Immunity, Inflammation, and Complement System
White Blood Cells What is normal WBC count? What are the subclasses of WBC's and what is the normal percent of each? What subclasses are considered granulocytes? What subclasses are considered agranulocytes?
5,000-10,000 /µL. Neutrophils (40-75%), Lymphocytes (20-45%), Monocytes/Macrophages (~8%), Eosinophils (1-6%), Basophils (<1%). Granulocytes: Neutrophils, Basophils, Eosinophils. Agranulocytes: Monocytes/Macrophages and Lymphocytes.
What is a cytokine?
A small cell-signaling peptide that is not inherently good or bad (e.g. erythropoeitin).
B-Cells Activated by? Function? How are antibodies produced?
Activated by TH2 (T-Helper Type II Cells). Once activated, proliferate into plasma cells which produce antibodies to assist in opsonization, lysis, neutralization, and antibody-dependent cell-mediated cytotoxictity. Once the antigen has been destroyed, they turn into Memory B-Cells. Antigens combine with surface immunoglobulins, the antigen-Ig complex is then absorbed and processed. When the TH2 cell activates the B-cells the B-cells can begin the above processes.
How is mannose-binding-lectin-protein activated? What does it do once activated? This is the beginning of what pathway?
Activated by binding mannose found on the surface of a cell-membrane surface. This exposes its enzymatic subunits. Once activated, the enzymatic subunits cleave C4 and C2 proteins into C4a, C4b, C2a, and C2b subunits respectively. The C4b and C2b subunits can then combine to form the C4bC2b complex known as "C3 convertase." The Lectin Binding Pathway. NOTE: Does not require antibodies and so is always active.
How, in general, are leukocytes activated?
Activated by microbes, products of necrotic cells, antigen-antibody complexes, and cytokines.
Humoral vs Cell-Mediated Immunity
Both are types of adaptive immunity. Humoral is dependent on antigen-specific antibodies and is driven by B-cells. Cell-mediated immunity, however, does not depend on antibodies, but cytokines, and is driven by T-cells.
What are the components of C1? How is it activated? What does C1 do once activated? This is the beginning of what pathway?
C1 is composed of 6 C1q subunits (Fc-antibody-binding subunits), 2 C1r and 2 C1s subunits (enzymatic portions of the C1 protein). C1 is activated when it binds an antibody-antigen complex. This binding causes a conformational change which exposes the enzymatic subunits. C1 cleaves C4 and C2 proteins into C4a, C4b, C2a, and C2b subunits respectively. The C4b and C2b subunits can then combine to form the C4bC2b complex known as "C3 convertase." The Classical Pathway.
Describe beginning of the Alternative Pathway. How is the pathway regulated?
C3 is spontaneously cleaved into C3a and C3b independently of "C3 Convertase" (although very slowly). The C3b subunits can then bind antigen surfaces, acting as an opsonin. Once bound, C3b can be bound by Factor B. Factor D cleaves C3b-bound Factor B into Ba and Bb subunits. The Ba subunit leaves, and a C3b-Bb complex is left behind on the antigen surface. This C3b-Bb complex is another form of the "C3 convertase" which can enzymatically cleave C3 into C3a and C3b. Thus, it acts as an amplifier to both the Lectin Binding and Classical Pathways. Regulated by Factors H and I.
Summary of What You Need to Know About MHC II, MHC I, CD4+ T-cells, and CD8+ T-cells. (Just read the back for this one).
CD4+ T-cells are also known as Helper T-Cells, of which there are two subcategories: TH2 (Activate B-cells) and TH1 cells (Activate Cytotoxic T-cells). CD8+ T-Cells are also known as Cytotoxic T-Cells. MHC I surface proteins are expressed by all nucleated cells. MHC II surface proteins are expressed only by APC's such as NK Cells and Dendritic Cells. When an antigen is digested by an APC, fragments of that digested antigen are attached to MHC II proteins. The MHC II-antigen complex is then expressed on the membrane surface of the APC for CD4+ Helper T-cell recognition. For cells infected by viruses (or parasites), intracellular processes break down the viruses, then attach pieces of the virus/antigen to a MHC I protein. The MHC I-antigen complex is then expressed on the cell membrane surface for recognition by CD8+ Cytotoxic T-Cells.
Helper T-Cells CD4+ or CD8+? What are the two subclasses of Helper T-Cells? What are the functions of the two subclasses? Function in general? What are they activated by?
CD4+. TH1 and TH2. TH1 Cells (T-Helper Type 1 Cells) release cytokines that activate inactive T-cells into cytotoxic T-cells. TH2 Cells (T-Helper Type 2 Cells) release cytokines necessary to activate B-cells and antibody secretion. Release cytokines to recruit specific kinds of white cells to the site of an infection. Activated by MHCII-antigen complexes.
Cytotoxic T-Cells CD4+ or CD8+? What are they activated by? Function?
CD8+. MHC I-antigen complexes. Once activated, releases lytic molecules to rupture the target cell(s).
What does complement protein deficiency/pathophysiology do?
Can result in autoimmune disorders, recurrent infections, or transplant infections. Also implicated in Reperfusion Injury.
What are the 3 pathways of the complement system and what is their end product?
Classical, Alternative, and Lectin Pathways. The end product of each is the Membrane Attack Complex.
Describe contact activation.
Contact activation begins with factor XII of the intrinsic coagulation pathway. Ultimately, it results in the activation of plasmin and bradykinin (vasodilator). Obviously, also leads to intrinsic pathway activation.
What 5 protein systems are activated in blood surface interactions?
Contact activation system, Extrinsic Coagulation, Intrinsic Coagulation, Fibrinolysis, and Compliment activation.
Define Inflammation Terminology Exudation? Exudate? Transudate? Edema? Pus?
Escape of proteins, fluid, and blood cells from the blood into the interstitial space. Inflammatory extra-vascular fluid rich in proteins and cellular debris and specific gravity > 1.20. Extra-vascular fluid low in protein content. Specific gravity <1.020. In other words, normal plasma ultrafiltrate, or interstitial fluid. Excess fluid in interstitial space or serous cavities. May be transudate or exudate. Purulent exudate rich in neutrophils and dead cell debris.
Describe Each Stage of Leukocyte Migration Extravasation? Margination? Rolling? Transmigration (aka Diapedesis)? Chemotaxis?
Extravasation: The process of white cells moving into the interstitial space. Margination: The process of WBC's moving toward the walls of the vessel. Rolling: WBC's adhere transiently to the vessel walls via selectin and integrin proteins. This helps them to slow down so that they can move through the vessel wall into the interstitial space. Transmigration (aka Diapedesis): The process of WBC's moving through the junctions between vascular endothelial cells. Chemotaxis: The process of WBC's moving through the interstitial fluid (following a trail of chemical signals) to the source of the problem.
True or False: In cardiac surgery, the CPB machine is the source of the greatest level of thrombin generation.
False, the surgical wound(s) are the source of greatest thrombin generation.
IgM Main Action
First antibody produced by a fetus, its main action is to activate the compliment system.
IgA Main Action
Found in tears, breast milk, mucous, saliva, and bronchiole secretions. Binds to and immobilizes antigens so that mucin can remove the antibody-antigen complex. Cannot activate the compliment system.
What are the 4 subclasses of IgG and the main action of each?
IgG1: Protects from most bacteria. IgG2: Destroys bacteria encased in a saccharide coat (the rest of the bacteria). IgG3: Activates compliment proteins. IgG4: Produces vasodilators which protect the bronchioles.
Antibodies What is another name for them? What are the five classes? How long to peak levels/potency? Function(s)? Which two are most common? What are they made of?
Immunoglobulins. IgG, IgM, IgD, IgA, IgE. ~14 days. Opsonizes foreign antigens (binds and marks them for destruction). IgG and IgM are most common. They are proteins made up of varying arrangements of amino acid chains. They have both light and heavy chains.
T-Cells Where do they mature? How are they activated (in general, without all the fancy receptor stuff)? What cells assist in their activation? What receptors are activated? What are the 3 main classes of T-Cells?
In the Thymus (Remember "T" for thymus). Must come in contact with a RECOGNIZABLE antigen before they can release cytokines to initiate a SPECIFIC CELL MEDIATED RESPONSE. Antigen Presenting Cells (APC's) such as NK cells and Dendritic Cells present bits of phagocytosed cells for the T-Cells to recognize. CD4 receptors are activated by MHC II-antigen complexes. CD8 receptors are activated by MHC I-antigen complexes. Helper, Cytotoxic, and Supressor.
Inflammation What are the two major components of inflammation? What is the goal of inflammation? Qualities of acute inflammation? Qualities of chronic inflammation? What stimulates inflammation?
Increase vascular supply/permeability (vascular) and attract immune cells (cellular) to the area of inflammation. Eliminate the cause of inflammation, remove debris, heal tissues. Rapid onset, short duration, emigration of neutrophils (increase in vascular permeability). Long duration, lymphocyte involvement, proliferation of blood vessels, tissue necrosis. Trauma/foreign bodies, toxins, tissue necrosis, immune reactions.
Innate vs Adaptive Immunity (Compare and Contrast)
Innate immunity is a rapid-response/first line-of-defense immune response and has limited proteins/mechanisms to aid in antigen recognition. Innate immunity does not involve any level of "memory." Adaptive immunity involves T and B lymphocytes. Involves immune system "memory." NOTE: Antigen-Presenting-Cells such as dendritic cells and NK cells are the bridge from innate to adaptive immunity.
What is C3 convertase and what is its role?
It is a C4b and C2b complex. This complex cleaves/converts C3 into C3a and C3b. C3b then attaches to the C4bC2b complex to make C5 convertase.
What is C5 convertase and what is its role?
It is a C4bC2bC3b complex that cleaves C5 into C5a and C5b. C5b can then combine with C6, C7, C8, and C9 to form the membrane attack complex (MAC).
What are the principal agonists of neutrophils?
Kallikrein and C5a.
IgD Main Action
MAY assist with the maturation of B-cells into Plasma Cells.
IgG Main Action
Most important and most potent. Very effective at binding and destroying antigens. Produced in greatest amounts on second exposure to an antigen. Can cross the placenta and is responsible for hemolytic disease of the newborn.
Types of Cytokines How are they named? What are the four types and their functions?
Named by the cell they are secreted by or what they act on. 1. Interleukins: Mostly secreted by T and B Cells. IL2,3,4, and 6. 2. Interferons: Produced by T-Cells, NK Cells, and Macrophages. Work on viruses and increase MHC production. 3. Chemokines: Stimulates WBC recruitment via chemotaxis. 4. Tumor Necrosis Factor.
What are the five main cells implicated in blood surface interactions?
Neutrophils, Monocytes/Macrophages, Lymphocytes, Endothelial Cells, and Platelets.
Protective qualities of vascular endothelium? Potentially harmful qualities of vascular endothelium?
Nitric oxide, adenosine, and prostacyclin help protect the endothelium against damage. Platelet activating factor (activates platelets and increases inflammation), Endothelin 1 (vasoconstrictor), Superoxide Anion, Histamine (vasodilation and increased vascular permeability).
What, in general, is the response of a leukocyte once activated?
Once activated WBC's begin production of ARACHIDONIC ACID METABOLITES, degranulation of lysosomal enzymes, secretion of cytokines, modulation of surface receptors, and phagocytosis.
Describe the kinds of antibody-mediated (humoral) antigen destruction.
Opsonization: Antigens are marked with antibodies for destruction. Also makes them less "slippery." Lysis: Antibodies activate compliment system which causes formation of a Membrane Attack Complex (MAC) which causes foreign cells to lyse. Antibody-dependent-cell-mediated cytotoxicity: Cell destruction carried out by white cells on opsonized antigens. Neutralization: Antibody renders the antigen/toxins harmless.
Describe the activation/recruitment of Neutrophils.
P-selectins on the surface of endothelial cells are expressed in response to pro-inflammatory mediators such as histamine. The P-selectins adhere to the surface of the neutrophils causing them to slow down and "roll" on the surface of the endothelium. This rolling allows Neutrophil Integrin proteins the opportunity to "grab hold of" the ICAM proteins with an even stronger adhesion. Once the Integrin proteins have adhered to ICAM, the neutrophil stops moving entirely and is able to begin transmigration. NOTE: The same inflammatory mediators that activate the endothelial cells to express P-selectin also activate and recruit the Neutrophils.
What is a Cytokine?
Protein molecules that help to signal other cells or to further a reaction.
What is a complement protein?
Protein that aids in the immune and inflammatory responses.
How does the complement system work with inflammation and the immune system?
Proteins C3a and C5a act as chemokines and inflammatory/immune mediators. They interact with endothelial cells to increase vasodilation, vasoconstriction, and vascular permeability. They also interact with and activate WBC's causing them to release lysosomal enzymes, ROS, cytokines, and other inflammatory mediators.
IgE Main Action
Stimulates Basophils and Mast Cells to release histamine. Involved in E-llergic (Allergic) reactions. Also causes asthma.
Supressor T-Cells Function? What can deficiency lead to?
Suppresses the function of other WBC's to prevent them from destroying antigens excessively. Deficiency of these cells can lead to autoimmune disorders.
SIRS What is it? Name 2 diagnostic criteria? How does CPB contribute? How does it relate to infection, sepsis, severe sepsis, and septic shock?
Systemic inflammatory response syndrome. Any of the following two criteria: Temp >38 or <36, Respiratory rate > 20/min or PaCO2 < 32mmHg, HR >90bpm, WBC count >12,000 or <4000 or >10% increase in neutrophil count. CPB stimulates Neutrophil activation, causes RBC damage, activates platelets, stimulates coagulation system, decreases T, B, and NK cell count. Infection --> SIRS --> Sepsis (SIRS + Infection) --> Severe Sepsis (Sepsis + End Organ Damage) --> Septic Shock (Severe Sepsis + Hypotension) --> Death
Lymphocytes What are the three main types of Lymphocytes? Function? Granulocytes? Where are they found when activated vs dormant? %?
T Cells and B-Cells (Adaptive Immunity) and Natural Killer Cells (Innate immunity). T Cells and B-Cells are responsible for Adaptive Immunity while Natural Killer Cells are responsible for Innate immunity. However NK cells are antigen presenting cells and are the bridge from innate to adaptive immunity. No, they are agranulocytes. When activated by foreign antigens, they are found in the blood stream. When dormant, they are found in the lymph nodes. 20-45% WBC count.
Know this: See back.
The Terminal Complement Complex (aka MAC) accelerates thrombin formation via prothrombinase. Also activates platelets.
How do we reduce the risk of SIRS/SIRAB on bypass?
Use steroids, smaller circuits, coated circuits, use filters, use less prime, etc.
Reperfusion Injury When does it occur? What happens? What sources are responsible for the generation of ROS? Endogenous _______ are depleted during ischemia, leading to increased amounts of free ROS.
When blood flow is re-established to ischemic tissue (e.g. when the aortic XC is removed and blood flow is re-established to the myocardium). NOTE: R/I is distinctly different from ischemic injury. Abrupt pH change, calcium influx, oxygen restoration, inflammation and myocardial edema lead to the opening of Mitochondrial Permeability Transition Pore and subsequent generation of reactive oxygen species (ROS). Xanthine Oxidase in endothelial cells, Re-energized Electron Transport Chain in mitochondria, and NADPH Oxidase in Neutrophils (hours later) are responsible for the generation of ROS. Hence, activated neutrophils are bad news in reperfusion injury. Antioxidants.
Monocytes/Macrophages When does a monocyte become a macrophage? Granulocyte? Function? Site of action? %?
When the immature monocyte leaves the blood and migrates to the tissues, it becomes a macrophage where it is ONLY THEN actively phagocytic. No, it is an agranulocyte. Phagocyte. Primarily in the liver sinusoids, spleen, and lungs. ~8% WBC count.
Eosinophils Granulocyte? Function? Site of action?
Yes. Involved in E-llergic (allergic) reactions. Responsible for innate (rapid response) immunity. Associated with Asthma. Skin, bronchi, bronchioles. 1-6% WBC count.
Neutrophils Granulocyte? Function? Site of action?
Yes. Primarily function as a phagocyte. Use chemotaxis (basically cellular "sniffing") to find sites of antigen activity or infection. Site of antigen activity or infection. 40-75% WBC count.
Basophils Granulocyte? Function? %?
Yes. Responsible for innate (rapid response) immunity. Function by chemotaxis and phaocytosis. Involved in allergy and asthma like the Eosinophil, but they also release Histamine and Heparin. <1% WBC count.
