Immune System Flashcards
What are two defense systems the immune system is made up of?
- Innate (nonspecific)
- Adaptive (specific)
Both are intertwined
What does the innate immune system do?
- First line of defense; external (skin and mucosae)
- Second line of defense; phagocytes, natural killer cells, inflammation (macrophages, mast, WBCs), antimicrobial proteins (interferons and complement proteins), fever
What does keratin do?
Provides resistance against acids, alkalis, and bacterial enzymes
What is mucin?
Thick sticky mucus that lines the digestive and respiratory passageways. Traps microorganisms.
What are defensins?
- A broad-spectrum antimicrobial peptide, increases in response to inflammation when surface barriers are breached.
- Help to control bacterial and fungal colonization in the exposed areas
What does TLR (toll-like receptors) do?
- Plays a central role in triggering immune responses. Allow the cells to recognize invaders and sound an alarm to initiate inflammation.
- 11 types, each recognizing a particular class of attacking microbe.
What are phagocytes?
WBC that ingest and digest foreign invaders
What are neutrophils?
Most abundant phagocytes, but die fighting; become phagocytic on exposure to infectious material
What are macrophages?
Develop from monocytes and are chief phagocytic cells; most robust phagocytic cell
- Free macrophages: wander through tissues e.g. alveolar macrophages
- Fixed macrophages: permanent residents of some organs, e.g. stellate macrophages in the liver
What’s the process of phagocytosis?
- Phagocyte adheres to pathogens
- Phagocyte forms pseudopods that eventually engulf the particles, forming a phagosome
- Lysosome fuses with the phagocytic vesicle, forming a phagolysosome
- Toxic compounds and lysosomal enzymes destroy pathogens
- Sometimes exocytosis of the vesicle removes indigestible and residual material
What is opsonization?
The coating of an antigen or particle (eg, infectious agent) by substances, such as antibodies, complement components, fibronectin, and so forth, that facilitate uptake of the foreign particle into a phagocytic cell.
What are natural killer cells?
- Nonphagocytic, large granular lymphocytes that police blood and lymph
- Can kill cancer and virus infected cells before adaptive immune system is activated
- Attack cells that lack self cell surface receptors
- Kill by inducing apoptosis in cancer cells and virus infected cells
What is inflammation?
A nonspecific response to any tissue injury.
What are some causes of inflammation?
Triggered whenever body tissues are injured
- Trauma
- Heat
- irritating chemicals
- Infections by microorganisms
What are the benefits of inflammation?
- Prevents spread of damaging agents
- Disposes of cell debris and pathogens
- Alerts adaptive immune system
- Sets the stage for repair
What are 4 cardinal signs of acute inflammation?
- Redness
- Heat
- Swelling
- Pain
- Impairment of function
What is complement and what does it do?
A group of plasma proteins that are activated if pathogens provoke the inflammation; to form potent inflammatory chemicals.
- Complement system consists of ~20 blood proteins, including C1-C9
- Nonspecific
- Enhances both innate and adaptive defenses.
What are the inflammatory chemicals that are released and what are the effects?
Histamine, kinins, and prostaglandins.
- Vasodilation of local arterioles
- Leaky capillaries
- Attract phagocytes to the area
What are two stages of inflammation?
- Inflammatory chemical release
- Vasodilation (hyperemia- congestion with blood, redness and heat) and increased vascular permeability (exudate- fluid containing clotting factors and antibodies to leak into tissue)
- Local swelling (edema)
- Swelling pushes on nerve endings (pain)
Phagocyte mobilization process
- Leukocytosis
- neutrophils multiply and flood the area followed by macrophages - Margination: phagocytes clinging to the inner walls of the capillaries and postcapillary venules
- endothelial cells project cell adhesion molecules (CAMs) into vessels - Diapedesis
- Neutrophils flatten and squeeze b/w endothelial cells, moving into interstitial spaces - Chemotaxis
- inflammatory chemicals act as chemotactic agents to promote positive chemotaxis (the migration of cells toward attractant chemicals or away from repellents) - If attack continues, monocytes arrive later
What are interferons?
- IFN: family of immune modulating proteins
- Cells infected with viruses secrete IFNs to warn healthy neighboring cells
- Not virus-specific
What substance raises body temp in fever?
Pyrogens are secreted by Leukocytes and macrophages that are exposed to foreign substances
- Acts as body’s thermostat in hypothalamus, raise body temp
- Benefits: Causes liver and spleen to isolate iron and zinc needed by microorganisms. Increases metabolic rate and rate of repair
What does the adaptive immune system do?
- Third line of defense attacks particular foreign substances (takes longer than innate)
- Specific defensive system that eliminates almost any pathogen or abnormal cell in body
What are the characteristics of adaptive immunity?
- Specific: recognizes and targets specific antigens
- Involves B and T lymphocytes
- Systemic: not restricted to the initial site
- Has memory: mounts an even stronger attack to known antigens
What is a shortcoming in adaptive defenses?
Must be primed by initial exposure to specific foreign substance
What are two main branches of adaptive defense system?
- Humoral (B cells) immunity: antibody-mediated
- Cellular (T cells) immunity: cell-mediated
What does humoral immunity target?
- Antibodies produced by lymphocytes, circulate freely in body fluids
- Bacteria, toxins, free viruses in the blood, aka extracellular
What does cellular immunity target?
Lymphocytes act against target cell directly by killing infected cells and indirectly by releasing chemicals that enhance inflammatory response or activating other lymphocytes or macrophages
Virus-infected and cancer cells, and cells of foreign grafts
What are antigens?
Substances that can mobilize adaptive defenses and provoke an immune response
- Targets of all adaptive immune responses
- Most are large, complex molecules not normally found in body
- Intruders aka nonself
What are the characteristics of antigens?
- Can be complete or
- incomplete: hapten: small peptides, nucleotides, some hormones)
- Contain antigentic determinants
- Can be a self-antigen
What are the two functional properties of complete antigens?
- Immunogenicity
- Reactivity
What is immunogenicity?
The ability to stimulate specific lymphocytes to proliferate/multiply
- E.g. bacteria, fungi, virus particles (small molecules such as peptides, nucleotides and hormones are NOT)
What is reactivity?
The ability to react with the activated lymphocytes and the antibodies released by immunogenic reactions
What are self-antigens?
Cells covered with proteins located on surface that are not antigenic to self, but to others in transfusions or grafts
E.g. MHC proteins
What is MHC I?
Found in all nucleated cells except RBC.
- Present endogenous antigens to cytotoxic T cells
- Originate inside the cells
What is MHC II?
Found only on antigen-presenting cells
- Present exogenous antigens to helper T cells
What three crucial types of cells are involved in adaptive immune system?
- Two types of lymphocytes: B cells (humoral) and T cells (cellular)
- APCs (antigen-presenting cells): Do not respond to specific antigens. Play essential supporting roles in immunity
What is APCs (antigen-presenting cells)?
Engulf foreign antigens and present fragments of antigens on MHC II to helper T cells for recognition
What are the major types of APCs?
- Dendritic cells
- Macrophages
- B cells (present foreign antigens to helper T cell to assist in their own activation)
What is an immunocompetence?
The ability to recognize its one specific antigen by binding to it.
How does humoral immunity work?
When B cell encounters target antigen, it provokes a humoral immune response
- B cells are activated
- Antibodies specific for that particular antigen are produced
- A clone of B cells forms
- Clone B cells become plasma cells, antibody secreting effector cells
- Secrete antibodies at rate of 2000 molecules per sec. for 4-5 days then die
Clone cells that do not become plasma cells become _______.
Memory cells
- Provide immunological memory
- Mount an immediate response to future exposure to same antigen
What is a primary immune response?
Cell proliferation and differentiation upon exposure to antigen for the first time
- Lage period 3-6 days
- Peak levels of plasma antibody are reached in 10 days
What is a secondary immune response?
Re exposure to same antigen gives faster, more prolonged and effective response
- Respond within hours
- Antibody level peak in 2-3 days at much higher levels
What is active and passive humoral immunity?
Active: When B cells encounter antigens and produce specific antibodies
Passive: When ready-made antibodies are introduced into body
Where do B cells mature?
In the bone marrow
Where do T cells mature?
In the thymus
Antibodies are also called?
Immunoglobulins (Igs): proteins secreted by plasma cells which make up gamma globulin portion of blood
- capable of binding specifically with antigen detected by B cells
- Have light and heavy chains
- Have variable and constant regions
- Grouped into one of five Ig classes
What do antibodies do?
- Inactivate and tag antigens
- Form antigen-antibody (immune) complexes
What are the defensive mechanisms used by antibodies?
- Neutralization
- Agglutination
- Precipitation
- Complement fixation
What is neutralization?
- Antibodies block specific sites on viruses or bacterial exotoxins
- The virus or exotoxin cannot bind to receptors on tissue cells
- Phagocytes destroy the antigen-antibody complexes
What is agglutination?
The clumping of particles together
What is precipitation?
Soluble molecules are cross-linked into large complexes that settle out of solution
What is complement activation?
A system of plasma proteins that can be activated directly by pathogens or indirectly by pathogen-bound antibody, leading to a cascade of reactions that occurs on the surface of pathogens and generates active components with various effector functions.
