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Naturally acquired active immunity?
- Body responds to pathogens, other antigens by mounting a specific immune response
- Get sick with the disease
- Body is naturally & actively responding
Naturally acquired passive immunity?
- Embryos and newborns acquire preformed antibodies from their mother
- Across the placenta – IgG
- In mother’s milk – IgA
- Child not actively producing own antibodies
Artificially acquired active immunity?
- Vaccines – live attenuated or heat-killed Ag
- Patient’s own body responds against antigen
- Basis of immunization
Artificially acquired passive immunity?
- Antibodies harvested from animals/humans, given to protect patients immediately
- Active immunity takes days to weeks to fully protect – delay may prove detrimental or fatal if protection not given immediately
- Rabies, hepatitis A
- May give antisera or antitoxins
What are the 5 attributes of adaptive immunity?
- Unresponsiveness to self
- Response to only 1 molecular shape
- (antigen, target is specific)
- Immune cells activated only in response
- to specific pathogens
- Once induced, cells of adaptive immunity
- proliferate to form clones
Unresponsiveness to self?
- No reaction against normal body
- Remembers specific pathogens and
- responds faster and more effectively in subsequent encounter
What are the general roles of B cells and T
cells in adaptive immunity?
- B lymphocytes (B cells) attack extracellular pathogens in humoral immune responses, using antibodies.
- T lymphocytes (T cells) carry out cell mediated immunity against intracellular pathogens
What are the primary lymphoid organs, and
secondary lymphoid organs?
- Primary:red bone marrow and thymus
- Secondary:lymph nodes – filter lymph
- spleen – filters blood
- Less organized mucosa-associated lymphatic tissue (MALT): tonsils, appendix, Peyer’s patches, ymphoid tissue in respiratory tract, vagina, bladder, mammary glands
Where do lymphocytes originate, and where do
- all originate in red bone marrow
- •B cells mature in bone marrow
- •T cells mature in thymus
- •B and T cells migrate to 2o lymphoid organs
Where are lymph nodes found, and what is their function?
- in neck, groin, armpit, abdomen
- Lymph nodes facilitate interactions between immune cells and pathogens
Describe the flow of lymphatic fluid.
- Leaks out of blood stream into tissues
- Collected from tissues by lymphatic vessels and carried to lymph nodes
- Lymph nodes filter the lymph
- Empties back into blood stream
What are antigens?
Substances that trigger specific immune responses.
What are epitopes?
(or antigenic determinant) is the three-dimensional shape of a region of an antigen that is recognized by the immune system
On microorganisms that multiply outside cells of body
- Body should not attack antigens on surface of its own normal cells
- This is “self tolerance”
Protozoa, fungi, bacteria, and viruses that reproduce inside body’s cells
Describe properties and types of antigens?
- Larger molecules better antigens than smaller ones
- Have more epitopes
- Proteins and glycoproteins are good antigens
- Carbohydrates and lipids less antigenic
- Small molecules, called haptens, (like penicillin) make poor antigens
- If bind to a large carrier molecule, can become antigenic
Describe B cells?
- B cells make immunoglobulins (Ig),= antibodies
- B cells have receptors for antigens
- Surface of B cell covered with many identical copies of B cell receptor
- Variable regions of heavy and light chains form antigen-binding site
what happens when B cells are activated?
When activated by a specific antigen (usually occurs in lymph node), B cell reproduces and make lots of clones; some become plasma cells, and some become memory cells for quick responses later when same antigen is encountered again
- Complement Activation- FC region binds to complement protein
- Neutralization - blocks action of toxin or attachment of pathogen
- Opsonization - makes phagocytosis easier
- Direct killing by oxidation
- Antibody-dependent cellular cytotoxicity Antibodies bind to pathogen’s epitopes
- Fc region binds to natural killer cells, which lyse pathogen (apoptosis) with proteins called perforin and granzyme
Antibodies are complementary to epitopes and consist of 2 light chains and 2 heavy chains, y-shaped molecules
What are the five classes of antibodies?
- Plasma cells first make
- 5 basic units linked together in a circle by a joining chain
- IgG is usually made next
- Most common, longest-lasting Ab
- Single unit
- Plays many roles in the body
- Can easily leave blood vessels to enter extracellular spaces, where invaders often are located
- The only antibody to cross placenta
- Associated w/ secretions– tears, breast milk
- Some are single units (monomers)
- Circulate in the blood
- Some are dimers - secretory IgA
- Tear ducts, mammary glands, and mucous membranes
- Protects body from infections in GI, respiratory, urinary, and reproductive tracts
- Nursing newborns get IgA from mother’s milk
- Attach to receptors on eosinophil
- trigger release of cell-damaging molecules onto the surface of parasites (particularly worms)
- Also, trigger mast cells and basophils to release histamine
- Therefore, it is the antibody of allergies
- Membrane-bound antigen receptors on B cells
- Like BCRs
- Exact function or importance is unknown
Describe the general function of cells and the TCR
- T cells are very specific (like B cells)
- Have T cell receptors (TCR) on their membranes for antigens
- 109 types of T cells
- T cells mature in the thymus, and react to foreign antigens presented by our own cells
Cytotoxic T cells?
- (Tc or CD8 cells)
- directly kill infected or abnormal body cells
- Virus-infected, bacteria-infected, protozoan infected, fungus-infected, some cancer cells and foreign cells from transplantation
Helper T cells?
- (TH or CD4 cells)
- Type 1 helper T cells (Th1 cells) Signal cytotoxic T cells and macrophages
- Type 2 helper T cells (Th2 cells) Communicate with B cells to activate them
- Helper T cells secret cytokines that regulate entire immune system, adaptive & innate
Regulatory T cells?
- Also called suppressor T cells
- Repress adaptive responses
- Prevent autoimmune diseases
What is clonal deletion?
- As we mentioned, both B and T cells randomly generate the shapes of their receptors on their surfaces (by rearranging certain genes to give us such variety)
- So, every population of maturing lymphocytes includes cells with receptors that match up with normal body cells-autoantigens
- Important that immune response not be directed against normal body cells
- Or result is an autoimmune disease
- 1.Body eliminates self-reactive
- lymphocytes via clonal deletion
- 2.In thymus - T cells, in bone marrow - B cells
- 3.Thymus cells express all of the body’s normal proteins, even hemoglobin, lysozyme, and muscle cell proteins, but they must be in association with MHC protein
- 4.If T cell responds to autoantigen, it’s destroyed
- 5.Results in self tolerance – if impaired causes?
- 6.T cells (unlike B cells) don’t recognize epitopes unless “presented” on MHC molecules
What is the function of MHC molecules?
- The body’s cells have unique polypeptides on cell surface so can distinguish self from nonself
- Discovered when trying to graft tissues, kept having rejection
- Named Major Histocompatibility Complex (MHC) because of this role in tissue compatibility
- The real role is to hold and position epitopes for “presentation” to T cells
Explain the difference between Class I MHCs and Class II MHCs.
- Class I MHCs on all cells except RBCs
- Class II MHCs on special antigen-presenting cells – like B cells, macrophages, and dendritic cells
What are cytokines?
- Soluble regulatory proteins that act as intercellular signals to direct activities in immune responses
- E.g., cytotoxic T cells do not respond to antigens unless they are first signaled to by cytokines
- Cytokines are secreted by various leukocytes and affect diverse cells
ILs signal among leukocytes – about 35
Antiviral proteins that may also activate phagocytes
Proteins that stimulate leukocyte stem cells to divide
Tumor necrosis factor?
Made by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation
Chemotactic cytokines – signal leukocytes to move to site of inflammation or infection
Describe antigen processing and presentation
- Processing exogenous antigens
- An APC, usually a dendritic cell, internalizes a pathogen and catabolizes its molecules, producing epitopes in a phagolysosome
- A vesicle with MHC II molecules fuses with the phagolysosome, each epitope fuses with the antigen-binding groove of the MHC molecules
- Vesicle then inserts these MHC-epitope complexes into the cytoplasmic membrane so that epitopes point outside