Re: How many T-Cells are in the human body?

Hello Brian,
I am not sure of the exact answer to your question, and it does vary among 
different people a bit.

Here is the way I come up with my best estimate:

1. Human blood has about one million T cells in every milliliter (ml).
(About 29ml is equal to one fluid ounce.)

2. The average adult human has about 10 liters (about 2 1/2 gallons) of 
blood.

3. There are 10,000 ml in 10 L. So, there are about one million x 10,000 T 
cells in the bloodstream. This comes to 10 to the 10th power or a 1 with 
10 zeros after it.

4. About 1/50 of all T cells are found in the blood. Most of the rest are 
in the spleen and lymph nodes. Some are also found in the bone marrow, 
liver, Peyer's patchs (small structures on the intestinal lining) and 
other tissues.

5. So, I would estimate the number of T cells in the human body to be 
about 5 x 10 to the 11th power, or a 5 with 11 zeros after it.

This number should be lower in smaller people because there is less room 
for T cells. It also should be lower in people who have any sort of 
difficulty that causes low T cell numbers, including cancer patients 
receiving chemotherapy or irradiation and also including AIDS patients.

Regards,
Jeff
jdorfman@nih.gov