An antibody is an immune system protein that can bind to a particular _______. Antibodies are seen in two forms: as receptors on the surface of _______ cells and as free-standing proteins that are _______ by these cells.

The cells of both antibody-mediated and cell-mediated immunity exist in great numbers in nodes of the body’s fluid- drainage network, the _______.

A B cell that has become activated against a given microbe divides rapidly to produce clones of two types of daughter cells: _______ cells, which produce the antibodies that will directly fight the invader, and _______ cells, which will remain in the body long after the infection has passed.

T cells specific to a given invader become activated by binding to a cell whose central function is to initiate adaptive immunity by displaying microbial antigens. These are the _______ cells, the most important of which is the _______ cell.

AIDS is devastating to the immune system because the virus that causes it has, as its primary target, the _______ cells that are central to both cell- and antibody-mediated immunity.

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?