Toll-like receptors control activation of adaptive immune responses

Mechanisms that control the activation of antigen-specific immune responses in vivo are poorly understood. It has been suggested that the initiation o f adaptive immune responses is controlled by innate immune recognition. Mam malian Toll-like receptors play an essential role in innate immunity by rec ognizing conserved pathogen-associated molecular patterns and initiating th e activation of NF-kappaB and other signaling pathways through the adapter protein, MyD88. Here we show that MyD88-deficient mice have a profound defe ct in the activation of antigen-specific T helper type 1 (T(H)1) but not T( H)2 immune responses. These results suggest that distinct pathways of the i nnate immune system control activation of the two effector arms of adaptive immunity.