Study Guide BIO205 Ch#16

• Body responds to pathogens, other antigens by mounting a specific immune response
• Get sick with the disease
• Body is naturally & actively responding

• Embryos and newborns acquire preformed antibodies from their mother
• Across the placenta – IgG
• In mother’s milk – IgA
• Child not actively producing own antibodies

• Vaccines – live attenuated or heat-killed Ag
• Patient’s own body responds against antigen
• Basis of immunization

• 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

• Specificity
• Inducibility
• Clonality
• Unresponsiveness to self
• Memory

• 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

• No reaction against normal body
• cells

• Remembers specific pathogens and
• responds faster and more effectively in subsequent encounter

• 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

• 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

• 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

• in neck, groin, armpit, abdomen
• Lymph nodes facilitate interactions between immune cells and pathogens

• 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

Substances that trigger specific immune responses.

(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

• 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

• 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

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
• Agglutination
• 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

• nIgM
• IgG
• IgA
• IgE
• IgD

• 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

• Monomer
• 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

• 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

• (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

• (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

• Also called suppressor T cells
• Repress adaptive responses 
• Prevent autoimmune diseases

• 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

• 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

• Class I MHCs on all cells except RBCs
• Class II MHCs on special antigen-presenting cells – like B cells, macrophages, and dendritic cells

• 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

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

• 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