Further notes about the morphostasis concept – split files

(11) More thoughts on the "battle" with micro–organisms

"One litre of pond water include members from all domains of life (virus, bacteria, archaea, eukarya) and contain up to 2 billion bacteria and 10¹² viruses."

• This quote about pond water, is taken from an article by Augustin, Fraune and Bosch . This article discusses hydra and highlights how TLRs and NOD–LRs are at the phylogenetic base of "immune systems".
• The title of the article, however, still comes in with the battling metaphor – "How Hydra senses and destroys microbes".
• Hydra sits at a "primitive body plan" position in the phyogenetic tree. There are, almost certainly, very important lessons to be learned here about the evolution of "immune systems" (or tissue homeostatic systems).
• Every "animal" is an ecology of different species sat in a milieu of even more micro–organisms. The vast majority of these do not pose a serious pathogenic threat though a large proportion of them would – probably – happily settle down to a meal of dead flesh once the animal has died.
• This ecology of species (mostly micro–organisms) carries out important functions. In numerous animals, these micro-organismal populations co–inhabit the gut and often do useful work in helping to process ingested material. Some organisms, like slime moulds, carry around a seeding supply of bacteria that are then farmed and used as future "crops".
• The vast majority of the members of this ecology of micro–organisms do not pose a threat. An animal is quite capable of adjusting to their presence in such a way that the responses to them appear invisible and non–inflammatory. This ecology of organisms still provide a substantive meal for many if not all animals (the phagocytes simply caricaturise this function so that we then begin to perceive it as a battle.
• If battleground conditions do emerge, they are substantially the result of a "tissue homeostatic system" turning of its own flesh. And, naturally, invading micro–organisms may discover that this debris is a substantive meal and the base fodder for a rapid proliferation.
• This battle metaphor is – to my way of thinking – dangerous and obfuscating (obfuscate: to make so confused or opaque as to be difficult to perceive or understand). It is the reason that "micro–organism" and "pathogen" are so freely interchanged in biology/medical papers. A pathogen should, logically, be nothing more than an (unspecified) agent that damages and/or causes disease in some animal or plant (or even a prokaryote or free living amoeboid cell).
• I would like to see immunologists and microbiologist try – at least for a while – to drop this "war with the microbes" metaphor and see whether it was essential in the first place. Hosts and pathogenic organisms co–evolve in an uneasy state of mutual ecological compromise. To be successful, a pathogenic microbe "must be careful" not to annihilate its food source. This is particularly true of highly specific pathogenic organisms that find it hard to adapt to surviving in a different species (e.g., mycobacterium tuberculosis contrasted to bovine or avian TB).