ABSTRACT
At mammalian body temperature, the plague bacillus Yersinia pestis synthesizes lipopolysaccharide (LPS)-lipid A with poor Toll-like receptor 4 (TLR4)-stimulating activity. To address the effect of weak TLR4 stimulation on virulence, we modified Y. pestis to produce a potent TLR4-stimulating LPS. Modified Y. pestis was completely avirulent after subcutaneous infection even at high challenge doses. Resistance to disease required TLR4, the adaptor protein MyD88 and coreceptor MD-2 and was considerably enhanced by CD14 and the adaptor Mal. Both innate and adaptive responses were required for sterilizing immunity against the modified strain, and convalescent mice were protected from both subcutaneous and respiratory challenge with wild-type Y. pestis. Despite the presence of other established immune evasion mechanisms, the modified Y. pestis was unable to cause systemic disease, demonstrating that the ability to evade the LPS-induced inflammatory response is critical for Y. pestis virulence. Evading TLR4 activation by lipid A alteration may contribute to the virulence of various Gram-negative bacteria.
Subject(s)
Lipid A/immunology , Plague Vaccine/immunology , Plague/prevention & control , Toll-Like Receptor 4/agonists , Virulence Factors/immunology , Yersinia pestis/immunology , Acyltransferases/genetics , Acyltransferases/metabolism , Animals , Cells, Cultured , Escherichia coli Proteins/genetics , Escherichia coli Proteins/metabolism , Humans , Lipid A/biosynthesis , Lipid A/pharmacology , Lipopolysaccharide Receptors/immunology , Lipopolysaccharides/immunology , Lipopolysaccharides/pharmacology , Mice , Mice, Inbred Strains , Toll-Like Receptor 4/antagonists & inhibitors , Vaccination , Virulence/immunology , Virulence Factors/genetics , Virulence Factors/pharmacology , Yersinia pestis/pathogenicityABSTRACT
Some of the earliest axon pathways to form in the vertebrate forebrain are established as commissural and retinal axons cross the midline of the diencephalon and telencephalon. To better understand axon guidance in the forebrain, we characterized the zebrafish belladonna (bel) mutation, which disrupts commissural and retinal axon guidance in the forebrain. Using a positional cloning strategy, we determined that the bel locus encodes zebrafish Lhx2, a lim-homeodomain transcription factor expressed in the brain, eye and fin buds. We show that bel(Ihx2) function is required for patterning in the ventral forebrain and eye, and that loss of bel function leads to alterations in regulatory gene expression, perturbations in axon guidance factors, and the absence of an optic chiasm and forebrain commissures. Our analysis reveals new roles for Ihx2 in midline axon guidance, forebrain patterning and eye morphogenesis.
