Biology Reference
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from another person would have quite a different distribution (donor 20),
and, significantly, in some cases their serum antibody would bind to some
larvae strongly and to others weakly or not at all (donor 13). These
experiments required careful controls because the pool of larvae used
would have been undergoing development, but the results nevertheless
indicated a high degree of diversity in surface antigens.
These observations clearly have important implications for the
immunobiology of ascariasis, but have not yet been pursued. One way to
look more closely at antigenic diversity of Ascaris larvae would be to use
monoclonal antibodies. Being monospecific, monoclonal antibodies
should discriminate between larvae that do and do not express a partic-
ular antigenic determinant (epitope) more effectively than can poly-
specific serum antibody from infected people. Just such an approach has
already revealed that larvae of Trichostrongylus colubriformis also exhibit
antigenic diversity.
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45
25
Normal human serum
Donor 18
40
20
35
30
15
25
20
10
15
10
5
5
0
0
0
100
200
300
400
500
600
700
800
0
200
400
600
800
25
25
Donor 20
Donor 13
20
20
15
15
10
10
5
5
0
0
0
200
400
600
800
0
200
400
600
800
Relative fluorescence intensity (arbitrary units)
FIGURE 3.5
Diversity of the antigens exposed on the surface of
Ascaris
larvae.
Infective larvae hatched from the same pool of eggs were incubated with serum from each
of three people infected with A. lumbricoides and the degree of antibody binding to indi-
vidual larvae measured using a microscope-based quantitative immunofluorescence
method. This showed that some people produce antibody that bind similarly to the larvae
(donor 18), some produce high levels of antibody to the larval surface (donor 20), but
antibody from others (donor 13) bind to some larvae intensely, some intermediately, but to
others not at all. The inference from this is that the surface antigens of the larvae are diverse.
It should be noted that the larvae used are cultured in vitro and undergoing development, so
careful controls had to be carried out. See.
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