Talk:Phagocyte

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B Lymphocytes as APCs?

When I was in grad school, the prototypical antigen-presenting cell was the naive B lymphocyte. Doesn't that make them professional phagocytes? I know they have opsonin binding (membrane bound Ig) and they have MHCII. In fact, isn't phagocytosis and antigen presentation by B cells necessary to develop a T-cell mediated antibody response? I know immunology moves pretty fast, so I could see definitions changing.173.8.220.209 (talk) 18:58, 6 August 2009 (UTC)

• All of the above is true, apart from phagocytosis. My understanding is that B cells are "selected" by their cognate antigen, are activated and subsequently proliferate clonally. The antigens that they present to the other cells of the immune system are not derived from phagocytosis as such, these cells take in small antigens—fragments of bacteria for example—bound to the B cell receptor, then process and present them. Their ability to kill by engulfing is very poor, hence their lack of "professional" status. Thanks for an interesting question, which made me think. Graham Colm ^Talk 20:20, 6 August 2009 (UTC)

• • Thanks for the reply, Graham. I guess that the major determination for identification of proffessional phagocytes would be the Fc or Complement receptors? Two things: first, Mast cells? Do they even internalize anything? I thought they just degranulated upon crosslinking of their high-affinity FcE's. Second, check out this link: http://www.ncbi.nlm.nih.gov/pubmed/19494270 . Note, the authors point out that the B cell doesn't kill the Salmonella, but it does internalize it and remove antigens for presentation. Interesting stuff. I miss immunology.173.8.220.209 (talk) 22:33, 6 August 2009 (UTC)

• • • Thanks again, this time for alerting me to this interesting paper, which I hadn't read. With regard to mast cells, as well as being potent poisoners of parasites, they can phagocytose opsonised bacteria.[1] Unlike lymphocytes, they can kill, which is not surprising given all those granules. Clearly, "professional" and "non-professional" are useful labels, but the ability of all the fascinating cells of the immune system to multi-task cannot be overlooked. Graham Colm ^Talk 17:48, 7 August 2009 (UTC)

• • • • I just checked my textbook on immunobiology (Janeway et al), according to which "Dendritic cells, macrophages, and B cells are often known as professional antigen-presenting cells". However, it also explains that B cells are not major phagocytes despite their ability to specifically ingest large amounts of antigen recognized by the BCR. This is mainly because of their extremely narrow specificity and the fact that they do not migrate into tissues like macrophages and dendritic cells love to, and thus less often come face to face with large numbers of pathogens, particularly intact ones. B cells also lack broad-specificity coreceptors that facilitate ingestion of entire microorganisms in macrophages and neutrophils (the latter of which are professional phagocytes but not professional APCs). So those phagocytes can ingest all sorts of things (and dendritic cells can go nuts with macropinocytosis), while B cells are basically limited to just the one antigen their receptor is specific for. So I think it makes sense to exclude B cells from the group of professional phagocytes, while including them in the group of professional APCs. Sakkura (talk) 14:28, 13 August 2009 (UTC)

Copyedit question

I'm puzzled by the following from Phagocyte#Phagocytosis: "Opsonin receptors increase the phagocytosis of bacteria that have been coated with complement or IgG antibodies." Does it mean "complement antibodies or IgG antibodies", or is "complement" a thing in its own right? Also, "Complement is the name given to a complex series of protein molecules found in the blood that destroy or mark cells for destruction." This seems to be saying that the word "complement" in this context, all by itself, means the series.

Complement, or more accurately the complement system, is not an antibody. It is composed of about 20 different proteins that work together to kill bacteria and other invaders. It also stimulates other cells of the immune system into action. The complement system is very old and probably predates antibodies. When these proteins are circulating separately in the body they are called complement proteins. During an infection these proteins come together on the surface of the invader and, along with other activities, punch a hole through the invader's cell membrane. For short these proteins, particularly when they have been activated and coalesce, are simply called "complement". Graham Colm ^Talk

Also, in Phagocyte#Non-professional_phagocytes, "Fibroblasts, for example, only make ineffective attempts to ingest foreign particles." Is "ineffective" the right word? If their attempts are ineffective, they are not phagocytes at all, right? --Milkbreath (talk) 02:35, 30 August 2009 (UTC)

"Ineffective" was the best word I could come up with. The main role of fibroblasts is the formation connective tissue, they can ingest some foreign matter, but are feeble and unpredictable at this. They can engulf but because phagocytosis is far from their prime function as it is currently understood, they are non-professional phagocytes. Graham Colm ^Talk 09:47, 30 August 2009 (UTC)

I've changed the complement sentences to read, "Opsonin receptors increase the phagocytosis of bacteria that have been coated with immunoglobulin G (IgG) antibodies or with complement. "Complement" is the name given to a complex series of protein molecules found in the blood that destroy cells or mark them for destruction." I've changed the fibroblast sentence to read, "Fibroblasts, for example, which can phagocytose collagen in the process of remolding scars will also make some attempt to ingest foreign particles." I hope that this is correct, but there seems to be a problem with the reference note. --Milkbreath (talk) 11:46, 30 August 2009 (UTC)

Thanks for your help with the article. After a lot of searching I have found a better citation. Graham Colm ^Talk 13:43, 30 August 2009 (UTC)

Hey, don't thank me, it's my article, too. By the way, reference 117 is broken. Perhaps you're more familiar with that aspect of this article and could more easily fix it than I could. --Milkbreath (talk) 18:18, 30 August 2009 (UTC)

Yes, that was my doing. I have fixed it for the time being. I shall format the reference, and the new one I added earlier today, properly later when I have the time. Will you accept my thanks for your being a valued collaborator? Graham Colm ^Talk 19:18, 30 August 2009 (UTC)

Aw, shucks ... OK. But all I did was pick a few nits off it. Nice job, guys. --Milkbreath (talk) 19:52, 30 August 2009 (UTC)

Inconsistence

Hello. Can't understand the compatibility between the initial definition: "Phagocytes are the white blood cells that protect the body by ingesting (phagocytosing) harmful foreign particles" and the erythrocytes and other stuff shown later in the article. --3coma14 (talk) 07:21, 12 May 2010 (UTC)

Bacteria

such as bacteria, that are not normally found in the body.

Its wrong, bacteria in normal can be found in body (such us, in the intestine)--Meddoc13 (talk) 17:19, 12 September 2010 (UTC)