infection of the same microbes, and is quicker,
more intense than the primary one.ImmunoLogICAL dIsorders
• The immune system is a remarkably effective
structure that incorporates specificity, inducibility
and adaptation.
• Failures of host defense do occur, however, and fall
into three broad categories : immunodeficiency,
autoimmunity and hypersensitivity or allergies.Immunodeficiencies
• Immunodeficiencies occur when one or more of the
components of the immune system are inactive due
to gene mutations, infections, malnutrition or
accident.• A person suffering from an immunodeficiency disease
is liable to suffer from diseases which normally would
not occur (opportunistic diseases).• SCID and AIDS are two common immunodeficiency
diseases.
• SCID or Severe Combined Immuno Deficiency
is a defect in the specialized white
blood cells (B and T-cells)
that represents a group
o f ra r e, s o m e t i m e s
fatal, c o n g e n i t a l
disorders
characterized by
little or no immune
response.
• AIDS or Acquired
I m m u n o D e f i c i e n c y
Syndrome means deficiency
of immune system, acquired during the lifetime of
an individual indicating that it is not a congenital
disease.
• AIDS is a disorder of cell mediated immune system
of the body. There is a reduction in the number of
helper T-cells which stimulate antibody production by
B-cells. This results in the loss of natural defence
against viral infection.
• HIV is a retrovirus that attacks helper T-cells. The
virus is spherical with a diameter of about 90-120 nm.
Its genome consists of a single-stranded RNA.
• After the entrance of the virus into the body of the
person, the virus enters into macrophages, where RNA
genome of the virus replicates to form viral DNA with
the help of reverse transcriptase enzyme.
• This viral DNA gets incorporated into the cell’s DNA,
and directs the infected cells to produce viruses.
• The macrophages continue to produce virus progeny
and in this way act like a HIV factory.
• Simultaneously, HIV enters into helper T-lymphocytes
(TH), replicates and produces progeny viruses.
• The progeny viruses released in the blood attack
other helper T-lymphocytes.
• This is repeated, leading to a progressive decrease
in the number of helper T-lymphocytes in the body
of the infected person.
• During this period, the person suffers from bouts of
fever, diarrhoea and weight loss.
• Due to decrease in the number of helper T lymphocytes,
the person starts suffering from infections that could
have been otherwise overcome, such as those due to
bacteria especially Mycobacterium, viruses, fungi and
even parasites like Toxoplasma.
• Virus of AIDS is transmitted
by transfusion of infected
blood or blood products,
use of contaminated
needles and syringes to
inject drugs or vaccines,
sexual intercourse with an
infected partner without
a condom, and from an
infected mother to a child
through placenta.