Immune System Flashcards
What are the two divisions of the immune system?
- innate immunity
- adaptive immunity
Innate Immunity
- composed of defenses that are always active against infection but lack the ability to target specific invaders over others
- called non-specific immunity
Adaptive Immunity
- the defenses that target a specific pathogen
- slower to act but can maintain immunological memory of an infection to be able to mount a faster attack in subsequent infections
- called specific immunity
- can be divided into two parts: humoral immunity (driven by B-cells and antibodies) and cell-mediated immunity (provided by T-cells)
How does the Innate Immune System work?
includes cells that ingest and destroy pathogens (like dendritic cells and macrophages), and also activate an inflammatory response, secreting cytokines that trigger an influx of immune cells from the blood, and recruit more phagocytes – monocytes and neutrophils
How does the Adaptive Immune System work?
- activated B-cells secrete antibody molecules that bind to antigens and destroy the invader directly or mark it for attack by others
- T cells recognize antigens displayed on cells or help activate B-cells and other T-cells which can directly attack infected cells
What organs are included in the immune system?
- adenoids
- tonsils
- lymph nodes
- thymus
- spleen
- peyer’s patches (small intestine)
- lymphatic vessel
- bone marrow
Bone Marrow
produces all of the leukocytes (WBCs) that participate in the immune system through the process of hematopoiesis
Spleen
location of blood storage and activation of B-cells, which turn into plasma cells to produce antibodies as part of adaptive immunity
Thymus
- small gland in front of the pericardium (sac that protects the heart)
- where T-cells mature
Lymph Nodes
- provide a place for immune cells to communicate and mount an attack
- B-cells can be activated here
Gut-Associated Lymphoid Tissue (GALT)
- immune tissue that is found in close proximity to digestive system
- sites of potential invasion by pathogens
- includes: tonsils, adenoids, peyer’s patches, lymphoid aggregates in the appendix
B-Cells
- Site of Development:
- Site of Maturation:
- Major Functions:
- Specific or Non-Specific?
- Humoral or Cell-Mediated?
- bone marrow
- bone marrow (but are activated in the spleen or lymph nodes)
- produce antibodies
- specific
- humoral
T-Cells
- Site of Development:
- Site of Maturation:
- Major Functions:
- Specific or Non-Specific?
- Humoral or Cell-Mediated?
- bone marrow
- thymus
- coordinate immune system and directly kill infected cells
- specific
- cell-mediated
What is the first line of defense in the innate immune system?
skin (integument) – provides a physical barrier, contains defensins (antibacterial enzymes)
What are other physical barriers of the immune system?
- mucus (lines respiratory tract, covers the eye, oral cavity) which produces a nonspecific bacterial enzyme called lysozyme
- hair
- earwax
What role does the GI Tract play in nonspecific immunity?
- stomach secretes acid which eliminates most pathogens
- potential invades not able to compete against the large bacterial population in the gut
What role does the Complement System play in nonspecific immunity?
- system consists of many proteins in the blood that act as a nonspecific defense against bacteria
- activated through a classical pathway (requires binding of antibody to a pathogen) or an alternate pathway (does not require antibodies)
- complement proteins put holes in cell walls of bacteria making them osmotically unstable
What role do Interferons play in nonspecific immunity?
- these are proteins that prevent viral replication and dispersion
- cause nearby cells to decrease production of viral and cellular proteins, and decrease the permeability of these cells making a virus harder to infect them
- upregulate MHC class I and II molecules, resulting in increased antigen presentation and better detection of infected cells by immune system
- cause “flu-like” symptoms
What cells comprise the Innate Immune System?
- macrophages
- natural killer cells
- granulocytes
- mast cell
- dendritic cell
Macrophages
- type of agranulocyte
- derive from blood-borne monocytes and can become resident population in a tissue (permanent)
- immune defender that engulfs and consumes pathogens
- release cytokines (chemical substances that stimulate inflammation and recruit additional immune cells)
What 3 things does a macrophage do when activated?
- phagocytizes bacteria invader through endocytosis
- digests the invader using enzymes
- presents little peptide pieces of the invader to other cells using a protein called major histocompatibility complex (MHC) – which binds to a pathogenic peptide (antigen) and carries it to the cell surface where it can be recognized by cells of the adaptive immune system
MHC Class I Molecules
- displayed by all nucleated cells in the body
- any protein produced within a cell can be loaded onto MHC-1 and presented on the surface of the cell, allowing immune system to detect if these cells have been infected – if infected cells present an unfamiliar protein on their surface
- considered an endogenous pathway because it binds antigens from inside the cell
MHC Class II Molecules
- mainly displayed by professional antigen-presenting cells like macrophages, dendritic cells, some B-cells, and certain activated epithelial cells
- considered an exogenous pathway fir antigen presentation because the exogenous antigen picked up from the environment, processed inside the cell, then presented on MHC-2
Pattern Recognition Receptors
- specialized cells found on macrophages and dendritic cells
- recognize the category of the invader and produce appropriate cytokines to recruit the right type of immune cells
Natural Killer Cells
- type of nonspecific lymphocyte
- can detect the down-regulation of MHC and induce apoptosis in these virally infected cells (cancer cells often do not present MHC-antigen complexes)
- cell that destroys the body’s own cells that have become infected
Granulocytes
-three cell types with tiny granules in their interiors – neutrophils, eosinophils, basophils – that participate in the inflammatory response
Neutrophils
- short-lived (last about 5 days)
- phagocytic cells that target bacteria
- follow bacteria using chemotaxis (sensing of certain products given off by bacteria and migration of neutrophils to follow these products back to the source )
- can also detect bacteria once it has been opsonized (marked with an antibody from a B-cell)
- when these are dead they form pus
Eosinophils
- contain bright orange granules
- primarily involved in allergic reactions and invasive parasitic infections
- once activated they release large amounts of histamine
How does histamine cause inflammation?
it induces vasodilation and the movement of fluid and cells (especially macrophages and neutrophils) from the bloodstream into tissues
Basophils
- contain large purple granules
- involved in allergic responses
- least populous leukocyte in the bloodstream
Mast Cells
- closely related to basophils but have smaller granules and exist in the tissues, mucosa, and epithelium
- release large amounts of histamine in response to allergens and cause inflammation
What is the most populous leukocyte in the blood?
neutrophils
What two types of cells are part of the adaptive immune system?
- B-Cells
- T-Cells
Humoral Immunity
- based on activation of B-Cells
- occurs in response to pathogens/bacteria/viruses/etc floating around in the body fluids
- immunity from serum antibodies produced by plasma cells
- can take as long as a week to become fully effective
- antibodies are produced by B-cells and are specific to the antigens of the invading microbe
- Humoral” refers to the bodily fluids where these free-floating serum antibodies bind to antigens and assist with elimination
Antibodies (Immunoglobins [Ig])
- can be displayed on the cell surface or float freely in the body
- binding of an antibody to an antigen results in a different response depending on the location
- Y shaped molecules made of two identical heavy chains and two identical light chains that are held together by disulfide linkages and noncovalent interactions
- has an antigen-binding region at the end of the variable region (domain) at the tips of the Y and a constant region (domain) that consists of the remaining part of the antibody
Antigen-Binding Region
- located on Y tips of antibody
- within this region there are specific polypeptide sequences that will bind only ONE specific antigenic sequence
Clonal Selection
only those B-cells that can bind the antigen with high affinity survive, which in turn creates a mechanism that generates specificity
Constant Region
region that cells such as natural killer cells, macrophages, monocytes, and eosinophils have receptors for, and that can initiate the complement cascade
Each B-Cell makes only one type of _____.
antibody – different types of antibodies can be used at different times during the adaptive immune response for different types of pathogens, or in different locations in the body
Isotype Switching
process by which cells can change which isotype of antibody they produce when stimulated by specific cytokines
Naive B-Cells
- cells that have not yet been exposed to an antigen
- wait in lymph nodes for their particular antigen to come along, and once they are exposed they proliferate and produce two types of daughter cells – plasma cells and memory B-cells
Plasma Cells
B-cells that produce large amounts of antibodies
Memory B-Cells
B-cells that stay in the lymph node and wait for re-exposure to the same antigen
Cytotoxic (Cell-Mediated) Immunity
- involves T-Cells
- immunity can be acquired through T-Cells from someone who is immune to the target disease or infection
- immunity response is carried out by cytotoxic cells
Positive Selection
- T-cells undergo this in the thymus
- refers to maturing only cells that can respond to the presentation of antigen on MHC (cells that can’t respond to this undergo apoptosis)
Negative Selection
- T-cells can also undergo this
- refers to causing apoptosis in cells that are self-reactive (activated by proteins produced in the organisms itself)q
Thymosin
- peptide hormone secreted by the thymic cells in the thymus
- facilitates T-Cell maturation
What are the 3 types of T-Cells?
- Helper T-Cells (Th)
- Suppressor T-Cells (Treg)
- Cytotoxic T-Cells (Tc)
Helper T-Cells
- also called CD4+ T-cells
- coordinate the immune response by secreting chemicals known as lymphokines (molecules that can recruit other immune cells)
- respond to antigens present on MHC-2 molecules
- most effective against bacterial, fungal, and parasitic infections
HIV
- occurs when an individual loses their Helper T-Cells
- immune system is unable to mount an adequate response to infection
Cytotoxic T-Cells
- also called CD8+ T-Cells
- capable of directly killing virally infected cells by injecting toxic chemicals that promote apoptosis into the infected cell
- respond to antigens presented on MHC-1 molecules
- most effective against viral (and intracellular bacterial or fungal) infections
Suppressor T-Cells
- also express CD4 but they also express a protein called Foxp3
- cells help to tone down the immune response once infection has been adequately contained
- have self-tolerance (turn off self-reactive lymphocytes to prevent autoimmune disease)
Memory T-Cells
- lie in wait until the next exposure to the same antigen
- when activated they result in a more robust/rapid response
CD x MHC = 8
- CD4+ cells respond to MHC-2 (4x2=8)
- CD8+ cells respond to MHC-1 (8x1=8)
What are the five types of infectious pathogens?
- bacteria
- viruses
- fungi
- parasites (including protozoa, worms, insects)
- prions (there is no immune defense against these)
How does the body react to Bacterial (Extracellular Pathogen) Infections (7)?
- macrophages engulf the bacteria and release inflammatory mediators (cytokines)
- macrophages digest the bacteria and present antigens from the pathogen on their surface via MHC-2
- cytokines attract inflammatory cells including neutrophils and more macrophages
- mast cells are activated by the inflammation and degranulate, resulting in histamine release and leakiness of capillaries (immune cells can leave and travel to near lymph node)
- dendritic cell leaves affect tissue and goes to lymph node where it presents antigen to B-cells, and also presents to T-cells to activate the T-cell response
- B-cells that produce the correct antibody proliferate through clonal selection to create plasma cells and memory cells
- antibodies travel through bloodstream to affected tissue and tag bacteria for infection
How does the body react to Viral (Intracellular Pathogen) Infections (3)?
- virally infected cell produces interferons which reduce permeability of nearby cells, reduce the rate of transcription/translation in these cells, and cause systemic symptoms
- infected cells present intracellular proteins on their surface via MHC-1
- CD8+ T-cells recognize MHC-1 and antigen complex so inject toxin into cell to promote apoptosis
Self-Antigens
- the proteins and carbohydrates that present on the surface of every cell of the body
- signal to immune cells that the cell is not threatening and should not be attacked
Autoimmunity
when the immune system fails to make the distinction between self and foreign and attacks cells expressing particular self-antigens
What are the two ways immunization can be achieved?
- active immunity
- passive immunity
Active Immunity
- immune system is stimulated to produce antibodies against a specific pathogen
- individual receives an injection containing an antigen that will activate B-Cells to produce antibodies to fight the specific infection
Passive Immunity
- results from the transfer of antibodies to an individual
- immunity is transient because only the antibodies, and not the plasma cells that produce them, are given to the individual
- ex: transfer of antibodies across placenta during pregnancy
The lymphatic system is made-up of ___-___ vessels that become ____ as they move toward the center of the body.
- one-way
- larger
Thoracic Duct
- formed from the joining of vessels in the posterior chest
- delivers the fluid into the left subclavian vein near the heart
- the point of connection between the lymphatic system and cardio system
What are the functions of the lymphatic system?
- equalization of fluid distribution
- transportation of biomolecules (fats from the digestive system into the bloodstream)
- immunity
Lacteals
small, lymphatic vessels located at the center of each villus in the small intestine
Chyle
lymphatic fluid carrying many chylomicrons, that has a milky-white appearance
