Key developments in the TLR field over time. Conceptual advances shown in red for both insects and mammals. Toll was identified as a developmental protein in 1985. CD14 was identified as a part of the LPS receptor in 1990; the IL-1 receptor was cloned in 1988 and noted to have domain homology to Toll in 1991. In 1994, mammalian TLRs were first identified, but incorrectly assumed to have developmental functions based on what was known in Drosophila at the time. In 1996, the dual immunologic/developmental character of Drosophila Toll was recognized. The immune function of a mammalian TLR was first demonstrated in 1998. Illustration made with assistance of Marie Dauenheimer.