Biology 205 problem set F: Immune system (* hand in answer in recitations)

*48) a) On the following diagram of an antibody molecule, indicate

i) a heavy chain

ii) a light chain

iii) the site(s) that bind antigen

b) How many genes are required to make a single antibody molecule?

c) What gene segments make up an antibody heavy chain gene?

d) Which gene segments encode the part of the antibody that binds antigen?

49) Briefly describe the genetic changes that occur in a developing B cell before it sees an antigen. Include allelic exclusion as part of your answer.

50) a) Which B cells respond to an infection by a substance not previously seen?

b) Which B cells respond to a second infection (one year later) by the same foreign substance?

c) What is the difference between the responding cells in part a and the responding cells in part b?

51) Which of the following types of somatic mutations might increase binding of an antibody to an antigen it recognizes:

change of one nucleotide in the Cm heavy chain gene segment

removal of one nucleotide in a D heavy chain gene segment

change of one nucleotide in a V light chain gene segment

52) To produce antibodies against a short peptide, one generally attaches the peptide to a larger protein "carrier," and then injects the carrier + peptide into a rabbit. The rabbit then produces antibodies against both the peptide and the carrier.

a) Do the same B cells produce antibodies against the carrier and against the short peptide?

b) Why is it necessary to use the carrier?

53) HIV, the virus that causes AIDS, recognizes the CD4 protein. What cells normally have this protein, and why does the virus cause immunodeficiency?

54) If a mouse is irradiated with X-rays, and then B cells from another mouse are introduced, will the resulting mouse defend itself against "attack" by a) a virus; b) a kidney from a foreign mouse; c) a harmless chicken protein injected into the bloodstream? Why or why not? What if T cells from another mouse are also introduced into the irradiated mouse?

55) Name one type of cell that has the following receptors on its surface:

a) CD4 but not CD8

b) CD8 but not CD4

c) both CD4 and CD8

d) MHC class II molecule

56) If a heart is transplanted from one animal to another, the recipient's immune system will reject the transplanted tissue.

a) What cells of the immune system recognize the foreign heart cells?

b) How do these cells distinguish foreign cells from host cells?

c) What happens to the foreign cells?

d) How does the immune system impose this fate on the foreign cells?

e) Why doesn't the immune system reject its own cells?