Many regard cancer as a fairly modern disease,
attributed to humans with a poor lifestyle and surrounded by environmental
pollutants. Although these factors may increase the likelihood of developing
cancer, abnormal growths may occur in any multicellular organism such as small plants, trees or even members of the ancient world, such as dinosaurs.
Plants and Trees
It's difficult to imagine organisms that can stretch to such abnormal shapes and can exist for hundreds of years may also suffer from abnormal growths. To humans, cancer is often a life threatening disease, but plants live quite happily with large abnormal growths.
It's difficult to imagine organisms that can stretch to such abnormal shapes and can exist for hundreds of years may also suffer from abnormal growths. To humans, cancer is often a life threatening disease, but plants live quite happily with large abnormal growths.
Growths can be seen on many trees, without causing much damage because unlike humans, trees are not comprised of organs, which carry out a unique role for the whole body. Human cancers often obstruct organs and impede their function, leading to health consequences. Instead trees have a mix of specialized tissue throughout their body, which can carry out specific functions. Therefore, growths rarely affect the whole organism (1).
![]() |
Figure 1 : An example of a tumour on a birch tree (Wikipedia, 2006) |
Humans
The majority of human cancers are caused by environmental mutagens or uncorrected faults during DNA replication, which can mutate or destroy DNA. However, tumours in humans as well as in plants can be the result of a viral infection (an oncovirus). A common example is the human papilloma virus that may cause cervical cancer. Frankly, because it's so well known, I'm not going to write about it. Instead, I would like to draw your attention to the Epstein-Barr Virus (EBV) aka the human herpes virus 4, which was the first virus identified as a cause of cancer (2).
This is extremely common in humans and a majority of adults have previously gained an adaptive immunity to it. EBV may create non-cancerous symptoms when present, such as a fever and other cold-like symptoms in children, or infectious mononucleosis (glandular fever) in adolescents.
Transmitted by saliva, EBV passes through the oropharyngeal epithelium and is met by B-lymphocytes. EBV infects B-lymphocytes and expresses protein, which leads to increased proliferation. Cytotoxic T-lymphocytes (CTL) in healthy individuals usually control proliferation levels. There may be very low levels of infected memory B-lymphocytes remaining. However, in immunosuppressed individuals there may be loss of EBV specific CTL. Infected circulating memory cells may spontaneously begin to proliferate and a lack of CTL may lead to lymphoma, commonly Hodgkin's and Burkitt's lymphoma (3).
References:
(1) http://www.nature.com/nrc/journal/v10/n11/full/nrc2942.html
(2) http://www.cancerresearchuk.org/about-us/cancer-news/podcast/looking-back-over-50-years-of-epstein-barr-virus
(3) http://clincancerres.aacrjournals.org/content/10/3/803.abstract
No comments:
Post a Comment