Immune System Part I Flashcards
what are the steps that occur after a cut/infection
- local infection, penetration of epithelium
- local infection of tissues
- lymphatic spread
- adaptive immunity
weapons of the immune system include:
- cells that kill or ingest infected or altered cells (CD8+ cytotoxic T-cells that kill virus infected cells)
- soluble proteins that can neutralize, immobilize, agglutinate, or kill pathogens (including antibodies and many others)
what is innate immunity
- nonspecific
- rapid response (hours)
- fixed
- limited number of specificities
- constant during response
what is adaptive immunity
- acquired
- involves B and T cells
- slow response (days to weeks)
- variable
- numerous highly selective specificities
- improve during response
what are white blood cells called
leukocytes
what is the purpose of red blood cells
transport oxygen and carbon dioxide
what are the 3 types of granulocytes and their purposes
- neutrophils: phagocytose and destroy invading bacteria
- eosinophils: destroy larger parasites and modulate allergic inflammatory responses
- basophils: release histamine in certain immune reactions
what are monocytes
become tissue macrophages, which phagocytose and digest invading foreign bodies
what are the 2 types of lymphocytes and their purposes
- B cells: make antibodies
- T cells: kill virus-infected cells and regulate activities of other leukocytes
what are natural killer cells
cells that kill virus infected cells and some tumour cells
what are platelets
cell fragments arising from megakaryocytes in bone marrow. initiate blood clotting.
what are the 2 circulatory systems
- cardiovascular
- lymphatic
interstitial fluid is returned to the bloodstream via the
lymphatic circulatory system
where does most of the immune action occur
in the lymph nodes
leukocytes:
- white blood cells
- circulate between the blood and the lymph
- includes: B cells and two types of T cells
how do the cells of the immune system get into the lymphatic system
by squeezing through specialized endothelial cells in lymph nodes
what happens after monocytes leave the bone marrow
- they circulate the bloodstream for ~8 hours
- they then migrate into tissues where they differentiate into tissue specific macrophages
differentiation of a monocyte into a macrophage involves:
- five to ten fold enlargement in cell size
- increased complexity and number of intracellular organelles
- increased phagocytic ability
tissue macrophages:
remain relatively fixed but can wander by amoeboid movement and in response to signals (2-4 month life span)
what does PAMPs stand for and what are they
Pathogen Associated Molecular Patterns, they are patterns on pathogen surfaces. They can be recognized by receptors on macrophage cell surfaces
what happens with PAMPS and macrophages
PAMPS on pathogens bind to pattern recognition receptors on macrophages. pathogens are then phagocytosed thereby activating the macrophage
what are three examples of PAMP receptors
- scavenger receptor
- mannose receptor
- toll-like receptors (TLR)
how do macrophages get activated
they remain in a resting state until they are activated by binding to a pathogen
what is the first cellular line of defence against a break in the epithelium, and what are the 2 primary functions of them
- macrophages
- 2 functions: phagocytosis and degradation of pathogen, activation of signal transduction pathway that generate inflammatory cytokines
cytokines:
substances secreted by cells of the immune system that have an effect on other cells
chemokines:
a type of cytokine that induce directed chemotaxis
how do macrophages act as antigen presenting cells
- a bacterium engulfed by a macrophage is encased in a vacuole (macrophages phagocytose pathogen)
- lysosomes fuse with the vacuole and digest the bacterium (digest pathogen)
- antigens from digested bacterium are presented to Helper T cells in the context of Class II MHC molecules
what are neutrophils
- most abundant granulocyte
- recognition of pathogen is similar to macrophages
- job is to kill pathogens (professional phagocytes)
- they do not present antigen
- extravasation into tissue at site of injury (in response to chemical signals secreted by other cells)
what are the 2 neutrophil killing mechanisms
- intracellular
- extracellular
leucocytosis:
transient increase in the number of circulating neutrophils is used as an indication of infection
dendritic cells:
- present antigens to T cells
what do dendritic cells do at the site of infection
- engulph pathogen by phagocytosis or pinocytosis
- after engulphing pathogen, they are induced to migrate via the afferent lymphatic vessels to the nearest regional lymph nodes
- in lymph nodes, they lose phagocytosis ability but gain the ability to present antigen to T cells
- they can present antigen in context of both Class I MHC and Class II MHC (cross presentation)
dendritic cells are an:
important link between the innate and adaptive immune system
what is the general immune response
- inflammatory response initiated by cytokine secretion from macrophages causes redness, heat, pain, swelling - which are needed to try and contain and eliminate the infection
- at the same time, signals are being sent to initiate a stronger immune response (adaptive immune response of T cells and B cells)
- adaptive immune response comes into play only if the innate immune response cannot clear the localized infection. adaptive response needs time to get ready to do this
B cell antigen receptor (BCR):
a membrane bound form of the antibody (immunoglobulin) the B cell will secrete after activation and differentiation
T cell antigen receptor (TCR):
does not recognize free antigen (pathogen), only antigen (piece of a pathogen) that is bound to an MHC molecule on an antigen presenting cell
Differentiate between B cells, TH cells, and TC cells
B cells: have an antigen binding receptor (antibody), have 1 specificity
T helper cells: are defined by the presence of the CD4 protein
Cytotoxic T cells: are defined by the presence of the CD8 protein
antigen antibody generator:
any molecule or molecular fragment that is either recognized by an antibody or a B cell receptor or can be bound by an MHC molecule and presented to a T cell receptor
epitope (antigenic determinant):
the portion of an antigenic molecule that is bound by an antibody or that is recognized by a T cell receptor in the context of presentation by an MHC molecule
lymphocytes:
- T cells and B cells
- released from the bone marrow
- very small cells with very few cytoplasmic organelles and condensed chromatin
what are lymphocytes when they first leave the bone marrow
inactive. they have no functional activity until they encounter an antigen
what is the general life cycle of a lymphocyte
- they circulate between blood and lymph
- if they encounter an antigen, they become effector cells
- if they don’t encounter an antigen, they undergo apoptosis
what happens when B cells are activated
they differentiate into plasma cells that make antibodies
what happens when an antigen/pathogen meets a B cell
- the B cell receptor will initially bind the antigen it is specific for and then phagocytose the antigen
- the antigen will be degraded and presented on the B cell surface in the context of class II MHC molecules to a helper T cell
- the helper T cell helps the B cell make antibodies
what are 3 examples of antigen presenting cells
- dendritic cells
- macrophages
- B-lymphocytes
cytotoxic T cells:
(CD8+) kill cells infected with virus
helper T cells:
regulate the activities of other white blood cells, help activate macrophages, B cells, and cytotoxic T cells
Class I MHC is always associated with:
CD8 and both are found on every nucleated cell in the body
Class II MHC is always associated with:
CD4 and is found only on professional antigen presenting cells: dendritic cells, macrophages, B cells
natural killer cells:
- circulate in the blood as large lymphocytes with distinct cytotoxic granules
- lack antigen specific receptors
- often first line of defense against some viruses
primary lymphoid tissue contains:
- bone marrow
- thymus
where do B cells and T cells mature
B cells: bone marrow
T cells: thymus
lymph nodes are an example of:
secondary lymphoid tissue
