immune iii

Question 1

Antibodies

Answer 1

• immunoglobulins = gamma globulin portion of blood
• proteins secreted by plasma cells
• capable of binding specifically with antigen detected by B cells
• grouped into 5 Ig classes

Question 2

Antibody structure

Answer 2

• T or Y shaped antibody monomer of 4 looping polypeptide chains linked by disulfide bonds
• 2 heavy chains with hinge region at “middles”
• two identical light chains
• variable regions at one end of each arm combine to form two identical antigen-binding sites
• Constant regions of stem determine antibody class and serve common funcs in all antibodies

Question 3

IgM

Answer 3

• Pentamer (biggest)
• 1st antibody released
• potent agglutinating agent
• readily fixes and acticates complement

Question 4

IgA

Answer 4

• secratory IgA
• monomer or dimer
• in mucus, breast milk, and other secretions
• helps prevent entry of pathogens

Question 5

IgD

Answer 5

• Monomer attached to surface of B cells

- Functions as B cell receptor

Question 6

IgG

Answer 6

• monomer
• 75-85% of antibodies in plasma
• from secondary and late primary responses
• crosses placental barrier

Question 7

IgE

Answer 7

• monomer active in some allergies and parasitic infections

- causes mast cells and basophils to release histamine

Question 8

B cell specieal antibody skill

Answer 8

• B cells can switch antibody classes, but retain antigen specificity
• IgM at first, then IgG
• almost all secondary responses are IgG

Question 9

Antibody targets and functions

Answer 9

• antibodies inactivate and tag antigens; do not destroy them –> form antigen-antibody complexes
• defensive mechanisms used by antibodies: neutralization, agglutination, precipitation, and complement fixation

Question 10

Neutralization

Answer 10

• simplest defensive mechanism
• antibodies block specific sites on viruses or bacterial exotoxins
• prevent these antigens from binding to receptors on tissue cells
• antigen-antibody comlexes undergo phagocytosis

Question 11

agglutination

Answer 11

• antibodies bind same determinant on more than one cell-bound antigen
• cross-linked antigen-antibody complexes agglutinate (e.g. clumping of mismatched blood cells)

Question 12

Precipitation

Answer 12

• soluble molecules are cross-linked

- complexes precipitate and are subject to phagocytosis

Question 13

Complement fixation and activation

Answer 13

• main antibody defense against cellular antigens (bacteria or mismatched RBCs)
• several antibodies bind close together on a cellular antigen –> complement-binding sites on stem regions of antibodies align –> triggers complement fixation to cells surface –> cell lysis

Question 14

activated complement functions

Answer 14

• amplifies inflammatory response
• promotes phagocytosis via opsonization –>positive feedback cycle that enlists more and more defensive elements
• activated complement forma MAC

Example of adaptive immune response enhancing innate response

Question 15

Cell mediated immunity: activation of T cells

Answer 15

first signal in activation:

• T cell receptors recognize and bind to a specific foreign antigen fragment that’s presented in antigen-MHC complexes
• CD4 and CD8 proteins are coreceptors

second signal required for activation

• costiulation: 20 known substances (cytokines, plasma membrane molecules)
• may prevent immune response from occuring accidentally
• anergy = recognition without costimulation (in both B and T cells) –> leads to prolonged state of inactivity

Question 16

Activation and clonal selection of helper T cells

Answer 16

• most that display CD4 develop into helper T cells –> some become regulatory T cells which moderate immunne response
• recognize exogenous antigen fragments associated with MHC-II molecules on the surface of an APC
• after activation, undergoes clonal selection
• Makes active helper T cells and memory helper T cells
• Active hleper T cells secrete cytokines (interleukin 2 needed for all immue resposes)
• Memory helper t cells aren’t active –> can quickly proliferate and differentiate if the antigen appears again

Question 17

Activation and clonal selection of cytotoxic t cells

Answer 17

• most taht display CD8 develop into cytotoxic T cells (CD8 T cells)
• recognize antigens combined with MHC-I
• Maximal activation also requires presentation of antigen with MHC-II to cause helper T cells to make IL-2
• Undergoes clonal selection
• Active cytotoxic T cells attack body cells
• Memory cytotoxic T cells don’t attack, but wait for an antigen to appear again

Question 18

Elimination of invaders

Answer 18

• cytotoxic T cells migrate to seek out and destroy infected target cells
• kill like NK cells
• major difference is T cells have specific receptor for particular microbe, but NK cells eat a ton of stuff

2 ways to kill: granzyes cause apoptosis; perforin and/or granulysin causes cytolysis

Question 19

immunological surveillance

Answer 19

tumor antigens displayed on cancerous cells targeted by cytotoxic T cells, macrophages, and NK cells

Question 20

Roles of helper T cells

Answer 20

• central role in adaptive immunne response
• activate both humoral and cellular arms
• once primed by APC presentation of antigen they help activate T and B cells, induce T and B cell proliferation, and their cytokines recruit other immune cells

Without helper T cells, there’s no immune response

Question 21

Helper T cells’ activation of B cells

Answer 21

• interact directly with B cells displaying antigen fragments bound to MHC II receptors
• release cytokines to stimulate B cells to divide more rapidly and begin atibody formation
• B cells may be activated without helper t cells by binding to T cell-independent intigens (response is weak and short, though)
• Most antigens require helper T cell co-stimulation to activate B cells: T cell-dependent antigens

Question 22

Helper T cell activation of CD8 cells

Answer 22

• CD8 cells require hleper T cell activation into destructive cytotoxic T cells
• cause dendritic cells to express co-stimulatory molecules required for CD8 cell activation

Question 23

Helper T cells amplification of innate defenses

Answer 23

• amplify responses of innate immune system
• activate macrophages –> more potent killers
• mobilize lymphocytes and macrophages and attract other types of WBCs

Question 24

Hypersensitivities

Answer 24

• immune responses to perceived threat cause tissue damage
• different types distinguished by their time course and whether antibodies or T cells involved
• Antibodies cause immediate and subacute hypersensitivities
• T cells cause delayed hypersensitivity

Question 25

Subacute Hypersensitivities

Answer 25

- caused by IgM and IgG transferred via blood plasma or serum - slow onset (1-3 hours) and long duration (10-15 hours) Cytotoxic (type II) reactions - antibodies bind to antigens on specific body cells, stimulate phagocytosis and complement-mediated lysis of cellular antigens - example: mismatched blood transfusion

Question 26

Delayed hypersensitivities (type IV)

Answer 26

- slow onset (1-3 days) - mechanism depends on helper T cells - cytokine-activated macrophages and cytotoxic T cells cause damage - example: allergic contact dermatitis (e.g. poison ivy) - agents act as haptens - TB skin test depends on this reaction

Question 27

Acquired immue deficiency syndrome (AIDs)

Answer 27

- Cripples immune system by interfering with activity of helper T cells - characterized by severe weight loss, night sweats, and swollen lymph nodes - opportunistic infections occur, including pneumocystis pneumonia and Kaposi's sarcoma

Question 28

AIDs and HIV

Answer 28

- caused by human immunodeficiency virus (HIV) transmitted via body fluids (blood, semen, and vaginal secretions) - HIV enters blood via blood transfusions, blood contaminated needles, sexual intercourse and oral sex, mother to fetus - HIV destroys hleper T cells and depresses cellular immunity

Question 29

autoimmune diseases

Answer 29

- immune system loses ability to distinguish self from foreign - production of autoantibodies and sensitized Tc cells taht destroy body tissues