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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5512_Библиотеки_им_академика_М_И_Перельмана.pdf
Introduction to Immunology and ciples of Segnosis
Streptococcus, Staphy
lococcus)
J741
Sthylococcal Coagulan
S.
pyogenes, Neisseria gonorrhoeae, S. pneumonia, Haemophilus inuenzae.
Haemaggluan, Haemaggluation-lnhibin, and Neuaan
Reacns ure 23.6b}
142 I
Medical Laborato Technology: Volume 2
haemagglutination inhibition negative agglutination
test
neutralization reaction
in vitro.
anti
streptolysin O test S. pyogenes
titre.
Complement tion
of indicator cells (Figure 23.6c). This method is not as sensitive as the labelled antibody
techniques, such as enzyme immunoassay or EIA, which are described later. Moreover, the
assay is lengthy, complicated to perform, and requires many controls and is therefore not
used routinely. Nevertheless, it is still used in reference laboratories to detect unusual viral or
fungal infections for which test kits are not available.
J743
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Medical Laborato Technology: Volume 2
J745
principle, reacting with the antibody and reagents, thereby forming a colour. The technolo
gy may be complex; however, it is simple to perform and interpret. Many over-the-counter
pregnancy tests are based on this principle. It is also applied to the diagnosis of inuenza and
Streptococcal (Group A) infection.
uorescent Ano Technique
The uorescent antibody (F tests are widely used in laboratories of developing countries
for the diagnosis of T. pallidum, M
such as lupus. In this test, a uorescent dye is cougated to the anti-human antibody. The
antibody is labelled by dyes such as acridine orange or uorescein isothiocyanate. These dyes
uoresce when excited by a beam of ultraviolet (UV) light, which has a high energy and
wavelength shorter than about 364 nm. Fluorescence, the reemission of light in the visible
range, occurs at a lower energy and longer wavelength of about 542 nm. Epiuorescence
microscopes must then be used to read and interpret reactions (Figure 23.6d). These are more
expensive than light microscopes.
FA tests can be direct or indirect and can be used to detect an antibody or an antigen in
a patient specimen. Using either method, the patient's specimen with the organism's anti
gen is reacted with a commercially available microorganism-specic antibody. In the direct
method, this antibody is uorescently labelled. In the indirect method, it is not labelled, but
is followed by a second labelled antibody. Presence of uorescing microorganisms of the
correct morphology indicates that the patient is infected with the suspect microorganism.
Indirect techniques are more sensitive than direct because more than one molecule of the
second uorescent-labelled antibody can bind to the rst antibody, increasing the amount of
uorescence.
cobacterium, Cr
y
ptosporidium, and autoimmune diseases
y
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746 I
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FIGURE 23.7a
a
J747
Prozone Phenomenon
The prozone phenomenon creates a practical problem in reporting the correct titre value when
using the occulation, agglutination, and precipitation tests. Occasionally, occulation or ag
glutination are inhibited via a negative reaction in lower dilutions of the serum that contains
(d)
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B
X,Y
m.
FIGURE 23.7b
the antibody (i.e., the rst few tubes), and a positive reaction is seen in higher dilutions. This
prozone phenomenon occurs because of excessive concentration of the antibody in serum.
The antibody coats the indicator particles (e.g., latex or red cells) that carry the antigen on
the surface. This antibody coating prevents particles from linking to each other, and hence a
reaction may not be observed. When the antibody concentration is reduced by an increased
dilution, the optimal proportion between the antigen (e.g., on latex particles or red cells) and
the antibody molecules (e.g., in serum) develops, and a visible occulation or agglutination
occurs. Hence, one must be careful in reporting the value of the titre; the titre is the highest
dilution of the serum after the initial inhibition is overcome.
14s I
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Introduction to Immunology and ciples of Segnosis
J749
Complement
com
°
REVIEW QUESTIONS
°
True or False:
onent
p
Chapter
Laboratory Procedures in
Serology
Kanai L Mukheee and Chhotelaal Pande
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