Microglia can exhibit widely differing functions at different stages in life both physiological and in response to, and in contribution to, various pathological situations as summarized in Table 1.
Although in reality it seems probable that at any given point in time, an individual microglial cell is likely to be undertaking several different functions, a major thrust of the microglial literature in recent years has been to define a number of ‘activation states’ in which microglia are performing a restricted set of functions.
Here we consider the extent, in the human CNS, to which the function or functions of a microglial cell can be deduced from observations of its morphology, gene expression and protein composition.