Immuno

Question 1

Differentiate positive vs. negative selection of T cells and where does each process occur?

Answer 1

• Positive: T cells expressing a TCR able to bind self MHC are allowed to survive; occurs in thymic cortex
• Negative: T cells possessing TCRs that bind with high affinity to self antigen or self MHC class I or II are eliminated by apoptosis; occurs in thymic medulla

Question 2

Septic arthritis in a young, sexually active adult should raise for suspicion for what organism?

Answer 2

Disseminated N. gonorrhea infection

Question 3

Which important cause of UTI’s does not cause hemolysis (gamma-hemolytic) when grown on blood agar?

Answer 3

Enterococcus - Gram-positive cocci in pairs and chains

Question 4

Leukocyte adhesion deficiency (LAD) type 1 results from the absence of what; leading to the inability to synthesize what?

Answer 4

Absence of CD18 —> inability to synthesize the beta-2 integrins Mac-1 and LFA1, affecting tight adhesion, crawling, and transmigration

Question 5

How does HBV assist with the life cycle of HDV?

Answer 5

HBsAg must coat the HDAg of HDV before it can infect hepatocytes and multiply

Question 6

Hyper IgM syndrome is most often due to a deficiency in what; how is it inherited?

Answer 6

CD40L deficiency; X-linked recessive

Question 7

Which antibodies are specific for limited scleroderma (CREST) and diffuse scleroderma?

Answer 7

• CREST syndrome = anti-centromere antibodies
• Diffuse scleroderma = anti-DNA topoisomerase I (Scl-70) antibodies

Question 8

What is the difference between Janway lesions and Osler nodes associated with Infective Endocarditis?

Answer 8

• Janeway: are nontender, macular, and erythematous lesions on the palms and sole; result of septic embolization from valvular vegetations
• Osler nodes: are tender, violaceous nodules located on the pulp of fingers and toes; due to immune-complex deposition in the skin