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Thursday, December 29, 2016

HUMAN TUMORS AND WHY DO THEY SUCCEED?


A child with Burkitt's lymphoma one of the man-made diseases or bio-weapons in Africa

A child with Burkitt's lymphoma one of the man-made diseases or bio-weapons in Africa



One of the most important questions in tumor immunology research today is whether immunology will have useful application to human malignancy. To date, the most convincing and stimulating studies involve the possible link between antigen specifically and etiology as established and experimental virus-induced tumors.

Recent findings of common tumor-specific antigens, combined with virological studies, indicate that Burkitt's lymphoma may be of viral origin. This was the first human tumor to be subjected to intensive immunology study. The fact that this tumor is largely confined to the humid, tropical portions of Central Africa suggested in arthropod vector and possible infectious etiology.

More importantly, it was found that the tumor could be cured by chemotherapy in a significant number of patients and several spontaneous and cures occurred in the absence of any therapy. In the serum of patients with Burkitt's lymphoma, specific circulating antibody against their own tumor cells was detected by immunofluorescence.

With one exception-nasopharyngeal carcinoma found in the Far East, sera from Burkitt's lymphoma patients rarely reacted with tumor cells from patients who had other types of tumors cells from patients who had other types of tumors or with normal controls. 

Likewise, sera from other tumor-bearing patients and from normal controls rarely reached with Burkitt's cell. These findings suggest that Burkitt's lymphoma is antigenic to its host and that it causes the production of the antibody that is absorbed on the surface of the tumor cell. 

In addition, cells from one Burkitt's patient share common antigens with those from other Burkitt's patients. This fact is reminiscent of the experimental findings for virus-induced tumors. A herpes-like viral particle, Epstein-Barr, EBV, has been recovered from Burkitt's cells. 

Isolation of a virus particle from cultured tumor cells, however, does not constitute proof that the virus is directly responsible for the malignancy. The uptake by cultured cells of passenger viruses from the environment is all too frequent. 

Although nasopharyngeal carcinoma, one of the common cancers in an orient, is a morphologically different tumor and has its own peculiar geographic pattern, virological, immunologic studies suggest that this tumor is also related to EBV. 

The virus particles recovered from Burkitt's lymphoma and from nasopharyngeal carcinoma are antigenically very similar to the virus associated with the common disease infectious mononucleosis. 

Whether these are the same particles that cause different clinical diseases under different circumstances or whether they are different viruses that 'wear similar clothes' is unclear.

Why Do Tumors Succeed?

Although we know that many tumors are antigenic and can induce an immune response, we do not know how frequently the immune systems of healthy individuals encounter and destroy aberrant cells. If the normal immune response is capable of preventing or inhibiting tumor growth.

The tumor may take three routes to ensure its success: take advantage of lapses in immune capacity, escape from immune control, and suppress the immune response. Currently, it is not known if any of these proposed mechanisms play a significant role in human cancer.

Studies of the immune capacity, particularly cellular immunity, in normal individuals reveal occasions when the immune capacity is significantly depressed. This most frequently associated with viral infections, including the common cold.

Other stressful situations, including general anesthesia and surgery, are associated immune depression. Many of these lapses are unavoidable, and most are transient. However, they suggest that the potential tumor may have occasional opportunities to become established.

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