Of mice and men: species variations of Toll-like receptor expression.

Toll-like receptors (TLRs) comprise a family of evolutionary conserved pattern recognition molecules that have an essential role in mammalian innate immune defense. Recent observations suggest that several TLR orthologues are expressed differently in mice and humans - variations among both species include the expression of TLR transcripts in different cell types and different transcription regulation on cellular activation. Apparently some TLR genes have been placed into a completely different regulatory context during evolution. It will be interesting and important to clarify whether the observed regulatory differences influence innate immune responses in a species-specific manner.