Chapter 8: The Immune System Flashcards
Innate immune system
Composed of defenses that are always active against infection, but lack the ability to target specific invaders over others; AKA nonspecific immunity
Adaptive or specific immunity
Defences 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
Bone marrow
Produces all of the leukocytes (white blood cells) that participate in the immune system through the process of hematopoiesis
Spleen
Site of blood storage and activation of B-cells which turn into plasma cells to produce antibodies as part of adaptive immunity; when B-cells leave the bone marrow, they are considered mature but naive; humoral immunity
Thymus
Site of T-cell maturation; a small gland in front of the pericardium (sac that protects the heart); agents of cell-mediated immunity
Lymph nodes
A major component of the lymphatic system, provide a place for immune cells to communicate and mount an attack; B-cells can be activated here as well
GALT
Gut-associated lymphoid tissue; include tonsils and adenoids in the head
Peyer’s patches
In the small intestine
Appendix
Has lymphoid aggregates
Lymphocytes
Responsible for antibody production, immune system modulation, and targeted killing of infected cells
First line of defence
Skin (integument); physical barrier between the outside world and our internal organs, excluding most bacteria, viruses, fungi, and parasites from entering the body
Defensins
Antibacterial enzymes can be found on the skin
Complement
Consists of a number of proteins in the blood that act as a nonspecific defence against bacteria; punch holes in the cell walls of bacteria, making them osmotically unstable
Classical pathway
Requires the binding of an antibody to a pathogen
Alternative pathway
Does not require antibodies
Interferons
Proteins that prevent viral replication and dispersion; cause nearby cells to decrease production of both viral and cellular proteins; also decrease the permeability of these cells, making it harder for a virus to infect them; upregulate MHC class I and II molecules, resulting in increased antigen presentation and better detection of the infected cells by the immune system; responsible for “flu-like” symptoms
Macrophages
1) Phagocytize the pathogen
2) Digest the pathogen with enzymes
3) Present little pieces of the invader (mostly peptides) to other cells using a protein called the major histocompatibility complex (MHC) - binds to a pathogenic peptide (also called an antigen) and carries it to the cell surface; also release cytokines - chemical substances that stimulate inflammation and recruit additional immune cells to the area
MHC class I molecules
All nucleated cells in the body display MHC class I molecules; any protein produced within a cell can be loaded onto MHC-1 and presented on the surface of the cell; AKA endogenous pathway; allows for monitoring cell health; cells that have been invaded by intracellular pathogens can then be killed by a certain group of T-cells to prevent infection of other cells
MHC class II molecules
Mainly displayed by professional antigen-presenting cells like macrophages, dendritic cells in the skin, some B-cells and certain activated epithelial cells; AKA exogenous pathway; may result in activation of both the innate and adaptive immune systems
Pattern recognition receptors
Special receptors on macrophages and dendritic cells; best described are toll-like receptors; able to recognize the category of the invader and allows for the production of appropriate cytokines to recruit the right type of immune cells
Natural killer cells
Protect against cancer and virally infected cells; detect the downregulation of MHC and induced apoptosis
Neutrophils
Most populous leukocyte in the blood and are very short-lived (a bit more than five days); phagocytic and target bacteria; can follow bacteria via chemotaxis; can also detect bacteria that have been opsonized; dead neutrophils = pus
Eosinophils
Contain bright orange-red granules and are primarily involved in allergic reactions and invasive parasitic infections; release large amounts of histamine when activated; increased vasodilation and increased leakiness of the blood vessels, allowing additional immune cells (especially macrophages and neutrophils) to move out of the bloodstream and into the tissue; inflammation is particularly useful against extracellular pathogens including bacteria fungi, and viruses
Basophils
Large purple granules and are involved in allergic reactions; least populous leukocyte in the bloodstream; mast cells are 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, leading to inflammatory response
What happens when an antigen binds to the surface of a mast cell?
Degranulation - exocytosis of granule contents, allowing the release of histamine and causing an inflammatory allergic reaction
Hypermutation
B-cells undergo hypermutation of its antigen-binding region at the end of what is called the variable region (domain) at the tips of the Y
Clonal selection
Only those B-cells that can bind the antigen with high affinity survive, providing a mechanism for generating specificity
Constant region
The region that natural killer cells, macrophages, monocytes, and eosinophils have receptors for, and can initiate the complement cascade; note that each B-cell make only one type of antibody but we have many B-cells
What are the five different isotypes of antibodies?
IgM, IgD, IgG, IgE, and IgA
Isotype switching
Cells can change which isotype of antibody they produce when stimulated by specific cytokines
Primary response
Initial activation takes 7-10 days
Secondary response
More rapid and robust due to memory cells
Positive selection
Maturing only cells that can respond to the presentation of antigen on MHC (cells that cannot respond to MHC undergo apoptosis because they will not be able to respond in the periphery)
Negative selection
Causing apoptosis in cells that are self-reactive (activated by proteins produced by the organism itself)
Thymosin
Peptide hormone secreted by thymic cells that facilitates maturation of T-cells ; once the T-cell has left the thymus, it is mature but naive; upon exposure to antigen, T-cells will also undergo clonal selection so that only those with the highest affinity for a given antigen proliferate
Helper T-cells
CD4+ T-cells; coordinate the immune response by secreting chemicals known as lymphokines - molecules capable of recruiting other immune cells (plasma cells, cytotoxic T-cells, and macrophages) and increasing their activity
HIV
Human immunodeficiency virus infection; prevents the immune system from mounting an adequate response to infection; loss of CD4+ cells
AIDS
Acquired immunodeficiency syndrome; even weak pathogens can cause devastating consequences as opportunistic infections
What stimulates CD4+ cells?
CD4+ T-cells respond to antigens presented on MHC-II molecules; MHC-II presents exogenous antigens, CD4+ T-cells are most effective against bacterial, fungal, and parasitic infections
Cytotoxic T-cells
CTL or Tc cells or CD8+ T-cells are capable of directly killing virally infected cells by injecting toxic chemicals that promote apoptosis into the infected cell; CD8+ T-cells respond to antigens presented on MHC-I molecules - endogenous antigens; CD8+ T-cells are most effective against viral (and intracellular bacterial or fungal) infections
Suppressor or regulatory T-cells
Also express CD4 but can be differentiated from helper T-cells because they also express a protein called Foxp3; cells help to tone down the immune response once infection has been adequately contained; also turn off self-reactive T lymphocytes to prevent autoimmune disease - self tolerance
Memory T-cells
Cells lie in wait until the next exposure to the same antigen; when activated, they result in a more robust and rapid response
Bacterial (Extracellular) infections
1) Macrophages and other APCs engulf the bacteria and subsequently release inflammatory mediators and present antigens on their surface (MHC-II)
2) Cytokines attract inflammatory cells, including neutrophils and additional macrophages
3) Mast cells are activated by the inflammation and degranulate, resulting in histamine release and increased leakiness of capillaries
4) Allows immune cells to leave the bloodstream to travel to the affected tissue
5) Dendritic cells then leave the affected tissue and travels to the nearest lymph node where it presents the antigen to B-cells
6) B-cells that produce the correct antibody proliferate through clonal selection to create plasma cells and memory cells - antibodies then travel through the bloodstream to the affected tissue, where they tag the bacteria for destruction
7) Dendritic cells also activate T-cells (particularly CD4+ cells) - two types: Th1 cells release interferon gamma which activates macrophages and increases their ability to kill bacteria and Th2 cells which help activate B-cells
Viral (intracellular pathogen) infections
The virally-infected cell will begin to produce interferons, which reduce the permeability of nearby cells (decreasing the ability of the virus to infect these cells), reduce the rate of transcription and translation in these cells (decreasing the ability of the virus to multiple_ and cause systemic symptoms (malaise, muscle aching, fever, and so on); these infected cells also present intracellular proteins on their surface in conjunction with MHC-I; CD8+ T-cells will recognize the MHC-I and antigen complex as foreign and will inject toxins into the cell to promote apoptosis; the infection can be shut down before it is able to spread to nearby cells; natural killer cells will recognize the absence of MHC-I and will accordingly cause apoptosis of this cell
Self-antigens
Proteins and carbohydrates present on the surface of every cell of the body; under normal conditions, these self-antigens signal to immune cells that the cell is not threatening and should not be attacked; when the immune system fails to make the distinction between self and foreign, it may attack cells expressing particular self-antigens - autoimmunity
Hypersensitivity reactions
Allergies and autoimmunity
Active immunity
The immune system is stimulated to produce antibodies against a particular pathogen; natural exposure - antibodies are generated by B-cells once an individual becomes infected; artificial exposure - vaccines with a weakened or killed form of the microbe or a part of the microbe’s protein structure
Passive immunity
Transfer of antibodies to an individual
Lymph nodes
Small, bean-shaped structures along the lymphatic vessels; contain a lymphatic channel as well as an artery and a vein; the lymph nodes provide a space for the cells of the immune system to be exposed to possible pathogens
Functions of the lymphatic system
1) Equalization of fluid distribution - net pressure drawing fluid into the vessel at the venule end is slightly less than the the net pressure pushing fluid out at the arterial end; lymphatic vessels drain these tissues and subsequently return the fluid to the bloodstream (prevents edema)
2) Transportation of biomolecules - the lymphatic system transports fats from the digestive system into the bloodstream
3) Immunity
Germinal center
Site where B-cells proliferate and mature in the lymph nodes in collections
