Experimental cerebral malaria: possible new mechanisms in the TNF-induced microvascular pathology

In order to contribute to the prevention of malaria morbidity and mortality, especially in endemic zones, we have carried out a series of studies on cytokine interactions in an experimental model of cerebral malaria (CM). This rapidly lethal syndrome develops, in some strains of mice, upon infection with Plasmodium berghei ANKA (PbA). A crucial mediator of neurovascular lesions appears to be TNF, found in high amounts in relation with cerebral complications, in both experimental and human CM. In experimental CM, in vivo injections of anti-cytokine antibodies have been used to analyze the cascade of reactions leading to brain vascular damage. In this review, we fill focus on the interplay of cytokines responsible for TNF overproduction in experimental malaria, therefore delineating the subset of T cells whose activation can lead to pathology, and effector mechanisms of neurovascular lesions characteristic of mouse cerebral malaria, with recent findings that appear to involve an unexpected cell type, the blood platelet.

Plasma cytokine levels in hemolytic uremic syndrome

The cytokines tumor necrosis factor-alpha (TNF-alpha) and its soluble TNF receptors 55 and 75 (sTNFR55, sTNFR75), interleukin-1 beta (IL-1BETA) and interleukin-6 (IL-6) were measured in plasma from 13 patients with the hemolytic uremic syndrome (HUS) on admission. No significant changes in the plasma levels of TNF-alpha and IL-1beta were detected in the HUS patients as compared to the plasma levels of the control groups. Levels of IL-6 were significantly elevated in the plasma of those HUS patients who had external manifestations, consisting of seizures, loss of consciousness, coma and pancreatic necrosis. Although the exact function of IL-6 in the plasma of HUS patients is still unknown and the group of HUS patients is small, plasma IL-6 is associated with the the severity and outcome of the disease. Plasma levels of sTNR55 and sTNFR75 were significantly elevated in all HUS patients compared to the healthy controls, but they were also elevated in the children with chronic renal failure. This indicates that elevated levels of circulating sTNFR should be carefully interpreted when kidney failure exists.

H-2D haplotype-linked expression and involvement of TNF-alpha in Th2 cell-mediated tissue inflammation

We recently reported that polyclonal anti-CD3 epsilon-pulsed Th2 cells mediate local tissue inflammation (DTH2) when injected into naive syngenic recipient mice, and that this response is entirely dependent on IL-4 in BALB/c (H-2d) mice. We now describe a different cytokine dependence in mice that bear a H-2b MHC haplotype. Injection of either soluble IL-4R (sIL-4R) or anti-TNF Ab partially inhibited swelling that was mediated by Th2 cells from high TNF-producing C57BL/6 mice. Anti-TNF and sIL-4R in combination were required to completely abrogate the swelling reaction and cellular infiltrate. Adoptive transfers across strain barriers showed that the TNF dependence was dictated by the origin of the transferred cells, rather than by the recipient. Experiments with intra-H-2 recombinant C57BL/10 strains indicated that TNF released by Th2 cells was correlated with the involvement of TNF in DTH2: Th2 cells from the H-2Db strains C57BL/10 and B10.A(2R) produced high amounts of bioactive TNF and mediated swelling that was partially inhibited by anti-TNF. In contrast, Th2 cells from B10.D2 and B10.A mice (H-2Dd) produced low levels of TNF, and anti-TNF had no effect on DTH2 in these strains. Our results suggest a linkage between the TNF dependence of DTH2, the capacity of Th2 cells to release TNF upon restimulation, and the donor H-2D haplotype; strain-dependent allelic expression of TNF seems to determine the involvement of this cytokine in DTH2.

H-2D haplotype-linked expression and involvement of TNF-alpha in Th2 cell-mediated tissue inflammation

We recently reported that polyclonal anti-CD3 epsilon-pulsed Th2 cells mediate local tissue inflammation (DTH2) when injected into naive syngenic recipient mice, and that this response is entirely dependent on IL-4 in BALB/c (H-2d) mice. We now describe a different cytokine dependence in mice that bear a H-2b MHC haplotype. Injection of either soluble IL-4R (sIL-4R) or anti-TNF Ab partially inhibited swelling that was mediated by Th2 cells from high TNF-producing C57BL/6 mice. Anti-TNF and sIL-4R in combination were required to completely abrogate the swelling reaction and cellular infiltrate. Adoptive transfers across strain barriers showed that the TNF dependence was dictated by the origin of the transferred cells, rather than by the recipient. Experiments with intra-H-2 recombinant C57BL/10 strains indicated that TNF released by Th2 cells was correlated with the involvement of TNF in DTH2: Th2 cells from the H-2Db strains C57BL/10 and B10.A(2R) produced high amounts of bioactive TNF and mediated swelling that was partially inhibited by anti-TNF. In contrast, Th2 cells from B10.D2 and B10.A mice (H-2Dd) produced low levels of TNF, and anti-TNF had no effect on DTH2 in these strains. Our results suggest a linkage between the TNF dependence of DTH2, the capacity of Th2 cells to release TNF upon restimulation, and the donor H-2D haplotype; strain-dependent allelic expression of TNF seems to determine the involvement of this cytokine in DTH2.

Protective effect of N-acetylcysteine in hapten-induced irritant and contact hypersensitivity reactions

The hapten-induced irritant and contact hypersensitivity reactions are experimental models of cutaneous inflammation in which tumor necrosis factor-alpha is an important mediator. N-acetylcysteine is an anti-oxidant that inhibits the action of the nuclear factor-kB, which promotes the transcription of many genes, including the gene for tumor necrosis factor-alpha. We tested the ability of N-acetylcysteine to antagonize the development of the irritant and contact hypersensitivity reactions induced by the epicutaneous application of trinitrochlorobenzene in mice. Systemic and topical treatment with N-acetylcysteine reduced skin swelling in both the irritant and contact hypersensitivity reactions; in the latter it also reduced the dermal leukocyte infiltrate. It also reduced the cutaneous expression of the mRNA for tumor necrosis factor-alpha in both conditions. These results show that N-acetylcysteine antagonizes the development of irritant and contact hypersensitivity reactions and that its action includes a reduction in the expression of tumor necrosis factor-alpha mRNA. N-acetylcysteine may be useful in the treatment of cutaneous inflammation mediated by tumor necrosis factor-alpha.

Role of polymorphonuclear neutrophil leukocytes and their integrin CD11a (LFA-1) in the pathogenesis of severe murine malaria

Infection of CBA mice with Plasmodium berghei ANKA results in severe malaria, which is characterized by mortality 6 to 10 days after infection and is associated with alterations of the brain microcirculation. These alterations consist of (i) intravascular sequestration of monocytes, (ii) an increase in vascular permeability as documented by Evans blue diffusion, and (iii) microhemorrhages. This syndrome may be due to an increase of production of tumor necrosis factor alpha which upregulates the endothelial expression of ICAM-1 and thus leads to adhesion of CD11a/CD18 (LFA-1)-bearing cells. During severe malaria, we found an important sequestration of the CD11a-bearing polymorphonuclear neutrophil leukocytes (PMN) in the lung but not in the brain. Treatment with a monoclonal antibody (MAb) against PMN, which induces profound neutropenia, prevented mortality and Evans blue diffusion in the brain and the lung, while it unexpectedly increased the occurrence of microhemorrhages. The anti-PMN MAb abolished PMN sequestration in the lung and also partially decreased monocyte sequestration in the brain and the lung. Treatment with an anti-CD11a MAb also prevented mortality, Evans blue diffusion, and PMN and monocyte sequestration. This study shows that PMN contribute to the mortality and the microvascular lesions resulting from severe malaria. This may be due to their CD11a-dependent sequestration in the lung and also to their indirect influence on vascular permeability and the sequestration of monocytes.

Tumor necrosis factor alpha (TNF-alpha) and TNF-beta and their receptors in experimental cutaneous leishmaniasis

Experimental infection of BALB/c mice with Leishmania major leads to lesions which progress without healing and visceralization, reproducing the most severe forms of human leishmaniasis, while resistant mice like CBA spontaneously resolve lesions and develop protective immunity. Given the conflicting data pertaining to the role of tumor necrosis factor alpha (TNF) in Leishmania infection, we analyzed the expression of TNF, tumor necrosis factor beta (lymphotoxin), and TNF receptor type I (TNF-RI) and type II (TNF-RII) genes in vivo and correlated TNF gene expression in vivo with the production of biologically active TNF by lymphoid cells in vitro. No significant difference in the expression of TNF mRNA was found between susceptible and resistant strains of mice during the course of infection. The depletion of CD4+ T cells in vitro did not change the level of TNF mRNA in BALB/c lymph node cells but led to the total disappearance of TNF mRNA in CBA mice. Unprimed spleen cells did not produce detectable amounts of TNF, whereas 1 week after infection, TNF bioactivity was detected and increased in both strains of mice until 5 weeks of infection. While neutralization of TNF activity in vivo did not alter the course of infection in BALB/c mice, in CBA mice it led to an increase in lesion size and a delay in the healing process but did not interfere significantly with the outcome of infection. Finally, no significant difference in the levels of lymphotoxin, TNF-RI, or TNF RII mRNA expression was found between both strains. The information resulting from these investigations supports the notion that, in vivo, TNF is not the decisive factor responsible for the resistant versus susceptible phenotype in leishmania infection.

Modulation of the transcripts for tumor necrosis factor-alpha and its receptors in vivo

We investigated the effects of a single bacterial lipopolysaccharide (LPS) injection in vivo on the gene expression of tumor necrosis factor-alpha (TNF) and its receptors: TNF receptor type I (TNF-R 55 kDa or TNF-R1) and TNF receptor type II (TNF-R 75 kDa or TNF-R2) in various tissues and white blood cells. While TNF mRNA rapidly accumulated in most tissues, TNF-R1 and TNF-R2 mRNA levels were found to be differentially regulated in lung, spleen, lymph nodes and white blood cells. In most cases, TNF-R mRNA levels did not parallel TNF mRNA levels. These observations indicate that TNF-R of both types of capable of modulating the host response to LPS, not only by shedding of their extracellular domains, but also by strict regulation of their gene expression.

Early hemodynamic and renal effects of tumor necrosis factor alpha: role of thromboxane

TNF alpha is an early mediator of endotoxemic shock. Its acute effect on renal hemodynamics is not known. In this study, the early hemodynamic and renal effects of TNF alpha were investigated in a rabbit model of shock, in which the measurement of the aortic blood flow before the bifurcation of the renal arteries allows one to differentiate between prerenal factors and hemodynamic renal response. Six groups of rabbits were studied, receiving either: (1) endotoxin, (2) endotoxin + thromboxane inhibitor Dazmegrel, (3) TNF alpha, (4) TNF alpha + Dazmegrel, (5) TNF alpha+indomethacin, or (6) placebo. Between 60 min and 3 hr after the injection, endotoxin induced a mean fall in arterial pressure of 32% (P < 0.01) and TNF alpha of 16% (P < 0.01). After endotoxin, the aortic blood flow decreased by 27% (P < 0.01) and after TNF alpha by 18% (P < 0.001). Both specific thromboxane inhibition and indomethacin abolished the TNF alpha central hemodynamic effect. The renal blood flow (-53%), the renal fraction of the aortic blood flow (-38%), and the glomerular filtration rate (-47%, P < 0.05) decreased 1 hr after endotoxin injection. In contrast, TNF alpha induced only a slight fall of the renal fraction of the aortic blood flow (-19%) after 2.5 hr. Glomerular filtration was not modified after TNF alpha injection most likely because of a 17% mean increase of filtration fraction in this group (P < 0.001). These data indicate that TNF alpha is implicated in the early hemodynamic changes of endotoxemic shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Profiles of cytokine production in relation with susceptibility to cerebral malaria

Infection with Plasmodium berghei ANKA (PbA) leads, in susceptible strains of mice, to the development of cerebral malaria (CM), a lethal syndrome that reproduces some features of human CM. To study a possible relationship between genetic susceptibility to CM and the cytokine expression pattern, we quantitatively evaluated gene expression on RNA extracted from various organs of malaria-infected mice, using strains that are susceptible and resistant to CM. Northern blot analysis and semi-quantitative PCR showed that CM is associated with an increased TNF-alpha mRNA accumulation in the brain of mice developing the neurologic complications of CM. An increased IFN-gamma mRNA accumulation and a decreased expression of IL-4 and TGF-beta genes were also observed in mice susceptible to CM. In vitro restimulation studies using crude malarial Ag showed that lymphoid cell proliferation was higher in CM-susceptible than in CM-resistant infected mice. Moreover, susceptible mice produced large amounts of IFN-gamma, in a dose-dependent manner, in response to PbA Ag, whereas cells from resistant mice failed to produce significant amounts of this cytokine. Conversely, IL-2 and IL-4 production was significantly higher in infected CM-resistant mouse cells. No difference was seen in the production of IL-3 and IL-5 between resistant and susceptible PbA-infected mice. Upon stimulation with various malarial Ag, comparable amounts of TNF-alpha were produced by macrophages of either strain of mice. Taken together, these findings indicate that susceptibility to CM resides at the level of T cells rather than macrophages. Furthermore, the cytokine production profile is consistent with a predominant Th1-like response in mice developing cerebral complications of malaria.

TNF-induced microvascular pathology: active role for platelets and importance of the LFA-1/ICAM-1 interaction

Pathogenic mechanisms of brain microvascular injury were studied in an experimental model of cerebral malaria (CM). The lesion, leading to perivascular microhemorrhages, is due to cytokine overproduction, and is associated with the sequestration of macrophages and parasitized erythrocytes in cerebral venules. In this in vivo model, we demonstrate that platelets are critical effectors of the neurovascular injury. First, electron microscopy indicated that during CM platelets adhere to and probably damage brain endothelial cells. Second, radiolabelled platelet distribution studies indicated that platelets sequestered in the brain and lung vasculature during CM. Non-cerebral malaria was not associated with cerebral sequestration of platelets. Third, in vivo treatment with a mAb to LFA-1 (which is expressed on platelets) selectively abrogated the cerebral sequestration of platelets, and this correlated with prevention of CM. Fourth, malaria-infected animals rendered thrombocytopenic were significantly protected against CM, further indicating that platelets are central to the pathogenesis of CM. Thus, a CD11a-dependent interaction between platelets and endothelial cells appears pivotal to microvascular damage. These data suggest a novel mechanism of action for anti-LFA-1 mAb in vivo and illustrate an unexpected role of platelets, in addition to monocytes, in vascular pathology.

Profiles of cytokine production in relation with susceptibility to cerebral malaria

Infection with Plasmodium berghei ANKA (PbA) leads, in susceptible strains of mice, to the development of cerebral malaria (CM), a lethal syndrome that reproduces some features of human CM. To study a possible relationship between genetic susceptibility to CM and the cytokine expression pattern, we quantitatively evaluated gene expression on RNA extracted from various organs of malaria-infected mice, using strains that are susceptible and resistant to CM. Northern blot analysis and semi-quantitative PCR showed that CM is associated with an increased TNF-alpha mRNA accumulation in the brain of mice developing the neurologic complications of CM. An increased IFN-gamma mRNA accumulation and a decreased expression of IL-4 and TGF-beta genes were also observed in mice susceptible to CM. In vitro restimulation studies using crude malarial Ag showed that lymphoid cell proliferation was higher in CM-susceptible than in CM-resistant infected mice. Moreover, susceptible mice produced large amounts of IFN-gamma, in a dose-dependent manner, in response to PbA Ag, whereas cells from resistant mice failed to produce significant amounts of this cytokine. Conversely, IL-2 and IL-4 production was significantly higher in infected CM-resistant mouse cells. No difference was seen in the production of IL-3 and IL-5 between resistant and susceptible PbA-infected mice. Upon stimulation with various malarial Ag, comparable amounts of TNF-alpha were produced by macrophages of either strain of mice. Taken together, these findings indicate that susceptibility to CM resides at the level of T cells rather than macrophages. Furthermore, the cytokine production profile is consistent with a predominant Th1-like response in mice developing cerebral complications of malaria.

Circulating plasma receptors for tumour necrosis factor in Malawian children with severe falciparum malaria

Tumour necrosis factor (TNF) concentrations are increased in the plasma during a malarial illness, and are highest in patients with severe or fatal disease. We have studied the plasma concentrations of two soluble receptors (sTNF-R1 and sTNF-R2), which act as binding proteins for TNF, in children with falciparum malaria. In 52 Malawian children with malaria, plasma concentrations of both sTNF-R1 (mean (S.D.) 4759(2552) pg/ml) and sTNF-R2 (59077(37102) pg/ml) were greatly increased when compared with levels of convalescence (sTNF-R1 718(68), and sTNF-R2 8015(7021) pg/ml), and in controls without malaria (486(1353) and 4380(2168)). Concentrations of both receptors correlated with plasma levels of TNF measured by immunoradiometric assay, but not with those of another cytokine, IL-6. The mean plasma concentrations of both immunoreactive TNF and soluble TNF receptors were greater in patients with cerebral malaria than those with uncomplicated malaria. Despite high levels of immunoreactive TNF in the plasma of patients acutely ill with malaria, no bioactive TNF could be detected in these patients by the WEHI cell bioassay. Soluble TNF receptors are present in greatly increased concentrations in the plasma of patients with malaria and may play a role in mediating or modulating the pathogenetic effects of the cytokine.

Analytical performances of commercial ELISA-kits for IL-2, IL-6 and TNF-alpha. A WHO study

The determination of cytokine levels in biological fluids by accurate and sensitive methods is an absolute need to be able to define the involvement of these mediators in various clinical situations. To test if this goal was achieved with ELISA kits, a comparative study was undertaken using various commercial kits (6 for IL-2, 8 for IL-6 and 9 for TNF-alpha). The major aims of the work were to critically analyze the analytical performances of the kits and to illustrate some of the pitfalls the users may face. Substantial differences were noted in terms of sensitivity and behaviour of commercial standards versus international reference preparations. These results clearly illustrate the urgent need for a real standardization of immunoassays for cytokine quantitation.

Tumor necrosis factor in the pathogenesis of infectious diseases

OBJECTIVES

To review the immunologic role of the cytokines and the specific role that tumor necrosis factor (TNF) plays in response to infection. The influence of bacterial lipopolysaccharide on TNF, the cytokine cascade, and resultant pathologies are also reviewed.

DATA SOURCES

A MEDLINE search of the international English language literature from 1960 to the present was reviewed, but data from the past 5 yrs primarily formed the basis for this review.

STUDY SELECTION

Those studies detailing the interaction of lipopolysaccharide, TNF, and other cytokines, and their roles in combating infection were emphasized. Investigations that described animal and human results served as the primary database.

DATA EXTRACTION

Animal studies were selected based on the relevance of the model to the pathogenesis of the human clinical syndrome. Where they provided supportive evidence, patient studies were selected on the basis of study design.

DATA SYNTHESIS

TNF plays a key role in the normal immune response to infection, limiting the spread of pathogens. Exaggerated physiologic responses occur under the influence of high concentrations of TNF that are released in response to overwhelming infection, resulting in aberrations in coagulation, cell adhesion, chemotaxis/transmigration, and vascular integrity. These pathologic effects may be inhibited by anti-TNF monoclonal antibodies and recombinant soluble receptor inhibitory proteins.

CONCLUSIONS

TNF exerts both physiologic and pathologic effects in response to infection; these events may lead to organ dysfunction and death. Anti-TNF therapies appear to attenuate the injurious effects of TNF.

An effector role for platelets in systemic and local lipopolysaccharide-induced toxicity in mice, mediated by a CD11a- and CD54-dependent interaction with endothelium

The role of platelets was investigated in two models of lipopolysaccharide (LPS)-induced toxicity in mice: the systemic reaction, provoked by intravenous LPS injection in D-galactosamine-sensitized recipients, which results in host death, and the local reaction, elicited in the skin by sequential injections of LPS and tumor necrosis factor alpha at 24-h intervals, which results in hemorrhagic necrosis. In both models, the depletion of platelets with a rabbit polyclonal or a mouse monoclonal antiplatelet immunoglobulin G afforded significant protection. In the local reaction, studies of the distribution of 111In-labelled platelets as well as optical and electron microscopy showed that platelets are localized in the dermal venules before hemorrhage occurs. Anti-CD11a (LFA-1) and anti-CD54 (ICAM-1) monoclonal antibodies prevented both platelet localization and hemorrhagic necrosis, and these determinants were detected on mouse platelets by immunofluorescence. The antiplatelet monoclonal antibody did not reduce the localization of polymorphonuclear leukocytes in the dermal venules, as shown by histological sections. Thus, in the local reaction, the stimulation with LPS and tumor necrosis factor alpha leads to a binding of platelets to the endothelium of venules by their beta 2 integrins, which seems necessary for the development of the hemorrhagic necrosis.

Expression and localization of tumor necrosis factor-alpha and its mRNA in idiopathic pulmonary fibrosis

The expression of tumor necrosis factor alpha and its mRNA was investigated in surgical biopsies from idiopathic pulmonary fibrosis by immunohistochemistry, in situ hybridization, and Northern blotting. Normal areas of lungs resected for cancer were used as controls. Tumor necrosis factor alpha mRNA levels were higher in idiopathic pulmonary fibrosis than in normal lungs as determined by Northern blots. In normal lungs, tumor necrosis factor alpha and its mRNA were identified in alveolar and interstitial macrophages. In fibrotic lungs, tumor necrosis factor alpha was detected in macrophages and, to a greater extent, in epithelial cells (presumably type II cells) lining the thickened septae. Tumor necrosis factor alpha mRNA was found only in some interstitial cells and some of the cells lining the alveolar septae. An elevated concentration of tumor necrosis factor = alpha, particularly within the alveolar epithelium, might contribute to the alveolar damage and proliferation of interstitial cells in idiopathic pulmonary fibrosis.

Protective effect of natural TNF-binding protein on human TNF-induced toxicity in mice

The in vivo protective effect of urinary TNF-binding protein (uTBP) on acute TNF-induced lesions and lethality was assessed in BALB/c mice. Two animal models, the local Shwartzman reaction and galactosamine (GaLN) induced TNF sensitization, were used. In the former, local cutaneous haemorrhagic necrosis induced by 10 micrograms of recombinant human TNF alpha (r-hTNF) was prevented with iv doses of uTPB as low as 1 microgram when administered concomitantly or 10 micrograms when injected intravenously 60 min before or 30 min after the lesion eliciting-dose of r-hTNF. In the latter model, injection of 1 microgram or r-hTNF caused the death of all mice within 36 h. Either 100 or 250 micrograms of uTBP given intravenously simultaneously with r-hTNF/GaLN totally prevented this mortality. In contrast to anti-human TNF monoclonal antibodies, these very same doses of uTBP significantly protected mice even when injected after the lethal r-hTNF dose. These data confirm in relevant in vivo pathological models the TNF inhibiting capacity of the natural soluble TNF receptor I.

Stabilisation of functional tumor necrosis factor-alpha by its soluble TNF receptors

Using two enzyme-linked immunosorbent assays (ELISA), one able to detect trimeric TNF-alpha, but not its monomeric form (T-ELISA), and the other able to detect trimeric plus monomeric TNF-alpha together (T+M-ELISA), the effect of two soluble TNF-alpha receptors (P55 and P75) on the dimethylsulphoxide (DMSO) induced conversion of TNF-alpha from a trimeric to a monomeric form was determined. When TNF-alpha was incubated in the presence of a 5% final concentration of DMSO, the level of trimer, as measured by the T-ELISA, dropped to between 25 and 50% of its initial concentration whereas no change in the level of TNF-alpha was observed with the T+M-ELISA. When the incubation was performed in the presence of P55 or P75, the reduction of trimeric TNF-alpha values in the presence of 5% DMSO decreased in proportion to the concentration of sTNF-R, whereas trimeric plus monomeric TNF-alpha values remained unaffected. These results suggest a shift of TNF-alpha from a trimeric to a monomeric form in the presence of DMSO, and that TNF-Rs play a major rôle in preventing this phenomena. This could have implications for therapeutic schedules.

Role of granulocyte-macrophage colony-stimulating factor in pulmonary fibrosis induced in mice by bleomycin

The role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in pulmonary fibrosis elicited in mice by the intratracheal instillation of bleomycin was investigated by (1) evaluation of GM-CSF mRNA levels, (2) administration of GM-CSF, and (3) administration of anti-GM-CSF antibody. A significant increase of the GM-CSF mRNA level was evident in the lung RNA on day 5 after bleomycin instillation, but not on day 15. Abdominal infusion of GM-CSF (0.5 micrograms/h during days 7-15) did prevent the collagen deposition induced by bleomycin, as measured by the lung hydroxyproline content on day 15. In contrast, anti-GM-CSF antibody markedly aggravated the collagen deposition. On histological sections the proportion of lungs showing fibrosing alveolitis was decreased by GM-CSF and increased by anti-GM-CSF IgG. The percentage and number of macrophages within the bronchoalveolar lavage (BAL) fluid was increased by GM-CSF infusion and decreased by anti-GM-CSF antibodies. This study demonstrates that pulmonary GM-CSF has an inhibitory influence upon the alveolar remodeling and collagen deposition associated with pulmonary fibrosis.

Humoral immune responses in volunteers immunized with irradiated Plasmodium falciparum sporozoites

Volunteers immunized with gamma-irradiated Plasmodium falciparum sporozoites serve as the gold standard for protective immunity against mosquito-borne malaria transmission and provide a relevant model for studying protective immune effector mechanisms. During a 7-12 month period, we immunized four volunteers via the bites of irradiated, infected mosquitoes. Following these exposures to attenuated sporozoites, all four volunteers developed antibodies to sporozoites as measured by an immunofluorescence assay and by an enzyme-linked immunosorbent assay using the circumsporozoite (CS) protein repeat-based molecule R32LR as capture antigen. Three volunteers also developed antibodies against the nonrepeating (flanking) regions of the CS protein; the level of these antibodies paralleled the serum activity to inhibit sporozoite invasion of hepatoma cells in vitro. These three volunteers were protected against malaria transmitted by the bites of five infected mosquitoes. Two of these protected volunteers received additional immunizing doses of irradiated sporozoites and were subsequently protected against challenge with a heterologous P. falciparum clone. No detectable fluctuations were observed in circulating levels of tumor necrosis factor, interferon-gamma, or interleukin-6 during the course of this study. Analysis of the humoral and cellular immune responses of these protected volunteers is expected to yield important clues to additional targets of immunity against the pre-erythrocytic stages of malaria parasites.