Transcript Immunity to parasites

Parasitology
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Introduction
Immunity to parasites

Over millions of years of evolutions, parasites
become well adapted to their hosts and show
marked host specificity.
e.g.
[ The malarial parasites of birds, rodents or
man can each multiply only in their own
particular kind of host].
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
There are some exceptions for the host
specificity.
e.g.
Toxoplasma not only able to invade and
multiply in all nucleated mammalian cells,
but can also infect immature mammalian
erythrocytes of birds.
The pig ‘s tapeworm can infect man.
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 Host
resistance
may
be
controlled
by
a number of immune response genes.

Studies revealed that even in a small community
people might vary greatly in their risk of infection
through differences in their exposure to the invasive
parasites.

The development of immunity is a complex process
arising from the interactions of many different kinds
of cells over a period of time.
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 The effect is often local.

Many cell types secreting several different
mediators , may be present at the site of immune
rejection.

Moreover, the processes involved in controlling
the multiplication of a parasite within infected
individual may differ from those responsible for
the ultimate development of resistance to
further infection.
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
In some helminthes infections a process called
“ Concomitant Immunity ”
occurs, whereby
an initial infection is not eliminated but established,
and the host then acquires resistance to invasion by
new worms of the same species.

In general, Humoral responses are necessary to
eliminate extracellular parasites such as those live in
blood or body fluids.
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
For
example,
antibody,
alone
or
with
complement can damage some extracellular
parasites, but better when acting with effector
cells as macrophages or neutrophils.

Thus malarial antibodies against extracellular
forms blocks their capacity to invade new cells
but
cell-mediated
response
prevent
the
development of the liver stage within liver cells.
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The First Line Defense Effector Cells
1
Macrophages
2
Neutrophils
3
Eosinophils
4
Platelets
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 Macrophages: Protect against small parasites and also
larger one, when stimulated by cytokines.
e.g.
[ It kills erythrocytic stage of malaria and
large larval stage of Schistosoma].
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 Neutrophils: Can kill large and small parasites.
e.g.
[ With complement it is more destructive to
larvae of S. mansoni & T. spiralis than
eosinophils].
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 Eosinophils: Are characteristically associated with
worm infections and evolved specifically
as a defense against the tissue stage of
parasites
that are too large to be
phagocytosed.
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 Platelets: Can also kill many types of parasites.
e.g.
[ Larval stage of flukes, toxoplasma and
Trypanosome cruzi ]
 Their activity enhanced by cytokines.
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 Praziquantel
is very safe, taken as a single or
divided dose according to the worm type.
 Dose
is calculated according to the patient weight.
 Praziquantel
is swallowed, not chewed; as it is very
bitter in taste.