Question

Antibodies combine with antigens ______.

Options

• at variable regions

• at constant regions

• only if macrophages are present

• both at variable regions and only if macrophages are present

Answer 1

Antibodies combine with antigens at variable regions.

Explanation:

Antibodies combine with antigens at their variable regions. These regions are specifically structured to bind to unique antigenic determinants. The constant regions of antibodies do not bind antigens; rather, they mediate other immune functions. Macrophages are not required for direct antibody-antigen binding, so options involving macrophages are incorrect in this context.