1) The body’s immune system protects in against invading organisms and toxic substances.
2) The body has two primary defensive strategies: nonspecific defenses that do not discriminate between one invader and the next, and specific defenses that provide protection against particular invaders. Specific defenses can produce immunity, defined as a state of long-lasting protection against particular invaders.
3) An antigen is any foreign substance--- often a protein from an invading organism—that elicits an immune system response.
4) Several varieties of white blood cell are important to immune function; these include T cells, B cells, and macrophages.
Antibody-Mediated and Cell-Mediated Immunity
1) There are two major components to actively acquired immunity: antibody-mediated immunity and cell-mediated immunity.
2) White Blood cells called lymphocytes are fundamental to both types of resistance, because lymphocytes develop onto both T cells (which are central to cell-mediated immunity) and B cells (which are central to antibody-mediated immunity)
3) Mature T and B cells are most often found in organs of the body’s lymphatic system, which is a system of vessels that captures interstitial fluids, subjects these fluids to scrutiny by immune system cells, and returns the fluid to the circulatory system.
Antibody-Mediated Immunity in Detail
1) An antibody is a circulating immune system protein that binds to a particular antigen. Antibodies exist as (1) receptors on the surface of B-cells that bind to specific antigens, and (2) as freestanding invader-fighting proteins that are secreted by the B cells and move through the blood stream.
2)
Antibody-mediated immunity
begins with the binding of an antigen to a B-cell receptor (antibody). This
binding produces a cascade of effects, including the production of a B-cell
clone--- a huge number of identical copies of the B-cell that bound to the
antigen.
3)
The B-cells produce
differentiate into plasma cells, which produce infection-fighting anti-bodies,
and memory B cells, which remain in the body long after the initial infection
from the specific invader has passed, providing permanent immunity against
it.
Cell-Mediated Immunity in Detail
1)
Cell-mediated immunity
provides protection in instances in which the body’s own cells are harmful after
having become infected by an invader.
2)
The central player in
cell-mediated immunity is the T cell, which comes in three varieties: cytotoxic
(or killer) T cells, helper T cells, and suppressor T
cells.
3)
An infected cell secretes an
interferon protein that elicits an attack by natural killer and macrophage
cells. Macrophages activated in the way ingest infected cells and display
fragments of proteins from the invader, bound with macrophage receptors, on the
macrophage’s surface. Macrophages that play this role are known as
antigen-presenting cells, or APCs.
4)
Helper T cells, binding with
the combined antigen/APC binding site, activities that includes the production
of helper cells, bringing about a cascade of activities that includes the
production of helper, cytotoxic, and suppressor T cells, and the stimulation of
B-cell clone development. The T-cell activity produces memory T cells for the
future invasions by a specific pathogen. Cytotoxic T cells bind with infected
cells and puncture their outer membranes.