CD4 cells: numbers/lifespan

[gvolts5]

I have these questions:

1.  How many CD4 cells in a mL?

2.  Does more than one copy of the virus attach to one CD4 cell?

3.  Can the virus attach to anything but a CD4 cell?

4.  Why doesn't the virus attach to T8 cells?

5.  Does the virus instantly attach to a CD4 cell or does it float around first?

6.  How long does it take for the virus to die if it can't attach to a CD4 cell?

7.  How long does it take the virus to kill off a CD4 cell?

8.  How many copies of the virus are usually made from one CD4 cell?

9.  Blixer made about 4.14 CD4 cells per day in his best month, has this record been topped?

10. What's the normal average number of CD4 cells a person usually makes per day?

11. What controls the number of CD4 cells that are produced?

12. Is there a drug that can make the body produce more CD4 cells?

thanks,
John

[gerry]

The articles at the UCSF site might help answer some of your questions:
http://hivinsite.ucsf.edu/InSite?page=kb-00#S2.1X

[Ann]

Hi gvolts,

You may also find this website helpful:

http://www.freebooks4doctors.com/

Hope that helps.

Ann

[newt]

Hello

In order:

1.  How many CD4 cells in a mL?

Normally, 500,000+ [corrected, see below] in a mL of peripheral blood

2.  Does more than one copy of the virus attach to one CD4 cell?

Yes.

3.  Can the virus attach to anything but a CD4 cell?

Yes, other white blood cells, for example.  CD4 is commonly used for counts etc cos it is this part of the immune system it attacks the most, and its easy to measure via a simple blood test. HIV virus also floats free in plasma & cerebrospinal fluid, and it is possible, though complicated and usually not clinically useful, to measure this.

4.  Why doesn't the virus attach to T8 cells?

They don't have the right protein shape / gene expression on the surface to allow HIV to join.

5.  Does the virus instantly attach to a CD4 cell or does it float around first?

Floats. Like a piranha.

6.  How long does it take for the virus to die if it can't attach to a CD4 cell?

A good queston.  There's no reason for it to die for a long time, it doesn't need to do anything to survive like eat or respirate, it's just some information to enable replication in the form of a string of proteins waiting for the right conditions to blossom.

7.  How long does it take the virus to kill off a CD4 cell?

Dunno.

8.  How many copies of the virus are usually made from one CD4 cell?

Dunno.  More than 1 for sure.

9.  Blixer made about 4.14 CD4 cells per day in his best month, has this record been topped?

Is there a world record. 

10. What's the normal average number of CD4 cells a person usually makes per day?

As long as your CD4 is over 300 you have, basically, a functional immune system. So who's counting?

11. What controls the number of CD4 cells that are produced?

Thymus (hence in T for thymus in "T-helper")

12. Is there a drug that can make the body produce more CD4 cells?

Some drugs eg human growth hormone, interferon interleukin [see below] (and one or two others) raise CD4 but only temporary like (well, maybe not for HGH...). T20 produces an interesting increase in CD4 count.  PIs and the new entry inhibitor Maraviroc seem to produce higher CD4 increases than NNRTIs like Sustiva.

- matt

Now playing: Slo Mo, Grab Hold

[newt]

This is one of many good primers on HIV & immunology on the Internet:

http://www.learner.org/channel/courses/biology/textbook/hiv/index.html

Slightly different, these are also good:

HIV Medicine: online textbook (clinical)

i-Base: Treatment training for advocates - PDFs and PowerPoint slide sets, everything from organs of the body to opportunistic infections

- matt

[gerry]

Hey Matt,

I will correct your answer to question #1 (it's a trick question, you know, see the other thread about mL and mm3).  CD4 is reported as "per mm3" so to convert it to per mL, just multiply it by 1000.

Cheers,
Gerry

P.S. Regarding item #7, it depends if the CD4 is resting or activated.  Activated CD4s only last a couple of days whereas the life span of resting CD4 cells is still being debated.

[newt]

mL / mm³ . . . thanks, always get it wrong (still  - matt

Now playing: London Gay Mens Chorus, Moon River

[Ann]

Matt,

Did you mean by chance interleukin instead of interferon? Interferon normally decreases CD4s but can also decrease hiv viral load. It did for me and others I know of as well. (or am I mistaken and it was the ribavirin doing that?)

Ann

[gvolts5]

Thanks Matt.  And thanks Ann for the links.  I'm sure you both already have the NIH webcast url.  I think a combination of lectures and readings works best.  And quizzes.  And writing papers.  Has a side-effect of drowsiness.

http://videocast.nih.gov/default.asp 

John

[Oh501sguy]

My god...you guys are really with it.  I've been poz going on 14 years and didn't know most of
that info.

I think I need to get with the program eh?

Chuck

[newt]

Annnnnn, yes interleukin . . . - matt

[thirtysomething]

Ask these question to your doctor and see if he is able to answer  all of it ;-)

[red_Dragon888]

these are questions I would never thought to ask.  thanks

[HIVworker]

Your questions have already pretty much been answered well by Newt and Gerry. However, I can help fill in some of the blanks based on what I have read.

2.  Does more than one copy of the virus attach to one CD4 cell?

One is enough, but more than one can attach and infect a cell. However, once a cell has been infected and is making HIV, due to a process that causes the CD4 receptor to downregulate, no more HIV particles can infect that cell.

3.  Can the virus attach to anything but a CD4 cell? 

We forgot macrophages.

5.  Does the virus instantly attach to a CD4 cell or does it float around first?

They can float around, looking for a T-cell, but there is some evidence that cells can pass HIV between them. This is thought to be important in initial infection as one idea is that dendritic cells harbor HIV and 'give' them to CD4 cells in what is called an immune synapse. Basically pouring HIV onto the CD4 cell as they communicate.

6.  How long does it take for the virus to die if it can't attach to a CD4 cell?

Although a virus doesn't require anything, in tissue culture experiments in vitro they are actually quite labile. Their half-life is a matter of hours at 37oC. This is outside of the body in human serum. The problem for HIV in vitro can be due to shedding of the gp120 protein or even lysis of the virus. The viral particles don't like manipulation, meaning they are labile.

7.  How long does it take the virus to kill off a CD4 cell?

Again in tissue culture the cells die within 3 days. This could be partly an artifact of cell-cell fusion - as infected cells (that express the fusion protein) fuse to non-infected cells. In cells that have a low amount of CD4, and fuse less frequently, the cells die a little slower. The loss of CD4 cells during infection is more likely to be a product of their destruction by CD8 cells - as they body becomes wise to a foreign body and kills them off. The drop in viral load after acute infection and during HAART is a product not of the virus being killed by the drugs/immune system but more likely due to the continued clearance of CD4 cells that are infected. The loss of infected CD4 cells leads to a loss of viral load.

8.  How many copies of the virus are usually made from one CD4 cell?

It can be a few thousand.

I hope that helps clarify a few things for you.

Rich

[ChrisNCoronado]

Matt & Rich -

You guys are everything that is RIGHT about AM in general and Living With, in particular.

Seriously, thanks.

-Chris