The influence of food restriction versus ad libitum feeding of chow and purified diets on variation in body weight, growth and physiology of female Wistar rats.

Ad libitum (AL) supply of standard chow is the feeding method most often used for rodents in animal experiments. However, AL feeding is known to result in a shorter lifespan and decreased health as compared with restricted feeding. Restricted feeding and thus limiting calorie intake prevents many health problems, increases lifespan and can also increase group uniformity. All this leads to a reduced number of animals needed. So-called standard chows are known to be prone to variation in composition. Synthetic foods have a more standard composition, contributing to group uniformity which, like diet reduction, may decrease the number of animals necessary to obtain statistical significance. In this study, we compared the effects of AL versus restricted feeding (25% reduction in food intake) on standard chow versus synthetic food of three different suppliers on body weight (BW), growth, several blood parameters and organ weights in growing female Wistar rats over a period of 61 days. Diet restriction led to a decreased growth and significantly reduced variation in BW and growth as compared with AL feeding. AL feeding on synthetic diets caused a significantly higher BW gain than on chow diets. Due to experimental design, this same effect occurred on food restriction. Blood parameters and organ weights were affected neither by diet type nor by amount. Incidentally, variations were significantly reduced on food restriction versus AL, and on synthetic diets versus chow diets. This study demonstrates that food restriction versus AL feeding leads to a significantly reduced variation in BW and growth, thereby indicating the potential for reduction when applying this feeding schedule.

Developmental aspects of the rat endolymphatic sac and functional implications.

The purpose of this study was to determine specific characteristics of endolymphatic sac (ES) cells of the developing rat that are considered to be involved in endolymph homeostasis. Because intermediate filament proteins (IFPs) are regarded as markers of cell differentiation and basal lamina proteins (BLPs) are essential in cell<=>matrix interactions, we determined the presence of IFPs [cytokeratins (CKs) and vimentin] and BLPs [collagen IV, heparan sulphate proteoglycan (HSPG) and laminin] at different developmental stages before and after birth. In addition, we studied the expression of two enzymes of oxidative metabolism: cytochrome oxidase and succinate dehydrogenase. The presence of CKs 8, 18 and 19 in all epithelial cells of the ES during the embryonic stage is characteristic of simple (glandular) epithelial cells. Interestingly, a distinct population of these cells shows additional expression of CK 7, which is a feature of secretory cells. These CK 7-positive cells also contain a high concentration of oxidative enzymes and are rich in mitochondria, indicating that they are light cells. It is suggested that light cells possess specific energy-requiring transport capabilities. Loss of CK 19 expression in the distal part and in a large region of the intermediate part of the ES implies that these cells do not differentiate any further and acquire the capacity to proliferate. Furthermore, prominent co-expression of vimentin with the CKs in the distal part of the ES may confer viscoelastic properties on this epithelium. This may facilitate expansion and thus enable cushioning of pressure fluctuations. Finally, the early prominent occurrence of HSPG in the basal lamina of the ES enables transport of ions. In this light our recent observations of early functioning NaK-ATPases in certain ES cells are interesting.

Cystatin M/E expression is restricted to differentiated epidermal keratinocytes and sweat glands: a new skin-specific proteinase inhibitor that is a target for cross-linking by transglutaminase.

Using serial analysis of gene expression on cultured human keratinocytes we found high expression levels of genes putatively involved in host protection and defense, such as proteinase inhibitors and antimicrobial proteins. One of these expressed genes was the recently discovered cysteine proteinase inhibitor cystatin M/E that has not been characterized so far at the protein level with respect to tissue distribution and additional biologic properties. Here we report that cystatin M/E has a tissue-specific expression pattern in which high expression levels are restricted to the stratum granulosum of normal human skin, the stratum granulosum/spinosum of psoriatic skin, and the secretory coils of eccrine sweat glands. Low expression levels were found in the nasal cavity. The presence of cystatin M/E in skin and the lack of expression in a variety of other tissues was verified both at the protein level by immunohistochemistry or western blotting, and at the mRNA level by reverse transcriptase polymerase chain reaction or northern blotting. Using biotinylated hexapeptide probes we found that cystatin M/E is an efficient substrate for tissue type transglutaminase and for transglutaminases extracted from stratum corneum, and that it acts as an acyl acceptor but not as an acyl donor. Western blot analysis showed that recombinant cystatin M/E could be cross-linked to a variety of proteins extracted from stratum corneum. In vitro, we found that cystatin M/E expression in cultured keratinocytes is upregulated at the mRNA and protein level, upon induction of differentiation. We demonstrate that cystatin M/E, which has a putative signal peptide, is indeed a secreted protein and is found in vitro in culture supernatant and in vivo in human sweat by enzyme-linked immunosorbent assay or western blotting. Cystatin M/E showed moderate inhibition of cathepsin B but was not active against cathepsin C. We speculate that cystatin M/E is unlikely to be a physiologically relevant inhibitor of intracellular lysosomal cysteine proteinases but rather functions as an inhibitor of self and nonself cysteine proteinases that remain to be identified.

Occurrence of NaK-ATPase isoforms during rat inner ear development and functional implications.

This study examined the presence of NaK-ATPase isoforms in the developing inner ear of the rat and studied the importance of functional subunit combinations in endolymph homeostasis. The findings were: (a) the combination alpha 1 beta 1 is found in epithelial, mesenchymal, and neural inner ear cells with an early starting expression 14 days postconception (dpc) in some endolymphatic sac cells; (b) from 1 day after birth (dab) expression of alpha 1 beta 2 is observed in marginal cells, vestibular dark cells, and certain vestibular nonsensory cells; (c) a transient expression of alpha 2 beta 1 is found in suprastrial fibrocytes and spiral ligament fibrocytes type II between 10 and 15 dab; (d) starting at 16 dpc the combination alpha 3 beta 1 is uniquely expressed in inner ear neural cells (as in other neural tissues). In conclusion, during development a switch from alpha 2 beta 1 towards alpha 1 beta 1 is observed in suprastrial fibrocytes and in spiral ligament fibrocytes type II. Thus, according to the biochemical characteristics of these combinations, a switch towards a NaK-ATPase with higher capacity takes place. In addition, prominent expression of the alpha 1 beta 2 combination in predominantly K+ ion transporting marginal and dark cells is in accordance with the characteristic of this combination and thus with the presumed function of these cells as important K+ suppliers for the endolymph. We believe this combination in certain vestibular nonsensory cells to be involved in K+ sensing. Early expression of the alpha 1 beta 1 combination in the endolymphatic sac, prior to that in the other parts of the inner ear, suggests that this structure may be involved to some extent in the development of the vestibulum and cochlea.

Phagocytosis and killing of Candida albicans by human neutrophils after exposure to structurally different lipid emulsions.

BACKGROUND: To test the hypothesis that structurally different lipid emulsions have distinct immune-modulating properties, we analyzed the elimination of Candida albicans by neutrophils after exposure to various emulsions. METHODS: Neutrophils from 8 volunteers were incubated in physiologic 5 mmol/L emulsions containing long-chain- (LCT), medium-chain- (MCT), mixed LCT/MCT-, alpha-tocopherol-enriched LCT/MCT (LCT/MCT-E), or structured lipids (SL). After washing, the neutrophils were incubated with C. albicans. Phagocytosis was measured as the number of yeast-associated neutrophils relative to the total neutrophil count. Killing was expressed as the percentage of Candida survival relative to the initial yeast cell count. RESULTS: No significant differences in yeast-neutrophil association could be demonstrated after neutrophil incubation in various lipid emulsions or medium, after correction for non-specific adhesion. However, although Candida survival after 1 hour incubation with non-lipid-exposed neutrophils amounted to 53% +/- 11% and was not influenced by LCT (60% +/- 11%), LCT/MCT (78% +/- 7%), LCT/MCT-E (72% +/- 12%), and SL (67% +/- 6%), pure MCT (70% +/- 13%) significantly impaired the killing capacity of neutrophils. CONCLUSIONS: The decreased killing capacity of neutrophils after exposure to medium-chain fatty acid-containing emulsions and the absence of this effect with LCT suggest that lipid emulsions influence the elimination of C. albicans depending on the triglyceride chain length.

Middle ear effusions and structure of the tympanic membrane.

OBJECTIVE: To study the effect of various middle ear effusions on the structure of the lamina propria of the tympanic membrane. METHODS: Sterile and infective middle ear effusions were induced by obstruction of the eustachian tube in specific pathogen-free (SPF) rats and in rats with upper airway infections (URI), respectively. The condition of the tympanic membrane was monitored at regular intervals. After varying survival times, the animals were killed and the tympanic membranes processed for light and electron microscopy. RESULTS: Sterile effusions always resulted in tympanosclerotic lesions. These lesions did not develop in the presence of primary-infected effusions. These effusions had a severe destructive effect on the lamina propria, followed by fibrosis. Generally, secondary infection did not markedly affect preexisting tympanosclerotic lesions. Moreover, calcification disappeared when re-aeration of the middle ear occurred, but the abnormal collagen depositions persisted. CONCLUSIONS: Both sterile and infective effusions result in comprehensive irreversible changes in the lamina propria of the pars tensa. The development of tympanosclerosis is confined to sterile effusions. Mechanical injury and compromised vascularization of the lamina propria are likely to be important etiological factors in the development of tympanosclerosis.

Failure to detect circulating Aspergillus markers in a patient with chronic granulomatous disease and invasive aspergillosis.

We report a patient with chronic granulomatous disease who developed invasive pulmonary aspergillosis and a subphrenic abscess. During treatment, high levels of Aspergillus antigen were detected in the abscess, but circulating antigen and Aspergillus DNA were undetectable in the serum.

With medium-chain triglycerides, higher and faster oxygen radical production by stimulated polymorphonuclear leukocytes occurs.

BACKGROUND: Parenteral lipid emulsions are suspected of suppressing the immune function. However, study results are contradictory and mainly concern the conventional long-chain triglyceride emulsions. METHODS: Polymorphonuclear leukocytes were preincubated with parenteral lipid emulsions. The influence of the lipid emulsions on the production of oxygen radicals by these stimulated leukocytes was studied by measuring chemiluminescence. Three different parenteral lipid emulsions were tested: long-chain triglycerides, a physical mixture of medium- and long-chain triglycerides, and structured triglycerides. Structured triglycerides consist of triglycerides where the medium- and long-chain fatty acids are attached to the same glycerol molecule. RESULTS: Stimulated polymorphonuclear leukocytes preincubated with the physical mixture of medium- and long-chain triglycerides showed higher levels of oxygen radicals (p < .005) and faster production of oxygen radicals (p < .005) compared with polymorphonuclear leukocytes preincubated with long-chain triglycerides or structured triglycerides. Additional studies indicated that differences in results of various lipid emulsions were not caused by differences in emulsifier. The overall production of oxygen radicals was significantly lower after preincubation with the three lipid emulsions compared with controls without lipid emulsion. CONCLUSIONS: A physical mixture of medium- and long-chain triglycerides induced faster production of oxygen radicals, resulting in higher levels of oxygen radicals, compared with long-chain triglycerides or structured triglycerides. This can be detrimental in cases where oxygen radicals play either a pathogenic role or a beneficial one, such as when rapid phagocytosis and killing of bacteria is needed. The observed lower production of oxygen radicals by polymorphonuclear leukocytes in the presence of parenteral lipid emulsions may result in immunosuppression by these lipids.

Infusion of lipoproteins into volunteers enhances the growth of Candida albicans.

Infusion of reconstituted high-density lipoproteins (rHDL) is being studied in clinical trials as an adjunctive therapy for gram-negative sepsis. Since no data are available on its possible effects in systemic candidiasis, we investigated the effect of rHDL infusion into volunteers on the growth of Candida albicans. C. albicans growth was 10- to 100-fold higher in the plasma of volunteers infused with 80 or 100 mg/kg rHDL than in plasma collected before infusion; administration of 60 mg/kg rHDL had marginal effects. In vitro, the isolated lipoprotein subfractions had a growth-promoting effect on C. albicans. These data suggest potential adverse effects of rHDL if infused into patients with systemic candidiasis. Thus, rHDL infusion into patients with sepsis caused by an unknown microorganism may be contraindicated.

Increased susceptibility of TNF-alpha lymphotoxin-alpha double knockout mice to systemic candidiasis through impaired recruitment of neutrophils and phagocytosis of Candida albicans.

TNF-alpha and lymphotoxin-alpha (LT) are members of the TNF family, and these cytokines play crucial roles in the defense against infection with Candida albicans. The aim of the present study was to investigate the role of endogenous TNF and LT during disseminated candidiasis in TNF-/-LT-/- knockout mice. The TNF- and LT-deficient animals had a significantly increased mortality following C. albicans infection compared with control mice, and this was due to a 10- to 1000-fold increased outgrowth of the yeast in their organs. No differences between TNF-/-LT-/- mice and TNF+/+LT+/+ were observed when mice were rendered neutropenic, suggesting that activation of neutrophils mediates the beneficial effects of endogenous TNF and LT. Histopathology of the organs, combined with neutrophil recruitment experiments, showed a dramatic delay in the neutrophil recruitment at the sites of Candida infection in the TNF-/-LT-/- mice. Moreover, the neutrophils of deficient animals were less potent to phagocytize Candida blastospores than control neutrophils. In contrast, the killing of Candida and the oxygen radical production did not differ between neutrophils of TNF-/-LT-/- and TNF+/+LT+/+ mice. Peak circulating IL-6 was significantly higher in TNF-/-LT-/- mice during infection. Peritoneal macrophages of TNF-/-LT-/- mice did not produce TNF, and synthesized significantly lower amounts of IL-1alpha, IL-1beta, IL-6, and macrophage-inflammatory protein-1alpha than macrophages of TNF+/+LT+/+ animals did. In conclusion, endogenous TNF and/or LT contribute to host resistance to disseminated candidiasis, and their absence in TNF-/-LT-/- mice renders the animals susceptible through impaired recruitment of neutrophils and impaired phagocytosis of C. albicans.

Local expression of cytokine mRNA in spleen and Peyer's patches of rats is involved in resistance against infection with Yersinia enterocolitica.

The immune-response against infection with Yersinia enterocolitica was studied in a rat model which resembles yersiniosis in humans. Lewis, Fischer and Brown Norway rats were inoculated with Y. enterocolitica and the cytokine mRNA expression in spleen and Peyer's patches was determined. In Brown Norway rats the infection was mild and Yersinia enterocolitica was fully cleared. In these rats the highest anti-inflammatory cytokine expression was found probably resulting in a protective host defence against the infection. In both the Lewis and Fischer rats Y. enterocolitica persisted. The anti-inflammatory cytokine expression was less pronounced in these two rat strains. The authors conclude that progression of disease, persistence of infection and development of reactive arthritis, may be related to the local expression of specific cytokines.

Recombinant murine granulocyte colony-stimulating factor protects against acute disseminated Candida albicans infection in nonneutropenic mice.

The effect of recombinant granulocyte colony-stimulating factor (rG-CSF) on acute disseminated Candida albicans infection in nonneutropenic mice was investigated. Mice treated with a single dose of rG-CSF showed a significantly reduced mortality (28% vs. 90%; P < .001). The outgrowth of C. albicans from the kidneys, spleens, and livers of rG-CSF-treated mice was significantly reduced (log cfu/g of kidney, 5.54 vs. 7.13; P < .001), as were circulating tumor necrosis factor-alpha and interleukin-1beta. After rG-CSF, the kidneys showed fewer infectious infiltrates, enhanced granulocyte influx, and almost complete absence of hyphal outgrowth. During peritoneal C. albicans infection, rG-CSF enhanced influx of granulocytes to the site of infection, and exudate granulocytes showed increased oxygen radical production. These results indicate that rG-CSF enhances host resistance to disseminated candidiasis in nonneutropenic mice through activation of granulocytes and their recruitment to the site of infection.

A primer on cytokines: sources, receptors, effects, and inducers.

Protection against pathogens is a prerequisite for survival of most organisms. To cope with this continuous challenge, complex defense mechanisms have evolved. The construction, adaptation, and maintenance of these mechanisms are under control of an extensive network of regulatory proteins called cytokines. A great number of cytokines have been described over the last 2 decades. This review consists of an overview of cytokines that are involved in immune responses and describes some historical and general aspects as well as prospective clinical applications. Major biological effects together with information on cytokine receptors, producers, inducers, and biochemical and molecular characteristics are listed in tables. In addition, some basic information is given on cytokine receptor signal transduction. Finally, the recent discoveries of cytokine receptors functioning as coreceptors in the pathogenesis of human immunodeficiency virus are summarized.

Differential induction of pro- and anti-inflammatory cytokines in whole blood by bacteria: effects of antibiotic treatment.

The in vitro production of interleukin-1beta (IL-1beta), IL-6, and the IL-1 receptor antagonist (IL-1ra) in whole blood upon stimulation with different bacterial strains was measured to study the possible relationship between disease severity and the cytokine-inducing capacities of these strains. Escherichia coli, Neisseria meningitidis, Neisseria gonorrhoeae, Bacteroides fragilis, Capnocytophaga canimorsus, Staphylococcus aureus, Enterococcus faecalis, Streptococcus pneumoniae, and Streptococcus pyogenes induced the cytokines IL-1beta, IL-6, and IL-1ra. Gram-negative bacteria induced significantly higher levels of proinflammatory cytokine production than gram-positive bacteria. These differences were less pronounced for the anti-inflammatory cytokine IL-1ra. In addition, blood was stimulated with E. coli killed by different antibiotics to study the effect of the antibiotics on the cytokine-inducing capacity of the bacterial culture. E. coli treated with cefuroxime and gentamicin induced higher levels of IL-1beta and IL-6 production but levels of IL-1ra production similar to that of heat-killed E. coli. In contrast, ciprofloxacin- and imipenem-cilastatin-mediated killing showed a decreased or similar level of induction of cytokine production as compared to that by heat-killed E. coli; polymyxin B decreased the level of production of the cytokines.

Interactions of Yersinia enterocolitica with polarized human intestinal Caco-2 cells.

The in vitro interactions of Yersinia enterocolitica, Salmonella typhimurium and Escherichia coli with polarized human colonic carcinoma (Caco-2) cells are described. Invasion of a confluent Caco-2 cell monolayer by Yersinia and Salmonella took place within 4 h after contact, which was in marked contrast to E. coli which did not invade Caco-2 cells. Cytoplasmic extrusions developed on the apical membrane and indicated the site of entrance of bacteria into the Caco-2 cells. Intracellular Yersinia and Salmonella were surrounded by a vacuolar membrane. Single as well as multiple bacteria were enclosed within a single vacuole. At 6 h after contact some of the intracellular yersiniae were found free in the cytoplasm. Furthermore, morphological signs of degeneration of Caco-2 cells such as vacuolization and autophagy were observed. Caco-2 cells infected with Salmonella also showed degenerative changes but the salmonellae resided within membrane-bound vacuoles in contrast to Yersinia. These observations are in contrast to those described for the invasion of other cells lines (not derived from intestinal epithelium) by Yersinia and may reflect more closely the interactions between Yersinia and the intestinal epithelium during gastrointestinal infection.

Persistent Yersinia enterocolitica infection in three rat strains.

Yersinia enterocolitica may persist for prolonged periods of time in humans sometimes resulting in the development of reactive arthritis. To elucidate factors predisposing for persistence we developed animal models. In Lewis and Fischer rats, viable bacteria could be demonstrated for prolonged time and abscesses could be found in the liver, spleen and lungs. Splenic abscesses were observed for more than 20 weeks. Yersinia enterocolitica persisted in Lewis and Fischer rats, but only Lewis rats developed reactive arthritis. In Brown Norway rats abscesses developed early during infection but in contrast to the other strains disappeared after 3 weeks. Culture of homogenized abscess-containing tissue of all three rat strains yielded Yersiniae. Immunofluorescence studies of the abscesses showed diffuse staining inside the abscesses only, indicating the presence of Yersinia enterocolitica antigen. Brown Norway rats, in contrast to Lewis and Fischer rats, developed a different serological reaction pattern against Yersinia enterocolitica antigens and this correlated with the disappearance of the abscesses.

Plasmodium berghei: recombinant interferon-gamma and the development of parasitemia and cerebral lesions in malaria-infected mice.

Mice infected with Plasmodium berghei K173-parasitized erythrocytes develop severe hypothermia followed by death as a consequence of murine cerebral malaria early in the second week after infection. A single intraperitoneal injection of 10(5) Units of IFN-gamma given between Day 4 and Day 6 postinfection results in a transient decrease of body temperature. No effect on parasitemia and cerebral malaria is obtained by this treatment. Daily injections of relatively low doses of IFN-gamma delays the patency of the infection for 2 days. Furthermore the proliferation rate of the parasites is reduced and the development of cerebral malaria is also delayed for 2 days. The reduction of body temperature, as found in untreated infected mice, is absent. Administration of IFN-gamma by means of a continuous delivery from intraperitoneally inserted osmotic pumps (1.2 x 10(4) Units of IFN-gamma/24 hr) also delays patency and inhibits parasitemia. Body temperature decreases during infection but mice are protected against the development of cerebral malaria. In nude mice, this treatment inhibits parasitemia to the same extent. However, reduction of body temperature was also prevented. High doses of IFN-gamma delivered by osmotic pumps (2.5 x 10(4) or 10(5) Units of IFN-gamma/24 hr) appear to be lethally toxic in conventional as well as in nude mice, independently of infection. Cerebral malaria-like symptoms are found in these mice. Treatment of infected C57BL/6J mice with antibody to IFN-gamma 4 days before and after infection as well as on the day of infection enhances parasitemia but does not affect the development of murine cerebral malaria. Single injections of anti-IFN-gamma-antibody 6 hr prior to infection or 7 days after infection have no effect. In CBA/Ca mice, treatment with anti-IFN-gamma-antibody enhances parasitemia; furthermore protection against cerebral malaria was obtained in part of the mice.

Tumour necrosis factor-alpha and macrophages in Plasmodium berghei-induced cerebral malaria.

The effect of tumour necrosis factor-alpha on malaria-infected mice was studied. C57Bl/6J mice infected with Plasmodium berghei K173 exhibited an increased sensitivity to exogenous TNF. Injection of 15 micrograms TNF was lethal to some of the animals when given 5-7 days after infection, while when given later on in the infection (i.e. days 8-10) amounts as low as 2.5 micrograms TNF appeared to be lethal in all mice. The pathology in infected mice treated with TNF resembled that found in the brains of infected mice dying with cerebral malaria. Infected mice treated with TNF, however, also developed severe pathological changes in other organs. On the contrary, treatment with sublethal amounts of TNF (1.0 micrograms or less) given on days 8 and 9 after infection, protected mice against the development of cerebral malaria. In addition, infected mice exhibited and enhanced sensitivity for treatment with lipopolysaccharide (LPS). Sublethal amounts of LPS, however, did not prevent mortality as in TNF-treated mice (LPS-treated mice died at about the same time as infected mice that developed cerebral malaria), but no cerebral haemorrhages were found in the majority of LPS treated, infected animals. Treatment with dexamethasone during infection protected mice against the development of cerebral malaria, but did not suppress their increased sensitivity to exogenous TNF. Treatment of mice with liposome-encapsulated dichloromethylene diphosphonate (lip-Cl2MDP), used to eliminate macrophages (an important source of TNF), prevented the development of cerebral malaria, but only when given before day 5 of infection. Mice protected by treatment with lip-Cl2MDP, however, remained sensitive for LPS on the eighth day of infection.

Effects of interleukin-8 on nonspecific resistance to infection in neutropenic and normal mice.

The effect of treatment with interleukin-8 (IL-8), a neutrophil-activating cytokine, was investigated in normal and neutropenic mice infected with a lethal dose of Pseudomonas aeruginosa, Klebsiella pneumoniae, or Plasmodium berghei. Intraperitoneal (i.p.) IL-8 treatment was associated with accelerated death when IL-8 was administered shortly before i.p. infection with P. aeruginosa or shortly after i.p. infection with P. aeruginosa and K. pneumoniae. Histopathological analyses demonstrated a tendency to more severe organ lesions in IL-8-treated mice. Only nonneutropenic mice that received IL-8 shortly before the infectious challenge and at the site of infection were protected by IL-8. Whether IL-8 is protective of or detrimental to the survival of infection appeared to depend on the presence of bacteria at the injection site and on the presence of neutropenia. IL-8 may be an important participant in the cascade of interacting cytokines that is induced by the lethal infectious challenge.

Interleukin-1 as a possible agent for treatment of infection.

Treatment of experimental animals with bacterial products, such as cell wall components of gram-negative bacteria, leads to enhanced resistance to a variety of microorganisms. Since interleukin-1 and other pro-inflammatory cytokines are induced by such bacterial products, it has been investigated whether these cytokines are also capable of enforcing host resistance. It has been possible to demonstrate that a low dose of interleukin-1 protects mice against death from either gram-negative or gram-positive bacteria, Candida albicans and Plasmodium berghei. The protection against lethal bacterial and fungal infection can be produced in both normal and neutropenic animals. Despite extensive investigations, the mechanism of protection is not understood. A possible mechanism, which is currently being investigated, is that interleukin-1 interferes with the deleterious action of the pro-inflammatory cytokines during the lethal phase of the infection.