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Describing the behavior of immune cells as categorizing cells in 'self' and 'non-self' is itself an example of engaging in metaphor. It's an example of anthropo

Describing the behavior of immune cells as categorizing cells in 'self' and 'non-self' is itself an example of engaging in metaphor. It's an example of anthropomorphising the behavior of cells. You can just as easily describe the behavior of immune cells as categorizing cells into 'healthy' and 'unhealthy' and killing the 'unhealthy' cells. Suddenly the disease is not about internal conflict, but about internal hygiene. And when the immune system kills 'foreign' cells, it's not because they are foreign, but because they are found to be 'unhealthy': deviating too much from what it considers 'healthy'. This is a simpler explanation. Apply Occam's razor: the immune system does not care about whether something is 'foreign': that's a more complex, and more precise, judgement than is needed to determine whether something needs to be killed. The broader category of 'unhealthy', deviating from the template/norm, is sufficient and that is the only thing the immune system needs to determine.

ubernostrum 10y ago
Except that the immune system's idea of what set of molecules to accept and what set to kill is not based on a generalized idea of what a "healthy cell" looks like -- otherwise we wouldn't have such trouble matching people for organ transplants, since our immune systems would just accept any generically healthy organ. Instead it's dependent on the (specific to the individual) set of genes controlling the major histocompatibility complex, and so is very much a "self" ("derived from my genes") versus "non-self" ("not derived from my genes") determination.
- Confusion 10y ago
  Yes, what is 'healthy' looks different for each individual. That doesn't mean that something is found to be 'healthy' because it is 'self'. The immune systems primary function is housekeeping: killing cells that are still completely 'self', but are old, worn down or dysfunctional in some other way. Killing 'invaders' and cancers is minor in terms of the numbers of cells destroyed. As your transplant example shows: something foreign can be found to be entirely 'healthy' by your immune system. So self vs. foreign is too narrow.

ubernostrum 10y ago

Except that the immune system's idea of what set of molecules to accept and what set to kill is not based on a generalized idea of what a "healthy cell" looks like -- otherwise we wouldn't have such trouble matching people for organ transplants, since our immune systems would just accept any generically healthy organ. Instead it's dependent on the (specific to the individual) set of genes controlling the major histocompatibility complex, and so is very much a "self" ("derived from my genes") versus "non-self" ("not derived from my genes") determination.

Confusion 10y ago
Yes, what is 'healthy' looks different for each individual. That doesn't mean that something is found to be 'healthy' because it is 'self'. The immune systems primary function is housekeeping: killing cells that are still completely 'self', but are old, worn down or dysfunctional in some other way. Killing 'invaders' and cancers is minor in terms of the numbers of cells destroyed. As your transplant example shows: something foreign can be found to be entirely 'healthy' by your immune system. So self vs. foreign is too narrow.