Genetic non-responsiveness of murine fibroblasts to bacterial endotoxin

Lipopolysaccharide: basic biochemistry, intracellular signaling, and physiological impacts in the gut

Lipopolysaccharide (LPS), a main constituent of Gram-negative bacterial membrane, specifically activates Toll-like receptor 4, leading to the production of pleiotropic cytokines/chemokines which in turn regulate inflammatory and innate and subsequent adaptive immune responses. Given that human gut harbors a large collection of commensal bacteria, LPS released by gut microbes is able to make the great impact on gut homeostasis through the intracellular signaling pathways engaged by host-microbial interaction. Emerging evidence indicates that LPS in the gut has a potency to elicit the pathogenesis of intestinal inflammatory diseases such as inflammatory bowel disease and necrotizing enterocolitis. In this review, we discuss the current understanding of the basic biochemistry of LPS, LPS-induced intracellular signaling, and physiological impacts of LPS in the intestine.

Periapical lesion progression and cytokine expression in an LPS hyporesponsive model

AIM

The purpose of this study was to compare periapical lesion progression and the expression of the bone modulating cytokines IL-1alpha, TNF-alpha, IL-4, IL-6 and IL-11 in periapical lesions of normal and C3H/HeJ (LPS hyporesponsive) mice.

METHODOLOGY

Pulps of both mandibular first molars from C3H/HeJ and BALB/c (normal) mice were exposed and inoculated with normal mouse oral microorganisms for 2, 4, 6, and 8 weeks. After euthanasia, specimens were prepared for histological examination. A quantitative evaluation of the lesional area and immunohistochemical stain counts was performed.

RESULTS

There were no statistically significant differences in progression of periapical lesions for both mouse strains with time (two-factor ANOVA, P > 0.05). The immunohistochemical staining revealed no overall differences between the two strains in levels of expression of the cytokines (P > 0.05). IL-11 expression did not change from control levels in BALB/c mice, but correlated with the expression of IL-6 and IL-4 in C3H/HeJ mice.

CONCLUSION

Responsiveness to LPS may not be significant in the pathogenesis of periapical lesions and in cytokine expression within the lesions, when the lesions are induced by non-specific oral flora.

Differential susceptibility of inbred mouse strains to dextran sulfate sodium-induced colitis

Dextran sulfate sodium (DSS)-induced murine colitis represents an experimental model for human inflammatory bowel disease. The aim of this study was to screen various inbred strains of mice for genetically determined differences in susceptibility to DSS-induced colitis. Mice of strains C3H/HeJ, C3H/HeJBir, C57BL/6J, DBA/2J, NOD/LtJ, NOD/LtSz-Prkdc(scid)/Prkdc(scid), 129/SvPas, NON/LtJ, and NON.NOD-H2g7 were fed 3.5% DSS in drinking water for 5 days and necropsied 16 days later. Ceca and colons were scored for histological lesions based on severity, ulceration, hyperplasia, and area involved. Image analysis was used to quantitate the proportion of cecum ulcerated. Histological examination revealed significant differences among inbred strains for all parameters scored. In both cecum and colon, C3H/HeJ and a recently selected substrain, C3H/HeJBir, were highly DSS susceptible. NOD/LtJ, an autoimmune-prone strain, and NOD/LtSz-Prkdc(scid)/Prkdc(scid), a stock with multiple defects in innate and adoptive immunity, were also highly DSS susceptible. NON/LtJ, a strain closely related to NOD, was quite DSS resistant. The major histocompatibility (MHC) haplotype of NOD mice (H2g7), a major component of the NOD autoimmune susceptibility, was not crucial in determining DSS susceptibility, since NON mice congenic for this MHC haplotype retained resistance. C57BL/6J, 129/SvPas, and DBA/2J mice showed various degrees of susceptibility, depending upon the anatomical site. A greater male susceptibility to DSS-induced colonic but not cecal lesions was observed. In summary, this study demonstrates major differences in genetic susceptibility to DSS-induced colitis among inbred strains of mice. Knowledge of these strain differences in genetic responsiveness to acute inflammatory stress in the large intestine will permit design of genetic crosses to elucidate the genes involved.

Something in the air: endotoxins and glucans as environmental troublemakers

This review provides a clear explanation of the current status of two common airborne contaminants, lipopolysaccharide and (1-->3)-beta-D-glucan, in the induction of indoor air-related disease. A full description of the origin of these two products is given together with information of their structure and function. Details of the biochemical mechanisms by which they interact with human cells and the physiological consequences of these interactions are outlined. Both compounds play a key role in the induction of airway inflammation and this paper highlights the environmental importance in the work place and home of these inhaled agents in terms of respiratory disease.

Interleukins and tumor necrosis factor in inflammation

Intense research efforts have been directed toward characterizing mediators that control the inflammatory response and regulate the growth, differentiation, and function of cells involved in inflammation. Tumor necrosis factor, or cachectin, and members of a heterogeneous group of peptides called interleukins exhibit a wide spectrum of activities, some of which appear to influence the evolution of inflammatory processes. This review outlines the observations that have led to our current understanding of the biology of tumor necrosis factor and the interleukins. Particular attention is directed toward the evidence suggesting that these cytokines function as mediators of inflammatory responses.

Immunomodulation of the antibody response to lipopolysaccharide in C3H/HeJ mice by complexing with heterologous ribosomes

We show that formaldehyde fixation of Salmonella typhimurium lipopolysaccharide (LPS) to ribosomes purified from Brucella abortus induced a primary immunoglobulin M (IgM) response to LPS in C3H/HeJ mice and upon revaccination resulted in elevated titers of IgM and induction of IgG antibody to the O antigens of LPS, as measured by an enzyme-linked immunosorbent assay. A similar LPS-Aspergillus fumigatus ribosomal complex yielded IgM and IgG antibody to LPS only after secondary stimulation. These results demonstrate that the hyporesponsiveness of C3H/HeJ mice with respect to antibody formation to LPS can be overcome by complexing this molecule to ribosomal particles and provide a theoretical mechanism for the action of some "ribosomal" vaccines. The results are compatible with the hypothesis that LPS in complex with the ribosomes is converted to a T-dependent form of the antigen to which the C3H/HeJ mice can respond.

Animal studies of toxic shock syndrome

Toxic shock syndrome (TSS) was first described in 1978 and since that year over 2990 cases have been reported to the Communicable Disease Center. The estimated case-fatality rate is 5.6%. The disease is characterized by fever, hypotension, rash, desquamation, and involvement of at least three other organ systems. Approximately 85% of the cases are menstrually related and tampon use has been identified as a risk factor. The remaining 15% of the cases occur in both sexes and are not specifically related to age or geographic location. In all cases where sought there is evidence for infection by Staphylococcus aureus. Nearly all S. aureus isolates are phage type 52/29 and elaborate a unique exotoxin (toxic shock toxin). This review explores both the successful and unsuccessful attempts to induce toxic shock or a TSS-like syndrome in animals other than man. The review identifies the baboon as an animal model of TSS and discusses the clinical and pathologic sequellae, in this species, after exposure to purified toxic shock toxin.

Effects of bacterial lipopolysaccharide on the production of colony-stimulating activity in C3H/HeJ mouse long-term bone marrow cultures

Bacterial lipopolysaccharide (LPS)-induced colony-stimulating activity (CSA) in murine long-term bone marrow culture system was investigated. Bone marrow culture cells of LPS-nonresponsive C3H/HeJ mice responded to LPS in terms of CSA production as efficiently as bone marrow culture cells of LPS-responsive C3H/slc mice. On the other hand, both peritoneal macrophages and bone marrow macrophages from C3H/HeJ mice did not produce CSA in vitro after treatment with LPS. Percoll density gradient separation of adherent layer cells in bone marrow cultures showed that two cell populations were present. One population was nonspecific esterase positive, productive of high CSA to LPS stimulation and light density cells, the other population was nonspecific esterase negative, productive of low CSA to LPS stimulation and high density cells, and CSA production stimulated by LPS in C3H/HeJ mice bone marrow culture cells was mainly attributed to the latter population of cells. These results suggest that CSA production stimulated by LPS in C3H/HeJ mice is regulated by different cell populations, respectively in vivo and in vitro.

Lipopolysaccharide and serum synergistically stimulate ornithine decarboxylase in Chinese hamster ovary cells

Lipopolysaccharide (LPS), the active component of bacterial endotoxin, caused no significant increase in ornithine decarboxylase (ODC) activity in serum-starved, Chinese hamster ovary fibroblasts. However, concurrent addition of LPS with 10% fetal bovine serum caused a synergistic 30 to 40-fold increase in enzyme activity as compared to the 10 to 20-fold increase seen after addition of serum alone. This synergism was not due to an alteration in the time course of enzyme induction after serum addition. The LPS-induced synergy of ODC induction by serum was inhibited by the concurrent addition of the specific LPS-antagonist, Polymyxin B.

Endogenous interferon production by endotoxin-responsive macrophages provides an autostimulatory differentiation signal

Previous studies have demonstrated that peritoneal macrophages (resident or thioglycolate-induced) derived from mouse strains fully responsive to gram-negative endotoxins continue to differentiate in vitro, as evidenced by an increased capacity to phagocytose via the Fc receptor with time in culture. In contrast, macrophages derived from endotoxin-hyporesponsive mouse strains (e.g., C3H/HeJ or C57BL/10ScN) exhibit no such increase in phagocytic capacity, and, in fact, significantly lose the capacity to phagocytose particles opsonized with immunoglobulin G with time in culture. This defect was found to be fully correctable by the addition to the cultures of an exogenous source of alpha, beta, or gamma interferon. In this study, we compared C3H/HeN (endotoxin-responsive) and C3H/HeJ (endotoxin-responsive) and C3H/HeJ (endotoxin-hyporesponsive) macrophages in an attempt to elucidate the mechanism responsible for this difference in phagocytic (differentiative) potential. The following observations support the hypothesis that endotoxin-responsive macrophages, in contrast to endotoxin-hyporesponsive macrophages, produce significantly higher levels of an autostimulatory differentiation signal that appears to be macrophage-derived interferon. (i) Anti-alpha/beta-interferon antibody greatly reduces the ability of C3H/HeN macrophages to phagocytose opsonized erythrocytes: (ii) C3H/HeJ macrophages can be made more phagocytic by coculture with C3H/HeN macrophages or by treatment with supernatants derived from C3H/HeN macrophage cultures; and (iii) C3H/HeN macrophages spontaneously lose Mac-1 antigen with time in culture. C3H/HeJ macrophages must be interferon-treated to be equivalently down-regulated.

The use of polymyxin B and C3H/HeJ mouse spleen cells as criteria for endotoxin contamination

We have performed experiments designed to evaluate the potential contribution of endotoxin contamination to lymphocyte reponses. Saline and EDTA extracts of 4 different strains of gram negative bacteria were examined for their capacity to initiate mitogenic responses in murine spleen cells. As compared to phenol extracts of these bacteria which contain primarily lipopolysaccharide-LPS, these saline and EDTA extracts were significantly less active in this assay. The mitogenic activity which was present was also manifest in spleen cells from the C3H/HeJ mouse, whereas phenol-extracted LPS preparations were inactive. In addition, mitogenic activity of saline and EDTA extracts was not blocked by polymyxin B, an agent known to abrogate LPS mediated responses. We conclude that LPS contamination may not normally be as significant a problem as had earlier been assumed. However, when endotoxin contamination is present, neither the use of C3H/HeJ spleen cells nor polymyxin B is an appropriate test to evaluate this possibility.

Role of complement in endotoxin initiated lethality in mice

We have examined the role of complement in eliciting a lethal response in C3H/HeJ and C3H/St mice. The results reported here indicate that endotoxin-initiated complement activation, leading to significant drops in circulating C3 levels, is not sufficient to cause lethality. The complement system in both strains was demonstrated to be responsive in vitro to activation both by E. coli 0111:B4 LPS I, an alternative pathway activator in other systems, as well as S. minnesota R595 LPS, which activates almost exclusively the classical pathway. In vivo injection of high (lethal) doses of E. coli 0111:B4 LPS I and S. minnesota R595 LPS causes a significant decrease in the circulating C3 levels of both strains after 4 hr. In contrast, circulating C3 levels were not significantly different from normal values in either strain following injection with minimal (lethal) amounts of E. coli 0111:B4 LPS II, a weakly anticomplementary LPS preparation. In all cases, lethality was observed in only the C3H/St mice, indicating that neither complement activation, nor the lack of it, is responsible for lethality in mice.