Biology: Chapter 8 Flashcards
Innate immunity
-Composed of defenses that are always active against infection, but lack the ability to target specific invaders
-Cells in the system activate inflammatory response, secreting proteins called cytokines that trigger an influx of immune cells from the blood
-Among the recruits are more phagocytes- notably monocytes and neutrophils
-Includes antimicrobial molecules and various phagocytes
Adaptive immunity
-Defenses that target a specific pathogen. System is slower to act, but can maintain immunological memory of an infection to mount a faster attack in subsequent infections
-Features B-cells and T-cells
-T- and B-cells spawn memory cells that promptly eliminate invaders encountered before
T-cells
-recognize antigens displayed on cells
-some directly attack infected cells (cell-mediated immunity)
-some activate more of themselves or B-cells
-mount the cell-mediated response and mature in the thymus
B-cells
-secrete antibody molecules that bind to antigens and destroy the invader directly or mark it for attack by others (humoral immunity)
-govern humoral response and mature in bone marrow
Noncellular nonspecific defenses of the innate immune system
-Skin (integument): provides a physical barrier between outside world and internal organs
-Defensins: antibacterial enzymes that can be found in the skin
-Sweat also has antimicrobial properties
-respiratory system
Gastrointestinal tract (innate immune system)
-Stomach secretes acid, resulting in the elimination of most pathogens
-The gut is colonized by bacteria
-most of these bacteria lack necessary characteristics to cause infection
-many potential invaders cannot compete with all bacteria in the gut and are kept at bay
Complement (innate immune system)
-Consists of a number of proteins in the blood that act as a nonspecific defense against bacteria
-Can be activated through classical pathway (requires the binding of an antibody to a pathogen)
-Can be activated by an alternative pathway (doesn’t require antibodies)
-Complement proteins punch holes in the cell walls of bacteria
-Cannot be modified to target a specific organism over others
Interferons (innate immune system)
-Proteins that prevent viral replication and dispersion
-Cause nearby cells to decrease production of both viral and cellular proteins and decrease permeability of these cells, making it harder for a virus to infect them
Cells of the innate immune system
macrophages, natural killer cells, granulocytes
Macrophages
-Type of agranulocyte that reside within the tissues
-Derive from blood-borne monocytes and become a resident population within a tissue
-Release cytokines which are chemical substances that stimulate inflammation and recruit additional immune cells to the area
Actions of an activated macrophage
-Phagocytizes the invader through endocytosis
-Digest the invader using enzymes
-Presents little pieces of the invader to other cells using a protein called major histocompatibility complex (MHC)
MHC I
-all nucleated cells in the body display these cells
-Any protein within a cell can be loaded onto it and presented on the surface of the cell which allows the immune system to monitor the health of these cells and detect if cells have been infected with a virus or pathogen
-considered endogenous pathway because it binds antigens that come from inside the cell
MHC II
-mainly displayed by antigen-presenting cells like macrophages
-Pick up pathogens from the environment, process them, and then present them on here
-considered exogenous pathway because the antigens originated outside the cell
Natural killer cells
A type of nonspecific lymphocyte that is able to detect the downregulation of MHC and induce apoptosis in virally infected cells
Neutrophils
most populous leukocyte in the blood, short-lived, phagocytic, and target bacteria
Eosinophils
-primarily involved in allergic reactions and invasive parasitic infections
-Release large amounts of histamine which is an inflammatory mediator which results in vasodilation and an increased leakiness of blood vessels, allowing additional immune cells to move out of the bloodstream and into tissue
Basophils
-involved in allergic responses
-Least populous leukocyte in the bloodstream
-Mast cells are closely related but have smaller granules and exist in tissues, mucosa, and epithelium
-Both basophils and mast cells release large amounts of histamine in response to allergens
Where are B-cells and T-cells created?
Bone marrow
Humoral immunity (adaptive immune system)
Involves the production of antibodies and may take as long as a week to become fully effective after initial infection
Responses from antibodies secreted into body fluids
-Once bound to a specific antigen, antibodies may attract other leukocytes to phagocytize those antigens immediately
-Antibodies may cause pathogens to clump together (agglutinate), forming a large insoluble complexes that can be phagocytized
-Antibodies can block the ability of a pathogen to invade tissues, essentially neutralizing it
Cell-surface antibodies
the binding of antigen to a B-cell causes activation of that cell, resulting in its proliferation and formation of plasma and memory cells
Mast cells surface antibodies
causes degranulation, releasing histamine and causing an inflammatory allergic reaction
Plasma cells
produce large amounts of antibodies
Memory B-cells
stay in the lymph node, awaiting reexposure to the same antigen
Memory B-cells
stay in the lymph node, awaiting re-exposure to the same antigen
Primary response
the initial activation which takes about 7-10 days
Secondary response (immune response)
will be more rapid and robust; memory cells jump into action if same microbe is ever encountered again and produce antigens specific to that pathogen
Positive selection (cell-mediated immunity)
allowing only the maturation of cells that can respond to the presentation of antigen on MHC (cells that cannot respond to MHC undergo apoptosis)
Negative selection (cell-mediated immunity)
causing apoptosis in cells that are self-reactive (activated by proteins produced by the organism itself)
3 Major types of T-cells
-Helper T-cells, cytotoxic T-cells, regulatory T-cells
Helper T-cells (CD4+)
-coordinate the immune response by secreting chemicals known as lymphokines
-These molecules are capable of recruiting other immune cells and increasing their activity
-Respond to antigens presented on MHC-II molecules so most effective against bacterial, fungal, and parasitic infections; the loss of these cells occurs in HIV infection
Cytotoxic T-cells (CD8+)
-capable of directly killing virally infected cells by injecting toxic chemicals that promote apoptosis into infected cell
-Respond to antigens presented on MHC-I molecules so most effective against viral (and intracellular bacterial or fungal) infections
Regulatory T-cells
-express lymphokines and a protein called Foxp3
-These cells help to tone down the immune response once infection has been adequately contained
-These cells also turn off self-reactive lymphocytes to prevent autoimmune diseases
Memory T-cells
lie in wait until the next exposure of the same antigen
5 Types of infectious pathogens
bacteria, viruses, fungi, parasites, and prions (for which there is no immune defense)
Bacterial (extracellular pathogen) infections
-Macrophages engulf the bacteria and release inflammatory mediators
-Cells digest bacteria and present antigens from the pathogen on their surfaces in conjunction with MHC-II
-Cytokines attract inflammatory cells
-Mast cells are activated by inflammation and degranulate, resulting in histamine release and increased leakiness of capillaries
-Dendritic cell then leaves the affected tissue and travels to the nearest lymph node, where it presents the antigen to B-cells
-B-cells create plasma cells and memory cells
-Antibodies then travel through the bloodstream to the affected tissue, where they tag the bacteria for destruction
-Dendritic cells also present the antigen to T-cells, activating a T-cell response
-After the pathogen has been eliminated, plasma cells die but memory B- and T-cells remain
Viral (intracellular pathogen) infections
-Virally infected cell will begin to produce interferons, which reduce permeability of nearby cells, reduce the rate of transcription and translation, and cause systemic symptoms
-Infected cells also present intracellular proteins on their surface in conjunction with MHC-I
-Cytotoxic cells recognize MHC-I and antigen complex as foreign and inject toxins into the cell to promote apoptosis
-Memory T-cells will be generated
Structure of the lymphatic system
-Made up of one-way vessels that become larger as they move toward the center of the body
-Vessels carry lymphatic fluid (lymph) and most joint to form a thoracic duct in the posterior chest, which delivers the fluid into the left subclavian vein
Lymph nodes
-small, bean-shaped structures along the lymphatic vessels
-Contain a lymphatic channel, as well as an artery and a vein
Function of the lymphatic system
Provides a secondary system for circulation
Lacteals
-small lymphatic vessels that are located at the center of each villus in the small intestine
-Fats, poached into chylomicrons by intestinal mucosal cells, enter the lacteal for transport
