bio 151 lec 12 13 cmer & lmi

Parungao-Balolong 2011

CELL-MEDIATED EFFECTOR RESPONSEBIOLOGY 151 Lecture 12

Sunday, February 20, 2011

RECALL: Humoral vs Cell-Mediated Response

✤ assumes different roles in protecting the host

✤ HUMORAL

✤ antibodies

✤ antigen-specific

✤ CELL-MEDIATED

✤ specific and non-specific to antigens



ANTIBODY PROTECTION LIES OUTSIDE THE CELL....

✤ SCENARIO: If antibodies were the only agents of immunity, pathogens that managed to evade them and colonize the intracellular environment would escape the immune system, RIGHT?

✤ GOOD THING..This is not the case!

✤ Cell-mediated immunity detect and eliminate cells that harbor intracellular pathogens

✤ EVEN...tumor cells that have undergone genetic modifications (they express antigens not typical of normal cells)Parungao-Balolong 2011


THE CELLS OF CMI....

✤ ANTIGEN-SPECIFIC CELLS

✤ CD8+cytotoxic T lymphocytes (TC cells or CTLs)

✤ Cytokine-secreting CD4+ TH cells that mediate delayed-type hypersensitivity (DTH)

✤ NON-SPECIFIC CELLS

✤ NK cells and non-lymphoid cell types (macrophages, neutrophils, and eosinophils)

✤ The activity of both specific and nonspecific components usually depends on effective local concentrations of various cytokines

✤ T cells, NK cells, and macrophages are the most important sources of the cytokines that organize and support cell-mediated immunity



HUMORAL AND CELL-MEDIATED IMMUNITY ARE INTERDEPENDENT✤ Cells such as macrophages,

NK cells, neutrophils, and eosinophils can use antibodies as receptors to recognize and target cells for killing

✤ Chemotactic peptides generated by the activation of complement in response to antigen-antibody complexes can contribute to assembling the cell types required for a cell-mediated response



TYPES OF EFFECTOR T-CELLS

✤ CD4+ (TH1 & TH2)

✤ CD8+ (CTLs)

✤ Unlike naive cells

✤ less stringent activation requirements

✤ increased expression of cell-adhesion molecules

✤ increased production of both membrane-bound and soluble effector molecules



THE CTLs: CYTOTOXIC T-CELLS

✤ generated by immune activation of T cytotoxic (TC) cells

✤ have lytic capability: critical in the recognition and elimination of altered self-cells (e.g., virus-infected cells and tumor cells) and in graft-rejection reactions

✤ class I MHC restricted (since virtually all nucleated cells in the body express class I MHC molecules, CTLs can recognize and eliminate almost any altered body cell)

✤ 2 phases of CTL-mediated immune response:

✤ first phase activates and differentiates naive TC cells into functional effector CTLs

✤ second phase, effector CTLs recognize antigen–class I MHC complexes on specific target cells, which leads them to destroy the target cells



3 SEQUENTIAL STEP REQUIREMENTS...

✤ An ant igen-spec i f i c s igna l 1 transmitted by the TCR complex upon recognition of a peptide–class I MHC molecule complex

✤ A co-stimulatory signal transmitted by the CD28-B7 interaction of the CTL-P and the antigen-presenting cell

✤ A signal induced by the interaction of IL-2 with the high-affinity IL-2 receptor, resulting in proliferation and differentiation of the antigen-activated CTL-P into effector CTLs



CTLs KILL CELLS IN 2 WAYS...

✤ A. Directional delivery of cytotoxic proteins (perforin and granzymes) that are released from CTLs and enter target cells

✤ B. Interaction of the membrane-bound Fas ligand on CTLs with the Fas receptor on the surface of target cells

✤ NOTE:

✤ The end result of both the perforin/granzyme and Fas-mediated pathways is the activation of dormant death pathways that are present in the target cell

✤ “CTLs don’t so much kill target cells as persuade them to commit suicide”



CTLs KILL CELLS IN 2 WAYS...

✤ PERFORIN-GRANZYME PATHWAY

✤ when introduced into the target cell from the CTL mediate proteolytic events that activate an initiator caspase

✤ Fas/FasL PATHWAY

✤ engagement on a target cell by Fas ligand on the CTL causes the activation of an initiator caspase in the target cell



NON-SPECIFIC CYTOTOXIC CELLS

✤ non-MHC dependent

✤ can also kill target cells

✤ NK cells, neutrophils, eosinophils, macrophages

✤ via antibody-dependent cell-mediated cytotoxicity (ADCC)

✤ bind to the Fc region of antibody on target cells and subsequently release lytic enzymes, perforin, or TNF, which damage the target-cell membrane



COMPARING NOTES...✤ CDC

✤ CDC activity

✤ antibody bound to its antigen activates reaction cascade of a group of serum proteins called complement system

✤ CDC is triggered by the binding of complement to the antibody bound to cell surface an antigen

✤ Activated complement system lyses the target cell

✤ ADCC

✤ ADCC activity

✤ Immune cells such as macrophages and NK cells recognize the antibody bound to the target cell and destroy the target cells such as tumor cells



http://www.kyowa-kirin.co.jp/antibody/english/about_antibody/mechanism.html#m3


http://www.kyowa-kirin.co.jp/antibody/english/glossary/index.html#glossary3












COMPARING NOTES...

✤ NEUTRALIZING ACTIVITY

✤ Neutralizing activity

✤ When ligands such as growth factor bind to their receptors, ligands activate target cells and cause damages

✤ When therapeutic antibody binds to its target, ligand or receptor, antibody interferes ligand-receptor interaction and prevents undesirable activities







NK CELLS AND THE PERFORIN-INDUCED PORE FORMATION

✤ NK cells mediate lysis of tumor cells and virus-infected cells by perforin-induced pore formation

✤ mechanism similar to one of those employed by CTLs



NK CELLS ACTIVITY REGULATION

• Activity regulated by balance of activating and killing receptors encoded in the NKC gene cluster

• Kill Mechanism

–Similar CTL •Granule release•Perforin

–Constitutive cytotoxicParungao-Balolong 2011



LEUKOCYTE MIGRATION AND INFLAMMATIONBIOLOGY 151 Lecture 13


WHAT YOU NEED TO KNOW

✤ Lymphocyte Recirculation

✤ Cell-Adhesion Molecules

✤ Extravasation (Neutrophils and Lymphocytes)

✤ Chemokines and Inflammation

✤ Inflammatory Process

✤ Anti-Inflammatory Agents



LEUKOCYTE MIGRATION

✤ Many type of leukocytes move from one part of the body to another

✤ LYMPHOCYTES: circulate continually in the blood and lymph and, in common with other types of leukocytes, migrate into the tissues at sites of infection or tissue injury

✤ RECIRCULATION:

✤ increases the chance that lymphocytes specific for a particular antigen will encounter that antigen



LEUKOCYTE MIGRATION & INFLAMMATION

✤ INFLAMMATION: a complex response to local injury or other trauma

✤ characterized by redness, heat, swelling, and pain

✤ involves various immune-system cells and numerous mediators

✤ CONTROLLED MIGRATION of LEUKOCYTE POPULATIONS:

✤ necessary for assembly and regulation of inflammatory responses



WHY MIGRATE?

✤ The immune system relies upon the continual circulation of leukocytes through the body

– For the Innate IR– variety of lymphocytes, granulocytes,

and monocytes can respond

– For the Adaptive IR– lymphocytes must contact Ag in either

tissue, lymph, or blood



LYMPHOCYTE RECIRCULATION

✤ Lymphocytes constantly re-circulate from blood to spleen, lymph nodes, and 3° lymphoid tissues

✤ Continual circulation provides systemic protection

✤ A complete circuit can be performed 1-2X per day

✤ ~1 in 105 lymphocytes can recognize a specific Ag

✤ therefore, constant circulation i n c r e a s e s c h a n c e o f lymphocytes contacting Ag



CELL-ADHESION MOLECULES (CAMs)

✤ So how does lueukocytes transit the bloodstream?

✤ They must bind to an endothelial cell first!

✤ Endothelial cells exhibit ‘cell adhesion molecules’ – CAM’s

✤ Lymphocytes, granulocytes, and monocytes form receptors which bind to CAM’s



1. SELECTINS (glycoproteins)

✤ has a distal lectin-like domain (bind to specific carbohydrate groups)

✤ interact primarily with sialylated carbohydrate moieties (often linked to mucin-like molecules)

✤ NOTE: 3 molecules (L, E and P) = Expression...

✤ Most circulating leukocytes (L-selectin)

✤ Vascular endothelial cells (E-selectin and P-selectin)

✤ responsible for the initial stickiness of leukocytes to vascular endothelium



2. MUCINS (ser and thr-rich heavily glycosylated proteins)

✤ extended structure allows them to present sialylated carbohydrate ligands to selectins

✤ EXAMPLES:

✤ L-selectin on leukocytes recognizes sialylated carbohydrates on two mucin-like molecules (CD34 and GlyCAM-1) expressed on certain endothelial cells of lymph nodes

✤ (PSGL-1) found on neutrophils interacts with E- and P-selectin expressed on inflamed endothelium



3. INTEGRINS (heterodimeric proteins = alpha and beta chains)

✤ expressed by leukocytes and facilitate both adherence to the vascular endothelium and other cell-to-cell interactions

✤ grouped into categories according to which beta subunit they contain

✤ bind to different CAMs that belong to the immunoglobulin superfamily expressed along the vascular endothelium

✤ must be activated before they can bind with high affinity to their ligands

✤ NOTE: important in leukocyte extravasation

✤ leukocyte-adhesion deficiency (LAD) = recurrent bacterial infections and impaired healing of wounds



4. ICAMS/ Ig-superfamily CAMs

✤ contain a variable number of immunoglobulin-like domains

✤ ICAM-1, ICAM-2, ICAM-3, and VCAM (expressed on vascular endothelial cells and bind to various integrin molecules)

✤ MAdCAM-1 (has both Ig-like domains and mucin-like domains)

✤ expressed on mucosal endothelium and directs lymphocyte entry into mucosa

✤ binds to integrins by its immunoglobulin-like domain and to selectins by its mucin-like domain



NEUTROPHIL EXTRAVASATION

✤ As an inflammatory response develops, various cytokines and other inflammatory mediators act upon the local blood vessels, inducing increased expression of endothelial CAMs = ACTIVATION or INFLAMMATION!

✤ Neutrophils are generally the first cell type to bind to inflamed endothelium and extravasate into the tissues

✤ HOW: neutrophils must recognize the inflamed endothelium and adhere strongly enough so that they are not swept away by the flowing blood

✤ Bound neutrophils must then penetrate the endothelial layer and migrate into the underlying tissue

✤ NOTE: Monocytes and eosinophils extravasate by a similar processParungao-Balolong 2011



✤ Four sequential steps:

✤ (1) rolling

✤ (2) activation by chemoattractant stimulus

✤ (3) arrest and adhesion

✤ (4) transendothelial migration

Parungao-Balolong 2011 recognize → adhere strongly → clinging to the vessel wall → penetrate



✤ Cell-adhesion molecules and chemokines involved in the first three steps of neutrophil extravasation

✤ Initial rolling is mediated by binding of E-selectin molecules on the vascular endothelium to sialylated carbohydrate moieties on mucin- like CAMs

✤ A chemokine such as IL-8 then binds to a G-protein–linked receptor on the neutrophil, triggering an activating signal.

✤ This signal induces a conformational change in the integrin molecules, enabling them to adhere firmly to Ig-superfamily molecules on the endothelium



NEUTROPHILEXTRAVASATION

✤ THE 4TH STEP:

✤ The steps in transendothelial migration and how it is directed are still largely unknown

✤ May be mediated by further activation by chemoattractants and subsequent integrin–Ig-superfamily interactions or by a separate migration stimulus



LYMPHOCYTE EXTRAVASATION

✤ Various subsets of lymphocytes exhibit directed extravasation at inflammatory sites and secondary lymphoid organs

✤ The recirculation of lymphocytes thus is carefully controlled to ensure that appropriate populations of B and T cells are recruited into different tissues

✤ SIMILAR WITH NEUTROPHILS

✤ extravasation of lymphocytes involves interactions among a number of cell-adhesion molecules

✤ overall process is similar to what happens during neutrophil extravasation and comprises the same four stages (contact and rolling, activation, arrest and adhesion, transendothelial migration)



LYMPHOCYTE EXTRAVASATION



CHEMOKINES: Key Mediators of Inflammation

✤ a superfamily of small polypeptides, most of which contain 90–130 amino acid residues

✤ selectively, and often specifically, control the adhesion, chemotaxis, and activation of many types of leukocyte populations and sub- populations

✤ they are major regulators of leukocyte traffic

✤ primarily involved in inflammatory processes, others are constitutively expressed and play important homeostatic or developmental roles




✤ “Housekeeping” chemokines

✤ are produced in lymphoid organs and tissues or in non-lymphoid sites such as skin, where they direct normal trafficking of lymphocytes, such as determining the correct positioning of leukocytes newly generated by hematopoiesis and arriving from bone marrow

✤ inflammatory chemokines

✤ are typically induced in response to infection

✤ contact with pathogens or the action of proinflammatory cytokines, such as TNF-alpha, up-regulate the expression of inflammatory cytokines at sites of developing inflammation




Chemokine-Receptor Profiles Mediate Leukocyte Activity



✤ Chemokines cause leukocytes to move into various tissue sites by inducing the adherence of these cells to the vascular endothelium

✤ After migrating into tissues, leukocytes are attracted toward high localized concentrations of chemokines resulting in the targeted recruitment of phagocytes and effector lymphocyte populations to inflammatory sites

✤ The assembly of leukocytes at sites of infection, orchestrated by chemokines, is an essential part of mounting an appropriately focused response to infection



✤ other mediators released by cells of the innate and acquired immune systems trigger or enhance specific aspects of the inflammatory response

✤ released by tissue mast cells, blood platelets, and a variety of leukocytes, including neutrophils, monocytes/macrophages, eosinophils, basophils, and lymphocytes

✤ four interconnected mediator-producing systems: the kinin system, the clotting system, the fibrinolytic system, and the complement system

✤ Hageman factor: common intermediate of KS, CS and FS

✤ When tissue damage occurs, these four systems are activated to form a web of interacting systems that generate a number of mediators of inflammation

OTHER MEDIATORS OF INFLAMMATION



KININ SYSTEM✤ kinin system: activated by tissue injury

✤ an enzymatic cascade that begins when a plasma clotting factor (Hageman factor)

✤ activated Hageman factor then activates prekallikrein to form kallikrein

✤ then cleaves kininogen to produce bradykinin

✤ BRADYKININ: a potent basic peptide that increases vascular permeability, causes vasodilation, induces pain, and induces contraction of smooth muscle

✤ KALLIKREIN: also acts directly on the complement system by cleaving C5 into C5a and C5b

✤ RECALL: C5a complement component is an anaphylatoxin that induces mast-cell degranulation, resulting in the release of a number of inflammatory mediators



CLOTTING SYSTEM

✤ clotting system: triggered by damage to blood vessels

✤ yields large quantities of thrombin

✤ THROMBIN: acts on soluble fibrinogen in tissue fluid or plasma to produce insoluble strands of fibrin and fibrinopeptides

✤ INSOLUBLE FIBRIN: crisscross one another to form a clot (serves as a barrier to the spread of infection)



CLOTTING SYSTEM

✤ The clotting system is triggered very rapidly after tissue injury to prevent bleeding and limit the spread of invading pathogens into the bloodstream

✤ FIBRINOPEPTIDES: act as inflammatory mediators, inducing increased vascular permeability and neutrophil chemotaxisParungao-Balolong 2011


FIBRINOLYTIC SYSTEM

✤ fibrinolytic system: removal of the fibrin clot from the injured tissue

✤ PLASMIN: end product formed by the conversion of plasminogen

✤ a potent proteolytic enzyme, breaks down fibrin clots into degradation products that are chemotactic for neutrophils

✤ contributes to the inflammatory response by activating the classical complement pathway



RECALL: COMPLEMENT SYSTEM

✤ complement system: complement split-products serve as important mediators of inflammation

✤ Binding of the anaphylatoxins (C3a, C4a, and C5a) to receptors on the membrane of tissue mast cells induces degranulation with release of histamine

✤ HISTAMINE: induce smooth-muscle contraction and increase vascular permeability

✤ C3a, C5a, and C5b67 act together to induce monocytes and neutrophils to adhere to vascular endothelial cells, extravasate through the endothelial lining of the capillary, and migrate toward the site of complement activation in the tissues

✤ Activation of the complement system thus results in influxes of fluid that carry antibody and phagocytic cells to the site of antigen entry



PHOSPHOLIPIDS AS INFLAMMATORY MEDIATORS



CYTOKINES AS INFLAMMATORY MEDIATORS



RECALL: INFLAMMATION



INTERFERON GAMMA AND CHRONIC INFLAMMATION


Chronic Inflammation Develops When Antigen Persists


RECALL: INFLAMMATION

✤ Swelling: (Tumor)

✤ Redness: (Rubor)

✤ Pain: (Dolore)

✤ Heat: (Calore)

✤ Loss of function: (Fasor)Parungao-Balolong 2011

vasodilation

edema

(within minutes)

(within a few hours)

phagocytosis


ANTI-INFLAMMATORY AGENTS

✤ Although development of an effective inflammatory response can play an important role in the body’s defense, the response can sometimes be detrimental

✤ Allergies, auto-immune diseases, microbial infections, transplants, and burns may initiate a chronic inflammatory response

✤ Various therapeutic approaches are available for reducing long-term inflammatory responses and thus the complications associated with them




✤ ANTIBODY THERAPIES: reduce leukocyte extravasation

✤ block the activity of various adhesion molecules with antibodies

✤ CORTICOSTEROIDS: cholesterol derivatives

✤ NSAIDS: non-steroidal anti-inflammatory drugs




✤ CORTICOSTEROIDS: cholesterol derivatives (prednisone, prednisolone, and methylprednisolone)

✤ causes a decrease in the number of circulating lymphocytes as the result either of steroid- induced lysis of lymphocytes (lympholysis) or of alterations in lymphocyte-circulation patterns

✤ lipophilic (can cross the plasma membrane and bind to receptors in the cytosol) = transported to the nucleus, where they bind to specific regulatory DNA sequences, regulating transcription up or down

✤ EXAMPLE: induce increased transcription of the NF-kappaB inhibitor (I-kappaB)

✤ Binding of this inhibitor to NF-kappaB in the cytosol prevents the translocation of NF-kappaB into the nucleus and consequently prevents NF-kappaB activation of a number of genes, including genes involved in T-cell activation and cytokine production




✤ CORTICOSTEROIDS: cholesterol derivatives (prednisone, prednisolone, and methylprednisolone)

✤ reduce both the phagocytic and killing ability of macrophages and neutrophils, and this effect may contribute to their anti-inflammatory action

✤ also stabilize the lysosomal membranes of participating leukocytes, so that decreased levels of lysosomal enzymes are released at the site of inflammation




✤ NSAIDs: non-steroidal anti-inflammatory drugs



NEXT: HYPERSENSITIVITIES



bio 151 lec 12 13 cmer & lmi

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vascular endothelium

cholesterol derivatives

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