Transgenic mice expressing an inducible suicide gene, which allows systemic and reversible elimination of macrophages, were developed. A macrophage-specific c-fms promoter was used to express enhanced green fluorescent protein and a drug-inducible suicide gene that leads to Fas-mediated apoptosis in resting and cycling cells of the macrophage lineage. Transgenic mice were fertile, of normal weight, and showed no abnormal phenotype before drug exposure. The transgene was expressed constitutively in macrophages and dendritic cells (DC) but not significantly in T cells or B cells. Induction of the suicide gene led to depletion of 70-95% of macrophages and DC in nearly all tissues examined. Depletion reduced the ability to clear bacteria from the blood and led to increased bacterial growth in the liver. Depleted mice displayed several abnormalities, including splenomegaly, lymphadenopathy, thymic atrophy, extramedullary hematopoiesis, and development of peritoneal adhesions. This new, transgenic line will be useful in investigating the role of macrophages and DC.

Significance An experimental system was developed in mice to study the long-term benefits of early exposure to secretory antibodies of the IgA class (SIgA) in breast milk. We found that breast milk-derived SIgA promoted intestinal epithelial barrier function in suckling neonates, preventing systemic infection by potential pathogens. Long-term benefits of early exposure to SIgA included maintenance of a healthy gut microbiota and regulation of gene expression in intestinal epithelial cells. These findings suggest that maternal antibodies provide benefits to the intestinal immune system of the breast-fed infant, which persist into adulthood.

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Tumor necrosis factor is a cytokine that mediates many of the biologic actions of endotoxin. Recent studies have shown that tumor necrosis factor administration may cause liver injury and that tumor necrosis factor may mediate the lethality of the hepatotoxin galactosamine. One of the most potent inducers of tumor necrosis factor production is endotoxin. Because patients with alcoholic liver disease frequently have endotoxemia and because many of the clinical manifestations of alcoholic hepatitis are known biologic actions of tumor necrosis factor, we thought it would be important to evaluate tumor necrosis factor activity in patients with alcoholic hepatitis. Basal and lipopolysaccharide-stimulated tumor necrosis factor release from peripheral blood monocytes, a major source of tumor necrosis factor production, was determined in 16 patients with alcoholic hepatitis and 16 healthy volunteers. Eight of 16 alcoholic hepatitis patients and only two of 16 healthy volunteers had detectable spontaneous tumor necrosis factor activity (p less than 0.05). After lipopolysaccharide stimulation, mean monocyte tumor necrosis factor release from alcoholic hepatitis patients was significantly increased to over twice that of healthy controls (25.3 +/- 3.7 vs. 10.9 +/- 2.4 units per ml, p less than 0.005). We conclude that monocytes from alcoholic hepatitis patients have significantly increased spontaneous and lipopolysaccharide-stimulated tumor necrosis factor release compared to monocytes from healthy volunteers. We suggest that some of the metabolic abnormalities and possibly some of the liver injury of alcoholic hepatitis may be due to enhanced tumor necrosis factor production.

The contribution of innate immunity to inflammatory bowel disease (IBD) remains an area of intense interest. Macrophages (MØ) and dendritic cells (DC) are considered important factors in regulating the onset of IBD. The goal of this study was to determine if intestinal mononuclear phagocytes (iMNP) serve a pathological or protective role in dextran sulfate sodium (DSS)-induced colitis in mice. Using a conditional MØ/DC depletion transgenic mouse line--MØ Fas-induced apoptosis--to systemically deplete iMNP, DSS colitis histopathology was shown to be more severe in MØ/DC-depleted compared with MØ/DC-intact mice. Similarly, localized iMNP depletion by clodronate-encapsulated liposomes into C57BL/6, BALB/c, and CB.17/SCID mice also increased DSS colitis severity, as indicated by increased histopathology, weight loss, rectal bleeding, decreased stool consistency, and colon length compared with MØ/DC-intact, DSS-treated mice. Histology revealed that iMNP depletion during DSS treatment led to increased neutrophilic inflammation, increased epithelial injury, and enhanced mucin depletion from Goblet cells. iMNP depletion did not further elevate DSS-induced expression of TNF-alpha and IFN-gamma mRNA but significantly increased expression of CXCL1 chemokine mRNA. Myeloperoxidase activity was increased in colons of MØ/DC-depleted, DSS-treated mice, compared with DSS alone, coincident with increased neutrophil infiltration in diseased colons. Neutrophil depletion combined with MØ/DC depletion prevented the increase in DSS colitis severity compared with MØ/DC depletion alone. This study demonstrates that iMNP can serve a protective role during development of acute colitis and that protection is associated with MØ/DC-mediated down-regulation of neutrophil infiltration.

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Intestinal epithelial cells (IECs) form a physical and immunological barrier that separates the vast gut microbiota from host tissues. MyD88-dependent Toll-like receptor signaling is a key mediator of microbial–host cross-talk. We examined the role of epithelial MyD88 expression by generating mice with an IEC-targeted deletion of the Myd88 gene (MyD88ΔIEC). Loss of epithelial MyD88 signaling resulted in increased numbers of mucus-associated bacteria; translocation of bacteria, including the opportunistic pathogen Klebsiella pneumoniae, to mesenteric lymph nodes; reduced transmucosal electrical resistance; impaired mucus-associated antimicrobial activity; and downregulated expression of polymeric immunoglobulin receptor (the epithelial IgA transporter), mucin-2 (the major protein of intestinal mucus), and the antimicrobial peptides RegIIIγ and Defa-rs1. We further observed significant differences in the composition of the gut microbiota between MyD88ΔIEC mice and wild-type littermates. These physical, immunological, and microbial defects resulted in increased susceptibility of MyD88ΔIEC mice to experimental colitis. We conclude that MyD88 signaling in IECs is crucial for maintenance of gut homeostasis.

Patients with alcoholic hepatitis often have hepatic polymorphonuclear leukocyte infiltration and neutrophilia. Interleukin-8 is a cytokine that stimulates neutrophil chemotaxis and release of lysosomal enzymes. It is made by several types of cells, including fibroblasts, Kupffer cells and hepatocytes. In this study, serial plasma interleukin-8 concentrations were measured with enzyme-linked immunosorbent assay in 40 consecutive patients with moderate-to-severe alcoholic hepatitis over a 6-mo period. Two control groups included 10 patients without clinically important liver disease admitted for treatment of alcohol dependence and 12 healthy male volunteers. The mean plasma interleukin-8 level on admission was markedly increased: 695 +/- 146 pg/ml in the alcoholic hepatitis patients. The alcohol-dependent control group and the normal volunteer controls had mean interleukin-8 concentrations of 106 +/- 28 pg/ml and 10 +/- 5 pg/ml, respectively. Initially increased interleukin-8 levels in alcoholic hepatitis patients decreased to a mean of 182 +/- 42 pg/ml over the first month; levels had decreased further to 124 +/- 79 pg/ml after 6 mo. Increased interleukin-8 concentrations in patients with alcoholic hepatitis suggest a role for interleukin-8 in the neutrophilia and hepatic polymorphonuclear leukocyte infiltration of alcoholic hepatitis.