Download More immunity stuff:

Cell-Mediated Immune Response
Dr. Shaffer
A&P II
page 1
More immunity stuff:
We’ve learned what antibodies are. But I’m sure you’ve heard of monoclonal antibodies. What are
they? They’re really just antibodies in the way we’ve learned them. In real life, if you injected a lab
animal, let’s say, a mouse, with some antigen, it would produce antibodies. These antibodies would most
likely be polyclonal antibodies because the antigen, like many antigens, could have multiple antigenic
determinants – each one triggering clonal selections and differentiation of a particular B-cell. Each of
those B-cells would make antibodies, and the antibodies circulating in the mouse’s blood would be
polyclonal that is, they would result from multiple different clones. Well, back in the seventies it was
learned that if you take a B-cell of the type you are interested in and fuse it with a tumor cell, you’ll get
lots and lots of those B-cells. (Tumor cells divide and divide like crazy). These hybrid cells grown in
culture will produce loads of just one antibody – a monoclonal antibody.
So what good are they? We’ve learned that almost anything can be an antigen, right? Usually antigens
are proteins, but not always. Let’s consider just one example of the use of monoclonal antibodies.
Human Chorionic Gonadotropin (hCG) is a hormone that is found in the urine of pregnant women.
Monoclonal antibodies are made that bind to hCG, then they are chemically modified so that they have an
indicator dye marker attached. Now, embed some of these modified antibodies on a piece of paper and,
viola you’ve got a little piece of paper that can tell you if you’re pregnant.
Monoclonal antibodies can be used to identify bacteria, identify blood groups, and even treat cancer.
What about those T-cells we’ve heard about . . .
You’ve got two main types of T-cells: Helper T-cells and Cytotoxic T-cells. Cytotoxic T-cells destroy
cells – more on those soon. Helper T-cells do a lot of things for your immune response. Both types are
incapable of reacting to “free antigens” like the B-cells do.
Helper T-cells are activated when they interact with self-nonself complexes on the surface of a cell. The
complexes can be found on the surface of an infected cell or an antigen presenting cell such as a
macrophage. Once activated the helper T-cell will proliferate, and as with B-cells, the helper T-cell that
proliferates is the one with just the unique match to the self-nonself complex. Helper T-cells help the
immune system in a number of ways, mostly by secreting stimulatory proteins (example: interleukin-2).
These proteins act on the T-cell itself stimulating even more division (leaving behind some memory cells
in the process). These proteins can affect B-cells, helping to activate them, and they stimulate cytotoxic
T-cells.
Cytotoxic T-cells destroy infected body cells. Activated cytotoxic T-cells identify the infected cells by
the same self-nonself combination that we saw with the helper T-cells. They bind to the infected cell and
release chemicals (example: perforin) that destroy the membrane of the infected cell. Injection of some
other chemicals through those holes in the membrane results in death of the infected cell.
Cell-Mediated Immune Response
Dr. Shaffer
A&P II
page 2
As I’ve stated, T-cells don’t recognize “free” antigens. They only recognize and respond to processed
protein fragments on our body’s own cells. In this way they are able to defend us against corrupted cells.
MHC proteins are displayed on the outside of cell. T-Cells look for two things on the
outside of the cell, self and non-self, before they act.
a. MHC proteins are like the cell’s finger prints.
1. They are unique to a individual
2. There are two types
b. Class I MHC proteins are made by most nucleated cells. Synthesized in the cell,
they have a peptide fragment (8-9 Amino Acids long)
1. fragment may be bits of cellular protein (self)
2. may also have endogenous antigens
c. Class II MHC proteins are found on APCs (antigen presenting cells).
Macrophages, Langerhann’s cells as well as B-cells and activated T-cells. Class II
MHCs help immune cells recognize each other (and not attack!).
1. peptide fragments are longer (14-17 A.A.) and made of
2. cellular and exogenous antigens
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The five major types of antibodies are:

IgA. IgA antibodies are found in areas of the body such the nose, breathing passages, digestive tract, ears,
eyes, and vagina. IgA antibodies protect body surfaces that are exposed to outside foreign substances. This
type of antibody is also found in saliva and tears. About 10% to 15% of the antibodies present in the body
are IgA antibodies. A small number of people do not make IgA antibodies.

IgG. IgG antibodies are found in all body fluids. They are the smallest but most common antibody (75% to
80%) of all the antibodies in the body. IgG antibodies are very important in fighting bacterial and viral
infections. IgG antibodies are the only type of antibody that can cross the placenta in a pregnant woman to
help protect the fetus.

IgM. IgM antibodies are the largest antibody. They are found in blood and lymph fluid and are the first
type of antibody made in response to an infection. They also cause other immune system cells to destroy
foreign substances. IgM antibodies are about 5% to 10% of all the antibodies in the body.

IgE. IgE antibodies are found in the lungs, skin, and mucous membranes. They cause the body to react
against foreign substances such as pollen, fungus spores, and animal dander. They may occur in allergic
reactions to milk, some medicines, and some poisons. IgE antibody levels are often high in people with
allergies.

IgD. IgD antibodies are found in small amounts in the tissues that line the belly or chest. How they work is
not clear.