Thursday, February 9, 2012

Background on Type IV Immune response (part 5 of x)

Info excerpted from MedScape

This is a continuation from 4 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)

Background on Type IV Immune response (part 4 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


Pathophysiology Of type IV immune response (hypersensitivity response)

The cellular events that result in delayed hypersensitivity reactions primarily involve T cells and macrophages. First, local immune and inflammatory responses at the site of foreign antigen up-regulate endothelial cell adhesion molecule expression, promoting the accumulation of leukocytes at the tissue site. The antigen is engulfed by macrophages and monocytes and is processed and presented to a T cell that has a specific receptor for that processed antigen. Macrophages secrete interleukin (IL)–1, IL-2, IL-6, and other lymphokines. Cytotoxic T cells can also be activated. The recruited macrophages can form giant cells. The characteristic histologic appearance of the macrophage–T-cell infiltrate is a granuloma. This type of infiltrate in the tissue is called granulomatous inflammation.

T Cells:  T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity

Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells (NK), antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells. CD4 cells or helper T cells provide protection against different pathogens. Cytotoxic T cells cause death by apoptosis without using cytokines, therefore in cell mediated immunity cytokines are not always present.
Cellular immunity protects the body by:
  1. activating antigen-specific cytotoxic T-lymphocytes that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens;
  2. activating macrophages and natural killer cells, enabling them to destroy pathogens; and
  3. stimulating cells to secrete a variety of cytokines that influence the function of other cells involved in adaptive immune responses and innate immune responses.
Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria. It also plays a major role in transplant rejection.

Macrophages function in both non-specific defense (innate immunity) as well as help initiate specific defense mechanisms (adaptive immunity) of vertebrate animals. Their role is to phagocytose (engulf and then digest) cellular debris and pathogens, either as stationary or as mobile cells. They also stimulate lymphocytes and other immune cells to respond to pathogens

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