Immune System Flashcards
Spleen’s function in immune system
Location of blood storage and activation of B-cells, which turn into plasma cells to produce antibodies as part of adaptive immunity.
Also acts as a storage area for white blood cells and platelets, and a filter of blood and lymph for the immune system.
Gut-associated lymphoid tissue (GALT)
Immune tissue found in close proximity to the digestive system, and is a site of potential invasion by pathogens.
Includes tonsils and adenoids in the head, Peyer’s patches in the small intestine, and lymphoid aggregates in the appendix.
Hematopoietic stem cells
Give rise to granulocytes and agranulocytes, and gives rise to red blood cells and platelets.
Defensins
Antibacterial enzymes found on the skin.
Complement system
Consists of a number of proteins in the blood that act as a nonspecific defense against the bacteria.
How can the complement system be activated
Through a classical pathway (which requires the binding of an antibody to a pathogen) or an alternative pathway (which does not require antibodies).
How does complement system work
Complement proteins punch holes in the cell walls of bacteria, making them osmotically unstable. Considered nonspecific defense because it cannot be modified to target a specific organism over others.
Interferons
Proteins that prevent viral replication and dispersion, and are produced by cells that have been infected with viruses.
Interferons also upregulate MHC class I and class II molecules, resulting in increased antigen presentation and better detection of the infected cells by the immune system.
Also responsible for many “flu-like” symptoms.
What are the 3 things an activated macrophage does.
- It phagocytizes the invader through endocytosis.
- Digests invader using enzymes
- Presents little pieces of invader (mostly peptides) to other cells using a protein called major histocompatibility complex (MHC).
Major histocompatibility complex (MHC)
Binds to a pathogenic peptide (antigen) and carries it to the cells surface, where it can be recognized by cells of the adaptive immune system. Comes in class I and II
MHC class I molecules
Present in all nucleated cells in the body. Only those cells that are infected would be expected to present an unfamiliar (nonself) protein on their surfaces.
The MHC-I pathway is often called what, and why
Often called the endogenous pathway because it binds antigens that come from inside the cell.
MHC class II molecules
Mainly displayed by professional antigen-presenting cells like macrophages. They pick up pathogens from the environment, process them, and then present them on MHC-II.
THe MHC II pathway is often called what, and why
The exogenous pathway, because these antigens originated outside the cell.
Pattern recognition receptors (PRR), including toll-like receptors (TLR)
Receptors present on macrophages and dendritic cells that are able to recognize the category of the invader (bacterium, virus, fungus, or parasite).
Natural killer (NK) 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 blood –> phagocytic and target bacteria using chemotaxis. Dead neutrophil collections responsible for pus formation
Eosinophils
Contain bright red-orange granules and are primarily involved in allergic reactions and invasive parasitic infections. –> release histamine
Basophils
Contain large purple granules and are involved in allergic responses –> least populous leukocyte in bloodstream under normal conditions
Mast cells
Closely related to basophils, but have smaller granules and exist in tissues, mucosa, and epithelium. Also release histamines.
Where do B-cells and T-cells mature, respectively
B-cells mature in the bone marrow, and T-cells mature in the thymus
What is humoral immunity and how long does it take to become effective
Involves the production of antibodies, and may take as long as a week to become fully effective after initial infection. Antibodies are produced by B-cells
What is another name for antibodies
Immunoglobulins (Ig)
For antibodies secreted into bodily fluids, what are 3 main possibilities of course of action
- Opsonization: when an antibody binds to an antigen, antibodies may attract other leukocytes to phagocytize those antigens immediately.
- Antibodies may cause pathogens to clump together or agglutinate, forming large insoluble complexes that can be phagocytized.
- Antibodies can block to the ability of a pathogen to invade tissues, essentially neutralizing it
Degranulation
Exocytosis of granule contents
What is the reason it takes so long to initiate the antibody response
Each B-cell undergoes hypermutation of its antigen-binding region, trying to find the best match for the antigen. Only those B-cells that can bind the antigen with high affinity survive, providing a mechanism for generating specificity called clonal selection
Variable region (domain)
Antigen-binding region at the end of each antibody. Within this region, there are specific polypeptide sequences that will bind one, and only one, specific antigenic sequence.
Isotype switching
Cells can change which isotype of antibody they produce when stimulated by specific cytokines.
What happens to naive B-cells when exposed to the correct antigen
B-cell will proliferate and produce 2 types of daughter cells.
Plasma cells produce large amounts of antibodies
Memory B-cells stay in the lymph node, awaiting reexposure to the same antigen.
Primary response
Initial activation takes approximately 7-10 days
Secondary response
The immune response that is more rapid and response: occurs if the same microbe is ever encountered again –> the memory cells jump into action and produce the antibodies specific to that pathogen.
What are the 2 types of selection T-cells undergo
Positive and negative selection
Positive selection
Refers to allowing only the maturation of cells that can respond to the presentation of antigen on MHC.
Negative selection
Refers to causing apoptosis in cells that are self-reactive (activated by proteins produced by the organism itself).
Thymosin
A peptide hormone secreted by thymic cells –> facilitated by maturation of T-cells
What are the 3 major types of T-cells
Helper T-cells (Th) also called CD4+ T-cells, suppressor T-cells, and killer (cytotoxic) T-cells
Helper T-cells (Th) / CD4+ T-cells
Coordinate the immune response by secreting chemicals known as lymphokines. These molecules are capable of recruiting other immune cells and increasing their activity.
CD4+ T-cells respond to antigens presented on MHC-II molecules –> better at fighting extracellular infections
Cytotoxic T-cells/also CD8+ T-cells
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 the MHC-I molecules –> most effective against viral and intracellular infections.
Suppressor or regulatory T-cells (Treg)
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
Similar to memory B-cells, these cells lie in wait until the next exposure to the same antigen. When activated, they carry out a more robust and rapid response.
5 types of infectious pathogens
Bacteria, viruses, fungi, parasites, and prions
Self-antigens
The proteins and carbohydrates present on the surface of every cell of the body.
Hypersensitivity reactions
Part of a family of immune reactions including allergies and autoimmunity
How does the human body try to prevent autoimmune reactions
Negative selection of T-cells in thymus: elimination of T-cells that respond to self-antigens. And
Immature B-cells that respond to self-antigens are eliminated before they leave the bone marrow
Active immunity
The immune system is stimulated to produce antibodies against a specific pathogen
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.
Basic structure of lymphatic system
Made up of one-way vessels that become larger as they move toward the center of the body. These vessels carry lymphatic fluid (lymph) and most join to form a large thoracic duct in the posterior chest, which then delivers the fluid into the left subclavian vein (near the heart).
Lymph nodes
Small, bean-shaped structures along the lymphatic vessels. Lymph nodes contain a lymphatic channel, as well as an artery and a vein.
They provide a space for cells of the immune system to be exposed to possible pathogens.
Purpose of lymphatic system in fluid distribution
They help drain tissues and subsequently return the fluid to the bloodstream
Lacteals
Small lymphatic vesssels –> located at the center of each villus in the small intestine. Fats, pachaged into chylomicrons by intestinal mucosal cells, enter the lacteal for transport.
Germinal centers
Collections in the lymph nodes where B-cells proliferate and mature
