Schistosomiasis Presenting as Recurring Sigmoid Volvulus in a Danish Man With an Inconspicuous Travel History-A Case Report

A healthy 72-year-old Danish male presenting with recurring sigmoid volvulus was found to be infested with Schistosoma mansoni. No other explanation for recurring volvulus was found. A travel history 12 years ago, which included bathing in the Botswana Okavango delta for 10 minutes, revealed the likely time and place of infection. To our knowledge, this is the first reported case of recurrent sigmoid volvulus and chronic intestinal schistosomiasis in a patient from a nonendemic area.

Effects of the vascular endothelial growth factor receptor-2 (VEGFR-2) inhibitor SU5416 on in vitro cultures of Plasmodium falciparum

BACKGROUND

Vascular endothelial growth factor (VEGF) is taken up by parasitized red blood cells during malaria and stimulates intra-erythrocytic growth of Plasmodium falciparum in vitro. The cause and consequence of this uptake is not understood.

METHODS

Plasmodium falciparum was cultured in vitro. Parasite growth and intracellular VEGF levels were assessed using flow cytometry. Intracellular VEGF was visualized by fluorescence immunocytochemistry. Phosphorylated tyrosine was measured by western blotting. In vivo assessment of intra-erythrocytic VEGF was performed in Plasmodium berghei ANKA-infected C57BL/6 mice.

RESULTS

VEGF accumulated intracellularly in infected red blood cells, particularly in schizonts. In vitro growth of P. falciparum was unchanged when co-cultured with the anti-VEGF antibody bevacizumab or with an anti-VEGF receptor-1 peptide. In contrast, the VEGF receptor-2 inhibitor, SU5416, dose-dependently inhibited growth. None of the treatments reduced intracellular VEGF levels. Thus, the anti-parasitic effect of SU5416 seemed independent of VEGF uptake. SU5416 reduced phosphorylated tyrosine in parasitized red blood cells. Similarly, the broad-spectrum tyrosine kinase inhibitor genistein dose-dependently inhibited P. falciparum growth and reduced tyrosine phosphorylation. Neither bevacizumab nor anti-VEGF receptor-1 peptide affected tyrosine kinase activity. Finally, in vivo uptake of VEGF in P. berghei ANKA was demonstrated, analogous to the in vitro uptake in P. falciparum, making it a possible model for the effects of VEGF signalling in vivo during malaria.

CONCLUSIONS

Inhibition of VEGFR-2 signalling reduces intra-erythrocytic growth of P. falciparum, likely due to tyrosine kinase inhibition. Internalisation of VEGF in P. falciparum-infected red blood cells does not rely on VEGF receptors. The function of in vivo uptake of VEGF can be studied in rodent malaria models.

Human genetic polymorphisms in the Knops blood group are not associated with a protective advantage against Plasmodium falciparum malaria in Southern Ghana

Background

The complex interactions between the human host and the Plasmodium falciparum parasite and the factors influencing severity of disease are still not fully understood. Human single nucleotide polymorphisms SNPs associated with Knops blood group system; carried by complement receptor 1 may be associated with the pathology of P. falciparum malaria, and susceptibility to disease.

Methods

The objective of this study was to determine the genotype and haplotype frequencies of the SNPs defining the Knops blood group antigens; Kn^a/b, McCoy^a/b, Swain-Langley1/2 and KCAM^+/- in Ghanaian patients with malaria and determine possible associations between these polymorphisms and the severity of the disease. Study participants were patients (n = 267) admitted to the emergency room at the Department of Child Health, Korle-Bu Teaching Hospital, Accra, Ghana during the malaria season from June to August in 1995, 1996 and 1997, classified as uncomplicated malaria (n = 89), severe anaemia (n = 57) and cerebral malaria (n = 121) and controls who did not have a detectable Plasmodium infection or were symptomless carriers of the parasite (n = 275). The frequencies were determined using a post-PCR ligation detection reaction-fluorescent microsphere assay, developed to detect the SNPs defining the antigens. Chi-square/Fisher’s exact test and logistic regression models were used to analyse the data.

Results

As expected, high frequencies of the alleles Kn^a, McC^b, Sl2 and KCAM^- were found in the Ghanaian population. Apart from small significant differences between the groups at the Sl locus, no significant allelic or genotypic differences were found between the controls and the disease groups or between the disease groups. The polymorphisms define eight different haplotypes H1(2.4%), H2(9.4%), H3(59.8%), H4(0%), H5(25.2%), H6(0.33%), H7(2.8%) and H8(0%). Investigating these haplotypes, no significant differences between any of the groups were found.

Conclusion

The results confirm earlier findings of high frequencies of certain CR1 alleles in Africa; and shed more light on earlier conflicting findings; the alleles McC^b, Sl2, Kn^b and KCAM^- or combined haplotypes do not seem to confer any protective advantage against malaria infection or resulting disease severity. Based on these findings, in a very well-characterized population, malaria does not seem to be the selective force on these alleles.

Complement binding to erythrocytes is associated with macrophage activation and reduced haemoglobin in Plasmodium falciparum malaria

We have examined IgG and complement factor C3d deposition on erythrocytes by means of the direct Coombs' test (DAT) and looked for an association with the anaemia seen in falciparum malaria in children living in an area of hyperendemic malaria transmission (in Ghana). In one study (in 1997), 53 out of 199 patients had a positive DAT. Of these, 45 samples reacted with anti-C3d antibodies, 2 with anti-IgG and 6 with both reagents. There were significantly lower haemoglobin (Hb)-levels and higher prevalence of spleen enlargement in DAT-positive than in DAT-negative patients. Hb-levels were independently associated with DAT and age. This initial study was designed to investigate the role of intravascular haemolysis (IVH), but we found no association between IVH and either DAT result or anaemia. Because of the risk of selection bias we repeated the study using consecutive enrollment of malaria patients and were able to confirm the results in a total of 49 DAT-positive and 183 DAT-negative patients. This second study (in 1998) was designed to look at the importance of erythrophagocytosis through measurement of plasma neopterin levels and total nitrite and nitrate as markers of NO-release. Both parameters were significantly higher in DAT-positive than in DAT-negative patients (P < 0.001), indicating that complement binding to erythrocytes was associated with macrophage activation. Plasma levels of haptoglobin, interleukin-10 and tumour necrosis factor-alpha did not vary between the groups. The studies support the role of complement activation and erythrophagocytosis in the pathogenesis of anaemia in falciparum malaria in African children.

Selection of glutamate-rich protein long synthetic peptides for vaccine development: antigenicity and relationship with clinical protection and immunogenicity

Antibodies against three long synthetic peptides (LSPs) derived from the glutamate-rich protein (GLURP) of Plasmodium falciparum were analyzed in three cohorts from Liberia, Ghana, and Senegal. Two overlapping LSPs, LR67 and LR68, are derived from the relatively conserved N-terminal nonrepeat region (R0), and the third, LR70, is derived from the R2 repeat region. A high prevalence of antibody responses to each LSP was observed in all three areas of endemic infection. Levels of cytophilic immunoglobulin G (IgG) antibodies against both GLURP regions were significantly correlated with protection from clinical P. falciparum malaria. Protected children from the Ghana cohort possessed predominantly IgG1 antibodies against the nonrepeat epitope and IgG3 antibodies against the repeat epitope. T-cell proliferation responses, studied in the cohort from Senegal, revealed that T-helper-cell epitopes were confined to the nonrepeat region. When used as immunogens, the LR67 and LR68 peptides elicited strong IgG responses in outbred mice and LR67 also induced antibodies in mice of different H-2 haplotypes, confirming the presence of T-helper-cell epitopes in these constructs. Mouse antipeptide antisera recognized parasite proteins as determined by immunofluorescence and immunoblotting. This indicates that synthetic peptides derived from relatively conserved epitopes of GLURP might serve as useful immunogens for vaccination against P. falciparum malaria.

Antibodies to variant antigens on the surfaces of infected erythrocytes are associated with protection from malaria in Ghanaian children

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a variant antigen expressed on the surface of infected erythrocytes. Each parasite genome contains about 40 PfEMP1 genes, but only 1 PfEMP1 gene is expressed at a given time. PfEMP1 serves as a parasite-sequestering ligand to endothelial cells and enables the parasites to avoid splenic passage. PfEMP1 antibodies may protect from disease by inhibiting sequestration, thus facilitating the destruction of infected erythrocytes in the spleen. In this study, we have measured antibodies in Ghanaian children to a conserved region of PfEMP1 by enzyme-linked immunosorbent assay and antibodies to variant molecules on erythrocytes infected with field isolates of P. falciparum by flow cytometry. Based on close clinical monitoring, the children were grouped into those who did (susceptible) and those who did not (protected) have malaria during the season. The prevalences of antibodies to both the conserved PfEMP1 peptide and the variant epitopes were greater than 50%, and the levels of immunoglobulin G (IgG) correlated with age. The levels of antibodies to both the conserved peptide and the variant epitopes were higher in protected than in susceptible children. After correcting for the effect of age, the levels of IgG to variant antigens on a Sudanese and a Ghanaian parasite isolate remained significantly higher in protected than in susceptible children. Thus, the levels of IgG to variant antigens expressed on the surface of infected erythrocytes correlated with protection from clinical malaria. In contrast, the levels of IgG to a peptide derived from a conserved part of PfEMP1 did not correlate with protection from malaria.

Perturbation and proinflammatory type activation of V delta 1(+) gamma delta T cells in African children with Plasmodium falciparum malaria

gamma delta T cells have variously been implicated in the protection against, and the pathogenesis of, malaria, but few studies have examined the gamma delta T-cell response to malaria in African children, who suffer the large majority of malaria-associated morbidity and mortality. This is unfortunate, since available data suggest that simple extrapolation of conclusions drawn from studies of nonimmune adults ex vivo and in vitro is not always possible. Here we show that both the frequencies and the absolute numbers of gamma delta T cells are transiently increased following treatment of Plasmodium falciparum malaria in Ghanaian children and they can constitute 30 to 50% of all T cells shortly after initiation of antimalarial chemotherapy. The bulk of the gamma delta T cells involved in this perturbation expressed V delta 1 and had a highly activated phenotype. Analysis of the T-cell receptors (TCR) of the V delta 1(+) cell population at the peak of their increase showed that all expressed V gamma chains were used, and CDR3 length polymorphism indicated that the expanded V delta 1 population was highly polyclonal. A very high proportion of the V delta 1(+) T cells produced gamma interferon, while fewer V delta 1(+) cells than the average proportion of all CD3(+) cells produced tumor necrosis factor alpha. No interleukin 10 production was detected among TCR-gamma delta(+) cells in general or V delta 1(+) cells in particular. Taken together, our data point to an immunoregulatory role of the expanded V delta 1(+) T-cell population in this group of semi-immune P. falciparum malaria patients.

High frequency of circulating gamma delta T cells with dominance of the v(delta)1 subset in a healthy population

TCR gamma delta(+) cells constitute <5% of all circulating T cells in healthy, adult Caucasians, and V(delta)1(+) cells constitute a minority of these cells. In contrast to TCR alpha beta(+) cells, their repertoire is selected extrathymically by environmental antigens. Although increased frequencies of V(delta)1(+) cells are found in several diseases, their function remains obscure. Here we show that the frequency of peripheral blood gamma delta T cells in healthy West Africans is about twice that of Caucasians, mainly due to a 5-fold increase in V(delta)1(+) cells, which is consequently the dominant subset. No age dependency of V(delta)1 frequencies was identified and the V(delta)1(+) cells in the African donors did not show preferential V(gamma) chain usage. Analysis of the CDR3 region size did not reveal any particular skewing of the V(delta)1 repertoire, although oligoclonality was more pronounced in adults compared to children. The proportions of CD8(+), CD38(+) and CD45RA(hi)CD45RO(-) cells within the V(delta)1(+) subset were higher in the African than in the European donors, without obvious differences in expression of activation markers. No significant correlations between levels of V(delta)1(+) cells and environmental antigens or immunological parameters were identified. Taken together, the evidence argues against a CDR3-restricted, antigen-driven expansion of V(delta)1(+) cells in the African study population. Our study shows that high frequencies of TCR gamma delta(+) cells with dominance of the V(delta)1(+) subset can occur at the population level in healthy people, raising questions about the physiological role of V(delta)1(+) T cells in the function and regulation of the immune system.

Naturally acquired antibodies to the glutamate-rich protein are associated with protection against Plasmodium falciparum malaria

The development of effective malaria vaccines depends on the identification of targets of well-defined protective immune responses. Data and samples from a longitudinal study of a cohort of children from coastal Ghana were used to investigate the role of antibody responses to 3 regions of the Plasmodium falciparum glutamate-rich protein (GLURP). The data show that levels of the GLURP-specific IgG that occurs in the nonrepeat region of the antigen are significantly correlated with clinical protection from P. falciparum malaria, after correction for the confounding effect of age. Furthermore, levels of cytophilic antibodies were found to be of particular importance for protection, lending support to the hypothesis that antibody-dependent cellular inhibition is the important element in GLURP-specific protective immunity.

Distinct patterns of cytokine regulation in discrete clinical forms of Plasmodium falciparum malaria

The pathogenesis of two of the most severe complications of Plasmodium falciparum malaria, cerebral malaria (CM) and severe malarial anaemia (SA) both appear to involve dysregulation of the immune system. We have measured plasma levels of TNF and its two receptors in Ghanaian children with strictly defined cerebral malaria (CM), severe malarial anaemia (SA), or uncomplicated malaria (UM) in two independent studies in an area of seasonal, hyperendemic transmission of P. falciparum. Levels of TNF, soluble TNF receptor 1 (sTNF-R1) and 2 (sTNF-R2) were found to be significantly higher in CM than in the other clinical categories of P. falciparum malaria patients. Levels of both receptors depended on clinical category, whereas only sTNF-R1 levels were significantly dependent on parasitemia. Detailed analysis of the interrelationship between these variables resolved this pattern further, and identified marked differences between the patient categories. While levels of TNF, sTNF-R1 and sTNF-R2 correlated with parasitemia in UM, this was not the case in CM and SA. Rather, there was a tendency towards high levels of TNF and its receptors in CM and low levels in SA without significant correlation to parasitemia in either category. This, and the fact that malaria-induced increases in plasma levels of IL-10 are much lower in SA compared to CM, suggest that distinct forms of dysregulation of the immune response to infection contribute to the pathogenesis of CM and SA.

Haptoglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria

The haptoglobin (Hp) phenotypes were determined by polyacrylamide-gel electrophoresis in plasma samples obtained in 1997 from 113 Plasmodium falciparum malaria patients (aged 1-12 years) with strictly defined cerebral malaria, severe malarial anaemia, or uncomplicated malaria and 42 age-matched healthy controls from the same area (coastal Ghana). Hp1-1 was significantly more prevalent among the patients (43%) than among healthy controls (7.1%), whereas Hp2-1 and Hp2-2 were underrepresented among the patients (11% and 2%, respectively) compared to the control donors (33% and 14%, respectively). No significant difference in frequency of Hp0 was observed between patients and controls. Among the malaria patients, the Hp1-1 phenotype was significantly more prevalent among patients with the complications of cerebral malaria and severe anaemia compared to patients with uncomplicated disease, whereas the reverse was seen with respect to Hp2-1 and Hp2-2. Our data suggest that the Hp1-1 phenotype is associated with susceptibility to P. falciparum malaria in general, and to the development of severe disease in particular.

Maintaining the immunological balance in parasitic infections: a role for TGF-beta?

Transforming growth factor beta (TGF-beta) is an important regulator of inflammation, being proinflammatory at low concentrations and anti-inflammatory at high concentrations. As such, TGF-beta might be important in maintaining the balance between control and clearance of infectious organisms on the one hand and prevention of immune-mediated pathology on the other. In this article, Fakhereldin Omer, Jørgen Kurtzhals and Eleanor Riley review the immunoregulatory properties of TGF-beta in the context of parasitic infections. Data from murine malaria infections suggest that TGF-beta modifies the severity of the disease, and a number of potential protective mechanisms are discussed. Evidence is accumulating that TGF-beta is important for the regulation of other host-parasite interactions and that parasites might directly influence TGF-beta-dependent pathways via the synthesis of TGF-beta or TGF-beta-receptor homologues.

Anaemia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren

A cohort of 250 Ghanaian schoolchildren aged 5-15 years was followed clinically and parasitologically for 4 months in 1997/98 in order to study the effect of asymptomatic Plasmodium falciparum infections on haematological indices and bone-marrow responses. Of the 250 children 65 met the predefined study criteria. Thus, 14 children were parasite-free throughout (group 1), 44 had P. falciparum in all blood samples collected but no symptoms of malaria (group 2), and 7 had 1 malaria attack during the study period (group 3). At the end of the study the mean haemoglobin (Hb) level in group 1 was 123 g/L, significantly higher than the value of 114 g/L in groups 2 and 3 (P < 0.02, adjusted for age and splenomegaly). The low Hb in group 2 was associated with subnormal plasma iron. Low Hb was associated with elevated erythropoietin (EPO) levels, and there was a positive correlation between EPO and reticulocyte counts. However, the reticulocyte response to EPO was more pronounced in uninfected than in infected children, suggesting a partial interference with erythropoiesis in asymptomatic infections. Children with asymptomatic infections had significantly higher plasma levels of tumour necrosis factor than uninfected children (geometric means 50 ng/L and 27 ng/L, respectively, P < 0.001) and this cytokine may contribute to bone-marrow suppression and disturbed iron metabolism. We suggest that asymptomatic malaria leads to a homeostatic imbalance in which erythrocyte loss due to parasite replication is only partially compensated for by increased erythropoiesis. The consequences of the reduced Hb levels on the development and cognitive abilities of children with asymptomatic infections, and the risk of precipitation of iron deficiency, deserve further study and should be considered in malaria control programmes that aim at reducing morbidity rather than transmission.

Leishmania-specific T cells expressing interferon-gamma (IFN-gamma) and IL-10 upon activation are expanded in individuals cured of visceral leishmaniasis

Peripheral blood mononuclear cells (PBMC) from patients who have recovered from visceral leishmaniasis often respond to Leishmania antigens in vitro by production of both IL-4, IFN-gamma and IL-10. In order to establish the cellular sources of these cytokines, we activated cells from individuals with a history of visceral leishmaniasis with Leishmania antigen for 6 days in culture, and identified cytokine production at the single-cell level by flow cytometry. The cytokines were only found in CD3+ cells and among these mainly within the CD4+ subset. The percentage of cytokine-producing cells was compared in Leishmania-activated PBMC cultures from the previous patients and from individuals living in a village where leishmaniasis does not occur. The percentage of IL-10- and IFN-gamma-containing cells was significantly higher in the previous patients than in the controls, indicating that Leishmania-specific T cells producing IL-10 and/or IFN-gamma had been expanded as a result of the infection. The cytokine-producing cells in the previous patients could be divided into three types: (i) cells producing IFN-gamma only; (ii) cells producing IL-4 only; and (iii) cells producing IFN-gamma and IL-10 simultaneously. The first and second group of cells can be described as Th1- and Th2-type cells, respectively. The third group could be a regulatory subset of T cells important for maintaining a balance between Th1- and Th2-type cells in these individuals.

Levels of antibody to conserved parts of Plasmodium falciparum merozoite surface protein 1 in Ghanaian children are not associated with protection from clinical malaria

The 19-kDa conserved C-terminal part of the Plasmodium falciparum merozoite surface protein 1 (PfMSP119) is a malaria vaccine candidate antigen, and human antibody responses to PfMSP119 have been associated with protection against clinical malaria. In this longitudinal study carried out in an area of stable but seasonal malaria transmission with an estimated parasite inoculation of about 20 infective bites/year, we monitored 266 3- to 15-year-old Ghanaian children clinically and parasitologically over a period of 18 months. Blood samples were collected at the beginning of the study before the major malaria season in April and after the season in November. Using enzyme-linked immunosorbent assay, we measured antibody responses to recombinant gluthathione S-transferase-PfMSP119 fusion proteins corresponding to the Wellcome and MAD20 allelic variants in these samples. Prevalence of antibodies recognizing the Wellcome 19 construct containing both epidermal growth factor (EGF)-like motifs in Wellcome type PfMSP119 was about 30%. Prevalence of antibodies to constructs containing only the first EGF domain from either Wellcome or MAD20 type PfMSP119 was about 15%, whereas antibodies recognizing a construct containing only the second EGF domain of MAD20 type PfMSP119 was found in only about 4% of the donors. Neither the prevalence nor the levels of any of the antibody specificities varied significantly with season, age, or sex. Significantly, and in contrast to previous reports from other parts of West Africa, we found no evidence of an association between antibody responses to PfMSP119 and clinical protection against malaria.

T-cell response in human leishmaniasis

In the present communication we provide evidence for the existence of a Th1/Th2 dichotomy in the T-cell response to Leishmania antigens in human leishmaniasis. Our data suggest that the pattern of IL-4 and IFN-gamma response is polarised in these patients. Lymphocytes from individuals recovered from cutaneous leishmaniasis (CL) responded by IFN-gamma production following stimulation with Leishmania antigens whereas cells from patients recovered from visceral leishmaniasis (VL) showed a mixed pattern of IFN-gamma and IL-4 responses. The cells producing these cytokines were predominantly CD4+. Furthermore, IL-10 plays an important role in the development of post kala azar dermal leishmaniasis (PKDL) from VL. The balance between the parasitic-specific T-cell response plays an important regulatory role in determining the outcome of Leishmania infections in humans.

Humoral and cellular immune responses to synthetic peptides of the Leishmania donovani kinetoplastid membrane protein-11

Native kinetoplastid membrane protein-11 (KMP-11), purified from crude extracts of Leishmania donovani parasites, activates T cells from individuals who have recovered from visceral leishmaniasis. In this work we used three 38-mer peptides spanning the amino acid sequence of the L. donovani KMP-11 as solid-phase ligands in enzyme-linked immunosorbent assays (ELISAs) and as stimulating antigens in lymphoproliferative assays in order to evaluate humoral and cellular immune responses to well-defined sequences of the protein. Antibody reactivity against the three peptides was measured in plasma from 63 Sudanese visceral leishmaniasis patients (VL) and the percentage of patients with anti-KMP-11 antibodies in ELISA were 37% (KMP-11-1), 30% (KMP-11-2) and 58% (KMP-11-3). The fraction of VL patients with measurable antibody reactivity in one or more of the three ELISAs was 79%. Cross-reactivity to the KMP-11 peptides was detected in plasma from Sudanese patients suffering from Leishmania major infections and in plasma from Sudanese and Danish patients infected with Plasmodium falciparum. In lymphoproliferative assays, 10 of 17 PBMC isolates from donors previously infected with L. donovani showed a response to one or more of the three KMP-11 peptides.

Low plasma concentrations of interleukin 10 in severe malarial anaemia compared with cerebral and uncomplicated malaria

BACKGROUND

Severe anaemia is a major complication of malaria but little is known about its pathogenesis. Experimental models have implicated tumour necrosis factor (TNF) in induction of bone-marrow suppression and eythrophagocytosis. Conversely, interleukin 10 (IL-10), which mediates feed-back regulation of TNF, stimulates bone-marrow function in vitro and counteracts anaemia in mice. We investigated the associations of these cytokines with malarial anaemia.

METHODS

We enrolled 175 African children with malaria into two studies in 1995 and 1996. In the first study, children were classified as having severe anaemia (n=10), uncomplicated malaria (n=26), or cerebral anaemia (n=41). In the second study, patients were classified as having cerebral malaria (n=33) or being fully conscious (n=65), and the two groups were subdivided by measured haemoglobin as normal (>110 g/L), moderate anaemia (60-90 g/L), and severe anaemia (<50 g/L). IL-10 and TNF concentrations were measured by ELISA in plasma samples from all patients.

FINDINGS

IL-10 concentrations were significantly lower in patients with severe anaemia than in all other groups. In 1995, geometric mean plasma IL-10 in patients with severe anaemia was 270 pg/mL (95% CI 152-482) compared with 725 pg/mL (465-1129) in uncomplicated malaria and 966 pg/mL (612-1526) in cerebral malaria (p<0.03). In 1996, fully conscious patients with severe anaemia also had significantly lower IL-10 concentrations than all other groups, including cerebral-malaria patients with severe anaemia and all patients with moderate anaemia (p<0.001). In both studies, TNF concentrations were significantly higher in cerebral malaria than in fully conscious patients (p<0.01). By contrast, the ratio of TNF to IL-10 was significantly higher in fully conscious patients with severe anaemia than in all other groups (p<0.001).

INTERPRETATION

Our findings identify severe malarial anaemia as a distinct disorder in which insufficient IL-10 response to high TNF concentrations may have a central role.

Increased eosinophil activity in acute Plasmodium falciparum infection--association with cerebral malaria

To assess the eosinophil response to Plasmodium falciparum infection a cohort of initially parasite-free Ghanaian children was followed for 3 months. Seven of nine children who acquired an asymptomatic P. falciparum infection showed increase in eosinophil counts, while a decrease was found in seven of nine children with symptomatic malaria, and no change was observed in 14 children who remained parasite-free. In a hospital-based study, paediatric patients with cerebral malaria (CM), severe anaemia (SA), or uncomplicated malaria (UM) had uniformly low eosinophil counts during the acute illness followed by eosinophilia 30 days after cure. Plasma levels of eosinophil cationic protein (ECP) and eosinophil protein X (EPX) were measured as indicators of eosinophil activation. In spite of the low eosinophil counts, ECP levels were increased on day 0 and significantly higher in patients with CM (geometric mean (95% confidence interval) 8.5 ng/ml (6.8-10.7 ng/ml)) than in SA (4.7 ng/ml (3.0-7.5 ng/ml)) and UM patients (4.3 ng/ml (3.6-5.3 ng/ml), P < 0.001). A similar pattern was found for EPX. It thus appears that the low eosinophil counts may be due to tissue sequestration and destruction rather than decreased production. The plasma levels of the granule proteins correlated with levels of tumour necrosis factor and soluble IL-2 receptor, implicating inflammatory responses and T cell activation as causes of the eosinophil activation. By contrast, the eosinophil induction did not appear to be part of a Th2-like response. Eosinophil granule proteins may be important in both control of malaria infection and the pathogenesis of severe malaria.

Rapid reemergence of T cells into peripheral circulation following treatment of severe and uncomplicated Plasmodium falciparum malaria

Frequencies and absolute numbers of peripheral T-cell subsets were monitored closely following acute Plasmodium falciparum malaria in 22 Ghanaian children from an area of hyperendemicity for seasonal malaria transmission. The children presented with cerebral or uncomplicated malaria (CM or UM, respectively) or with severe malarial anemia. For all patients the frequencies and absolute numbers of peripheral T cells were lower than normal during the acute stage of disease. This lowering was most pronounced in the CM group and least pronounced in the UM group. Of particular interest, the CM patients showed markedly reduced frequencies of CD4+ cells, the number of which also normalized slower than in the other clinical groups. In all patients, the T-cell frequencies gradually approached normal values after the initiation of therapy, whereas the absolute numbers rapidly reverted from lower than normal to higher than normal before returning to steady-state levels. Furthermore, the initially reduced T-cell surface density of the T-cell receptor/CD3 complex, which rapidly normalized, was a general finding for all three clinical groups, suggesting a state of peripheral T-cell hyporesponsiveness during acute malaria. The data presented suggest a rapid therapy-induced reemergence of T cells that had been temporarily removed from the peripheral circulation as a consequence of the malaria attack and that the degree of the disease-induced T-cell reallocation correlates with disease severity.

Antibody responses to Rhoptry-Associated Protein-1 (RAP-1) of Plasmodium falciparum parasites in humans from areas of different malaria endemicity

Plasma IgM and IgG antibody reactivities against the recombinant Plasmodium falciparum protein, Rhoptry Associated Protein-1 (rRAP-1) were measured by ELISA in individuals from Sudan, Indonesia, Kenya and The Gambia living in areas of different malaria endemicity. IgG and IgM reactivities to rRAP-1 increased with malaria endemicity. IgG reactivities were associated with spleen rates in Indonesia with high malaria endemicity while IgM reactivities were associated with spleen rates in Kenya with low malaria endemicity. IgG and IgM reactivities to rRAP-1 increased during acute episodes of P. falciparum malaria in Sudanese adults and IgG reactivities remained high one month after treatment in all adults tested. Antibody reactivities to rRAP-1 in Gambian children in the dry season were higher in children with parasitaemia than in children without detectable parasitaemia. Antibody reactivities were not associated with protection against clinical episodes in the following rainy season but higher antibody reactivities were detectable at the end of the rainy season. There was no difference in antibody reactivity to rRAP-1 between Gambian children with mild or severe malaria.

Immunity to tetanus and diphtheria in rural Africa

To assess the effect of the Expanded Program on Immunization (EPI) in rural Africa, blood samples were collected in two Kenyan sublocations. Serum antibodies against tetanus toxoid were measured in 155 individuals 1-70 years of age. Titers greater than the protective level of 0.01 IU/ml were found in 47% of the population. Protection was significantly higher in children born after the launching of the EPI (68%) and in women who had been at childbearing age since then (69%). Significantly lower protection was demonstrated in other age and sex-groups. The level of protection in children was equal in the two populations, whereas protection in fertile women was significantly lower in the population living a long distance from a health center. Diphtheria anti-toxin was measured in the samples from one sublocation, and 70 of 84 individuals (83%) had antibody levels greater than the protective level. No age or sex difference could be found, and there was no correlation between response levels to diphtheria and tetanus. This implicates natural infections as an important source of diphtheria antibodies. Our findings demonstrate a need for better coverage of the adult population against tetanus. Furthermore, diphtheria transmission still appears to take place, underscoring the importance of diphtheria vaccination of travelers to rural Africa.

Reversible suppression of bone marrow response to erythropoietin in Plasmodium falciparum malaria

To study the importance of bone marrow inhibition in the pathogenesis of malarial anaemia, haematological and parasitological parameters were followed in patients with acute malaria. Three patient categories were studied, severe malarial anaemia (SA), cerebral malaria (CM) and uncomplicated malaria (UM). Red cell distribution width (RDW) was used as a surrogate marker of release of young erythrocytes and reticulocytes. Initially RDW was low in all patients in spite of markedly increased concentrations of erythropoietin (EPO). 3 d after institution of treatment and coinciding with parasite clearance RDW increased dramatically, reaching the highest levels 1-2 weeks later. Although severe anaemia was corrected by blood transfusion during the first 3 d of treatment, the peak RDW correlated significantly with the initial EPO levels. This suggests that Plasmodium falciparum infection causes a rapidly reversible suppression of the bone marrow response to EPO. Furthermore, the inhibition of bone marrow response was a general finding irrespective of initial haemoglobin levels suggesting that the severity of anaemia depends upon the degree of peripheral erythrocyte destruction in patients with suppressed bone marrow response to EPO.

The gamma/delta T-cell response to Plasmodium falciparum malaria in a population in which malaria is endemic

Frequencies and absolute numbers of peripheral gamma/delta T cells have been reported to increase after episodes of Plasmodium falciparum malaria in adults with limited or no previous malaria exposure. In contrast, little is known about the gamma/delta T-cell response to malaria in children from areas where malaria is endemic, who bear the burden of malaria-related morbidity and mortality. We investigated the gamma/delta T-cell response in 19 Ghanaian children from an area of hyperendemic, seasonal malaria transmission. The children presented with cerebral malaria (n = 7), severe malarial anemia (n = 5), or uncomplicated malaria (n = 7) and were monitored from admission until 4 weeks later. We found no evidence of increased frequencies of gamma/delta T cells in any of the patient groups, whereas one adult expatriate studied in Ghana and three adults admitted to the hospital in Copenhagen, Denmark, all with uncomplicated, primary P. falciparum malaria, showed increased gamma/delta T-cell frequencies similar to those previously reported. All patients had lowered absolute numbers of peripheral gamma/delta T cells at admission, changing to increased numbers by days 7 to 14 and then returning to normal levels. The study raises questions regarding age and degree of previous exposure as determinants of malaria-induced gamma/delta T-cell responses.

Interplay between promoter and structural gene variants control basal serum level of mannan-binding protein

Mannan-binding protein (MBP) is a serum lectin participating in the innate immune defense by opsonizing various microorganisms for phagocytosis. Opsonization defect due to MBP deficiency and low levels of the protein can partially be explained by the dominant effect of three different mutations in the structural part of the MBP gene. Large interracial differences in the frequencies of these variants have previously been described, but they cannot explain the large interindividual variation in MBP serum concentration. We describe the existence of additional polymorphisms at positions -550 (H/L variants) and -221 (X/Y variants) in the promoter region of the gene. The promoter haplotypes, HY, LY, and LX, show associations with high, medium, and low levels of MBP serum concentrations, respectively. Moreover, this represents a genetic system with additive effect of haplotypes in which a low producing LX haplotype in the homozygous state down-regulates the basal expression of MBP as effectively as a single structural variant. Populations of pure Eskimos, Caucasoids, and black Africans show marked interethnic differences in the frequencies of promoter haplotypes regulating the expression of the normal peptide, with the HY haplotype frequency varying from 0.83 in Eskimos via 0.33 in Caucasoids to 0.08 in Africans. The LY haplotype frequency varies from 0.04 in Eskimos via 0.39 in Caucasoids to 0.23 in Africans. The LX haplotype frequency varies from 0.03 in Eskimos via 0.24 in Caucasoids to 0.23 in Africans. The effect of the promoter variants can explain almost all of the ethnic differences not explainable by the structural variants alone.

Interplay between promoter and structural gene variants control basal serum level of mannan-binding protein

Mannan-binding protein (MBP) is a serum lectin participating in the innate immune defense by opsonizing various microorganisms for phagocytosis. Opsonization defect due to MBP deficiency and low levels of the protein can partially be explained by the dominant effect of three different mutations in the structural part of the MBP gene. Large interracial differences in the frequencies of these variants have previously been described, but they cannot explain the large interindividual variation in MBP serum concentration. We describe the existence of additional polymorphisms at positions -550 (H/L variants) and -221 (X/Y variants) in the promoter region of the gene. The promoter haplotypes, HY, LY, and LX, show associations with high, medium, and low levels of MBP serum concentrations, respectively. Moreover, this represents a genetic system with additive effect of haplotypes in which a low producing LX haplotype in the homozygous state down-regulates the basal expression of MBP as effectively as a single structural variant. Populations of pure Eskimos, Caucasoids, and black Africans show marked interethnic differences in the frequencies of promoter haplotypes regulating the expression of the normal peptide, with the HY haplotype frequency varying from 0.83 in Eskimos via 0.33 in Caucasoids to 0.08 in Africans. The LY haplotype frequency varies from 0.04 in Eskimos via 0.39 in Caucasoids to 0.23 in Africans. The LX haplotype frequency varies from 0.03 in Eskimos via 0.24 in Caucasoids to 0.23 in Africans. The effect of the promoter variants can explain almost all of the ethnic differences not explainable by the structural variants alone.

A prospective sero-epidemiological study of visceral leishmaniasis in Baringo District, Rift Valley Province, Kenya

The incidence of visceral leishmaniasis (VL) was studied in 30 clusters with an average of 98 individuals in each cluster in a defined, endemic rural area of Baringo District, Kenya. The clusters were centred around recent cases of VL. Anti-leishmanial antibodies were measured by the direct agglutination test (DAT) and a clinical examination was performed on 2 occasions between April 1991 and May 1993. Of 2934 individuals tested by the DAT during the first visit, 78 (2.7%) were seropositive, 54 with and 24 without a history of VL. The seroconversion rate was 9/1000 person-years of observation (95% confidence interval 5.1-12.92) among 2332 seronegative individuals retested the following year. During the entire study period, VL was diagnosed in 10 patients, with an incidence rate of 2.2/1000 person-years of observation (95% confidence interval 0.8-3.6). Household contacts of individuals with previously confirmed VL had a higher frequency of DAT positivity than the rest of the population. This difference was significant for both sexes. These results suggest transmission in and around houses.

Interleukin-4 and interferon-gamma production by Leishmania stimulated peripheral blood mononuclear cells from nonexposed individuals

Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) production by Leishmania reactive peripheral blood mononuclear cells (PBMC) from non-exposed individuals was investigated. IFN-gamma was measured in culture supernatants after antigen stimulation. For the measurement of IL-4, antigen stimulated cells were pulsed with PMA and ionomycin before IL-4 release was measured. L. donovani and L. major antigens induced IL-4 production (105-1748 pg/ml) in 13 and seven cultures, and IFN-gamma production (1.7 - > 66 IU/ml) in 14 and 11 of 20 cultures, respectively. IL-4 production rose steeply after 6 days of antigen stimulation suggesting a response due to antigen recognition. Both IL-4 and IFN-gamma production was abrogated by depletion of CD2+ or CD4+ but not CD8+ cells. CD2+ or CD4+ but not CD8+ enriched cultures produced cytokines as unseparated PBMC. Thus, in non-exposed individuals circulating Leishmania reactive CD4+ T cells could be demonstrated. The cells from different individuals showed different patterns of IFN-gamma and/or IL-4 production upon antigenic stimulation. In experimental leishmaniasis the early balance between IFN-gamma and IL-4 is important for the clinical outcome. Our findings call for studies of the importance of cytokine production by cross-reactive T cells for the outcome of L. donovani infections in humans and show that the method for IL-4 detection is useful for this purpose.

Interferon-gamma and interleukin-4 production by human T cells recognizing Leishmania donovani antigens separated by SDS-PAGE

Crude preparations of Leishmania donovani proteins were separated by preparative SDS-polyacrylamide gel electrophoresis. Fractions of separated proteins were recovered by electroelution directly from the gel into separate chambers. The isolated protein fractions were tested for induction of proliferation and interferon-gamma (IFN-gamma) production in cultures of peripheral blood mononuclear cells (PBMC) from individuals who had recovered from visceral leishmaniasis caused by L. donovani. The release of interleukin-4 (IL-4) by PBMC stimulated with the isolated L. donovani antigen fractions was measured after treatment with phorbol-myristate-acetate and ionomycin. The cells proliferated in response to all protein fractions with molecular weights in the range < 12 kDa to 85 kDa. In general, IFN-gamma was secreted in response to stimulation with all the protein fractions, whereas IL-4 production was infrequently observed. The results show that T cells from individuals who have been cured of visceral leishmaniasis recognize and respond to a wide range of leishmanial antigens. There was no evidence of particular fractions constantly giving either IFN-gamma or IL-4-producing responses.

Dichotomy of the human T cell response to Leishmania antigens. I. Th1-like response to Leishmania major promastigote antigens in individuals recovered from cutaneous leishmaniasis

The T cell response to antigens from Leishmania major promastigotes was investigated in peripheral blood mononuclear cells from Sudanese individuals with a history of cutaneous leishmaniasis (CL), Sudanese individuals with positive DTH reaction in the leishmanin skin test but with no history of skin lesions, and in Danes without known exposure to Leishmania parasites. Proliferation and production of interferon-gamma (IFN-gamma) and IL-4 in antigen-stimulated cultures was measured. Lymphocytes from individuals with a history of CL proliferated vigorously and produced IFN-gamma after stimulation with either a crude preparation of L. major antigens or the major surface protease gp63. These cultures produced no or only little IL-4. Also cells from leishmanin skin test-positive donors with no history of CL produced IFN-gamma and no IL-4 in response to L. major antigens. Cells from the unexposed Danes were not activated by gp63. The cells from Danish donors produced either IFN-gamma or IL-4, but not both cytokines after incubation with the crude preparation of L. major antigens. The data show that the T cell response to Leishmania antigens in humans who have had uncomplicated CL or subclinical L. major infection is an IFN-gamma-producing Th1-like response.

Dichotomy of the human T cell response to Leishmania antigens. II. Absent or Th2-like response to gp63 and Th1-like response to lipophosphoglycan-associated protein in cells from cured visceral leishmaniasis patients

The T cell response to different Leishmania donovani antigens was investigated using peripheral blood mononuclear cells (PBMC) from Kenyans cured of visceral leishmaniasis and non-exposed Danes. Crude promastigote and amastigote antigens both induced proliferation and interferon-gamma (IFN-gamma) production in PBMC from cured patients, while cells from non-exposed donors gave weak responses. A similar pattern was induced by lipophosphoglycan-associated protein (LPGAP). By contrast, the major surface protease of Leishmania, gp63, induced only a weak proliferative response without IFN-gamma production in five of 17 samples from cured patients. Four of the five responding cultures produced IL-4, i.e. the response to this antigen was of the Th2 type. Furthermore, sera from acutely ill visceral leishmaniasis patients contained high levels of IgG antibodies to gp63. The Th2-like response to gp63 in patients cured of visceral leishmaniasis differs from the Th1-like response to the same antigen observed in patients cured of cutaneous leishmaniasis.

Dichotomy in the human CD4+ T-cell response to Leishmania parasites

Leishmania parasites cause human diseases ranging from self-healing cutaneous ulcers to fatal systemic infections. In addition, many individuals become infected without developing disease. In mice the two subsets of CD4+ T cells, Th1 and Th2, have different effects on the outcome of experimental Leishmania infections. Th1 cells producing interferon-gamma (IFN-gamma) mediate resistance, whereas Th2 cells producing interleukin-4 (IL-4) and IL-10 are associated with susceptibility and exacerbation. Evidence is accumulating that a Th1/Th2 dichotomy in the T-cell response to Leishmania exists also in humans, and that the balance between subsets of parasite-specific T cells may play an important regulatory role in determining the outcome of the infections.

Studies on the prevalence of leishmanin skin test positivity in the Baringo District, Rift Valley, Kenya

The leishmanin skin test (LST) was applied in 26 clusters of an average of 97 individuals in Baringo District, Kenya. These clusters were centered around recent cases of visceral leishmaniasis (VL). Of 2,411 individuals tested, 254 (10.5%, 155 males and 99 females) had a positive reaction. Among cured VL patients, the frequency was approximately 30% and no sex difference was observed. In the population as a whole, LST positivity increased with age to a stable level from approximately 15 years of age, reflecting an endemic situation. The level of LST positivity was 25-30% and 10-15% in males and females, respectively. Uninfected household contacts of VL cases had a higher frequency of LST reactivity than the rest of the population. This relationship was significant only in females and children, the prevalence ratio being 2.3 (95% confidence interval 1.3-4.1), 1.9 (1.1-3.5), and 1.4 (0.8-2.5) for females, children, and males, respectively. The frequency of LST positivity was higher individuals living in wood houses than in individuals living in house with mud or stone walls. Again, this difference was significant only in females and children (P = 0.02 and P = 0.04), but not in males (P = 0.7). The results suggest that children and women are exposed to the parasite in or around their houses, whereas adult males are, in addition, exposed elsewhere.

A new frequent allele is the missing link in the structural polymorphism of the human mannan-binding protein

Human mannan-binding protein (MBP) is a serum lectin participating in the innate immune defence. Low MBP concentrations are explained by the dominant action of a point mutation at codon 54 of the MBP gene in Eskimos, partially in Caucasians, but not in Africans. A previously described point mutation at codon 57 was very frequent (0.23) in East Africans, low in Caucasians (0.02), and absent in Eskimos. The African population only conformed to Hardy-Weinberg expectation when assuming the existence of an unknown allele, which was subsequently found as a point mutation at codon 52. This allele appeared with a relatively high frequency (0.05) in both Africans and Caucasians, but was absent in Eskimos. Hardy-Weinberg equilibrium is now seen in the investigated ethnic groups. All cases of MBP deficiency may be explained by these three variants.

Interferon-gamma and interleukin-4 in human Leishmania donovani infections

Clinical and immunological similarities between Leishmania donovani infections in humans and L. major infections in mice suggest that some of the pathophysiological mechanisms are the same in the two conditions. Both infections can result either in a fatal systemic disease or in a self-limiting infection with few and mild symptoms. In the murine model the outcome of the infection is critically related to the cytokines produced by T lymphocytes activated by leishmanial antigens. Activation of the IFN-gamma producing Th1 subset of CD4 positive T cells results in cure and survival, whereas activation of the IL-4 secreting Th2 subset results in a progressive disease with fatal outcome. A similar Th1/Th2 dichotomy in the cytokine response to L. donovani may exist in humans, and may have influence on the outcome of infection. In murine leishmaniasis the levels of IL-4 and IFN-gamma at the time of infection can direct the T cell response into Th1 or Th2 type. If similar mechanisms operate in humans, the outcome of L. donovani infections may depend on the local cytokine environment in which early activation of Leishmania specific T cells takes place. Cytokines secreted by cross-reactive memory T cells, activated by antigens from the invading micro-organism, may contribute to determine this environment.

Production of interferon-gamma and interleukin-4 by human T cells recognizing Leishmania lipophosphoglycan-associated protein

The Leishmania protein LPGAP which is co-isolated with lipophosphoglycan is a specific activator of T cells from individuals who have recovered from American leishmaniasis. We have tested the effect of LPGAP on peripheral blood mononuclear cells (PBMC) from Kenyan donors cured from L. donovani infections. LPGAP induced vigorous proliferation and production of interferon-gamma (IFN-gamma) by the cells. In addition PBMC incubated with LPGAP released interleukin-4 (IL-4) after pulsing with ionomycin and phorbol myristate acetate. Single cells were isolated from LPGAP-stimulated cell lines and expanded as T-cell clones. LPGAP-reactive T-cell clones were activated by crude preparations of both promastigotes and axenic grown amastigote-like parasites. Among 9 CD4+ T-cell clones recognizing LPGAP, cells secreting predominantly IFN-gamma as well as cells secreting predominantly IL-4 were identified. The results show that both IFN-gamma producing (Th1-like) and IL-4 producing (Th2-like) T cells recognizing LPGAP are expanded after infection with L. donovani in humans.

Measurement of serum antibodies against native Leishmania gp63 distinguishes between ongoing and previous L. donovani infection

An enzyme-linked immunosorbent assay (ELISA) using native gp63 for detection of serum antibodies to Leishmania was evaluated. The test identified antibodies in sera from 16 of 16 visceral leishmaniasis (VL) patients and 9 of 12 sera from patients with Trypanosoma brucei infection. In comparison, sera from 80 Danish controls and 40 control donors from a malaria endemic area of Ghana without known exposure to Leishmania were negative, as were sera from 12 Kenyan malaria patients and 9 schistosomiasis patients. After cure of VL, sera rapidly became negative. Only 1 of 7, 1 of 21, and 1 of 27 sera from cured VL patients 6-12 months, 1-2 years and > 2 years after cure were positive. Thus, in contrast to other serological tests for VL, the gp63 ELISA seems to distinguish an ongoing from a past infection. This might prove useful both for diagnostic and epidemiological purposes.

Field application of an ELISA using redefined Leishmania antigens for the detection of visceral leishmaniasis

Two soluble antigens from Leishmania donovani of 116 kDa and 70 kDa molecular mass, and a soluble mixture of crude antigens, were used in an enzyme-linked immunosorbent assay (ELISA) for the detection of visceral leishmaniasis (VL) in the field, and compared with the direct agglutination test (DAT). The tests were carried out on 8 VL patients, 34 normal individuals from an area endemic for the disease, and 68 former visceral leishmaniasis patients 1-5 years after treatment. The 70 kDa ELISA and the DAT had a sensitivity and specificity of 100% (95% confidence interval 63-100%), while the 116 kDa ELISA and the soluble crude antigen ELISA were 37.5% (9-76%) and 50% (16-84%) sensitive, respectively. When using ELISA (116 kDa or 70 kDa), 68-69% of sera tested 1-2 years, and 92-94% of sera tested 5 years, after treatment were negative. In contrast, when DAT or ELISA with crude antigen were used, the negativity rate was 31% 1-2 years, and 53% 5 years, after treatment. DAT was therefore not an accurate test for diagnosis in the field. The use of the 70 kDa antigen in ELISA was an accurate alternative to DAT in the detection of VL.

Leishmania donovani-reactive Th1- and Th2-like T-cell clones from individuals who have recovered from visceral leishmaniasis

Infections in humans by Leishmania donovani parasites can result in a fatal disease, visceral leishmaniasis (VL), or in a self-limiting asymptomatic infection. In murine models of the infection employing Leishmania major, the course of the disease can be directed into a VL-like syndrome by interleukin-4 (IL-4)-producing Th2 cells, or cure may result by Th1 cells secreting gamma interferon (IFN-gamma). The present study examined the potential of human T cells to generate Th1 or Th2 responses to L. donovani. The profiles of IFN-gamma, IL-4, and lymphotoxin secretion after antigen stimulation were analyzed in a panel of L. donovani-reactive CD4+ human T-cell clones generated from individuals who had recovered from VL after antimonial treatment. Two of the T-cell clones produced large amounts of IL-4 without production of IFN-gamma, seven clones produced both IFN-gamma and IL-4, and eight produced only IFN-gamma. This is the first report of a Th1- and Th2-type response in human leishmaniasis. These results suggest that in analogy with murine models, there is a dichotomy in the human T-cell response to L. donovani infections. Preferential activation of IL-4-producing Th2-like cells may be involved in the exacerbation of human VL, whereas activation of IFN-gamma-producing Th1 cells may protect the host from severe disease. Identification of leishmanial antigens activating one or the other type of T cells will be important in the development of vaccines against leishmaniasis.

Measurement of antigen-dependent interleukin-4 production by human peripheral blood mononuclear cells. Introduction of an amplification step using ionomycin and phorbol myristate acetate

The study of T cell responses in parasitic disease and allergy in humans has been limited by difficulties in the measurement of interleukin-4 (IL-4) in supernatants from antigen-stimulated peripheral blood mononuclear cells (PBMC). To obtain measurable amounts of IL-4 in vitro, we have added an amplification step to the antigen-specific response. Human PBMC were stimulated by tetanus toxoid (TT) or tuberculin (PPD) for 6 days and then pulsed with ionomycin and phorbol myristate acetate (PMA) for 24 h. TT-stimulated cells from nine revaccinated donors but not from seven unvaccinated donors and four that had only received childhood vaccinations against tetanus produced high levels of IL-4 (median (range) 1500 (300-3800), 316 (0-1600), and 270 (100-410) pg/ml, respectively, as measured by an enzyme linked immunosorbent assay, P = 0.005). PPD did not increase IL-4 production above the background level, although the majority of PPD-stimulated PBMC proliferated and produced interferon-gamma (IFN-gamma) in cultures without ionomycin and PMA. TT-induced IL-4 production correlated positively with proliferation. Culture supernatants did not interfere with IL-4 immunoreactivity and failed to affect ionomycin and PMA induced IL-4 production. The findings suggest that proliferating antigen-specific T cells were the source of IL-4 in these experiments. The method should prove useful for comparing the IL-4 producing ability of antigen-specific T cells from different individuals.

Diallelic polymorphism may explain variations of the blood concentration of mannan-binding protein in Eskimos, but not in black Africans

Mannan-binding protein (MBP) is a lectin which, upon binding to certain carbohydrates, activates the classical pathway of complement without the involvement of antibody or C1q. Deficiency of the MBP is associated with an opsonic defect and recurrent infections during early life. An amino acid substitution in the exon 1 at codon 54 in the MBP gene (GGC [glycine] to GAC [aspartic acid]) has been shown to be closely associated with low MBP concentration in Caucasoids. The gene frequency of the mutant allele in this population has been estimated at 0.13. In the study described here, we investigated the association between the mutant allele and MBP protein concentration in Eskimos from East-Greenland and black Africans from the Baringo District in Kenya. The frequency of the GAC allele was identical in Eskimos and Caucasoids (0.13). No overlap with regard to MBP concentration between the genotypes was found in the Eskimos. In contrast, the Africans revealed a low frequency of the GAC allele (0.009). However, the median MBP protein concentration was approximately 5 times lower among the Africans than the Eskimos. In 12.6% of the Africans and in 2.5% of the Eskimos, MBP was undetectable. Thus, MBP deficiency is the most frequent immunodeficiency so far described. The high prevalence of MBP deficiency among healthy individuals indicates that MBP deficiency also confers some selective advantages. We advance the hypothesis that MBP deficiency is maintained in populations because MBP deficiency decreases the infectivity of some intracellular micro-organisms which are dependent on opsonization.

Immunity against diphtheria and tetanus in human immunodeficiency virus-infected Danish men born 1950-59

To evaluate the possible need for vaccination against diphtheria and tetanus of patients infected with the human immunodeficiency virus (HIV), antibodies were measured in blood samples from 78 Danish HIV-infected men, born 1950-59, who could be expected to have received primary vaccination before they contracted the HIV infection. No patients (95% confidence interval: 0-4) had tetanus antibodies below the protective level, whereas 24 of the 78 patients (16-33) were unprotected against diphtheria. In the background population of the same age group and sex, 5% and 10% have been found unprotected against tetanus and diphtheria, respectively. No relationship between disease stages and antibody levels could be found. Neither was there any difference between patients with normal and reduced numbers of CD4+ lymphocytes. From 25 patients two blood samples were taken at an interval of at least one year. Anti-tetanus titres showed a decrease comparable to that found in the background population, whereas the change in anti-diphtheria titres was more variable with rising antibody concentrations in nine patients. The fall off in antibodies did not increase with progression of the disease. It is concluded that HIV-positive younger men who have followed the vaccination program against tetanus prior to the HIV infection can be expected to be protected, whereas revaccination against diphtheria must be considered.

Cellular and humoral immune responses in a population from the Baringo District, Kenya to Leishmania promastigote lipophosphoglycan

In a cross-sectional house-to-house study in a leishmaniasis-endemic area in Kenya, the cellular and humoral immune response to Leishmania lipophosphoglycan (LPG) was determined. Clinical data, peripheral blood mononuclear cells, and plasma were obtained from 50 individuals over the age of eight years. Lymphoproliferation and interferon-gamma (IFN-gamma) production by these cells were examined. It was shown that cells from all six individuals in the population with a history of kala-azar responded to LPG in the lymphocyte proliferation assay, and four of these six responded in the IFN-gamma assay. In contrast, cells from 12 of 44 individuals from the study area with no history of kala-azar and none of the five Danish control samples responded to LPG. Antibodies against LPG were detected by enzyme-linked immunosorbent assay in 45 of 50 plasma samples. Our findings clearly show that mononuclear cells from kala-azar patients cured of infection were able to respond to the LPG preparation. The finding of a specific cellular immune response to LPG in 12 of 44 individuals with no history of kala-azar is consistent with previous epidemiologic studies, in which it has been shown that a proportion of L. donovani infections run a subclinical course. The high frequency of individuals with antibodies against LPG might indicate that a majority of the population had been exposed to the parasite.(ABSTRACT TRUNCATED AT 250 WORDS)

[Diagnosis of Pneumocystis carinii pneumonia in HIV-positive patients. The diagnostic value of induced sputum and exercise test]

The object of investigation is to illustrate the values of two noninvasive procedures: the induced sputum test and the exercise test in the diagnosis of Pneumocystis carinii pneumonia (PCP). Both of the procedures are described. Fifty HIV-positive men in whom interstitial pneumonia was suspected participated. PCP was diagnosed in 16 patients, in ten of these by the induced sputum test, the sensitivity of which is, therefore, 35-85% (95% confidence limits). The exercise test, an investigation for demonstration of exercise induced oxygen desaturation, was of good predictive value. Thus, seven out of nine patients with positive exercise test results had PCP as compared with two out of 19 with normal exercise test results, p = 0.0009. The sensitivity was thus 40-97%. In five out of the six patients with false negative results to the induced sputum test, the exercise test was performed and was positive in all of the case. The method is rapid and simple and merely requires access to an exercycle and a pulse-oxymeter preferably with a recorder. It is concluded that the exercise test and the induced sputum test are valuable investigations which supplement one another in cases of suspected PCP and which avoid the need for bronchoscopy in 53-80% of the patients.

Activation of human T lymphocytes by Leishmania lipophosphoglycan

This study describes Leishmania antigen-induced activation of lymphocytes isolated from Kenyan donors, previously treated for visceral leishmaniasis, and from Danish and Kenyan controls. Peripheral blood mononuclear cells (PBMC) from cured Kala-Azar patients proliferated and produced Interferon-gamma in vitro in response to lipophosphoglycan (LPG) isolated from Leishmania major. The proliferative response was mainly due to activation of CD2-positive T cells. PBMC from controls did not respond to LPG, but to sonicates prepared from both L. major and L. donovani promastigotes. The surface glycoprotein GP 63 failed to activate PBMC from any of the donors tested. These results show that the individuals cured from visceral leishmaniasis had expanded T-cell clones recognizing LPG, conceivably as a result of Leishmania infection. The LPG preparation was without detectable protein contamination. Thus, the results suggest that human T lymphocytes can respond to glycolipid antigens.

[Clostridium septicum and colonic cancer]

During the period 1980-1987, Clostridium septicum was identified at Statens Seruminstitut, from anaerobic blood cultures in six patients. Five of the patients had cancer of the colon or rectum (c. coli) and one had cancer of the ovary. Correspondingly great incidence of solid tumours, particularly c. coli with C. septicum infection without preceding trauma or compromizing of immunity has been reported in the literature. Meticulous bacteriological identification should be undertaken on anaerobic culture as the finding of C. septicum in the blood should instigate investigation for c. coli or another form of solid tumour if no other explanation for the infection is available.