790
UNIT 4
Maintenance of the Body
21
Allografs
are grafs transplanted From individuals who are
not genetically identical
but belong to the
same
species.
Xenografs
are grafs
taken from another animal species
, such
as transplanting a baboon heart into a human.
Transplant success depends on the similarity oF the tissues
because NK cells, macrophages, antibodies, and especially T
cells act vigorously to destroy any Foreign tissue. Autografs and
isografs are the ideal donor tissues. Given an adequate blood
supply and no inFection, they are almost always successFul be-
cause the MHC proteins are identical.
SuccessFul xenografs From genetically engineered animals
are still just a promise on the horizon. Consequently, the type
most Frequently used is also the most problematic: the allograf.
±e organ is usually obtained From a living human donor (in
the case oF kidney, liver, or bone marrow) or harvested From a
human donor who has just died (heart or lung).
BeFore an allograf is attempted, the ABO and other blood
group antigens oF donor and recipient must be determined, be-
cause these antigens are also present on most body cells. Next,
recipient and donor tissues are typed to determine their MHC
antigen match. MHC variation among human tissues is tremen-
dous, so matching all MHC antigens is impossible. In general,
however, the closer the match, the less likely is rejection.
²ollowing surgery the patient is treated with
immunosup-
pressive therapy
. ±is involves drugs oF the Following cat-
egories: (1) corticosteroid drugs to suppress inflammation;
cells and molecules oF the adaptive immune response.
Figure
21.20
gives an overview oF the entire primary immune response,
both innate and adaptive. ±e lesson to take away with you is
that without helper T cells,
there is no adaptive immune response
because the helper cells direct or help complete the activation oF
both B cells and T cells. ±eir crucial role in immunity is pain-
Fully evident when they are destroyed, as in AIDS (see p. 793).
Organ Transplants and Prevention
of Rejection
Describe the four varieties of grafts.
Indicate the tests ordered before an organ transplant is
done, and methods used to prevent transplant rejection.
Organ transplants, a viable treatment option For many patients
with end-stage cardiac or renal disease, have been done with
mixed success For over 50 years. Immune rejection presents a
particular problem when the goal is to provide such patients
with Functional organs From a living or recently deceased donor.
±ere are Four varieties oF grafs:
Autografs
are tissue grafs transplanted From one body site
to another in the
same person
.
Isografs
are grafs donated to a patient by a
genetically iden-
tical individual
, the only example being identical twins.
Table 21.6
Selected Cytokines
CYTOKINE
FUNCTION IN IMMUNE RESPONSE
Interferons (IFNs)
 
Alpha (
) and
beta (
)
Secreted by many cells. Have antiviral effects; activate NK cells.
Gamma (
)
Secreted by lymphocytes. Activates macrophages; stimulates synthesis and expression of more class I and II MHC
proteins; promotes differentiation of T
H
cells into T
H
1.
Interleukins (ILs)
 
IL-1
Secreted by activated macrophages. Promotes inflammation and T cell activation; causes fever (acts as a pyrogen that
resets the thermostat of the hypothalamus).
IL-2
Secreted by T
H
cells. Stimulates T and B cell proliferation, T
Reg
cell development, and NK cell activation.
IL-4
Secreted by some T
H
cells. Promotes differentiation to T
H
2; promotes B cell activation; switches antibody production to
IgE.
IL-5
Secreted by some T
H
cells and mast cells. Attracts and activates eosinophils; causes plasma cells to secrete IgA
antibodies.
IL-10
Secreted by macrophages, T
H
, and T
Reg
cells. Inhibits macrophages and dendritic cells; turns down cellular and innate
immune response.
IL-12
Secreted by dendritic cells and macrophages. Stimulates T
C
and NK cell activity; promotes T
H
1 differentiation.
IL-17
Secreted by T
H
17 cells. Important in innate and adaptive immunity and recruiting neutrophils. Involved in
inflammation in many autoimmune diseases.
Suppressor factors
A generic term for a number of cytokines that suppress the immune system, for example TGF-
and IL-10.
Transforming growth
factor beta (TGF-
)
A suppressor factor similar to IL-10; stimulates T
Reg
and T
H
17 cell development.
Tumor necrosis factors
(TNFs)
Produced by lymphocytes and in large amounts by macrophages. Promote inflammation; enhance phagocyte
chemotaxis and nonspecific killing; slow tumor growth by selectively damaging tumor blood vessels; promote cell
death by apoptosis.
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