATION

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• ITAMs associate with other kinases such as ZAP-70 and fyn

• Fyn activates phopholipase C (PLC) which cause release of intracellular calcium (calcium flux)

• Calcium binds to calcineurin and activates transcription factors (NF-AT, NF-kappa B, AP-1)

INTRACELLULAR SIGNALING

IN T CELL ACTIVATION

LAT signaling pathology (LSP)

• LAT - Linker for activation of T cells

• Functional defect of Lat gene results in –• Lymphoproliferative syndrome – LSP

• It is manifested by polyclonal proliferation of CD4+ T cells, secreting chronically in excess cytokines typical for Th2 response

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SIGNALING IN B CELL ACTIVATION

• Tyrosine kinases lck, lyn ,fyn become activated via Ig and Ig of B cell receptor

• They phosphorylate BCR ITAM domains

• These can then bind Syk, another kinase, which activates phospholipase C (PLC-)

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WHAT ARE TRANSCRIPTION FACTORS?

• Answer: transcription factors are complex protein molecules residing in cytoplasm, which after stimulation and assembly are able to enter cell nucleus and induce several genes transcription.

• The most common: NF-κB, NF-AT, AP-1

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LYMPHOCYTE RECIRCULATION

• Lymphocytes recirculate continuously between blood and lymphoid organs

• 80% of lymphocytes enter the lymph nodes via specialized vessels called high endothelial venules (HEV)

• The remaining lymphocytes enter the lymph nodes together with dendritic cells and antigens via afferent lymphatics

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LYMPHOCYTE RECIRCULATION - 2

• Lymphocytes leave the lymph nodes via efferent lymphatics

• Lymphocyte recirculation allows the lymphocytes to meet their cognate antigens and other leukocyte subsets to evoke an efficient immune response

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IMMUNOGLOBULINS KEY CONCEPTS

• Isotype: antigenic differences between

classes, subclasses and types

• Allotype: antigenic differences between Ig constant domains of various individuals

• Idiotype: antigenic differences within variable domains reflecting antigen binding site

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IMMUNOGLOBULINS KEY CONCEPTS - 2

• Isotype (class) switching: the change of produced Ig (from IgM to other Ig),

usually in secondary immune response

• Polyclonal Ig: a mixture of Igs having either kappa or lambda chains (3:1 ratio in humans)

• Monoclonal Ig: either kappa or lambda light chain – incidence in tumors such as myeloma, or produced in vitro (monoclonal Abs)

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Main Immunoglobulin Classes

• IgG – the most abundant Ig. Exists in 4 subclasses (IgG1, IgG2, IgG3, IgG4)

• IgA – exists as serum and secretory Ig present on mucosal surfaces, 2 subclasses (IgA1 and IgA2).

• IgM – present in bloodstream is composed of 5 molecules forming pentamer. Protects from sepsis. Produced mainly in spleen.

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Immunoglobulin classes - 2

• IgD –with IgM forms antigen receptor on B cells. In serum in trace amounts.

• IgE – anti-parasitic. Participates in allergic reactions. Very short lifetime when free, but stable when bound to cell surface such as mast cells.

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FEATURES OF IMMUNOGLOBULIN SUPERFAMILY

• Large family of ancestrally related genes-probably >100 (MHC molecules, TCRs, some cytokine receptors etc.)

• Most products involved in immune system function or other cell – cell interactions

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THANK YOU! Sorry for a huge

amount of difficult new data and terms!