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In healthy adults, the number of T4 cells make up

between 32% and 68% of the total number of lymphocytes

a large group of white blood cells that include T4 cells

In fact, the lab uses the T4 percentage to determine

the number of T4 cells in a sample of blood.

 

The T4 percentage is sometimes

a more reliable measurement than the

T4 count because it tends to vary less

between measurements. For example, one

person's T4 count may vary between 200

and 300 over a several month period while

their T4 percentage remains constant at,

say, 21%. Provided that the T4 percentage

stays at 21% or higher, the immune system

still appears to be functioning properly,

regardless of what the T4 count is. At the

same time, a T4 percentage at or below 13% –

regardless of what the actual T4 count is –

usually means that the immune system is damaged

and that it is time to begin prophylactic treatment

(drugs to prevent diseases) for opportunistic

infections like PCP.

 

Imagine that you have all the letters of the alphabet

floating around inside your Tcells. When you are healthy,

you have lots of each letter. When your body is under attack

by a particular germ, virus, bacteria or parasite, the immune

system must "spell out" a particular word in order to combat it.

 

For example, let's say I had the onset of an infection.

In order to fight it, my immune system would need to

"spell out" the word "zebra." Each cd4/cd8 represents

a letter or "type" of fighter cell. If I didn't have

any "b's" left, then I wouldn't be able to fight the

infection with the same effectiveness, but it could

still pull through. Now if I was missing "b's" and "z's"

and was running low on "r's" then it gets almost impossible

for my body to fight off this infection. And if another

infection sets in that also requires any of those same

letters, then I could be in serious trouble.

 

When your T-Cells are low, and they climb back up, it's

a good thing. Absolutely. Tcells reproduce BUT they only

reproduce copies of themselves, of course. So, basically,

when you run out of "b's" you're out of "b's forever.

There are none there to reproduce and that "type" of figher

cell is now extinct in your system. But that's ok. If you

take care of yourself and stay on top of your health, you

can still avoid any nasty attacks on your immune system.

 

This is why it's called an "opportunistic infection."

If there are missing "letters" in your body's defense

system, then the "opportunity" is there for an infection

to progress and eventually overwhelm you and possibly kill you.

 

The more Tcells you preserve in the beginning, the more

of each letter you can hang onto.

 

 

 When the immune system becomes suppressed,

 some of the letters are lost. However, it's not

 clear at what T-cell count -- less than 200??? --

 that holes in the alphabet occur. It's also not clear

 if this happens to everyone. For example, some people

 with seriously suppressed T-cell counts may still

 have enough (albeit a low number) of all the letters

 to keep opportunistic infections at bay... at least

 for a period of time. Obviously, people who lose

 important letters run the greatest risk of becoming

 sick (unfortunately, there are no laboratory tests

 to check for all these letters).

 

Now, as for people who start treatment, it's true that

the letters that are still present begin multiplying.

However, research has determined that, once the virus

is put under control, the bone marrow begins turning

out "naive" T-cells... sort of like blank Scrabble

pieces. Provided that the virus remains under control,

those blank Scrabble pieces can be trained to respond

to certain germs that can invade the body... which means

that they adopt a letter that is missing from the alphabet.

And over time, these cells multiply... which further

helps keep people out of harms way. It can take several

months for all the letters to be replaced... and sometimes,

certain letters really are gone for good... but there's

plenty of evidence to suggest that antiretroviral treatment

is effective in bringing back letters that are necessary

to fight disease.