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Course: Immunology
Lecturer: Dr. Weam Saad
Lecture: Immune-Tolerance, Immunedificiency and Autoimmunity.
Immunodeficiency
It is the disability of the immune system to fight infectious diseases and
cancers, peoples with immune deficiency are called immune deficient or
immune-compromised or immune-suppressed. These people are easy to get
opportunistic infections which occur more severely than other peoples with
normal immune system, e.g. flu virus can kill human with immune deficiency.
Types of Immune-deficiency:
1. Primary Immune deficiency:
Primary immunodeficiency cases are inherited defects of the immune
system. These defects may be in the specific or nonspecific immune
mechanisms. They are classified on the basis of the site of lesion in the
developmental or differentiation pathway of the immune system. Individuals
with immunodeficiencies are susceptible to a variety of infections and the type
of infection depends on the primary site of immunodeficiency (Table 1).
2.
Secondary Immune deficiency:
This type of immunodeficiency occurs due to external factors and not
inherited. Factors that cause this type of immune deficiency are:
a) Infections that cause Immune deficiency:
The most common example is acquired immunodeficiency syndrome
(AIDS). Secondary immunodeficiency which is caused by HIV virus. This
virus infects T-cells and cause suppression of immune response. Also some
other infections with viruses, bacteria, protozoa and helminthes can lead to
this type immune deficiency.
b)
Physiological diseases that cause Immune deficiency:
Some cancer types can cause immunodeficiency like Leukemia and Lymphoma.
Also some physiological diseases can cause immunodeficiency like diabetes
mellitus.
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c) Aging: can cause Immune deficiency due to reduction in the size of thymus,
a decrease in CD markers of immune cells.
d) External and environmental factors:
Like effects of immunosuppressive drugs, chemotherapy, radiation exposure and
malnutrition or anemia.
Table 1. Characteristic infections of the primary immunodeficiencies
component
primary pathogen
primary site
clinical example
T-cells
intracellular, bacteria
viruses, protozoa,
fungi,
non-specific
SCID, DiGeorge
B-cells
Pneumococcus,
Streptococcus,
Haemophilus
lung, skin, CNS
IgG, IgM deficiency
IgG, IgM deficiency
Enteric bacteria and
viruses
GT, nasal, eye
IgA deficiency
phagocytes
Staphylococcal,
Klebsiella
Pseudomonas,
lung, skin, lymph
node
chronic granulomatous
disease (CGD)
complement
Neisseria,
Haemophilus,
Pneumococcus,
Streptococcus
CNS, lung and skin
C3 components
deficiency
Immune-Tolerance
Tolerance is the specific immunological non-reactivity to an antigen, the most
important form of tolerance is non-reactivity to self-antigens, it is possible to induce
tolerance to non-self-antigens. When an antigen induces tolerance, it is
called tolerogen.
There are many mechanisms for self-antigen tolerance like T-suppressor cells,
receptor editing, Clonal ignorance and Clonal deletion. Sometime human body
needs for induction of tolerance to non-self-antigens like in the cases of tissues or
organs transplantation, e.g. kidneys transplantation and bone marrow grafting.
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Autoimmunity
Defined as an immune response against the human own antigens of the body
due to breakdown of self-tolerance or immune-tolerance to the self-Antigens, that
will cause many diseases called Autoimmune diseases. Scientists suggest the genetic
susceptibility for autoimmune diseases.
Many mechanisms are involved in autoimmunity diseases; Cross reactive
antigens may lead to autoimmunity, Antigens on some pathogens have cross reactive
determinants which with self-antigens and any immune response against these
determinants may lead to reaction against the antigens of the body. For example,
Post streptococcal nephritis and carditis, antibodies during syphilis and association
between Klebsiella and ankylosing spondylitis are examples of autoimmunity due to
cross reactivity. While sometimes the body forms antibodies against its own
Antigens like the autoimmune disease of Systemic Lupus Erythematosus (SLE)
when Auto-antibodies are formed against the body antigens and attack organs and
tissues.