A Good Holobiont has a Good Immune System. Managing your Microbial Environment

 

An incredible book by Philipp Dettmer: an ambitious attempt to tell the whole story of the human immune system in an understandable form even for the non-specialist. The result is a 345-page tome, lavishly illustrated, and written in an entertaining style. Remarkably well done, but not easy to digest nevertheless. I went through the whole thing once, but I need to restart from the beginning and reread it again. And, probably, I'll need a third pass. Afterward, I may be able to say that I know just a little bit about how the immune system works. 

And think that this is just an introduction that neglects or just mentions several important details. For instance, it mostly skips the role of the microbiome. But that must be hugely important: after all, human beings are holobionts. We can't survive without our microbiome, and it is likely that the huge numbers of small critters that populate our body play a fundamental role in managing the microbial system "holobiont-style." It means that the immune system is not a sort of Nazi militia that shoots down everything it doesn't recognize and doesn't like. It must be able to recognize those parts of the microbiome which are helpful and those which are not. And note that, in some cases, the same species of microbes can play the role of pathogen or symbiont, depending on the general conditions of the rest of the system. That's how good holobionts behave: they adapt to each other. We need to be colonized by microbes in order to survive. It is just a question of being colonized by the good ones. And it is the job of the immune system to ensure that it happens!

Amazing, as I said. It gives you a glimpse of the immense complexity of just a section for the even more immense complexity of the ecosystem -- that some call "Gaia." The goddess gave every one of us a complete defense and management system that kept our ancestors alive for the past 400 million years or so as multicellular organisms, and also a few billion years as single-cell organisms. If we are here, it means that the immune system of our ancestors worked well enough to interact with, and protect them from, the zillions and zillions of microscopic creatures that we eat, inhale, or come in contact with one way or another. 

But, wait.... aren't we supposed to be much smarter than Gaia, that poor old lady? We are so smart that we discovered that we can do better than just relying on that old stuff that uses billions of antibodies, t-cells, macrophages, and more. You know, those squishy things that evolved over a few billion years, what are they for? Instead, just a piece of cloth placed onto your mouth and nose, and -- voilà -- NOW you are safe! 

New Mysteries of the Human Microbiome: Cancer and Fungi

 

The idea that cancer is caused by a fungus, or that it may even be a form of fungus has been proposed by the Italian physician Tullio Simoncini. His ideas have been thoroughly demonized and Simoncini himself has seen his license of practicing medicine revoked. 

Now, don't make me intervene in a matter of which I know very little and, for sure, I am not saying that Simoncini is right. I am just noting that, after what we saw happening with the COVID19 story, the demonization of everything which is not "official" in medicine should be taken with a lot of caution.

The thing which I think matters is how complicated things are in everything that has to do with human health. Cancer is normally described as a mutation that makes cells lose their discipline and start reproducing wildly. Things are not so simple as that, I think. The human body has defenses that can rapidly get rid of any rogue cell and it is strange that these defenses become ineffective when dealing with tumors. And, indeed, the story of cancer growth is much more complicated than that. 

Simoncini may have had an interesting intuition when he proposed an important role of fungi in human cancers. You can read the story in this recent paper

https://www.cell.com/cell/pdf/S0092-8674(22)01127-8.pdf

which is structured as a headache machine from the first ten lines of text. Nevertheless, I think the point it makes is clear: all the cancer types the authors studied had some fungi associated with them. That is a new piece of information that goes in parallel with the fact that cancers also harbor special bacteria. What is the role of this microbiome? Nobody knows and, correctly, the authors state that "they have not established causation," even though it seems that the presence of fungi is, sometimes, associated with more aggressive cancers.  

I think it is possible to say that cancers are holobiont-like assemblies of cells, bacteria, and fungi. If they are, that could explain their resilience and their stubbornness. Holobionts are machines that optimize their own survival, and, in this case, it is unfortunate that the cancer holobiont doesn't seem to care about the survival of its host. Maybe, in the future, we'll learn more about this subject and perhaps we'll find a way to exploit this knowledge to help people who are struck by cancer. For the time being, we can be awed, as usual, at the incredible complexity of life in all its forms. 

More discussions on cancer and fungi at

https://www.algora.com/Algora_blog/2022/10/02/7787

https://www.nature.com/articles/d41586-022-03074-z

https://www.healthline.com/health/is-cancer-a-fungus

Holobiont Science: Sometimes a Little Vague, but Always Interesting

 

Holobiont science is sometimes a little vague, but always interesting. Here is an example.In this paper, http://www.zoologia.hu/list/Why_infest.pdf, Rozsa and Apari argue that head lice in humans is a useful symbiont because it generates an immune response that helps protect humans from body lice, which can be dangerous as vector for harmful bacteria. (the photo above is from the paper)

 

It is an interesting story where you learn that there are at least two types of lice living with humans. And you learn that apes have only one kind, probably because they are uniformly hairy. Rozsa and Apari go on suggesting that the "touching heads" human habit has the specific purpose of diffusing health lice in such a way to spread the immunity to body lice. Apes, they say, don't touch each other's heads because they don't have such a need. 

 

Which is, as I said, very interesting, but is it true? Honestly, it gives you the idea that the authors are piling up one hypothesis after the other, none of them being really supported by data. For instance, in the places where I live, there is no habit of touching heads as a form of salutation or an expression of friendship. Then, are we sure that apes touch heads less frequently than humans do? I don't think we have solid statistics on that point. Besides, why are body lice dangerous, but not head lice? One more mystery of holobionts! 

 

But it is nevertheless a nice idea that adds a little more to the complexity of the idea of holobionts. And the picture that illustrates the paper (in lieu of non-existing data) is truly charming. Two distinguished professors exchanging lice. Wonderful!