All women have an increased risk of developing breast cancer for the first 5-10 years after giving birth. One possible reason for this link is involution. Involution occurs after lactation (or after childbirth if the mother doesn't breast feed). It is the body's way of restructuring the mammary tissue to return back to its pre-pregnancy state. This is done in part by apoptosis of epithelial cells in the mammary gland. Other mammary epithelial cells become phagocytic and eat the dead cells, but macrophages will also arrive at the scene.
It has been shown that these macrophages get stimutated to the M2 variety of macrophage. Because M2 macrophages are anti-inflammatory, which is tumor promotional, these M2 macrophages may be what links breast cancer with pregnancy.
My project was to test an in vitro model of this mechanism with mouse cells. Before I started my project, mammary epithelial cells were grown, stimulated to become phagocytic, and then fed apoptotic cells. This was all done in order to mimic what occurs in an involuting mammary gland. The supernatant (conditioned media) was collected off these cell cultures and used for my experiments.
I first wanted to verify that I could get M2 macrophages from activation with the supernatant. I did this by taking bone marrow derived macrophages activated with the conditioned media. There are several controls for the conditioned media as well as controls of known M1 and known M2 macrophages. The phenotypes of the conditioned media activated macrophages were confirmed to match the M2 phenotype by western blots of the cytokines produced.
To test whether the macrophages activated by conditioned media would respond to antigen in an inflammatory way, I stimulated the cells with LPS and measured pro-inflammatory cytokines. This data is still being analyzed.
I noticed that one of the cytokines, CD86, was lowered in both the M2 macrophages and my conditioned media activated macrophages. CD86 is required to activate T cells, so having decreased amounts would indicate that they may not be able to activate T cells. A future direction would be to do a T cell activation assay to test this out.
So far my data supports the hypothesis. Unfortunately, there is only so much that can be done in one rotation.
This is very fascinating; I've heard of the connection before but never understand the mechanisms nor the restructuring of the mammary epithelium...now it all appears much clearer. Though it is limited, I think the research could be continued.
ReplyDeleteMacrophages here appear to be detrimental now because they are immunoreactive to self-tissue in the breasts. However, I don't know how this could pose as much of an issue for cancer, where you are dealing with an excessively-growing tumor instead of general destruction of the epithelial cells. Are there other cells that produce CD86 that could compensate to activate T cells in lieu of the macrophages? I would think that since the majority of women do not develop breast cancer, there must be multiple routes to this expression as occurs in many other pathways in the body.
Perhaps I have not read enough of the outside research, but these are my first thoughts. Truly interesting connection though, something I had not considered.
Naturally, you don't want an inflammatory response to the clearing up of dead self tissue, so it is a good thing that T cells are suppressed and pro- inflammatory cytokines are turned off. This enviroment is adventageous for cancer though, so it can grow without inhibition.
ReplyDeleteI should have also mentioned, that I wasn't looking at what caused the cancer to develop in the first place, just what might be allowing it to trive in mammary glands until it grows to a point where the immune system can't get rid of it. Once the tumors become metastatic, possibly related to the same mechanisms that makes epithelial cells phagocytic, they can spread to a more important organ like the lungs or brain.
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