The involvement of TNF, IL-1 and IL-6 in the immune response to protozoan parasites

Eye fluke effects on Danish freshwater fish: Field and experimental investigations

Eye flukes in fish are common in freshwater lakes. Fish become infected by the penetration of cercariae released from freshwater snails, and high infection pressures may be associated with mortalities in a Danish lake. Examination of two other freshwater lakes, combined with laboratory study, supported the notion. We investigated 77 freshwater fish from two lakes and the infection level suggested the occurrence of a high cercarial infection pressure in the Danish lakes. Dominant genera were Tylodelphys and Diplostomum covering a range of species identified by PCR and sequencing of the 18S (partial)-ITS1-5.8S-ITS2-28S (partial) of the rDNA. Cercariae of the prevalent species Diplostomum pseudospathaceum were used to infect zebrafish Danio rerio for the elucidation of short-term effects on the fish host. Zebrafish did not display abnormal behaviour when exposed to 200-400 cercariae, but a dosage of 600 and 1,000 cercariae/fish proved lethal. When fish were exposed to sublethal dosages, 19 out of 27 immune genes were significantly regulated and three genes encoding cytokine (IL 4/13B, IL-6 and IL-8) were upregulated at 3 hr post-infection (hpi), whereas others were downregulated especially at a later time point. We suggest that direct massive cercarial penetration of fish surfaces may be detrimental and may represent a threat to fish populations.

Serum profile of IL-1β and IL-17 cytokines in patients with visceral leishmaniasis

Leishmania is an intracellular protozoan parasite, mainly infects macrophages of mammalian tissues. Inflammatory related cytokines have a crucial role in the pathogenesis of leishmaniasis. The aim of the present study was to evaluate serum concentrations of IL-1β and IL-17 in patients with active visceral leishmaniasis (VL) and control group. Serum concentrations of both IL-1β and IL-17 cytokines were assessed by ELISA in Leishmania infantum infected patients (n = 25) and healthy individuals (n = 25) from Meshkin-Shahr, northwest of Iran. Mean serum concentrations of IL-1β in the patients and control groups were 47.34 ± 23.82, and 20.49 ± 9.38, respectively, which was statistically significant (p < 0.001). Furthermore, mean IL-17 concentration in patients with VL (243.96 ± 73.46) was twice higher comparing to control group (106.38 ± 129.06) (p < 0.001). Several cytokines are involved in the regulation of immunity against VL. The present data has shown that, increased serum concentrations of IL-1β and IL-17 are present in the patients with VL. Further investigations are needed to enhance our knowledge about the regulatory role of these cytokines in leishmaniasis.

VIRULENCE OF MIXED-CLONE AND SINGLE-CLONE INFECTIONS OF THE RODENT MALARIA PLASMODIUM CHABAUDI

Most evolutionary models treat virulence as an unavoidable consequence of microparasite replication and have predicted that in mixed-genotype infections, natural selection should favor higher levels of virulence than is optimal in genetically uniform infections. Increased virulence may evolve as a genetically fixed strategy, appropriate for the frequency of mixed infections in the population, or may occur as a conditional response to mixed infection, that is, a facultative strategy. Here we test whether facultative alterations in replication rates in the presence of competing genotypes occur and generate greater virulence. An important alternative, not currently incorporated in models of the evolution of virulence, is that host responses mounted against genetically diverse parasites may be more costly or less effective than those against genetically uniform parasites. If so, mixed clone infections will be more virulent for a given parasite replication rate. Two groups of mice were infected with one of two clones of Plasmodium chabaudi parasites, and three groups of mice were infected with 1:9, 5:5, or 9:1 mixtures of the same two clones. Virulence was assessed by monitoring mouse body weight and red blood cell density. Transmission stage densities were significantly higher in mixed- than in single-clone infections. Within treatment groups, transmission stage production increased with the virulence of the infection, a phenotypic correlation consistent with the genetic correlation assumed by much of the theoretical work on the evolution of virulence. Consistent with theoretical predictions of facultative alterations in virulence, we found that mice infected with both parasite clones lost more weight and had on average lower blood counts than those infected with single-clone infections. However, there was no consistent evidence of the mechanism invoked by evolutionary models that predict this effect. Replication rates and parasite densities were not always higher in ∗∗∗mixed-clone infections, and for a given replication rate or parasite density, mixed-clone infections were still more virulent. Instead, prolonged anemia and increased transmission may have occured because genetically diverse infections are less rapidly cleared by hosts. Differences in maximum weight loss occured even when there were comparable parasite densities in mixed- and single-clone infections. We suggest that mounting an immune response against more that one parasite genotype is more costly for hosts, which therefore suffer higher virulence.

Nippostrongylus brasiliensis: ability of plasma to prime free radical generation by leukocytes in response to adult worms not due to gamma-interferon or tumour necrosis factor

Plasma-borne factors prime leukocytes from both infected and uninfected rats for radical generation in response to N. brasiliensis. The concentration of these factors is increased following infection and reaches maximal levels on day 8 post-infection (p.i.) as demonstrated by the striking ability of plasma from infected rats to prime leukocytes from uninfected rats to produce free radicals in response to adult worms. The cytokines, gamma-interferon and tumour necrosis factor (TNF) can be detected in plasma during infection with a variety of organisms and several lines of immunological and pathophysiological evidence, including radical generation, weight loss, anaemia and diarrhoea, implicate generation of these proteins in response to infection with N. brasiliensis. We therefore investigated whether gamma-interferon and TNF were detectable in the plasma of rats infected with N. brasiliensis and whether the presence of these cytokines correlated with the ability of plasma to enhance radical generation in response to N. brasiliensis. However, gamma-interferon was not detected in the plasma of rats at any time after infection with N. brasiliensis and neutralizing monoclonal antibody to rat gamma-interferon had no effect on the ability of plasma to prime free radical generation. TNF was detected in the plasma of heavily-infected rats but only at very low levels (< 1 ng/ml), though copius in vivo synthesis of TNF could be induced by treatment of the infected rats with lipopolysaccharide (LPS). However, neither parasite-induced nor parasite plus LPS-induced plasma TNF correlated with the ability of plasma to enhance radical generation in response to N. brasiliensis.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in the TNF-alpha promoter region associated with susceptibility to cerebral malaria

Tumour-necrosis factor-alpha (TNF-alpha) is believed to have an important role in the pathogenesis of severe infectious disease and fatal cerebral malaria is associated with high circulating levels of this cytokine. In a large case-control study in Gambian children we find that homozygotes for the TNF2 allele, a variant of the TNF-alpha gene promoter region, have a relative risk of 7 for death or severe neurological sequelae due to cerebral malaria. Although the TNF2 allele is in linkage disequilibrium with several neighbouring HLA alleles, we show that this disease association is independent of HLA class I and class II variation. These data suggest that regulatory polymorphisms of cytokine genes can affect the outcome of severe infection. The maintenance of the TNF2 allele at a gene frequency of 0.16 in The Gambia implies that the increased risk of cerebral malaria in homozygotes is counterbalanced by some biological advantage.

Murine tumour necrosis factor plays a protective role during the initial phase of the experimental infection with Trypanosoma brucei brucei

Soluble extracts from salivarian trypanosomes (Trypanosoma brucei brucei, T. evansi and T. congolense) were shown to be capable of inducing murine tumour necrosis factor (mTNF) secretion, both in vivo and in vitro, whereas the soluble extract of an intracellular trypanosome (T. cruzi) failed to do so. Furthermore, the role of mTNF during the initial phase of experimental infections with T. brucei was studied by treating infected mice with mTNF-inducing trypanosoma soluble extract and with neutralizing monoclonal anti-mTNF antibodies. Treatment of the infected animals with different doses of T. brucei soluble extract resulted in a lower first parasitaemia peak (low lysate dose) and in a longer survival time or in a nearly total inhibition of parasite development (high lysate dose). Cotreatment of the infected mice with both anti-mTNF antibodies and a high dose of soluble extract completely restored the parasite development in both trypanosusceptible C3H/He mice and trypanosubtolerant CBA Ca mice, indicating a protective role of mTNF during the parasitaemia. Collectively these results suggest a negative influence of mTNF on T. brucei development in vivo.

Pneumocystis carinii induction of tumor necrosis factor-alpha by alveolar macrophages: modulation by pentamidine isethionate

Pneumocystis carinii, and the inflammatory response it provokes, together contribute to irreversible lung damage in immunocompromised patients. P. carinii cysts were found to be capable of inducing tumor necrosis factor-alpha (TNF) release from alveolar macrophages in a concentration-dependent manner. At physiologically achievable concentrations, pentamidine isethionate (pentamidine) substantially reduces such production. Pretreatment of alveolar macrophages (AM phi) with interferon-gamma (IFN-gamma) synergizes with P. carinii to produce increased levels of TNF, a condition which pentamidine was also able to antagonize. Pentamidine treatment did not interfere with the phagocytic ability of AM phi. Considering clinical reduction of TNF could lessen P. carinii pneumonia (PCP) induced inflammation, the efficacy of pentamidine in the treatment of PCP may be partially associated with its ability to inhibit the release of inflammatory mediators such as TNF.

Cytokine responses to parasite antigens: in vitro cytokine production to promastigotes of L. aethiopica by cells from non-Leishmania exposed donors may influence disease establishment

The various cytokine responses associated with stimulation by parasites is discussed with emphasis on Leishmania parasites. Cells from normal individuals can respond to Leishmania antigens in vitro but the state of the antigen used for stimulation influences the outcome. We have used cells from non-Leishmania exposed donors and stimulated them in vitro with variously treated promastigotes of L. aethiopica. The levels of some cytokines released into the supernatant were measured. All the Leishmania preparations tested induced high levels of IL-6, whereas IFN-gamma production to the different stimuli was variable in the individual donors. The ability of these supernatants to inhibit intracellular forms of L. aethiopica was sometimes stronger in L. aethiopica-induced than in PHA-induced cultures. Such strong non-Leishmania specific responses, if they exist in vivo, may influence whether disease is established when the host encounters Leishmania parasites.

Modulation of tumor necrosis factor release from alveolar macrophages treated with pentamidine isethionate

Alveolar macrophages in AIDS patients have a marked increase in tumor necrosis factor release in active Pneumocystis carinii pneumonia. We have demonstrated that pentamidine, an aromatic diamidine currently used to treat AIDS-related P. carinii pneumonia, is an effective inhibitor of cellular tumor necrosis factor release from lipopolysaccharide-stimulated rat alveolar macrophages at concentrations greater than 10(-8) M. Inhibition of release is not dependent upon the continued presence of pentamidine in the culture medium during the release phase. In addition, this blockage occurs at neither the transcriptional level as determined by Northern blot analysis nor the translational level as determined by Western blot analysis. Timed addition studies suggest that pentamidine is targeting relatively early events following lipopolysaccharide administration. Pentamidine appears to alter early lipopolysaccharide-induced cellular processes associated with the release of tumor necrosis factor from macrophages.