Essay About Helper T Cells And Effects Of Hiv Mutations

The Effects of Hiv Mutations on the Immune System
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INTRODUCTION The topic of this paper is the human
immunodeficiency virus, HIV, and whether or not mutations
undergone by the virus allow it to survive in the immune system. The cost of
treating all persons with AIDS in 1993 in the United States was $7.8 billion,
and it is estimated that 20,000 new cases of AIDS are reported every 3 months
to the CDC. This question dealing with how HIV survives in the immune system
is of critical importance, not only in the search for a cure for the virus
and its inevitable syndrome, AIDS (Acquired Immunodeficiency Syndrome), but
also so that over 500,000 Americans already infected with the virus could be
saved. This is possible because if we know that HIV survives through
mutations then we might be able to come up with a type of drug to retard
these mutations allowing the immune system time to expunge it before the
onset of AIDS. BACKGROUND In order to be able to fully comprehend and analyze
this question we must first ascertain what HIV is, how the body attempts to
counter the effects of viruses in general, and how HIV infects the body.
Definition HIV is the virus that causes AIDS. HIV is classified as a RNA
Retrovirus. A retrovirus uses RNA templates to produce DNA. For example,
within the core of HIV is a double molecule of ribonucleic acid, RNA. When
the virus invades a cell, this genetic material is replicated in the form of
DNA . But, in order to do so, HIV must first be able to produce a particular
enzyme that can construct a DNA molecule using an RNA template. This enzyme,
called RNA-directed DNA polymerase, is also referred to as reverse
transcriptase because it reverses the normal cellular process of
transcription. The DNA molecules produced by reverse transcription are then
inserted into the genetic material of the host cell, where they are
co-replicated with the hosts chromosomes; they are thereby distributed to
all daughter cells during subsequent cell divisions. Then in one or more of
these daughter cells, the virus produces RNA copies of its genetic material.
These new HIV clones become covered with protein coats and leave the cell to
find other host cells where they can repeat the life cycle. The Body Fights
Back As viruses begin to invade the body, a few are consumed by macrophages,
which seize their antigens and display them on their own surfaces. Among
millions of helper T cells circulating in the bloodstream, a select few are
programmed to “read” that antigen. Binding the macrophage, the T cell becomes
activated. Once activated, helper T cells begin to multiply. They then
stimulate the multiplication of those few killer T cells and B cells that are
sensitive to the invading viruses. As the number of B cells increases, helper
T cells signal them to start producing antibodies. Meanwhile, some of the
viruses have entered cells of the body – the only place they are able to
replicate. Killer T cells will sacrifice these cells by chemically puncturing
their membranes, letting the contents spill out, thus disrupting the viral
replication cycle. Antibodies then neutralize the viruses by binding directly
to their surfaces, preventing them from attacking other cells. Additionally,
they precipitate chemical reactions that actually destroy the infected cells.
As the infection is contained, suppresser T cells halt the entire range of
immune responses, preventing them from spiraling out of control. Memory T and
B cells are left in the blood and lymphatic system, ready to move quickly
should the same virus once again invade the body. HIVs Life Cycle In the
initial stage of HIV infection, the virus colonizes helper T cells,
specifically CD4+ cells, and macrophages, while replicating itself relatively
unnoticed. As the amount of the virus soars, the number of helper cells
falls; macrophages die as well. The infected T cells perish as thousands of
new viral particles erupt from the cell membrane. Soon, though, cytotoxic T
and B lymphocytes kill many virus-infected cells and viral particles. These
effects limit viral growth and allow the body an opportunity to temporarily
restore its supply of helper cells to almost normal concentrations. It is at
this time the virus enters its second stage. Throughout this second phase the
immune system functions well, and the net concentration of measurable virus
remains relatively low. But after a period of time, the viral level rises
gradually, in parallel with a decline in the helper population. These helper
T and B lymphocytes are not lost because the bodys ability to produce new
helper cells is impaired, but because the virus and cytotoxic cells are
destroying