The receptors capable of recognizing the pathogenassociated molecular patterns are Toll-like receptors (TLR) and scavenger receptors. Ten members of the TLR family have been identified in humans (7) . The Toll was originally described as a type I transmembrane receptor that controls the embryonic dorsal-ventral pattern of Drosophila (8) . In fact this pioneering work identified a group of ten different genes which when deleted produced qualitatively similar phenotypes. Null mutations on any of these genes lead to a failure to differentiate patterns on the dorsoventral axis and resulted on embryonic lethality. The identification of the sequence of Toll led to the recognition that its carboxyl terminal domain was significantly related to that of the vertebrate interleukin-1 receptor (IL-1R) (8) . IL-1R activation is part of a cascade of events linked to an acute phase response to infection. This suggested that TLRs could not only be involved in development but also in the initial responses to infection in vertebrates. This hypothesis received further support from the work of Lemaitre et al., who found that Toll and other genes from the dorsal group played a role in innate immune responses to pathogenic fungi and bacteria (9) .