I wonder whether Jonathan really  had asked us  about which orпan/tissue from one can best get macrophages for culturing (as most of answerers  evidently understood him) or about organs in which a significant population of resident (sic!) macrophages plays  an important functional role. I believe these are two different questions. and answers are not the same.  It is rather easy to get macrophages for in vitro experiments from peritoneum by washing it (even without preliminary activation) but I am not sure that  their role in situ is great1). On the contrary, the red pulp of the spleen would not be able to catch senescent erythrocytes from the blood for utilisation if it were not rich in resident macropgages, but if you look simply for a convenient source of macropgahes for culture,  the spleen or the liver (in which Kupfer cells also have a very important function) would not be the best choice.

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1) Moreover, I am not sure that peritoneal macrophages meet definition of the resident ones as a tissue-specific poulation of macrophages self-maintaining locally  with only  minimal contribution from circulating monocytes.

Hi Jonathan ,

Even without activation, resident macrophages can be isolated from certain organs/tissues like; Peritoneal cavity and Spleen. Apart from these Lungs (alveolar), Liver (Kupffer Macrophages) and Brain (Microglial cells) are other source organs where macrophages reside in a reasonable number.

Best

Bronchoalveolar space is very rich place about resident Macrophages

peritoneal cavity and spleen would be a good source.

Lung is a macrophage rich organ in both alveolar and interstitial compartments. Flow cytometry may distinguish either multiple populations or a range of phenotypes. Recent studies in mice suggest that alveolar macrophages come from a unique precursor in early gestation. This population is long-lived and can proliferate locally.

I propose the liver and the lung for the study.

Human model: the best way is to extract nearly pure resident macrophages from Broncho-Alveolar Fluid in a non-inflammatory context (a sensitive condition). If contaminated by non macrophage cells, a purification by adhesion is easy.

Mouse model: a very attractive protocol is to prepare Bone-Marrow derived macrophages from tibia and femur. The yield is high, with nearly 100% pure and with full resident macrophage properties.

BMDM is a great way to get a lot of primary macrophages, but is a little bit artificial because you must treat with cytokine for several days to get differentiation. 

You can go for alveolar macs, but they are a really weird macrophage population, defined by CD11c and Sigelc F expression.

Depends on your needs, but in most cases when I need primary macrophages that are unactivated for an in vitro experiment  I take from the peritoneum. You can also use thioglycollate to cause macrophage recruitment in the peritoneum but that is an inflammation condition and the macrophages will be activated.

I wonder whether Jonathan really  had asked us  about which orпan/tissue from one can best get macrophages for culturing (as most of answerers  evidently understood him) or about organs in which a significant population of resident (sic!) macrophages plays  an important functional role. I believe these are two different questions. and answers are not the same.  It is rather easy to get macrophages for in vitro experiments from peritoneum by washing it (even without preliminary activation) but I am not sure that  their role in situ is great1). On the contrary, the red pulp of the spleen would not be able to catch senescent erythrocytes from the blood for utilisation if it were not rich in resident macropgages, but if you look simply for a convenient source of macropgahes for culture,  the spleen or the liver (in which Kupfer cells also have a very important function) would not be the best choice.

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1) Moreover, I am not sure that peritoneal macrophages meet definition of the resident ones as a tissue-specific poulation of macrophages self-maintaining locally  with only  minimal contribution from circulating monocytes.

Hi. In this link there are some tips to you.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2834554/

The largest pool of resident / tissue macrophages you'll find in the lamina propria of the gastrointestinal tract. However, since intestinal macrophages are quite special in their behaviour (e.g. Inflammation anergy) they might not be suitable for your plans. Their phacocytic activity is supposed to not be diminshed / restricted.

Thank you for all of the answers. As Boris pointed out, the question that I asked could be answered in two ways, but my primary interest was not in extracting cells, just more a theoretical question as to what tissue types in the body have high levels of resident macrophages.  We are studying synovium, and even in healthy people, macrophages make up ~20-50% of the resident cells.  I was wondering if this tissue is unique in its very high percentage of macrophages.   It looks like the lung, GI tract, liver and brain also have a high number of resident macrophages, although I am not clear on what the relative percentages would be.  

In the lamina propria, macrophages are said to constitute for 10-20 % of mononuclear cells (e.g. http://dx.doi.org/10.1016/j.jim.2014.05.002 or http://www.jleukbio.org/content/70/2/241.full). Especially the second article cites numerous sources that investigated / quantified intestinal macrophages (I didn't have access to all of them).

Dear Jonathabn, I am glad that I undersood your Q correctly. To add: (1) do not forget spleen; (2) in rats liver's  histology we usually see (in controls) about    30-40       Kupfer cells per  100 hepatocytes

Hi Jonathan, the lungs is a great source of macrophages. The differential cell counts of the bronchoalveolar lavage fluid show around 90% of alveolar macrophages in the alveoli.They are self maintained and derive from fetal macrophages. They have an interesting biology and they are responsive to several stimuli (LPS, Poly IC and other bacteria). I would highly recommend them. thank you

The spleen has the highest population of macrophages. These cells are referred to as  the littoral cells. Blood can not be used as the source of macrophages  because these cells  are only found in tissues and organs. Their progenitor,  the monocytes are the ones you found in the blood.  The next organ highly populated  with macrophages is the liver. 

I recall reading a paper that indicated about 5-10% macrophages in the spleen in mice.  In B6C3F1 hybrid mice, we routinely find nearly 90% macrophages among cells that can be obtained by peritoneal lavage (e.g., The Journal of Immunology, 2004, 173: 2715–2724; TOXICOLOGICAL SCIENCES 117(2), 314–324 (2010). We usually get about 2-3 x 10^6 per mouse from one lavage with 7-8 ml of PBS with 1% FBS.

Hi Jonathan, I would go for lungs, both alveolar and interstitial macrophages. You can also collect them separately by first performing lung lavage, followed by isolating the macrophages from the lung.

Just adding that bone marrow macrophages are also a good source to have many cells. I prefer not to use peritoneal, as these cells are more monocytic than macrophage like.

I believe that peritoneum is going to be the easiest and not laborious source for resting macrophages. Spleen and Bone Marrow like Christian Drouet said, are tissues that have high levels of resting macrophages too but their explantation is more difficult than peritoneum.

Macrophages are present in large quantities in almost all tissues: from the skin through the lymphoid organs, digestive tract and organs of the airways.

There are two main types of cells: the resident macrophages and interstitial macrophages (or invasive) in an amount approximately equal, if the tissue is not pathological.

If infiltrating macrophages have equal status regardless of the tissue, it is very different for resident macrophages with a specific profile for the tissues.

For example, the lung is constituted of 10% pseudo macrophages, which have as the specific marker CD208 (DClamp).

Synoviocytes are just as interesting because the FLS which are probably of monocytic origin, also share specific markers such as CD13 and many others that we have now under study

Hi not long ago it was published that a huge amount of monocytes, non-circulant but still undifferentiated, was kept in the very spleen where it is thought they can be used like an emergency reservoir for critical need. They are supposed not to be macrophages, but perhaps it can interest you.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2803111/

Is the proportion of macrophages in lung lamina propria of a healthy human also 10-20% as in the gut or less?

liver is the largest solid organ of the body with high number of tissue resident macrophages(kupffer cells)

The observation of Swirski FK et al (Science 2009) has already been mentioned; this demonstration is taken as a reference with my students. To open the concept of a macrophage resident tissue, may I put forward 2 comments

-1. The current paradigm stating that monocytes circulate freely but irreversibly differentiate into dendritic cells (DCs) or macrophages upon tissue entry makes the concept of high level of resident macrophages difficult to consider.

-2. Everybody can observe that vaccination (vaccines with adjuvant) introduces in any child an increase of body temperature, mainly depending on tissue (sub cutaneous) macrophage and DC activation, with subsequent TNF, IL1 and IL6 diffusion, in conjunction with PG local production.

Spleen