Chapter 9

Question 1

MHC class I

Answer 1

Present on the surface of all nucleated cells.

Question 2

MHC class II

Answer 2

Present on the surface of all professional antigen presenting cells.

Question 3

Antigen Presenting cells

Answer 3

Dendritic, Macrophages, and B cells. Dendritic cells and Macrophages pick up antigens at infected area.

Question 4

Dendritic cells

Answer 4

They function by processing antigen material and present it on the cell surface to the T cells of the immune system. They act as messengers between the innate and the adaptive immune systemsOnce activated, they migrate to the lymph nodes where they interact with T cells and B cells to initiate and shape the adaptive immune response.

Question 5

Antigen processing

Answer 5

Antigens processed for MHC proteins to display epitopes. Different processes for endogenous and exogenous antigens.

Question 6

Processing of endogenous antigens (MHC I)

Answer 6

Antigens from endogenous pathogens, such as virus, are processed by endogenous pathway, in which the proteasome degrades the antigen into smaller peptides, which are transported to the endoplasmic reticulum. In the ER the peptide is attached to a MHC class I molecule and delivered to the cells surface for presentation to a CD8+ T cell.

Question 7

Processing of exogenous antigens (MHC II)

Answer 7

Exogenous antigens are taken into the cells by a phagosome, joined to an MHC class II molecule, and taken to the cells surface for presentation to a CH4 T cell.

Question 8

Cell-mediated Immune responses

Answer 8

Respond to intracellular pathogens and abnormal body cells. The most common intracellular pathogens are viruses. The response is also effective against cancer cells, intracellular protozoa, and intracellular bacteria. Effector cells are the cytotoxic T cells (CTL) expressing CD8.

Question 9

Activation of a clone of cytotoxic (CD8+) T cells

Answer 9

Antigen presenting cells present antigen to naive cytotoxic lymphocytes by linking the antigen to MHC-I molecule which is recognized by CD8 molecule on the surface of cytotoxic T cells.

Question 10

Killing by activated cytotoxic lymphocytes

Answer 10

1) Virus infects cell
2) Cell expresses viral antigen
3) Infected cell is killed by cytotoxic T cell by activation of nuclease that cleaves host and viral DNA

Question 11

Cytotoxic lymphocytes (CTLs) kill using 2 primary mechanisms

Answer 11

Perforin-Granzyme Cytotoxic pathways and CD95 pathway.

Question 12

Perforin-Granzyme Cytotoxic pathway

Answer 12

T-cell sits on virally infected cell, then releases vesicles with perforin that forms pores on the infected cell, another vesicle with granzyme enters through the pores made by the perforin and once inside causes the cell to apoptosis.

Question 13

CD95 cytotoxic pathway

Answer 13

CD95 receptor is presented by the host cell and then the Cytotoxic T cell presents a ligand CD95L which interacts and activates with the CD95 receptor. This activates the apoptosis pathway.

Question 14

Memory T cells

Answer 14

Some activated T cells become memory T cells. Persist for months or years in Lymphoid tissue. Immediately functional upon subsequent contacts with epitome specific to its TCR.

Question 15

Humoral Immune responses

Answer 15

Adaptive responses mounted against exogenous pathogens. Provides the soluble component of adaptive immunity (humors).

Question 16

T-independent activation of B cells

Answer 16

Does not require T cell help. T-independent antigens can directly stimulate the B cells to produce antibody without the requirement for T cell help In general, polysaccharides are T-independent antigens.

Question 17

T-dependent activation of B cells

Answer 17

Requires signals provided by T-helper cells. Most important. Antigen presenting cells stimulate CD4 T cell to become an effector Th1 or Th2 cells. Th2 cells then activate B cells.

Question 18

Process of B cell activation

Answer 18

1) B-cell binds to virus through viral coat protein
2) Virus particle is internalized and degraded
3) Peptides from internal proteins of the virus are presented to the T cell, which activates the B cell.
MHCII binds with the CD4 on the T cell as well as CD40 binding to CD40L. Once binding is over the Th2 cell releases IL-4 which activates the B cell to start producing antibodies (AgM).

Question 19

Plasma Cells

Answer 19

Majority of the cells produced during B cell proliferation become plasma cells. Initial plasma cells produce large quantities of antibodies in lymphoid tissues (IgM). Individual plasma cells are short lived.

Question 20

Plasma cells in the germinal center

Answer 20

Cells with improved binding to Ag will replicate (affinity maturation), undergo class switching (to IgG) and become plasma cells, unimproved cells will die. IgG secreting plasma cells migrate to the bone marrow and are long lived

Question 21

Memory B cells

Answer 21

Produced by B cell proliferation but do not secrete antibodies. Have BCRs complementary to the antigenic determinant that triggered their production. Long-lived cells that persist in the lymphoid tissue. Initiates antibody production if antigen is encountered again.

Question 22

Primary response

Answer 22

3 day lag period. Initially produces IgM then produces IgG

Question 23

Secondary response

Answer 23

Once antigen encountered quickly starts producing IgG and IgM. Produces more IgG.