ABSTRACT
Animals can respond rapidly to infection even if they have not previously encountered the invading microbe. This innate response occurs in plants and insects, as well as mammals, and includes the secretion of antimicrobial molecules and proinflammatory cytokines. The mechanism of pathogen detection has been clarified by the recent identification of Toll-like receptors (TLR) as essential components of the innate pathogen recognition system. Several TLR-dependent systems mediate the immediate response of vertebrates to invading bacteria. Current concepts of TLR structure, specificity and mechanism of action are reviewed. It is suggested that integration of TLR-dependent signals provide the host with its first perception of the presence
and nature of an invading microbe. Implications for future research into human infectious disease pathogenesis are discussed.
