IMMUNOLOGIC FACTORS
It is correct to assume that considering the large number of cell
divisions that take place within any living organism, there would
be some cell-division that would result in the production of cell
deviates that do not respond to controlling mechanisms.
- These cells if allowed to multiply could demonstrate all the
characteristics that we associate with malignancy i.e.rapid
growth, invasion of local tissues and metastasis to distant
organs.
- It is,therefore, surprising that different species demonstrate
only a few cases of malignancies. Some explaination needs to be
considered.
* Burnett in 1970 put forth the concept of an immune-
surveillance system.This system in essence,possesses the
ability of detecting the surface differences of these
deviant cells and as a consequence eliminates them from
within the host.
* This competence is EXPRESSED through the lymphoid system and
if their system is alert it would be capable of eliminating
relatively small number of cells.There is evidence that
genetic factors may be responsible in determining the
effectiveness of this immune system. Guinae pigs and
rabbits are resistant to induction of all viral tumours.
* Failure of this immune surveillance system could occur when
there is immunosuppression, this has been demonstrated to be
true, in cases of human renal transplantation where
immunosuppression is used as a technique to faciltate the
acceptance of the transplant(to depress rejection).
* Immune suppression could occur, naturally in old age and
other inter-current disorders like prolonged illness.
* Immune tolerance could be another mechanism for evasion of
this surveillance system.
- It has been shown that experimental animals, if exposed to
specific antigens before maturation, can induce a state of
immune tolerance to these antigen.
- Another mechanism could be a reduction or loss of
antigens from the cells-surface of tumour cells.
- This has been referred to as antigenic modulation
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