Further notes about the morphostasis concept – split files

(55) Fresh thoughts about phylogenetic/ontogenetic roll-out of immune defences

I have suggested, in "Flushing out the phlogiston", that the defence barrages are rolled out in an ontogenetic sequence that follows the phylogenetic acquisition of each new barrage. These constitute a series of defence shells or barrages that deal with threats in an inner to outer shell sequence. When an inner barrage deals effectively with the crisis (the threat/organism/disorder is successfully neutralised) then there is no need for an outer barrage (shell) to be mobilised.

Now, I have overlooked an important consequence of this in that activation of complement, opsonisation and consequent ingestion by a cell (amateur or professional phagocyte), will lead to a successful neutralisation. There is no need to go on to recruit aggressive adaptive immune activity and, indeed, the outcome is the quiet disposal of the threat and – quite likely – a classification of any generated debris as suitable for future tolerance. That is why we see pathogenic organisms ("pathogerms") targeting the complement system to circumvent this protection and allow them to go on to do damage (create a nutrient substrate).

Apoptosis is, itself, an innate barrage that – because debris has been efficiently cleared – leaves no necessity to roll out aggressive adaptive immune responses to relevant (cleared) debris.

One of my other assumptions was that B-cells, with their free antibodies, were relatively late arrivals on the scene. However, this misses the evolutionary emergence of (first) IgM surface receptors on B-cells and (second) the generation of a factory process for releasing free IgM into the circulation. The B-cell can be viewed as just a fastidious antigen presenting phagocyte that ingests "targeted" (recognised) debris. This fastidiousness contrasts with other APCs that are generally promiscuous about the debris they present to T-cells. So, the origin of B-cells may predate T-cells where, like cytotoxic T-cells, the original function was to deliver a "kiss of death" to particular cells to resorb tissues, like finger webs and tadpole tails. The "factory" process of free antibody release into the circulation may have turned up long afterwards.