beta-Defensins are small antimicrobial peptides of the innate immune system produced in response to microbial infection of mucosal tissue and skin. We demonstrate that murine beta-defensin 2 (mDF2beta) acts directly on immature dendritic cells as an endogenous ligand for Toll-like receptor 4 (TLR-4), inducing up-regulation of costimulatory molecules and dendritic cell maturation. These events, in turn, trigger robust, type 1 polarized adaptive immune responses in vivo, suggesting that mDF2beta may play an important role in immunosurveillance against pathogens and, possibly, self antigens or tumor antigens.

We have explored the cis-acting elements necessary for the LPS-mediated activation of the mouse TNF-alpha promoter by transfecting a set of 5' deletion mutants linked to the CAT reporter gene into primary bone marrow-derived macrophages. A major drop in inducibility by LPS was seen upon deletion of a region mapping between nt -655 and nt -451. Gel retardation assays revealed that LPS induced the appearance in this region of several specific DNA-protein complexes mapping to sequence motifs with strong homology to the kappa B enhancer. Constructs containing two or more copies of one of the kappa B enhancer motifs linked to a heterologous promoter were inducible by LPS. Additional deletion of a region between nt -301 and nt -241, which contains a MHC class II-like "Y box" and formed a Y box-specific complex with a protein whose concentration was increased by LPS, caused a nearly complete loss of inducibility by LPS. We speculate that NF-kappa B and/or related proteins are involved in the LPS-induced transcriptional activation of the TNF-alpha gene, and that factors interacting with the Y box can additionally modulate the activity of the gene in macrophages.

Tumor necrosis factor (TNF, TNFalpha) is implicated in various pathophysiological processes and can be either protective, as in host defense, or deleterious, as in autoimmunity or toxic shock. To uncover the in vivo functions of TNF produced by different cell types, we generated mice with TNF ablation targeted to various leukocyte subsets. Systemic TNF in response to lipopolysaccharide was produced mainly by macrophages and neutrophils. This source of TNF was indispensable for resistance to an intracellular pathogen, Listeria, whereas T-cell-derived TNF was important for protection against high bacterial load. Additionally, both T-cell-derived TNF and macrophage-derived TNF had critical and nonredundant functions in the promotion of autoimmune hepatitis. Our data suggest that T-cell-specific TNF ablation may provide a therapeutic advantage over systemic blockade.

In order to definitively ascertain the functional contribution of lymphotoxin (LT) expressed by B cells, we produced mice with the LTbeta gene deleted from B cells (B-LTbeta KO mice). In contrast to systemic LTbeta deletion, in B-LTbeta KO mice only splenic microarchitecture was affected, while lymph nodes and Peyer's patches (PP) were normal, except for PP's reduced size. Even though B-LTbeta KO spleens retained a small number of follicular dendritic cells (FDC) which appeared to be dependent on LTbeta produced by T cells, IgG responses to sheep red blood cells were markedly reduced. Thus, the organogenic function of B-LTbeta is almost entirely restricted to spleen, where it supports the correct lymphoid architecture that is critical for an effective humoral immune response.

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