The Immune System Flashcards
Innate Immunity: Nonspecific Defense of the Host
Refers to the line of defenses that are present at birth. They are always present and provide immediate protection to sites of infection. It does not involve specific recognition of a microbe and does not have a memory response (immunological memory).
Component(s) of Innate Immunity
First Line of Defense (e.g. skin and mucous membranes)
Second Line of Defense (e.g. natural killer cells, phagocytes, inflammation, fever, and antimicrobial substances)
Adaptive Immunity: Specific Defense of the Host
Based on a specific response to a specific microbe once a microbe has breached the innate immunity defenses. It provides a slower response to sites of infection and does contain a memory response (immunological memory).
Component(s) of Adaptive Immunity
Third Line of Defense (e.g. specialized lymphocytes, T cells, B cells, and antibodies)
Activation of Innate Immune Response
Activated by the protein receptors in the plasma membrane of defensive cells. Protein receptors attach to PAMP’s found on the surface of pathogens. Attachment to PAMP’s induce defensive cells to release cytokines.
Protein Receptors = TLR’s
PAMP’s = lipopolysaccharide of gram (-) species; peptidoglycan of gram (+) species; flagellin of flagella; DNA or RNA; fungal and parasitic components
Cytokine
A small protein released from human cells that regulate the intensity and duration of an immune response. It’s role is to recruit macrophages, dendritic cells, and other defensive cells to isolate and destroy the microbes as part of the inflammatory response. It may directly or indirectly induce fever and pain as well as T cell or B cell proliferation involved in Adaptive Immunity.
Divisions of the Immune System
Innate Immunity and Specific Immunity
The Cells of Innate Immunity
Macrophages, Mast Cell, Granulocytes, Dendritic Cells, Natural Killer Cells
Macrophages
Cells of the innate immunity. They are a type of agranulocyte that are derived from monocytes and reside within tissues. Their function is to ingest pathogens and present them on major histocompatibility complex (MCH) molecules. They also secrete cytokines.
Examples of Macrophages
- Microglia in the CNS
- Langerhans cells in the skin
- Osteoclasts in the bone
Mechanism of Macrophages
- Phagocytizes pathogen via endocytosis
- Digests pathogen via enzymes
- Presents peptides of pathogen to other cells via MHC
Phagocytosis
An important second line of defense. The phases of phagocytosis are as followed:
- Chemotaxis
- Adherence
- Ingestion
- Digestion
Chemotaxis
First phase of phagocytosis. Occurs when chemotactic chemicals attract phagocytes to pathogens. Examples of chemotactic chemicals include:
- microbial products
- components of WBC’s
- damaged tissue cells
- cytokines
- peptides derived from complement
Adherence
Second phase of phagocytosis. Occurs when the phagocytes plasma membrane attaches to the surface of a pathogen. Examples include:
- Binding of PAMP’s to TRL’s
- Opsonization
Ingestion
The third phase of phagocytosis. Occurs when the phagocytes plasma membrane extends pseudopods to engulf the pathogen creating a phagosome. The phagosome membrane contains enzymes that pumps protons inside the phagosome reducing the pH and activating hydrolytic enzymes.
Digestion
The fourth phase of phagocytosis. Occurs when the phagosome pinches off the plasma membrane and enters the cytoplasm where it binds to lysosomes, forming a phagolysosome. Digestive enzymes of the phagolysosome attack the pathogen and the residual body is moved to the cell boundary for waste discharge outside the cell.
Major Histocompatibility Complex (MHC)
Set of cell surface molecules. It’s function is to bind to peptide fragments derived from pathogens and display them on the cell surface for recognition by T cells. MHC molecules come in two main classes:
- MHC-I
- MHC-II
MHC-I Molecules
Present in all nucleated cells and displays endogenous antigen (proteins from within the cell) to cytotoxic T-cells (CD8+ cells).
MHC-II Molecules
Present in professional antigen-presenting cells (e.g. macrophages, dendritic cells, B-cells, and epithelial cells) and displays exogenous antigen (proteins from outside the cell) to helper T-cells (CD4+ cells).
Pattern Recognition Receptors (PPR’s)
Proteins expressed by innate immune cells (e.g. macrophages and dendritic cells) capable of recognizing PAMP’s on pathogens.
An example of a PPR are toll-like receptors (TLR’s).
Natural Killer Cells
Cells of the innate immune system. They are a type of nonspecific lymphocyte capable of detecting downregulation of MHC and induce apoptosis in pathogens.
Granulocytes
Cells of the innate immune system. Include basophils, eosinophils, and neutrophils.
Mnemonic: BEN
Neutrophil Granulocyte
Most abundant WBC (leukocyte) in the blood and are short lived; lifespan of 5 days. They are phagocytic and are capable of following bacteria via chemotaxis.
Eosinophil Granulocyte
Primarily involved in allergic reactions and invasive parasitic infections. Activation causes these cells to release histamine, an inflammatory mediator, causing vasodilation and passage of macrophages and neutrophils into tissue.
Basophil Granulocyte
Least abundant WBC (leukocyte) in blood. Primarily involved in allergic responses and parasitic infections. They contain both histamine and the anticoagulant heparin, which prevents blood from clotting too quickly.
Mast Cells
Similar in appearance and function to Basophil Granulocytes. However, they arise from different cells lines and do not circulate in the bloodstream, but instead are located in connective tissue.
Adaptive Immune System: Humoral Immunity
Aspect of immunity that is mediated by antibodies, complement proteins, and antimicrobial peptides found in extracellular fluids. Mainly centered on antibody production by plasma cells, which are activated by B-cells.
Adaptive Immune System: Cell-Mediated (Cytotoxic) Immunity
Aspect of immunity that involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of cytokines in response to an antigen. Mainly centered on the functions of the T-cell.
B-cells
Cell of the adaptive immunity that governs the humoral response. B-cells are both created and mature in the bone marrow. Activated in the spleen and lymph nodes.
T-cells
Cells of adaptive immunity that mount the cell-mediated (cytotoxic) response. T-cells are created in the bone marrow but mature in the thymus.
Antibodies
Also called immunoglobins [Ig] and are large Y-shaped proteins made up of two identical heavy chains and two identical light chains held together by disulfide linkages and noncovalent interactions. Functions of antibodies vary based on location:
- antibodies in body fluid
- antibodies on cell-surface
Function(s) of Body Fluid Antibodies
Opsonization, agglutination, neutralization
Function(s) of Cell-Surface Antibodies
Degranulation (exocytosis of granule bodies), allowing release of histamine and causing inflammatory allergic reaction.
Variable Region (Antigen-Binding Region)
A region located within an antibody that contains specific polypeptide sequences capable of binding to only one specific antigenic sequence (antigen). Once activated, this region undergoes hypermutation to improve the specificity of the antibody produced.
Constant Region
A region located within an antibody and is responsible for determining the mechanism used to destroy an antigen (e.g. natural killer cells, macrophages, monocytes, and eosinophils) initiating the complement cascade.
Antibody Isotopes
IgM, IgD, IgG, IgE, IgA
Mnemonic: MEGA D
Def.) Somatic Hypermutation
Cellular mechanism by which the immune system adapts to new foreign elements that confront it.
Def.) Isotype Switching
Cellular mechanism by which immune cells change which isotype of antibody they produce stimulated by specific cytokines.
Naive B-Cells
B-cells which have not yet been exposed to an antigen. These cells remain in the lymph nodes for their particular antigen to come along. Upon contact with their antigen, they will proliferate into two daughter cells:
- Plasma Cells
- Memory B-Cells
Plasma Cells
One of two daughter cells of naive B-cells responsible for producing large amounts of antibodies. Plasma cells will eventually die.
Memory B-cells
One of two daughter cells of naive B-cells responsible for remaining in lymph nodes until reexposure to same antigen. Memory B-cells may last the lifetime of an organism.
