Host Immunity 3

Question 1

Major Histocompatibility Complex, or MHC

Answer 1

• 2 classes: MHC I and II
• function as two different antigen processing pathways for 2 different kinds of antigens, which activate different types of T cells

Question 2

3 types of pathogens MHC help eliminate

Answer 2

1. extracellular
2. intracellular
   a) free in cytosol
   b) intravesicular

Question 3

MHC class I can be present on

Answer 3

all nucleated cells including antigen presenting cells

Question 4

MHC class 2 can be present on

Answer 4

only APCs (b cells, macrophages, and dendritic cells)

Question 5

MHC class 1 function and result

Answer 5

• present antigen to cytotoxic T (CD8+) cells

- result: T cell - mediated toxicity

Question 6

MHC class 2 function and result

Answer 6

• present antigen to T (CD4+) helper cells

- result: T cell - mediated help

Question 7

endogenous antigens and intracellular pathogens

Answer 7

-proteasomes process antigens , in the form of peptide fragments, from viral proteins within the cytoplasm, which are then attached to MHC class I and transported out of the cells to cytotoxic T cells, which are activated to kill the infected cell

Question 8

exogenous antigens and endosomes

Answer 8

• when a macrophage engulfs a bacteria, it breaks down the bateria into peptides that are bound to MHC class 2 in vesicles
• CD4 Th1 cell recognizes the peptide Ag and activates the macrophage (which engulfed the bacterium for delayed type hypersensitivity response (DTH) OR
• if a B cell engulfed the bacterium, rather than a macrophage: CD4 Th2 cell recognizes the Ag which activates the B cell for Antibody response

Question 9

Antigen presenting cells include what types of cells, and which type of MHC?

Answer 9

• macrophages, dendritic cells, B-cells

- must be MHC class 2

Question 10

dendritic cell function

Answer 10

• to take infection to lymph node and stimulate adaptive immunity
• can take minutes to hours for the acute inflammatory response to occur
• 7-10 days for adaptive immune response
• dendritic cells are best APC to activate T cells and they serve as a CRITICAL BRIDGE between innate and adaptive immune response

Question 11

Help T cells CD4+ are divided into

Answer 11

Th1 and Th2 cells

Question 12

Th1 cells functions

Answer 12

• activate cell mediated immunity through the release of CYTOKINES, which enable:
• activating macrophages enabling them to destroy intracellular pathogens
• activate neutrophils
• stimulate production of antibodies for enhanced attachment during phagocytosis
• enable T8 lymphocytes to proliferate into activated cytotoxic t lymphocytes that can destroy infected cells

Question 13

Th2 cells functions

Answer 13

• recognize antigens presented by B-lymphocytes, and produce cytokines that:
• enable B-lymphocytes to create and secrete antibodies
• enable B-lymphocytes to activate eosinophils and produce increased amounts of IgE against helminths

Question 14

Cytotoxic T CD8+ cells functions

Answer 14

• major defense against viruses, intracell bacteria, and tumor cells
• naive T8 lymphocytes must be activated by cytokines of Th1 cells

Question 15

T cell vs Bcell antigen recognition

Answer 15

• T cells recognize processed antigens on MHC

- B cells and their antibodies recognize antigens that arnt processed/without MHC

Question 16

macrophages bound with t cells must be activated via

Answer 16

• pattern recognition receptors (PRR) binding to pathogen-assocation molecule patterns (PAMP)
• IFN-y from Th1 T cells in DTH reaction
• note: macrophages are critical in control on intravesicular bateria

Question 17

Th1 are helpers for…

Th2 are helpers for…

Answer 17

Th1 = cell mediated immunity
Th2 = B cells as part o the humoral immune responses

Question 18

antibody dependent cell-mediated cytotoxicity (ADCC)

Answer 18

• cell-mediated immune defense whereby an effector cell actively lyses a target cell, whose membrane surface antigens have been bound by specific antibodies
• ie. NK cells, macrophages, neutrophils, and eosinophils

Question 19

Effector immune response to leshmania: susceptible vs resistant phenotype

Answer 19

susceptible: Th2 response increases, causing B-cells to produce antibodies, no parasites killed; Th1 response decreases
resistant: Th1 response increases, while Th2 decreases; macrophages activated for intracellular killing

Question 20

eosinophils are an example of

Answer 20

antibody dependent cell-meditated toxicity (ADCC); specifically against helminths