First we settle the issue of the surface of the small intestine in a healthy individual. The surface, due to the foldings and stretchings is close to the size of a tennis court, say 300 m2.

300 m2 = 3 x 106 cm2 . Adult human has some 1012 lymphocytes, and maybe 1011 macrophages. If we assume that 10% of all macrophages are in the small intestine (this would be an upper limit, the true number is probably less), then there are 1010 macrophages in the small intestine, which in turn gives 3,000 macrophages per cm2 . If this seems for the reader a too large number, than one could say that each an area of 3 mm2  is patrolled by a macrophage. One square mm is a huge area for a macrophage. But of course the topography is such that they crowd where they are needed. Due to uneven distribution there can be area where a hundred fold “crowding” occurs.

Answer: 3,000 macrophages per cm2 small intestine

Thank you very much for your answer and your very helpful input! (I apologise for the delayed response)

I came to slightly different results, which are a bit higher (because actually I found 3000 macrophages / cm2) rather few.

I based my calculation now on the following:

• amount of lymphocytes is quite well known (1-2 x 1012 on average; http://www.ncbi.nlm.nih.gov/books/NBK26921/), accounting for 20-25 % of the total White Blood Cell Count (WBC)
• I used this to calculate back to what might be expected as 100 % (between 5-8 x 1012)
• of this total count, monocytes account for 3-8% (somewhere between 1.5-6.4 x 1011; http://kirschner.med.harvard.edu/files/bionumbers/Blood%20cell%20data.pdf)
• I stuck to the max 10 % of the monocytes ending up in the intestine (I didn't find any numbers confirming that, but keeping in mind that the intestine is described as the largest pool of tissue marophages I think it's reasonable to assume; doi:10.1038/mi.2010.66; http://gut.bmj.com/content/63/12/1980.full.pdf), ending up with 1.5-6.4 x 1010
• also sticking to the surface area of 300 m2 I arrived at a minimum of 5000 macrophages per cm2 

Altogether, I'm quite happy with these numbers. Even saying between 3000 and 5000 is fine for me. I needed to know which amount I mustn't come below.

Thanks again!

Actually.... I just came across this http://www.sciencedaily.com/releases/2014/04/140423111505.htm, doi:10.3109/00365521.2014.898326.

So if that is true... the intestinal area is only 27-37m2 and the amount of macrophages per cm2 at least 3.24x104.

I don't have full access to the paper and only briefly looked through stuff related to it. Does anybody have a qualified opinion regarding the new info on the intestinal surface area?

Dear Angela, the tennis court metaphor is from Prof. Helena Tlaskalova, specialist of Mucosal immunity (Academy of Sciences, Prague), and it is to be found everywhere in literature (this does not make in more true, but nobody challenged this notion). Look up this: The human small intestines have the surface area of a of a tennis court! The intestines connect the stomach to the anus and are part of your digestive tract. The small .. ...

www.omgfacts.com/....

Please, type in Google the following words: tennis court intestine.

Continue from there

Ivan