The Immune Response I

Question 1

Describe the Th1 cell response.

Answer 1

After being transported to the APC cell membrane, the antigenic peptide MHC class II complex is presented to CD4+ T (helper) cells. CD4+-Th1 cells are activated and the cell clone divides logarithmically and secretes IL-2, IFN-y, and TNFa.

Question 2

What is secreted in the Th1 cell response?

Answer 2

IL-2, IFN-y, TNFa.

Question 3

What is the function of IL-2?

Answer 3

IL-2 is necessary for T and B cell transformation.

Question 4

What is the function of IFN-y?

Answer 4

IFN-y is a potent macrophage and natural killer (NK cell) activator. It enhances cell mediated immunity and triggers HLA antigen presentation by endothelial cells.

Question 5

What is downregulated by IFN-y?

Answer 5

IL-4 synthesis by Th2 cells; In this way, it suppresses antibody formation.

Question 6

What is the function of TNF-a?

Answer 6

Activation of macrophages, stimulation of the acute-phase response, and collaborating with IL-1 in the acute phase response.

Question 7

Describe the Th2 cell response.

Answer 7

Following antigen activation AND stimulation by IL-2, the CD4+-Th2 cell responds by transforming, differentiating, and dividing logarithmically while secreting IL-4, IL-5, IL-10, IL-13.

Question 8

What is secreted in the Th2 cell response?

Answer 8

IL-4, IL-5, IL-10, IL-13.

Question 9

Which CD4 pathway activates B cells?

Answer 9

Th2 pathway

Question 10

What cell types are activated by the Th1 CD4+ pathway?

Answer 10

Macrophages, NK cells, T cells. (Cell mediated Immunity)

Question 11

What is the function of IL-4?

Answer 11

Favours development of antibody synthesis by stimulating B-cell differentiation; downregulates IFN-y by TH-1 cells and can thus suppress CMI. IL-4 is necessary for IgE production.

Question 12

What is downregulated by IL-4?

Answer 12

IFN-y by Th1 cells- this suppresses CMI.

Question 13

What is the function of IL-5?

Answer 13

To function synergistically with IL-4 and IL-2 to help in B cell differentiation; facilitation of IgA synthesis; stimulation of growth and differentiation of eosinophils.

Question 14

What is the function of IL-10?

Answer 14

Functions like IL-4 by inhibiting Th1 cell release of IFN-y and IL-2, thereby negating macrophage activation by IFN-y.

Question 15

What is the function of IL-13?

Answer 15

Mimics IL-4 actions, inhibiting Th1 cytokine release.

Question 16

Describe the initial B cell response.

Answer 16

Antigen selects the clone of B cells with the membrane bound IgM antigen receptor that is specific for the antigen epitope. Binding of antigen along with stimuli from T cell cytokines IL-2 and IL-4 triggers differentiation of the B cell clone into a large blast cell and logarithmic division occurs.

Question 17

What is the function of IL-5 in B cell maturation?

Answer 17

Allows the B cell to acquire the cytoplasmic machinery necessary for antibody synthesis; H and L chains are synthesized and assembled.

Question 18

What is the function of IL-6 in B cell maturation?

Answer 18

Contributes to terminal differentiation of B cells into a plasma cell; secretion of IgM then occurs.

Question 19

Which MHC pathway involves presentation of intracellular organisms (viruses, parasites, etc)?

Answer 19

MHC I

Question 20

Which MHC pathway involves endocytosis/ phagocytosis of antigen?

Answer 20

MHC II

Question 21

What cytokines influence the switch to IgG?

Answer 21

IL-4, IFN-y