Immune System Flashcards
what are the three types of immunity?
innate (general), humoral (specific, B cells/antibodies), cell-mediated (specific, T cells/killers)
innate immunity
general, nonspecific protection of the body against various invaders, rapid (ex. skin, lysozyme, acidity, macrophages/neutrophils, complement system that can nonspecifically bind foreign cells for destruction)
humoral immunity
specific protection by antibody proteins (immunoglobulins) that specifically recognize and bind to microorganisms leading to their destruction and removal from the body
what is the structure of antibodies?
two copies of both light chains and heavy chains joined by disulfide bond, contains a constant region (defines antibody class, ex. IgG, IgA, IgM, IgD, IgE) and variable region (antigen binding region)
IgM
found in blood and B cell surface, involved in initial immune response, pentameric structure in blood, monomeric structure on B cell as antigen receptor
IgG
found in blood, involved in ongoing immune response, the majority of antibody in the blood is IgG, can cross the placental barrier
IgD
found on B cell surface, serves with IgM as antigen receptor on B cells
IgA
found in secretions (saliva, mucus, tears, breast milk), secreted in breast milk; helps protein newborns, dimeric structure
IgE
found in blood, involved in allergic reactions
antigen (Ag)
the molecule that an antibody binds to
what determines the specificity of antigen binding?
the fit of antigen in a small three-dimensional cleft formed by the variable region of the antibody protein
epitope
the small site that an antibody recognizes within a larger molecule (i.e. an antigen can have multiple recognition sites for different antibodies)
can very small molecules elicit antibody production?
no, unless bound to an antigenic large molecule in which the small molecule becomes antigenic and is known as a hapten
when are the 3 possible outcomes when an antibody binds to an antigen?
1) directly inactivate the antigen (ex. can’t bind or enter cells)
2) induce phagocytosis by macrophages and neutrophils
3) antibodies on surface can activate the complement system to form holes in the cell membrane and lyse the cell
primary immune response
the first time a person encounters an antigen during infection, in which there is a time interval for B cells to proliferate and secrete antibodies
secondary immune response
swifter and stronger than primary immune response, symptoms don’t develop, B memory cells become activated and start producing antibodies
clonal selection
method of selecting B cells (or T cells) with specific antigen binding
what are characteristics of B cells?
- immature B cells derived from stem cells in bone marrow
- genes encoding antibody proteins assembled by recombination, so many different B cell clones with different variable regions exist
- immature B cells express antibody molecules on the surface
- when antigen binds to antibody, immature cell is stimulated to proliferate and differentiate into plasma cells (actively produce and secrete antibody proteins) and memory cells (pre-activated, dormant B cells with antibody on membrane surface)
- actually activated by T helpers that recognize MHCII and release cytokine factors (lymphokines and interleukins) that activate B cell proliferation
vaccination
used to improve the response to infection by exposing the immune system to an antigen associated with a virus or bacteria, thus building up the secondary immune response if the live pathogen is encountered in the future
what are the two types of t cells?
T helpers (CD4-associate with alarm, MHCII) and T killer (cytotoxic T cells, CD8 cells, MHCI)
where to T cells develop?
derived from bone marrow but develop in the thymus during childhood (thymosin hormone)
what is the role of T killer cells?
to destroy abnormal host cells
characteristics of T cells
- antigen-binding site is specific and also formed from recombination
- recognizes cell by binding to both the antigen and MHC complex
major histocompatibility complex (MHC)
cell-surface proteins that are recognized and monitored by the immune system for foreign agents in the cell, two types (MHCI and MHCII)
MHC I
found on the surface of every nucleated cell, randomly picks up peptides from inside of the cell and displays them on the cell surface, specifically recognized by T killer cells
MHC II
only antigen-presenting cells (APC’s) have MHCII, including macrophages and B cells which phagocytize particles or cells and displays fragments, recognized and bound by T helpers which then activate B cells and T killer cells
bone marrow
the site of synthesis of all cells of the blood from a common progenitor
spleen
filters the blood and is a site of immune cell interaction (similar to lymph nodes), also destroys aged RBCs
thymus
site of T cell maturation, shrinks in adults, most active in children
tonsils
masses of lymphatic tissue in the back of the throat that help to catch pathogens which enter the body through respiration or ingestion
appendix
similar to tonsils, mass of lymphatic tissue at the beginning of the large intestine that help to catch pathogens
why are the tonsils and appendix often removed?
because both are not required for survival and can become infected
tolerance
ability of the immune system to only recognize and destroy foreign antigen while ignoring all normal proteins and cell structures
how to ensure B cells and T cells don’t destroy own cells?
recombination can produce self antigens, thus a selection process is undergone to eliminate any self-reactive cell. selection present in the bone marrow and lymph nodes, if binds to normal cell surface proteins (apoptosis) or bind to normal soluble proteins (unresponsive, anergic)
B cell or T cell clone
B or T cells that are identical and specific to a particular antigen, formed by proliferation stimulated by antigen in a specific context
autoimmune reaction
immune system attacks normal body cells or proteins
