Douglas J. Perkins

Reduced Interleukin-12 and Transforming Growth Factor—β1 in Severe Childhood Malaria: Relationship of Cytokine Balance with Disease Severity

Interleukin (IL)-12 and transforming growth factor (TGF)-beta1 regulate the balance between pro- and anti-inflammatory cytokines in animal models of malaria. Since the cytokine balance may be an important determinant of whether a protective or a pathogenic immune response develops, plasma cytokine ratios were examined in Gabonese children with various degrees of malarial severity. Severe disease was characterized by high-density parasitemia and severe anemia. IL-12 and TGF-beta1 were significantly lower, whereas tumor necrosis factor (TNF)-alpha and IL-10 were significantly higher in children with severe malaria. The ratios of TGF-beta1/IL-12 and IL-10/IL-12 were significantly higher in the severe, compared with the mild, malaria group. In contrast, ratios of TGF-beta1/TNF-alpha and IL-10/TNF-alpha were significantly lower in the severe malaria group. These results suggest that the inflammatory cascade in severe malaria is characterized by suppression of the protective effects of TGF-beta1 and IL-12, and that overproduction of TNF-alpha may promote deleterious effects, such as severe anemia.

Nitric Oxide Synthase Type 2 Promoter Polymorphisms, Nitric Oxide Production, and Disease Severity in Tanzanian Children with Malaria

Nitric oxide (NO) plays an important role in host resistance to infection with a variety of organisms. Two recent reports from Gabon and Gambia identified associations of malaria disease severity with the inducible NO synthase (NOS2) promoter G-954C and short allele (<11 repeats) pentanucleotide microsatellite polymorphisms, respectively. It was postulated that there would be a correlation of these polymorphisms with malaria disease severity and with measures of NO production in our cohort of Tanzanian children with malaria. In Tanzanian children, 15% were heterozygous or homozygous for the G-954C polymorphism, and 13% had the short-allele microsatellite polymorphism. There was no significant correlation of either polymorphism with disease severity or with measures of NO production and NOS2 expression. Black and white Americans differed significantly in the frequencies of these polymorphisms. The various association of these gene polymorphisms with malaria severity in different populations underscores the complexity of host resistance to malaria.

Blockade of nitric oxide formation down-regulates cyclooxygenase-2 and decreases PGE2 biosynthesis in macrophages.

Elevated levels of nitric oxide (NO) produced by expression of inducible nitric oxide synthase (iNOS/NOS type 2) and high levels of prostaglandins (PGs) generated by expression of inducible cyclooxygenase (COX‐2/PGH2 synthase‐2) are important mediators of immune and inflammatory responses. Previous studies have shown that endogenous levels of NO˙ can influence the formation of PGs. We examined the mechanism by which NO˙ regulates PG biosynthesis in macrophages. Treatment of a murine macrophage cell line (ANA‐1) with lipopolysaccharide (LPS, 10 ng/mL) and interferon‐γ (IFN‐γ, 10 U/mL) for 20 h elicited high levels of nitrite (NO2 −) and prostaglandin E2 (PGE2) that were inhibited in a dose‐dependent fashion by the NOS inhibitor, aminoguanidine (AG), with IC50 values of 15.06 and 0.38 μM for NO2 − and PGE2, respectively. Stimulation of cultures with LPS and IFN‐γ for 20 h induced de novo iNOS protein expression that was not altered by the addition of AG (0.1, 10, or 1000 γM). In contrast, treatment of cultures with LPS and IFN‐γ for 20 h promoted COX‐2 mRNA and protein expression that were decreased in a dose‐dependent fashion by AG (P < 0.05 with 10 and 1000 μM). LPS and IFN‐γ‐induced COX‐2 protein expression was not decreased in cultures treated with AG for 2 h, illustrating that AG does not inhibit the formation of COX‐2 protein. Analysis of partially purified enzyme extracts demonstrated that AG did not directly inhibit the enzymatic activity of COX. Additional experiments revealed that NO^ donors (S‐nitroso‐N‐aceytl‐d‐l‐pencillamine, SNAP, at 0.1, 10, and 1000 μM) did not induce de novo COX‐2 protein expression or potentiate COX‐2 expression in cells treated with LPS and/or IFN‐γ. Our results suggest that, while endogenous NO˙ is not required for de novo COX‐2 mRNA and protein expression, NO˙ is necessary for maintaining prolonged COX‐2 gene expression. J. Leukoc. Biol. 65: 792–799; 1999.

Reduction of NOS2 overexpression in rheumatoid arthritis patients treated with anti-tumor necrosis factor α monoclonal antibody (cA2)

OBJECTIVEnPeripheral blood mononuclear cells (PBMC) from patients with rheumatoid arthritis (RA) have increased expression of nitric oxide synthase type 2 (NOS2) protein and enhanced formation of nitric oxide (NO) that correlate with disease activity. NO may play a role in the inflammation of RA. Treatment of RA patients with a chimeric monoclonal antibody against tumor necrosis factor alpha (TNFalpha; cA2) results in clinical improvement in the majority of patients. The present study was designed to determine if cA2 therapy decreases PBMC NOS2 protein expression and NOS enzyme activity in RA patients.nnnMETHODSnRA patients receiving background oral methotrexate participated in a double-blind, placebo-controlled clinical trial in which they were randomly assigned to receive a single infusion of either placebo or cA2 at 5, 10, or 20 mg/kg. NOS2 protein and NOS enzyme activity were measured in PBMC at baseline and 4 weeks following cA2 therapy. These results were compared with the degree of clinical change in disease activity.nnnRESULTSnAt baseline, elevated levels of NOS2 protein and NOS enzyme activity were more frequently detected in PBMC from RA patients than in those from healthy controls. Treatment of the RA patients with cA2 significantly reduced NOS2 protein expression and NOS enzyme activity. Changes in NOS activity following treatment correlated significantly with changes in the number of tender joints.nnnCONCLUSIONnThese results indicate that TNFalpha likely plays an important role in enhancing NOS2 expression in RA, and that the antiinflammatory effects of cA2 treatment may be mediated by a reduction of NO overproduction.

Inverse Relationship of Plasma Prostaglandin E2 and Blood Mononuclear Cell Cyclooxygenase-2 with Disease Severity in Children with Plasmodium faldpavum Malaria

Prostaglandins (PGs) derived from inducible cyclooxygenase (COX)-2 are important proinflammatory mediators of the host-immune response to infection. Since the role of host-derived PG in human malaria is unknown, plasma bicyclo-PGE2 (a stable catabolite of PGE2), peripheral blood mononuclear cell COX-2 protein, and mRNA were measured in Gabonese children with and without malaria (n=129). Relative to healthy children, bicyclo-PGE2 and COX-2 protein were lower in children with mild (P=.007 and P=.026, respectively) and severe malaria (P=.002 and P=.010, respectively). COX-2 mRNA was also reduced in children with malaria. Investigation of COX-2 regulatory cytokines revealed an inverse correlation (P<.001) between plasma levels of bicyclo-PGE2 and interleukin (IL)-10, a cytokine that suppresses COX-2 expression. On the basis of these results, elevated PGE2 in healthy malaria-exposed children may protect against malaria, whereas IL-10-induced decreases in PGE2 during acute malaria may increase susceptibility to severe disease.

Immunity to Placental Malaria. III. Impairment of Interleukin(IL)–12, not IL-18, and Interferon-Inducible Protein–10 Responses in the Placental Intervillous Blood of Human Immunodeficiency Virus/Malaria–Coinfected Women

Pregnant women are highly susceptible to malaria, and human immunodeficiency virus (HIV) infection increases this susceptibility. In our previous studies, placental malaria (PM), HIV infection, and HIV/PM coinfection were all associated with decreased interferon (IFN)-gamma production by maternal placental (intervillous) blood mononuclear cells (IVBMC). This study investigated whether in vitro production of the IFN-gamma regulatory cytokines interleukin (IL)-12 and IL-18 and the chemokine IFN-inducible protein (IP)-10 by IVBMC is altered in women who have been exposed to malaria and are infected with HIV. IL-12 production from IVBMC was significantly lower in HIV-positive women, regardless of PM status, in contrast to HIV-negative, PM-negative women. IL-18 and IP-10 production by IVBMC was reduced in HIV-positive, PM-negative women but elevated in HIV-positive, PM-positive women. These results reveal a substantial impairment of IL-12 production by IVBMC in HIV-positive women, implicating this cytokine as a potentially critical regulator of malaria antigen-specific IFN-gamma responses in HIV-infected and HIV/PM-coinfected women.