Thursday, May 20, 2010

How Cancerous Tumors Can Avoid the Immune System

The danger that cancer poses to the patient is the ability of cancerous cells to metastasize – spread throughout the body. This is referred to as a malignancy. Cancers can arise in any tissue i.e. from lung, liver, brain, stomach etc. Cancerous cells are characterized by their capacity to divide out of control, their primitive function and their ability to metastasize. The body’s natural defense against malignant tumors is afforded by the immune system through the production of so-called effector T cells or cytotoxic T lymphocytes that circulate throughout the body, and attack cells that have become malignant.

In response, cancerous cells have been shown to be able to suppress the immune system’s effectiveness. One of the mechanisms that they employ is to reduce the expression of certain proteins on their cell surface that can alert the immune system to their presence; substances that trigger immune responses are referred to as antigens. A common example of an antigen is the proteins in ragweed pollen that elicit an allergic response in some individuals. Another method of evasion has been shown to occur, namely that certain tumors can secrete proteins that inhibit effector T cell responses and promote regulatory T cells that can inhibit immune responses.

As a result of the elegant studies of Doctor Jacqueline D. Shields from the Institute of Bioengineering in Switzerland, yet another mechanism of circumventing the immune system has been discovered. It was found that certain melanomas – an aggressive form of skin cancer – can reorganize their cellular environment (stromal microenvironment) into structures that are similar to the lymphoid tissue of the immune system. This reconstruction results in fooling the immune system to the extent that it recruits regulatory T cells that actually promote tolerance and enhance tumor progression.

Studies of this kind shed significant light on the progression of Cancers, and reinforce the important role that immune surveillance plays in the body’s natural defense mechanisms. By elucidating the actual manner in which tumors can thwart these defenses, the possibility of developing effective therapies is appreciably enhanced.

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