Toll-like receptors are the primary _______ of microbial infection in the human body and also serve to ______ both the innate and adaptive immune responses.

Invading microbes can be ingested whole by various members of the class of immune system cells known as ______.

An antigen is any substance that _______.

The human body’s first line of defense against invading pathogens is not the immune system, but rather a set of physical ______ to infection, the most important of which is .

The innate immune response will target any object in the body perceived to be _____, while the adaptive immune response targets ______.

When smallpox raged in England in the 18th century, most of its victims were young children. Meanwhile, the people least likely to die from it were senior citizens. Why should this have been so?

An antigen is:

a. any immune system protein.

b. any substance that elicits an immune system response.

c. any cell that functions in the immune system response.

d. the ultimate product of a vaccination.

e. a particular land of lymphocyte.

Public health officials agree that, since the 1960s, asthma has been increasing among children in developed countries such as the United States. Among the tentative explanations for this increase is the “hygiene hypothesis,” which holds that the problem is that many children are growing up in environments that are “pristine”—very clean and devoid of household pets. What could the linkage be between an immune system condition such as asthma and growing up in a pristine environment?

The pathogens that the immune system fights generally are (select all that apply):

a. poisons.

b. living things.

c. microbes.

d. produced by the body itself.

e. fungi, bacteria, or viruses.