Question

A host organism needs time, often days, to mount an immune response against a new antigen, but memory cells permit a rapid response to pathogens previously encountered. A vaccine to protect against a particular viral infection often consists of weakened or killed virus or isolated proteins from a viral protein coat. When injected into a person, the vaccine generally does not cause an infection and illness, but it effectively teaches the immune system what the viral particles look like, stimulating the production of memory cells. On subsequent infection, memory cells recognize and bind to the virus and trigger a rapid immune response. Some pathogens, including HIV, have developed mechanisms to evade the immune system, making it difficult or impossible to develop effective vaccines against them. Assume that a host\'s antibodies and T-cell receptors are available to bind to any structure that might appear on the surface of a pathogen and that, once bound, the pathogen is destroyed. What strategy could a pathogenic virus use to evade the immune system?

A. Antibodies on the virus mutate often.

B. The viral particles do not encode proteins.

C. The viral antigens are altered repeatedly.

D.Viral particles prevent immune cells from making antibodies.

E. The virus can target, infect, and destroy immune system cells.

Answer 1

What strategy could a pathogenic virus use to evade the immune system?

C. The viral antigens are altered repeatedly.

E. The virus can target, infect, and destroy immune system cells.

Many pathogens, including HIV have evolved mechanisms by which they can repeatedly alter the surface proteins in which immune system components initially bind. Therefore, the host organism regularly faces new antigens and requires time to mount an immune response to each one. As the immune system responds to one variant, new variants are created. HIV uses an additional strategy to evade the immune system: it actively infects and destroys immune system cells.