Wednesday, February 8, 2012

Background on Type IV Immune response (part 4 of x)

Info  excerpted from MedScape

This is a continuation from 3 prior posts:

Seeking information.......Granulomas, histiocytosis, type IV immune response.... (part 1 of x in this series)

So what is the cause of these pseudotumors after the second revision? (part 2 of x in this series)

Granulomas, necrotic pseudotumors post revision.....what is the story on this? (part 3 of x)

I am examining this topic of type IV immune response as researchers in the prior posts suggested that the appearance of these "tumors" post surgery might be related to this type of response.  I have no idea what they are related to so I thought I would investigate this topic since I am faced with this question in my own situation now.

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Delayed hypersensitivity reactions are inflammatory reactions initiated by mononuclear leukocytes. The term delayed is used to differentiate a secondary cellular response, which appears 48-72 hours after antigen exposure, from an immediate hypersensitivity response, which generally appears within 12 minutes of an antigen challenge. These reactions are mediated by T cells and monocytes/macrophages rather than by antibodies. They are also termed type IV hypersensitivity reactions.

Delayed hypersensitivity is a major mechanism of defense against various intracellular pathogens, including mycobacteria, fungi, and certain parasites, and it occurs in transplant rejection and tumor immunity. The central role of CD4+ T cells in delayed hypersensitivity is illustrated in patients with AIDS. Because of the loss of CD4+ cells, the host response against intracellular pathogens such as Mycobacterium tuberculosis is markedly impaired. The bacteria are engulfed by macrophages but are not killed.

If T-cell function is abnormal, the patient presents with opportunistic infections, including infection with mycobacteria, fungi, parasites, and, often, mucocutaneous candidiasis. Undesirable consequences of delayed-type hypersensitivity (DTH) reactions include illness such as contact dermatitis and allograft rejection. Examples of DTH reactions are contact dermatitis (eg, poison ivy rash), tuberculin skin test reactions, granulomatous inflammation (eg, sarcoidosis, Crohn disease), allograft rejection, graft versus host disease, and autoimmune hypersensitivity reactions. Of note, the Rhus genus of plants, which includes poison ivy, poison oak, and poison sumac, all cause identical rashes.
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 For those of you who are reading this for the first time definitionscan be found in the prior posts listed above.


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