"The information described in this article is very useful to a variety of scientists and clinicians who investigate immunology, infectious diseases, immunologic disorders, cancer, and so on."

This review article presents an overview of innate immunity research focusing on Toll-like receptors (TLRs). Immunity senses invasion of pathogenic microorganisms as non-self and eliminates them by virtue of two aspects of the immune systems—innate and adaptive immunity. Until recently, the mechanism by which the innate immune system recognizes non-self was unclear. Identification of mammalian TLRs as non-self recognition receptors made immunologists aware that innate immunity is an excellent system to discriminate invasion of pathogens and induction of immune responses.

Since then, molecular mechanisms of TLR-mediated activation of innate immunity have been intensively analyzed and rapidly revealed. Furthermore, TLR-independent microbial detection systems and the involvement of TLRs in several immunologic disorders have been disclosed. The information described in this article is very useful to a variety of scientists and clinicians who investigate immunology, infectious diseases, immunologic disorders, cancer, and so on.

In this review article, we describe the molecular mechanisms of activation of innate immunity by TLRs, which sense invasion of pathogenic microorganisms including bacteria, viruses, fungi, and parasites. TLRs recognize specific patterns of microbial components, and induce expression of genes, which conducts development of antigen-specific adaptive immunity as well as inflammatory responses.