SPECIFIC IMMUNITY (See Tortora, page 443, Fig. 17.18, pg. 428, fig. 17.3)
CD4+ = T-helper cells and T-delayed hypersensitivity cells;
CD8+ = T-cytotoxic cells and T-suppressor cells
B-Cells (PLASMA CELLS)
make antibody. (gamma globulin, antiserum, antitoxin).
ANTIGEN = any molecule to which a specific immune response can be generated:
specific means that lymphocytes are activated;
antigens are usually foreign but not always.
proteins and carbohydrates are good antigens.
antigens can be soluble or insoluble.
cells and particles are really aggregates of antigens.
(but we often refer to bacteria, viruses, etc. as antigen - this is imprecise but OK as long as you remember that there are many antigens associated with these).
some molecules (small) are not immunogenic, but if attached to something bigger then they will become antigenic. these things are called HAPTENS.
microbes / cells are a composite or aggregate of antigens. each antigen on a bacterial cell will provoke a unique specificity of antibody. See page 428 Tortora.
moreover, somtimes antigens on different (unrelated) cells are similar enough so that an antibody made to one will react with another. this is a cross-reaction.
an antigen is actually composed of multiple antigenic determinants or EPITOPES. Antibodies are made to the epitopes. A hapten is like a free epitope. Look at the pictures on pgs 428 - 430; figs.17.4 , 17.5 and 17.6.
There are FIVE CLASSES OF ANTIBODIES, the molecules of each class have the same basic structure. See fig 17.6 (pg430) and table 17.1 (page 431).
The molecule shown in fig 17.6 is called a MONOMER.
It is composed of 2 heavy chains (2 H chains) and 2 light chains (2 L chains).
Each chain has a V-REGION (binds to an epitope) and a C-REGION.
The two C-regions of the heavy chains come together to form the EFFECTOR REGION also called the Fc REGION.
The effector region is the part of the antibody that attaches to macrophages during opsonization and this part also reacts with complement in the classical complement activation pathway.
The different antibody classes have different H-chains but they can have the same L-chains.
FUNCTIONS OF ANTIBODY - SEE Pg. 434, Fig. 17.9:
Antibody binds to antigenic determinants (epitopes) and this:
1. INACTIVATES THE ANTIGEN as in neutralizing toxins or blocking receptors;
2. CROSSLINKS ANTIGENS which leads to:
* PRECIPITATION of proteins and
* AGGLUTINATION of cells;
3. ACTIVATES COMPLEMENT and destroys invading cells;
4. OPSONIZES BACTERIAL CELLS AND VIRAL PARTICLES and helps in phagocytosis.
CLINICAL (DIAGNOSTIC) TESTS WHICH USE ANTIBODY
The binding of antibody to antigen forms the basis of the clinical tests described in chapter 18.
In diagnosing many diseases it is important to determine if a person has antibodies.
The presence of antibody in the serum is evidence that the disease organisms are present or that they have been present.
Also, REAGENT ANTIBODIES are made in many animals. these highly specific, very sensitive reagents can detect tiny amounts of all manner of molecular substances (hormones, toxins and pollutants).
Some important Serological tests include:
1.) ELISA -- ENZYME LINKED IMMUNOSORBANT ASSAY (See Tortora pg.460, fig. 18.15). For example the assay might be constructed like this:
a.) virus coated on wells of the microtiter plate
b.) add serum containing the antibody needed to be measured.
c.) incubate, wash
d.) add anti-human antibody linked to enzyme (urease)
e.) incubate, wash
f.) add substrate (urea) and a pH indicator.
g.) urea will be broken down to ammonia by the urease only if human-anti-virus antibody is present. (Why?) Ammonia will cause the pH to become basic and the pH indicator will change color. The color change is a convenient indicator that the human antibody is there.
2.) FLUORESCENT ANTIBODY TECHNIQUES
FLUORESCENT MICROSCOPY -- ( See Tortora pg.458, fig.18.13)
a.) Reagent antibody labeled with fluorescent dyes (FITC and TRITC).
b.) React the antibody with a specimen believed to contain the antigen.
c.) Observe under a fluorescent microscope (ultraviolet light excites fluorescent dye to emit visible light), if the antigen is there it will glow.
FLUORESCENCE ACTIVATED CELL SORTER -- FACS (See Tortora pg.459, fig.18.14)
This instrument will count and physically separate cells that have been stained with fluorescent antibodies. For instance, one could count the number of CD4+ and CD8+ cells in a sample.
3.) AGGLUTINATION AND PRECIPITATION TESTS
These types of tests have long been used to diagnose bacterial and viral diseases, autoimmune diseases and even pregnancy. Be sure to read what your book says about them.
Precipitation reactions: Tortora figures 18.2, 18.3, 18.4
Agglutination reactions: Tortora figures 18.6, 18.7, 18.8, 18.9, 18.10