A Project of the New Mexico AIDS Education and Training Center. Partially funded by the National Library of Medicine
Fact Sheets can be downloaded from the Internet at http://www.aidsinfonet.org
AIDS InfoNet www.aidsinfonet.org
Fact Sheet Number 124
CD4 CELL TESTS
WHAT ARE CD4 CELLS?
CD4 cells are a type of lymphocyte
(white blood cell). They are an
important part of the immune system.
CD4 cells are sometimes called T-cells.
There are two main types of T-cells. T-4
cells, also called CD4, are “helper”
cells. They lead the attack against
infections. T-8 cells
“suppressor” cells that end the immune
response. CD8 cells can also be “killer”
cells that kill cancer cells and cells
infected with a virus.
Researchers can tell these cells apart
by specific proteins on the cell surface.
A T-4 cell
is a T-cell with CD4
molecules on its surface. This type of T-
cell is also called “CD4 positive,” or
IMPORTANT IN HIV?
When HIV infects humans, the cells it
infects most often are CD4 cells. The
virus becomes part of the cells, and
when they multiply to fight an infection,
they also make more copies of HIV.
When someone is infected with HIV for
a long time, the number of CD4 cells
they have (their CD4 cell count) goes
down. This is a sign that the immune
system is being weakened. The lower
the CD4 cell count, the more likely the
person will get sick.
There are millions of different families of
CD4 cells. Each family is designed to
fight a specific type of germ. When HIV
reduces the number of CD4 cells, some
of these families can be totally wiped
out. You can lose the ability to fight off
the particular germs those families were
designed for. If this happens, you might
develop an opportunistic infection (See
Fact Sheet 500).
WHAT FACTORS INFLUENCE
A CD4 CELL COUNT?
The CD4 cell value bounces around a
lot. Time of day, fatigue, and stress can
affect the test results. It’s best to have
blood drawn at the same ti