The Immune System

Douglas LarsonSarver Heart Center

Room 6152 626-0944dflarson@u.arizona.edu

Course Format

• Mondays – basic concepts

• Wednesdays – applied concepts

• Fridays – problem based learning

• Exams – 50% multiple choice and

50% essay

• Final – NIH grant take-home grant

Today’s Outline

• Innate and Adaptive immune systems

• Major Histocompatibility Complex (MHC)

• Human Leukocyte Antigen (HLA)

• Antigen Presentation

• Cytokines

• Th1 versus Th2

• Effector functions

Question

• What are the 2 major arms of the immune system?

The Immune System

Adaptive and Innate Immunity

• The adaptive immune response confers lifelong protective immunity to re-infection with the same pathogen.

• The innate immunity, which many microorganisms could be engulfed and digested by phagocytic cells

Innate vs. Adaptive

Innate

CytotoxicityPhagocytosis

Adaptive

Cytotoxicity

Cytolysis

stem

stem

CD4+

B-cell

CD8+

Cytolysis

Macrophage

Sequence of Immune Response

Innate Immune System

Immediate response No memory No specific recognition

ADAPTIVE IMMUNE SYSTEM

T-lymphocytesT-cytotoxic Cytoyoxic

B-lymphocytesPlasma cells Antibodies

Response takes 7 to 10 days

Adaptive Immune System

Adaptive Immune Response

T-Cells and Antigen Presenting Cells

Major Histocompatibility Complex(MHC)

•There are two major classes of MHC molecules associated with T-cell function, namely:

MHC Class I MHC Class II.

Major Histocompatibility Complex

•The major function of the molecules encoded by the Mhc is to facilitate the display of unique molecular fragments on the surface of cells in an arrangement that permits their recognition by immune effectors such as T-lymphocytes.

Major Histocompatibility Complex

HUMAN LEUKOCYTE ANTIGEN (HLA)

HUMAN LEUKOCYTE ANTIGEN (HLA)

•The HLA is related to MCH Class I and II expression

•HLA is related to risk for autoimmune diseases and allograft transplantation survival.

HLA - Autoimmunity

•Rheumatoid ArthritisDR4

•Multiple Sclerosis DR2

•Myasthenia gravis B8

•Ankylosing spondylitis B27

•Diabetis (Type I) DR3, 4

Antigen Presenting Cells

Antigen Presenting Cell

•Macrophages,

•Vascular endothelial cells,

•B-cells, and

•Dendritic cells (Heart)

•Express the major histocompatibility complex (MHC) molecules and can present antigen to the T-cells.

Major Histcompatibility Complex

MHC - Antigens•An antigen (Ag) is a specific

molecule that is recognized by an Ab or T-cell Receptor (TcR).

The soluble Mediators of T-cell Immunity

Soluble Mediators of Immunity

•Cytokines secreted signaling molecules

•The nomenclature and functions of well-defined T-cell cytokines.

•Each cytokine has multiple activities on different cell types. The mixture of cytokines secreted by a given cell type produces many effects through what is called a ‘cytokine network’.

CYTOKINES

•Interleukins

•Colony Stimulating Factors

•Interferons

•Chemokines

•Growth Factors

Macrophage - Cytokines

• Macrophages process and present antigen, produce chemokines and cytokines such as interleukin (IL)-1, IL-6, IL-12, IL-18, tumor necrosis factor (TNF)-, and IL-10, and phagocytose apoptotic and necrotic cells.

• Acting directly or under the influence of other immune cells, macrophages capture extra- and intracellular pathogens, eliminate invaders, and deliver them to appropriate subcompartments of lymphoid organs

Macrophage -Cytokines

• other cell types:

• microglial cell of the brain,

• alveolar macrophages,

• Kupffer cells of the liver,

• Synovial cells of joints,

• Mesangial cells of the kidney,

• and vascular endothelial cell of blood vessels

MacrophagePhagocytesCan prime T-cells10 –18 Well developed golgi complexExpress MHC Class II.Secrete IL-1, IL-6, TNF-, and INFsExpress CD14, CD64, CD35, CD11a,b,c,

MFR(mannosyl-fucosly receptors)Serve as a major antigen presenting cell

Macrophage - Cytokines

•Pro-inflammatory cytokines•IL-1•TNF-•IL-6

•These are secreted as an early response to an immune stimulus.

Pro-inflammatoryCytokines

Tumor Necrosis Factor

• Tumor necrosis factor (TNF) was originally described as a factor responsible for lipopolysaccharide (LPS)-induced hemorrhagic necrosis of tumors in animals.

TNF was later independently identified as “cachectin,” a factor responsible for wasting of animals during parasitic infections and patients with heart disease and cancer.

Tumor Necrosis Factor• Produced as a pro-hormone of 233 amino

acids, TNF- is anchored in the cell membrane and then processed to a 157 residue mature protein by cleavage of a 76 residue signal peptide.

• In response to a wide variety of infectious or inflammatory stimuli (e.g.,LPS, viruses, fungal or parasitic antigens, IL-1, TNF-), both transcription and translation of TNF precursor is increased, and large amounts of mature protein are rapidly released into the circulation.

Tumor Necrosis Factor

• The soluble form of TNF, consisting of 157 amino acids, is derived from the transmembrane precursor by proteolytic cleavage. The specific metalloproteinase responsible for this process (TNF converting enzyme or TACE) is an 824-amino acid transmembrane protein whose catalytic portion is part of the extracellular domain.

Tumor Necrosis Factor

•The cellular effects of TNF- are highly pleiotropic.

•At low concentrations,TNF- effects paracrine or autocrine regulation of leukocytes and endothelial cells and, thus, serves as an important regulator of the inflammatory response.

Pro-inflammatory Cytokines

IL-6•Mobilizes acute phase proteins

•Mannose binding protein

•C-reactive protein

•opsonin

•act like C1q

IL-6 activation of CRP

•Acute Phase Proteins C-reactive Proteins

Innate immune function Binds to molecular groups on

bacteria and fungi Facilitates opsonization Activates C'

CRP -Acute Phase Proteins

IL-6 and CHF

• IL-6 has been implicated in pathogenesis of CHF.

• IL-6 is elevated with CHF and associated with NYHA classification.

• IL-6 also has been implicated in osteoporosis that develops with CHF

• Elevated IL-6 is associated this a poor prognosis.

Roig J Am Coll Cardiol 82;688-90:1998

CYTOKINES

•Interleukins

•IL-1a, IL-1b, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-10, IL-11, IL-12, IL-13,

IL-14, IL-15

IL-2

• IL-2 is produced by CD4+ TH and CD8+ cells. It is the most potent of growth factors and activators.

•The IL-2r consists of two chains, each of which can bind IL-2 with low affinity, and following stimulation the high affinity receptor is expressed with up to 50,000/cell.

The low/High-affinity IL-2 receptor (CD25)

•

IL-2 Modulation by Immunosuppressants

IL-2 Gene Expression IL-2r 2nd Messenger

Lymphocyte•T lymphocytes or T cells

•Helper T cells (CD4+), which activate other T-cells, B-cells and macrophages

•Cytotoxic T cells (CD8+), which kill cells infected with viruses and fungi, tumors, and transplanted tissues.

CD4 - Th1 and Th2 cells

•T-helper (CD4) cells are defined by cytokine profile secretion

•Th1 cells help the immune responses of CD8+ and macrophages function.

•Th2 cells help the activation of B-cells toward antibody formation.

Lymphocyte

•T-helper: CD4+

•TH1 secretes IL-2, IFN, and TNF which promote T-cytotoxic (TC)

•TH2 secretes IL-4, IL-5, IL-6, and IL-10 which promote B cell

CYTOKINES

Tc B

Th1 Th2

IFN (-)

IL-10 (-)

IL-2 (+)

IL-4 (+)

Th0IL-12 IL-4

T-cell Cytotoxicity

CD8 - Cytotoxic T-cell

•Once naive T cells have completed their development in the thymus, they enter the bloodstream, from which they migrate through the peripheral lymphoid organs – and attach to the High endothelial venules (HEV).

CD8 - Cytotoxic T-cell

•Activated effector T cells, armed effector T cells, are triggered to perform their effector functions immediately upon contact with cells bearing the peptide:MHC complex for which they are specific.

T-cytotoxic: CD8+

• Effector arm of the immune response• Soluble mediators:

•Perforins, •Serine esterase, •Endonuclease•Tumor Necrosis Factor (TNF), •Interferon a,b,g (INF )•Activation via Class I MHC

and TCR

Cytotoxic T-Cell (CD-8+)

•Viruses infect all cells

•When replicating intracellularly, they are unaffected by antibodies and macrophages

•Virally infected cells are eliminated by cytotoxic T-cells.

•To prevent destruction of healthy cells their activity must be tightly controlled.

Necrosis vs. Apoptosis

•Necrosis: is the death of cells or tissues due to chemical or physical injury.

•Necrosis leaves extensive cellular debris that needs to be removed by phagocytes, while apoptosis does not.

Necrosis vs. Apoptosis

•Apoptosis, or programmed cell death, is a form of cell death in which the cell activates an internal death program.

•It is characterized by nuclear DNA degradation, nuclear degeneration and condensation, and the phagocytosis of cellular residuals.

Induction of apoptosis

Natural killer cells (NK)

• Derived from bone marrow• 15% of lymphoid pool• No T-cell receptor (TCR)• Respond to non-MHC expressing cells• Inhibited by MHC Class I expression• Respond to IL-2• Able to kill certain tumors, virus-

infected cells, and IgG coated Targets.• Release IL-1, GM-CSF, and IFN-

Natural killer cells (NK)

T-Cell Immunology

Notes

Class notes and Powerpoints will be posted on a WEB site.

• Goto http://perfusion.arizona.edu

• Course PHCL 582

• Username: phcl582

• Password: s06ua582