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.

Tumor necrosis factor (TNF) plays a critical role in the host response to the intracellular pathogen Listeria monocytogenes (LM). TNF exists in soluble and membrane-bound forms and exhibits both unique and overlapping activities. We examined the role of membrane TNF in the absence of secreted TNF for host resistance in knockin mice in which the endogenous TNF was replaced by a regulated, noncleavable allele (mem-TNF). Macrophages expressing mem-TNF produced nitric oxide and displayed normal bactericidal activity. Although mice completely deficient in TNF (TNF ؊/؊ ) succumbed to LM infection within 4 days, mem-TNF mice controlled LM infection at a low dose (10 4 CFU) but succumbed at a higher dose of infection (10 5 CFU). In contrast to complete TNF deficiency, mem-TNF mice developed confined microabscesses that expressed inducible nitric oxide synthase. The transfer of lymphocytes from immunized mem-TNF, but not TNF ؊/؊ , mice protected TNF ؊/؊ mice from fatal infection. Taken Protective immunity to Listeria monocytogenes (LM) infection, both in humans and experimental animals, is based on orchestrated action of T cells, macrophages, and cytokines, including interferon (IFN)-␥, interleukin (IL)-12, and tumor necrosis factor (TNF). 1 A critical role for TNF in anti-LM defense is inferred from neutralization and gene deletion experiments in mice. 2,3 In addition, the TNFrelated cytokines lymphotoxin (LT)-␣ and LT-␤ are also required to control LM infection. 4 Both secreted TNF and LT-␣ signal through p55 and p75 TNF receptors (TNFR1 and TNFR2, respectively). The cell-bound LT-␣␤ heterotrimers recognize the LT-␤R. TNF-R1 signaling appears to be critical for the control of LM infection 2,3 and LT-␤R also plays a distinct role, while the contribution of TNFR2 is less well defined.TNF is expressed by a variety of cells, including macrophages and T cells, and is a major regulator of inflammation and leukocyte trafficking. 5 TNF is first produced as an integral membrane protein and is subsequently cleaved by the metalloproteinase-disintegrin TACE (TNF-␣ converting enzyme) 6,7 into the secreted trimeric TNF. Although the role of TNF in controlling intracellular bacterial infections is uncontested, the function of membrane TNF in host resistance is less understood.Several biological functions of membrane TNF have been described, such as cytotoxicity, polyclonal activation of B cells, induction of IL-10 by monocytes, induction of chemokines, and ICAM-1 expression on endothelial cells. 8 -10 The transgenic overexpression of membrane TNF has demonstrated an in vivo role in the control of LM and mycobacterial infection. [11][12][13] However, these models were potentially nonphysiological as transgenic expression of a membrane-only form of TNF results in artificially high and nonselective expression of membrane TNF. The recent generation of mice with functional, normally regulated and expressed membrane-bound TNF, obtained by knocking-in an uncleavable ⌬1-9, K11E TNF allele (mem-TNF mice), represents a major advance and allo...