Opinion: I am Many
Microchimerism takes away the assurance that our immune system is our own, the cells or even the genetic line inside us are our own
By Pramod K Nayar
We begin with a historical case. In 2002, an applicant for state welfare in Washington, Lydia Fairchild, had to subject herself and her children to standard blood and DNA tests. The tests indicated that her children were not a genetic match with her and that, therefore, she was not their mother. The state actually filed a case of fraud against Fairchild.
Subsequent research revealed that that the genetic mismatch across generations was due to chimerism: Fairchild carried two genetically distinct cell lines inside her. By sheer coincidence, a similar case was reported in the highly respected New England Journal of Medicine. Fairchild was let off for a simple reason: she was a chimera.The Chimera is a trans-species creature of mythology: it was a hybrid of a lion, a goat and a serpent. But now, apparently, it is not just a myth. Some of us are more than one. All of us, in fact, are more than one.
The Probiotic Turn
We have evolved into creatures afraid of most critters.
Hypersanitation in the modern age has ensured that we cleanse everything of microbes. (The pandemic reasserted this.) But biologists tell us this is wrong. In what Jamie Lorimer calls a probiotic turn in his book, The Probiotic Planet, we see biologists and medical doctors call for:
a nuanced taxonomy of life-forms and a more selective armory of control methods than the modern antibiotic (or Pasteurian orthodoxy). It retains a vigilant control over specific pathogens, but it also permits the existence of those organisms that restrict the spread of disease and encourages those that deliver desired functions and services.
The focus, Lorimer points out, is to read ecological systems more carefully and be driven by more than fear. This reading has to be across scales: from the individual human body to the community to the planet’s larger ecosystems. Lorimer writes:
Going probiotic goes well beyond a preference for live yogurt; it links a range of efforts that aim to change the composition of biophysical systems to modulate the rhythms and intensities of their ecological interactions. These projects look for tipping points within these ecologies and manage their dynamics so that they stay within desired boundaries. They control, restore, and enhance the functioning of eco-systems to secure a desired set of systemic properties—in these two cases, biodiversity and immunity.
Lorimer is pointing to the necessary recognition of species co-existence. But in order to understand this, we need to move beyond the myth of the individual self. This myth has been busted for some years now.
My Microbial Self
That evolution occurs through the absorption of other forms of life into our primordial state of being is now an established and accepted fact. As evolutionary biologists, especially in the wake of the early studies of Lynn Margulis and others would say, evolution is mainly effected through cooperation rather than competition. This suggests that our concept of the human as a self-contained, unitary and bounded being is a myth. Hence the claim by Scott Gilbert and others in an influential essay published in Quarterly Review of Biology, reflected in the very title: ‘A Symbiotic View of Life: We Have Never Been Individuals’
What makes us human, besides the various anatomical and physiological features and functions, is the sheer volume of other life forms inside us. Other such organic material is incorporated into the structure and function of the body, of which the microbes in the gut are the best known examples. Recent studies by JA Gilbert et al in Nature Medicine (2018) have proposed a ratio of 1:1 for human to non-human cells, going up to around 1:3 if all microbial elements are taken into account.
All humans, therefore, are a human microbiome, a term that refers to the total DNA content of microbes inhabiting our bodies: in the mouth, the skin, urogenital areas, the eyes, the lungs and even the brain, as some claim. Increasingly, scientists believe that even our immune system develops through the assimilation of such ‘others’ into our biome. That is, the immune system develops as a response to the inflow of external organisms – some of which of course may trigger conditions causing dis-ease. The immune system, for long taken as unique and as defining the boundaries of the self, is hardly that.
The Human Microbiome Project proved that the human is not singular as a species. Far from it. We are an uneven but balanced mixture of bacterial, fungal, parasitical and viral components right from the cellular level, and in this mix, the ‘pure’ human cell is a minority (those worrying about the majority/minority divide can now have a new topic to worry about!).Holobionts are a collection of a host and multiple species attached to it, living in a symbiotic relation. Humans are holobionts because the microbes and viruses inside us contribute to the functioning of the whole.
We are a collective. There, clearly, is no individual.
Inside Me, An Other
New theories of microchimerism add one more layer of complication. Microchimerism is a theory — contestedby many — to explain the presence of different cells and DNA materialwithin the same organism. The transfer and assimilation of such material occur during pregnancy (maternal–foetal microchimerism), organ transplantation or blood transfusion. In the case of twin foetuses, one may be absorbed by the other in the womb so that only one foetus grows, the other is obliterated although its DNA is absorbed into the survivor (the foundation for Stephen King’s horror tale, The Dark Half). That is, the self absorbs the other into itself.
Microchimerism focuses on the existence of other-DNA within the genetic material of an individual. Mismatched DNA in an individual — that can produce conditions such as heterochromia (differently coloured eyes) —is a tell-tale sign, those believing in microchimerism argue, of DNA transfer and assimilation.
With transplantationcontext, microchimerism is even more likely, and this may lead to changes in the immunological status of the recipient. First, in order to minimise rejection, the body’s defence, the immunological system, is deliberately eroded. Second, the recipient has to be maintained on a usually life-long regimen of immunosuppressant drugs. This allows the received organ to continue functioning without the host’s immune system battling it as an ‘outsider’. Third, the immune-cells of the donor organ may recognise the cells of the recipient as outsiders and attack them (commonly referred to as graft versus host disease).
In short, then, microchimerism takes away the assurance that our immune system is our own, the cells are our own or even that the genetic line inside us is our own.
I am many.
(The author is Senior Professor of English and UNESCO Chair in Vulnerability Studies at the University of Hyderabad. He is also a Fellow of the Royal Historical Society and The English Association, UK)