Cancer cells and virus-infected body cells can be killed before activation of adaptive immunity by

A. Tunica intima:The tunica intima is the innermost layer composed mainly of endothelial cells that provide a smooth surface to reduce friction and regulate vessel tone chemically. While it plays roles in coagulation and permeability, it does not generate the force needed to maintain blood pressure. Its structure is not designed for active contraction or pressure regulation.

B. Tunica externa:The tunica externa is the outer connective tissue layer that protects the vessel and anchors it to surrounding structures. Although it provides structural support, it does not contain the smooth muscle necessary to adjust vessel diameter. Without this contractile ability, it cannot directly influence blood pressure.

C. Tunica media:The tunica media contains smooth muscle fibers and elastic tissue that allow vessels-especially arteries-to constrict or dilate. These changes in vessel diameter regulate peripheral resistance, which is a major determinant of blood pressure. Its contractile strength makes it the primary structural layer responsible for maintaining and adjusting blood pressure.

D. Subendothelial:The subendothelial layer is a thin connective tissue region beneath the endothelium. It provides minor structural support but lacks smooth muscle or elastic fibers needed for active regulation. Because it cannot constrict or dilate, it plays little to no role in controlling blood pressure.

A. Lymph nodes:Lymph nodes provide sites where B lymphocytes can encounter antigens and become activated, but they do not directly release antibodies. They function mainly as filtering and immune activation centers.

B. T lymphocytes:T cells mediate cellular immunity by directly attacking infected or abnormal cells or helping activate other immune cells. They do not produce antibodies themselves.

C. Medullary cords:Medullary cords are structures within lymph nodes that contain plasma cells and macrophages. While they house antibody-producing cells, they do not themselves secrete antibodies.

D. B lymphocytes:B cells differentiate into plasma cells upon activation. While they can produce some antibodies initially, the bulk antibody secretion is carried out by the plasma cells they generate.

E. Plasma cells:Plasma cells are fully differentiated B lymphocytes specialized for antibody production. They secrete large quantities of antibodies specific to a particular antigen, making them the primary source of circulating antibodies in adaptive immunity.