23. Immunity and Immunodiagnosis of Viral Infections

Question 1

How do interferons inhibit viral replication?

Answer 1

• Interferons alpha and beta are produced by virus-infected host cells
• inhibit viral replication by inducing production of proteins that degrade viral RNA and block protein synthesis
• are species-specific, but not virus-specific

Question 2

Why are both humoral immunity and cell-mediated immunity important for the elimination of viruses from the host?

Answer 2

Humoral immunity = abs act on free virus particle.

Cell-mediated immunity = important in attacking viruses inside of cells

Question 3

What are the ways that antibodies can help us eliminate viruses?

Answer 3

1. Viral Neutralization
2. Opsonization
3. ADCC
4. Complement activation (classical pathway)
5. Agglutination of viral particles

Question 4

What type of T cell is important in cell-mediated immune responses against viruses?

Answer 4

cytotoxic T lymphoctes (CTL or Tc)

Question 5

How would the ability to down-regulate expression of MHC Class I molecules protect a virus?

Answer 5

This inhibits antigen presentation on T cells.

Question 6

Suppose a patient had IgG antibodies to the rubella virus, but had no detectable IgM antibodies against rubella. What do these results indicate about the patient’s immune status to rubella?

Answer 6

IgG only indicates a past exposure or immunization thus leading to the developement of immunity.

Question 7

Suppose a patient had an anti-CMV titer of 8 at the time of initial testing, and an anti-CMV titer of 64 two weeks later. What do these results indicate?

Answer 7

The patient has a current CMV infection indicated by the 4-fold rise in antibody titer.

Question 8

Which viruses are associated with infectious mononucleosis, German measles, measles, and chicken pox?

Answer 8

Infectious mono = Epstein Barr Virus
German measles = Rubella virus
Measles = Rubeola virus
chicken pox = Varicella virus

Question 9

What serologic marker indicates infectivity for Hepatitis B?

Answer 9

(+) HBsAg

Question 10

What serologic marker indicates immunity to Hepatitis B?

Answer 10

(+) Anti-HBs

Question 11

What is the clinical significance of the following antibodies: IgM anti-HAV; Anti-HCV?

Answer 11

IgM anti-HAV = current Hep A infection

Anti-HCV = exposure to Hep C or molecular method indicates current Hep C infection