An example of metaphorical language in technical writing:
"The cellular and humoral innate immune system is an efficient army to fight invading pathogens, to clear toxic debris while preserving normal self cells. The difference between a harmful intruder and a dying cell is often subtle and it is therefore imperative that a code of conduct is operating. Professional phagocytes (microglia) and to a lesser extent amateurs (astrocytes, neurones) are programmed to eat but receive inhibitory or 'repulsive' signals expressed by normal self cells as a matter of safe guard. Remarkably, these "don't eat me" signals (SAMPs [self-associated molecular patterns]), either expressed at the cell membrane (e.g., CD55) or secreted and found loosely attached to the cell surface (e.g., complement factor H), are recognised by inhibitory PRRs expressed by phagocytes."
Elward, Kristina & Gasque, Philippe (2003) "Eat me" and "don't eat me" signals govern the innate immune response and tissue repair in the CNS: emphasis on the critical role of the complement system. Molecular Immunology 40 (2003) 85-94
There are a range of terms here which are likely to appear as figures of speech ('army', 'invading', 'intruder' * and 'code of conduct') however some of these have become accepted as having a fixed technical meaning ('don't eat me signals', 'professional phagocytes').
* Read 'Disease and immunity – a biological myth'
