Acquired immunodeficiency syndrome (AIDS) is caused by the human immunodeficiency virus (HIV). HIV is a retrovirus that infects CD4 T-lymphocytes and causes immunosuppression. The virus is transmitted via bodily fluids like blood, semen, vaginal secretions. HIV enters cells, converts its RNA to DNA then incorporates into the host cell's genome. This leads to a reduction in CD4 cells and impairment of immune function. Over time AIDS develops, characterized by opportunistic infections as the immune system is compromised.

2.  Acquired immunodeficiency Syndrome (AIDS)
retroviral disease caused by human
immunodeficiency virus (HIV).
 The disease is characterized by
immunosuppression, secondary neoplasma &
neurological manifestation.

3.  Transmission of AIDS essentially requires the
exchange of body fluids (semen, vaginal
secretions, blood, milk) containing the virus
or virus-infected cells.
 Major routes of HIV transmission sexual
contact, parenteral inoculation & from
infected mothers to their newborns.

4.  AIDS is caused by a retrovirus – human
immunodeficiency virus (HIV), belonging to
lentivirus family.
 Retroviruses contain RNA as genetic material.
 On entry into the host cell, they transcribe
DNA which is a complementary copy of RNA.
 The DNA, in turn is used as a template to
produce new viral RNA copies.

5.  HIV-1 & HIV-2 isolated from AIDS patients.
 HIV-1 is more common,
 Found in AIDS patients of USA, Canada, Europe
& Central Africa.
 HIV-2 is mainly found in West Africa.
 Both the viruses are almost similar except they
differ in certain immunological properties.

6.  The virus is spherical with a diameter of about
110 nm.
 It contains a core, surrounded by a lipid
envelop derived from host plasma membrane.
 The core of the HIV has two strands of
genomic RNA & four core proteins, P24, P18,
reverse transcriptase (P56/P51) & endonuclease
(P32).

7.  The lipid membrane of the virus is studded
with two glycoproteins gP120 &gP41.
 The surface antigen gP120 is very important
for the viral infection & the detection of AIDS.
 Genome and gene products of HIV:
 HIV genome contains 3 structural genes –
gag, pol & env that, respectively, code for
core proteins, reverse transcriptase &
envelop proteins.

8.  AIDS primarily affects the cell-mediated
immune system which protects the body
from intracellular parasites such as viruses,
protozoa & mycobacteria.
 This is caused by a reduction in CD4 (cluster
determinant antigen4) cells of T-lymphocytes,
besides impairment in the functions of
surviving CD4 cells.

9.  HIV virus enters CD4 T-lymphocytes.
 Virus binds to specific receptors.
 RNA of HIV is transcribed into DNA by
reverse transcriptase.
 Viral DNA gets incorporated into host
genomic DNA.
 Virus remain locked in host DNA genome for
months or years, considered as latent period.

10.  Viral DNA undergo replication & translation,
producing viral RNA & viral proteins.
 Viral RNA & viral proteins on assembly, result
in new viruses.
 The newly synthesized viruses leave the host
cells by forming buds on plasma membrane.
 Extensive viral budding is associated with lysis
& death of CD4 cells.
 AIDS associated with the reduction in CD4 cells.

11.  HIV also infects the cells of central nervous
system.
 The various clinical symptoms, fever,
diarrhea, weight loss, neurological,
complications, generalized
lymphadenopathy, secondary neoplasma
due to immunosuppression caused by HIV.

12.  Acute phase:
 This represents the initial body response to
HIV infection.
 High rate of production of viruses which are
lodged in lymphoid tissues & antiviral
immune response of the body.
 This period may last for about 8-12 weeks.

13.  Chronic phase:
 This period may last for 5 to 10 years or even
more, the body tries to contain the virus.
 The immune system is largely intact.
 The person appears normal.
 HIV antibodies are found in the circulation,
this phase is also referred to as seropositive
period.

14.  Crisis phase:
 Failure in defense system of body, caused by
immunosuppression by HIV.
 The plasma level of virus is increased.
 CD4 T-lymphocyte concentration drastically
falls.
 A patient with lower than 200 CD4 T-
lymphocytes/µl blood is considered to have
developed AIDS.
 Patients die between 5-10 years.

15.  The detection of antibodies in circulation by
ELISA (enzyme-linked immunosorbant assay).
 Western blot technique, more specific test for
the HIV antibodies, is employed for
confirmation of ELISA positive cases.
 PCR can be used to detect the presence of the
HIV genome in the peripheral blood
lymphocytes.

16.  Zidovudine or AZT (3'-azido 2',3'-
dideoxythymidine) & Didanosine used to
treat AIDS.
 Mechanism of action:
 AZT is taken up by the lymphocytes &
converted to AZT triphosphate which inhibits
the enzyme HIV reverse transcriptase.

17.  AZT triphosphate competes with dTTP for the
synthesis of DNA from viral RNA.
 AZT is added to the growing DNA chain &
the synthesis is halted.
 This drug is not toxic to the T-lymphocytes.
 AZT is found to be toxic to the bone marrow
cells, therefore, the patients develop anemia.

18.  Textbook of Biochemistry - U Satyanarayana
 Textbook of Biochemistry - DM Vasudevan