Chapter 17 Flashcards
adaptive immunity
- also specific immunity or acquired immunity
- it is immunity that is adapted to a particular microbial invader or foreign substance
Humoral immunity (type of adaptive immunity)
- involves the production of antibodies by the B-cells in response to a foreign invader
- antibody mediated
- B cells produce Ab in response to antigens
- antibodies defend against bacteria, viruses and toxins that are circulating freely in the blood plasma
Cell-mediated immunity (type of adaptive immunity)
- involves protection by activated T-cells
- depends on T cells and does not use antibodies
- response to invasion of intracellular bacteria and viruses located in phagocytic cells and infected cells, fungi, cancer cells and transplant tissue
naturally acquired (4 types of acquired (adaptive immunity)
- active immunity- antigens enter body and the body produces Ab and activated T-cells
- ex: Ag- bacteria and viruses
- passive immunity- Ab pass from mother to fetus via the placenta or breast milk
- mother is exposed to community diseases and makes Ab so fetus/ newborn is protected from the “current” disease in the community
- first breast milk produced after birth, colostrum, has high concentration of Ab
Artificially acquired (4 types of acquired (adaptive) immunity)
- active immunity- can receive vaccines and the body produces Ab and specialized lymphocytes
- passive immunity- preformed Ab given as injection to provide temporary protection
- Ab obtained from people who have had the disease and their body made Ab
- short-term protection because the Ab break down after a period of time and are not replaced w/o another injection
vaccines
- killed microbes (heat or chemicals)
- toxoid- inactivated toxin
- attenuated (weakened) live microbes
- provide long-term protection
- may need boosters
antigens
- usually foreign substances
- large molecules: M.W, > 10,000
- antigenic determinants or epitopes are specific regions of the antigen that react w/ antibodies
- example: bacterial cell has several epitopes on surface -> several types of Ab will be made against the bacterial cell
- smaller molecules do not stimulate Ab production but can combine w/ a larger molecule such as a protein and stimulate Ab production
- ex of Ag: bacterial capsules, cell walls, flagella, fimbriae
- viral capsid and envelope
- pollen transplanted tissue
Hapten (antigen)
low M.W. molecule that isn’t antigenic unless combined w/ a carrier molecule
antibodies
- antibody= immunoglobin
- antibody is a large protein molecule produced by B cells in response to the presence of an antigen
- are highly specific and can combine w/ the type of antigen that stimulated its production
- Ab neutralize or help destroy the Ag
- very specific and only bind to one type of Ag
Antibodies (4 polypeptide chains)
- 2 identical heavy chains
- 2 identical light chains
- chains linked with disulfide bonds (-S-S-)
- variable region- unique for the Ag that the Ab binds to
- constant region same for all of a persons Ab
five classes
- IgG
- IgM
- IgA
- IgD
- IgE
-some are monomers, dimers and pentamers
development of B and T cells
- both develop from stem cells in bone marrow (adult) and liver (fetus)
- site of final maturation determines which type of cell will be produced
- stem cells that migrate to the thymus become T-cells
- cells that remain in the bone marrow become B-cells
B-cells
- mature B-cell has about 100,000 IgM and IgD antibodies on the surface of the cell
- mature B cells migrate to the lymph nodes and spleen
- these Ab are specific for the same epitope
- when the Ab detect and bind with the Ag for which they are specific, B cell is activated
- activated C cell undergo clonal expansion or proliferation
activation of B cells
- all cells in the body have markers that identify the cell as belonging to the host. sometimes called “self” markers
- molecules are called major histocompatibility complex (MHC)
- MCH II found on antigen presenting cells- those cells that phagocytosize antigens and embed pieces of the antigen in their cell membrane
- MHC I- found on other cells in the body
-the B cell that is activated by the AG will engulf the antigen and present the Ag on the cell membrane with the MHC II
activation of B cells cont.
- the receptor on the T helper cell recognizes the MHCII + Ag fragment and is activated
- T helper needs both the Ag and MHC II for activation
- T helper produces cytokines (chemical messengers) which in turn activate the B cell
- activated B cell begins clonal expansion
- some B cells mature into plasma cells which produce Ab
Clonal selection
-stem cells -> B cells
-B cells are each specific for one antigen
-millions of diff B cells specific for one type of antigen
when the B cell attaches to the antigen for which it is specific, the B cell becomes activated
-cell divides
-some cells become long-lived memory cells which will detect the antigen in the future
-some B cells proliferate into plasma cells
-plasma cells secrete large amounts of Ab specific for the antigen
-secrete 2000 Ab per second
-plasma cell lives only a few days
clonal selection :end
- some B cells and T cells may become sensitized against the hosts own cells; they do not have self tolerance
- in these cases the B and T cells do not recognize “self”
- B and T cells are destroyed by a process called clonal deletion
apoptosis
- Human body makes 100 million lymphocytes/day so an equal number must die
- B cells that do not encounter an antigen under go programmed cell death: called apoptosis
Some diseases are linked to malfunctions of apoptosis
AIDS –excess apoptosis
Leukemia – too little apoptosis
capases (apoptosis)
family of enzymes responsible
cell death (apoptosis)
genome cut into pieces; membranes bulge called blebbing
outcomes of Ab-Ag binding
- Agglutination
- Opsonization
- Antibody-dependent cell-mediated cytotoxicity
- Neutralization
- Activation of complement
- Inflammation – due to complement
See Figure
immunological memory
-Ab titer is the concentration of Ab in the serum
-Primary response:
Takes a few days for Ab to be produced
First Ab produced is IgM; second produced is IgG
Then gradual decline in titer
-Secondary response Anamnestic response After 2nd exposure Due to memory B cells Quicker response and higher levels of IgG Ab produced May occur weeks, months or years later
monoclonal Ab
- Culture of cells that produce only one type of antibody
- Normally would get a mix of B cells producing a mix of Ab if just sampled the spleen
- Made from hybridomas: myeloma cells + spleen cells (which have some B cells mixed in)
- Monoclonal Ab called Mabs
- Originally made with mouse cells so there were allergic reactions
- Goal to make fully human antibodies
- Having a source Ab that is pure has enabled rapid tests to be developed for the clinical diagnostic lab
- Pure Ab produced by the hybridomas
Examples:
Pregnancy test
Diagnosis of disease
T cells and Cell-mediated immunity
- Involves specialized lymphocytes, primarily T cells, that respond to intracellular antigens
- Defends against bacteria and viruses that have invaded cells, fungi, protozoans, helminths (parasites), tissue grafts, and cancer cells
- Cytokines – chemical messengers produced by T cells
cytokines
-chemical messengers produced by T cells
4 main functional groups of cells
Helper T cells – central role in immune response, TH
Cytotoxic T cells – destroy target cells on contact, TC
Delayed hypersensitivity T cells – certain allergic reactions
Suppressor T cells – turn off immune response when antigen not present
Can also classify the cells based on cell-surface receptor, CD -clusters of differentiation
CD4 cells are primarily helper T cells and include the long-lived memory cells
CD8 cells become cytotoxic T lymphocytes
development of T cells
- T cells develop from stem cells in the bone marrow or fetal liver
- The stem cells migrate to the thymus where they differentiate into T cells
- T cells then migrate to the lymph nodes, spleen and lymph system and the Peyer’s patches of the gastrointestional tract
- Peyer’s patches are secondary lymph tissue
Cytokines
- Chemical messengers produced by T cells
- Interleukins- communication between white blood cells
- Interferons – protect cells against viral infections
- Chemokines – induce migration of leukocytes into infected areas
- TNF – tumor necrosis factor – involved in inflammatory response
T cells and Antigen Presenting cells
- T cells recognize antigens only when they have been processed by an antigen presenting cell, APC
- APC include macrophage, dendritic cells, and B cells
- Cell engulfs the antigen, digests it into pieces, and combines the pieces with the MHC II molecules on the cell membrane
antigen presenting cells -APC’s
- Three types of cells can serve as APC’s
- B cells
- Macrophage
- Dendritic cells
- The antigens are presented with MHC II receptors on the cell surface
- Antigen presentation necessary to activate T cells
T-cells and Antigen Presenting Cells
- TH, T helper cells (CD4 T cells) have receptors on the cell surface
- The TH cells have been sensitized to a specific antigen
- The TH cell receptor encounters the Ag-MHC II complex, it binds
- The APC produces a cytokine that stimulates the T cell and then the T cell produces cytokines of its own
- T cell proliferates to produce memory cells and effector cells (another term for “functional” cells)
T helper cells
- After activation the TH cells differentiate into TH1 cells, TH2 cells, and memory cells
- TH 1 cells – activate cells in cellular immunity
- Macrophage
- CD8 cells (cytotoxic cells)
- Natural killer cells
- TH2 cells – produce cytokines related to allergic reactions and parasitic infections
Cytotoxic T cells
- Cytotoxic T cells, CD8, are precursors to cytotoxic T lumphocytes, CTLs
- A CTL is an effector cell that attacks cells that are “non-self”
- Examples of non-self cells are cells infected by bacteria and viruses, tumor cells, and transplanted tissue cells
- After the cytotoxic T cell, CD8, detects the antigen-MHC I complex on the cell surface, it differentiates into a CTL
Cytotoxic T cells cont.
- The CTL attaches to the target cell and releases a pore-forming protein, perforin
- Perforin causes a hole to form in the target cell
- Granzymes, protease enzymes that cause apoptosis, enter target cell through pore
- Apoptosiss occurs
both T and B lymphocytes divide
- B cells -> plasma cells + memory cells
- T cells -> activate T cells + memory cells
Humeral vs. Cell-mediated immunity
- activated B cells -> plasma cells -? produce Ab against original Ab
- activated T cells -> regulate and participate in specific immune response
Products of B lymphocytes : Antibody Structure and Functions
- Progeny of dividing B-cell clone are
- plasma cells -> antibodies
- B memory cell
- B regulatory cells
- plasma cells programmed to synthesize and secrete antibodies into tissue fluid and blood
- when antibodies attach to antigen, the antigen is marked for destruction or neutralization
- humeral immunity
How T cells Respond to Antigen: cell mediated immunity (CMI)
- when activated by antigen, T cell gives rise to one of three different types of progeny
- Th1 cells- activate macrophages and help Tc cells
- Tb2 cells- assist B-cell processes
- Tc cells- lead to the destruction of infected host cells and other “foreign cells”
- plus T regulatory and T memory cells
Epitope (antigens: size and shape)
- portion of the antigen (amino acids) recognized by lymphocyte receptor
- large foreign objects such as bacteria may have several types of antigenic determinants on them (flagella, capsule, cell surface)
Haptens (antigens: size and shape)
-antigens that are too small to elicit an immune response
antigen presenting cells - APC’s
- during B cell activation, the B cell engulfed the antigen and “presented” the antigen on the cell surface
- the T cell recognized the “presented” antigen and was activated
- in most immune reactions, the antigen must be presented to the lymphocyte
3 types of cells that can serve as APC’s
- B cells
- Macrophage
- 3.dendritic cells
- antigens are presented with MHC II receptors on the cell surface
- antigen presentation necessary to activate T cells
