Microchimerism And Theories

January 29, 2008

The February issue of Scientific American was awaiting me as I arrived home today. Its major theme was the next generation of physics, which I found to be interesting. Even more intriguing, however, I found the article concerning microchimerism Your Cells Are My Cells to be.

What originally caught my interest was the term microchimerism as I had encountered the similar term “chimera” before. Admittedly, it was in an episode of CSI (4:23), but I found the concept of merged fraternal twins to be highly fascinating (and equally question-rendering). I, for one, could not truly get my head around the term, for of all the knowledge I possess, the possibility of two different sets of cells coexisting, was lacking. I yet to this day have to find an explaination of the phenomenom which comforts my wondering mind.

Regarding the Scientific American article, written by a J. Lee Nelson, it rendered some of my confusion obsolete, but in turn, it awoke new questions. The article presented the subject of microchimerism and that most (if not all) people are microchimeric. The reson for this being so has not yet fully been explained, but of what is known this far, mother and child exchanges cellular material during pregnancy. This astonishing fact was unearthed due to the discovery of cells containing Y-chromosomes in women who have been pregnant with sons, the time elapsed since being unsignificant.

The microchimerism may be both harmful and protective to the tissues. Foreign immune cells may harm the host tissue and create reumatism-like symtoms. The host’s immune cells may also, in turn, attack transferred cells in tissue. The effects of microchimerism are however not all harmful, in fact, the transferred cells may become an incorporated part of the host tissue and quite possibly aid the tissue in its regeneration process.

That the transferred cells may help the host tissue to regenerate, coupled with the fact that women with arthritis often experience improvements of their condition while pregnant, makes my mind wander off among possible theories.

Of course, me lacking further education in all concerned areas of study, may be negative in the context, that I construct theories regarding things I know nothing about. Of course, there are a selected few out in the world who have come up with excellent theories regarding things, all because they did not know a lot about all the problems associated with their new theories. In the end, however, these uninformed theories have proven vital to the evolution of future hypothesises.

I think that microchimerism has evolved because of its positive qualities. That it at times is harmful may be an effect that evolution this far has been unable to correct. A mutation that leads to a deformed haemoglobin molecule has proven to render its carrier immune to malaria. Two versions of this mutation does however affect the individual in a harmful way, they develop sickle-cell anemia. I believe that something similar to this perk of life, is true for microchimerism.

Because people are individuals with individual sets of DNA, they are as a result better adapted to face different challenges. Even mothers and their children are different, all because of the random mutations which happen every once in a while and the re-sequencing of the DNA base-pairs. A mother may because of this be immune toward a certain illness or condition, while her child is not. That they during her pregnancy exchange cells, may impede the effect of their individual differences to some degree. So, by exchanging cells with her child, a mother may protect her offspring. In the same way, she may be protected by new mutations which may have arisen in her child’s genetic material. In my opinion, microchimerism exists because of its possible beneficial qualities, that two generations may benefit from benign mutations that have arisen in one generation.

The article further argues, that a child may pass some of its cells along to its mother and that the mother in turn may pass some of those cells along to her next child, means that a beneficial mutation may come to assist a new generation as a whole. This may also have sped up the rate of evolution, which generally is a slow process. By enabling a mutation that has originated in one individual to be transferred to several others, though in a lesser quantity, decreases the chances of a beneficial mutation being lost. Evolution is painstakenly slow – a mutation may happen only once in a million years and in one individual. If this individual later would perish because of external forces, without passing its mutation on to the next generation, the million years that rendered the mutation would have been for nothing. If the mutation however had been assigned a safe haven in the genetic material of a sibling (or mother) it can survive and benefit the further evolution of a species.

Let me illustrate this through an example. Say that a mouse population is affected by a disease which degrades tissue, leading to death before reproduction. One of the mice is pregnant and one of its fetuses has developed a mutation that will render it immune toward the disease. The mutated fetus and its mother exchanges cells, as do the other fetuses, making the mutation spread to the mother and siblings. After birth, the mouse with the mutation is caught by a cat and killed, meaning that it never will reproduce. Its mother and siblings do however carry some of its cells. A later pregnancy of the mother’s may incorporate the mutation into the new litter, as will the siblings as they reproduce. The siblings will be able to reproduce because some of their cells are those of their deceased sibling. If they become infected, the mutated cells may protect the tisssues around them, because of their immunity, enabling the mice carrying the mutated cells to reproduce to a further extent when compared to the mice which do not carry similar mutated cells. All it takes is for one of the descendants of the cell-carrying mice to have fused with one of the mutated cells at a very early stage in its fetal development, creating a true chimera. This chimeric mouse is immune to the disease, as well as possibly being able to pass the mutated cells along as one of its own. Its offspring will thrive and not be affected by the diesease, eventually rendering the disease extinct. This concludes that the mutation and the microchimerism assist each other in helping a species evolve.

As above mentioned, pregnant women experience a dampening of arthritis symtoms when compared to those experienced before and after the pregnancy. As it is during pregnancy that cells are exchanged between the mother and child, the child’s cells seem to have traits that ease the mother’s symtoms. This is however just a side-effect, I theorize. The cell’s main trait must be that they excrete a substance which will enable them to fuse with the mother’s tissue. The substance excreted is what affects the mother’s auto-immune condition. As foreign cells usually are attacked by the body’s immune system, it must be “tamed” beforehand. This is what the substance does.

The author of the Scientific American-article has explored this topic already, even if the results are not yet crystal-clear. I do however believe that further study of the subject will provide new possibilities for mankind. The extraction of the immune system-taming substance, for example, will provide new hope for those in need of tissue or organ transplants, as well as those suffering from auto-immune conditions.

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