Enzyme-linked immunosorbent assay (ELISA). This is an objective test for either
antigens or antibodies using a reagent. There are two types of test. These are:- Direct ELISA. The objective is to identify the antibody for a specific anti-
gen. The antibody is placed in the microtiter plate wells where it adsorbs
to the surface of the well. The antigen is then placed in each well. Wells are
then washed. The antigen that reacts to the antibody will be retained and
remain there after the washing. Next a second antibody for the antigen is
added and adsorbed to the well wall. The antigen is sandwiched between
two antibody molecules if the test is positive; otherwise the test is negative.
Direct ELISA is used to detect drugs in urine. - Indirect ELISA. The objective is to identify the antigen for a specific anti-
body. A known antigen is placed in the microtiter plate wells where it
adsorbs to the surface of the well. The antibody is placed in each well and
will bind to the antigen to form an antigen-antibody complex. The wells
are washed to remove antibodies that did not bind. AntiHISG that has
been linked with an enzyme is then placed into the well and reacts to the
antigen-antibody complex in the well. All unbound HISG is rinsed. A
substrate for the enzyme is added. If there is a color change, then the
test is positive.
Radioimmunoassay (RIA). Uses radioactive tags to mark antigens and antibodies.
Samples are then scanned to determine the presence of the tag.Quiz
- What process requires that a needle tip of antigen be placed in a vein of
a patient to give the patient immunity to the antigen?
(a) Half-life process
(b) Jenner process
(c) Variolation process
(d) Antiviral process - Herd immunity requires an entire population to be immunized against an
antigen.
(a) True
(b) False
(^228) CHAPTER 15 Vaccines and Diagnosing Diseases