Further notes about the morphostasis concept – split files

(39) "The origin of immunity is in the management of the microbiome"

This theme is becoming increasingly popular. By this view, the primary "purpose" of the primordial immune system is to manage the microbiome. Managing pathogenic organisms, by this view, came later. Now, I can appreciate that the proportion of non–pathogenic microbe to pathogenic microbe species is very heavily weighted towards non–pathogenic species. In consequence, the activation of adaptive immune responses are, equally, heavily weighted towards responding to non–pathogenic commensals/symbionts (effectively, the microbiome). However, this can be equally viewed as "how to respond to micro–organisms" in general based on

• the generic presence of microbial signatures (MAMPs)
• the proliferative behaviour of the microbes (a recent paper proposes that CO – carbon monoxide – and ATP are important )
• the damage that these microbes inflict on host tissues

Now we can see that tolerance can be enrolled to respond to non–damagers and aggression can be enrolled to respond to damagers. Equally, non–damagers that regularly get presented alongside some repeated but unrelated damage signal will probably provoke a similar aggressive adaptive immune response. And the corollary to this (tolerance induction) may be favoured when presentation is associated with a coincident but unrelated tolerance inducing circumstance. If this observation is valid then "the origin of immunity" rests with tissue homeostasis/integrity; the microbiome must favour homeostasis if it is to be tolerated.

Critically, this "management of the microbiome" view has, once again, pegged "the purpose of the immune system" to the management of microbes. This is reminiscent of the original "splat the bug" conceptions of the immune system. Here, the management of pathogenic organisms was universally regarded as its overriding purpose (lasting from the early realisation that the immune system is active during infection through until at least the early 1990s). This ignores any role the immune system may have in all other pathological processes (eg, damage management – particularly response to cell death, cancer, neoplasia in general, regeneration, the metamorphosis of form from infants to nonagenerians, in metabolic homeostasis and so on).