Microbial Toll/interleukin 1 receptor proteins: A new class of virulence factors

Quite a number of microbes possess genes which encode for proteins containing a Toll/interleukin 1 receptor domain. This domain is key for the physical interaction of eukaryotic Toll-like receptors with their adaptor molecules like MyD88 enabling innate immune cells to recognize invading pathogens and to initiate appropriate defense responses. Recent findings imply that microbial Toll/interleukin 1 receptor proteins impair Toll-like receptor signaling. As a consequence, secretion of pro-inflammatory cytokines is dampened, and microbial replication is enhanced. This group of proteins can thus be classified as a new family of virulence factors able to modulate the Toll-like receptor signaling cascade. This review summarizes current knowledge of the biology of this fascinating group of molecules.