Course: ImmunologyLecturer: Dr. Weam Saad
Lecture: Immune -Tolerance, Immune dificien cy and Autoimmunity.
ImmunodeficiencyIt 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 depend s 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
(AID S). 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, bacteri a, 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
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 immunodeficienciescomponent primary pathogen primary site clinical example
non -specific SCID, DiGeorge
lung, skin, CNS
IgG, IgM deficiency
IgG, IgM deficiency
Enteric bacteria and
viruses G T, nasal, eye IgA deficiency
lung, skin, lymph
CNS, lung and skin C3 components
Immune -ToleranceTolerance is the specific immunological non -reactivity to an antigen , the most
important form of tole rance is non -reactivity to self -antigens, it is possible to induce
tolerance to non -self -antigens. When an antigen induces tolerance, it is
There are many mechanisms for self -antigen tolerance like T -suppressor cells ,
receptor editing , Clonal ign orance 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.
AutoimmunityDefined 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
antigen s may lead to autoimmunity, Antigens on some pathogens have cross reactive
determina nts which with self -antigens and an y 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 some times 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