Page 826 - Fundamentals of anatomy physiology

Lymphedema by itself does not pose a major threat to life. The Chapter 22 The Lymphatic System and Immunity 813
danger comes from the constant risk that an uncontrolled in-
fection will develop in the affected area. Because the interstitial NK (natural killer) cells. Each type has distinctive biochemical
fluids are essentially stagnant, toxins and pathogens can accu- and functional characteristics (Figure 22–5).
mulate and overwhelm local defenses without fully activating
the immune system. Most lymphocytes are T cells, and the primary types of
T cells include cytotoxic T (TC) cells, helper T (TH) cells, sup-
Lymphocytes pressor T (TS) cells, and memory T cells. Cytotoxic T cells are
involved in direct cellular attack. These lymphocytes are the
Lymphocytes account for 20–40 percent of circulating leuko- primary cells involved in the production of cell-mediated immu-
cytes. However, circulating lymphocytes are only a small frac- nity, or cellular immunity. The interplay between helper T cells
tion of the total lymphocyte population. The body contains and suppressor T cells helps establish and control the sensitiv-
some 1012 lymphocytes, with a combined weight of more than ity of the immune response. For this reason, these cells are also
a kilogram (2.2 lb). known as regulatory T cells.

Types of Lymphocytes We will examine these T cells throughout this chapter.
Other types of T cells also take part in the immune response.
Three classes of lymphocytes circulate in blood: (1) T (thymus- For example, inflammatory T cells stimulate regional inflamma-
dependent) cells, (2) B (bone marrow–derived) cells, and (3) tion and local defenses in an injured tissue. Suppressor/inducer T
cells suppress B cell activity but stimulate other T cells.

Under proper stimulation, B cells differentiate into plasma
cells that secrete antibodies. These antibodies are soluble

Figure 22–5 Classes of Lymphocytes.

Classes of Lymphocytes

subdivided into

T Cells B Cells NK Cells 22

Approximately 80% of circulating differentiate into B cells make NK cells make
lymphocytes are classified as up 10–15% up the remaining
T cells. of circulating 5–10% of
lymphocytes. circulating
lymphocytes.
Plasma Cells
Cytotoxic Helper T Cells Suppressor Memory T Cells When stimulated, B
T Cells T Cells cells can differentiate
Helper T cells Memory T cells into plasma cells, which
Cytotoxic T cells stimulate the Suppressor T are a subset of produce and secrete
attack foreign cells activation and cells inhibit T cells that antibodies.
or body cells function of the activation respond to a
infected by viruses. both T cells and function previously
and B cells. of both T cells encountered
and B cells. antigen.