Plasmodium falciparum: the importance of IgM in the rosetting of parasite-infected erythrocytes.
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Animals↗
Biomedical subjects
G Pasvol
Publications and source records attributed to G Pasvol.
38 000 MW antigen-specific major histocompatibility complex class I restricted interferon-gamma-secreting CD8+ T cells in healthy contacts of tuberculosis.
CD8+ T lymphocytes are required to protect mice against Mycobacterium tuberculosis, although in early infection the mechanism appears not to be via perforin or granzyme-mediated lysis of the infected target, and may be via interferon-gamma (IFN-gamma) production. We therefore investigated whether CD8+ T cells specific for the immunoprotective 38 000 MW antigen of M. tuberculosis could be detected in infected humans. Using a recombinant vaccinia virus expressing the 38 000 MW antigen of M. tuberculosis (rV38) and a control vaccinia virus (rVras) we demonstrated that both viruses stimulated IFN-gamma production from freshly isolated peripheral blood mononuclear cells (PBMC) in a 36-hr enzyme-linked immunospot assay. Cell depletion and antibody blockade established that the bulk of the 38 000 MW antigen-specific IFN-gamma response was mediated by CD8+, major histocompatibility complex class I-restricted T cells, whereas the anti-vaccinia virus response was predominantly mediated by CD4+ T cells. In further evaluations PBMC from all seven healthy tuberculosis-exposed contacts had a 38 000 MW antigen-specific IFN-gamma response, whereas seven patients with untreated sputum-positive pulmonary tuberculosis had very low levels of 38 000 antigen-specific IFN-gamma-producing cells. These preliminary observations demonstrate the utility of recombinant vaccinia viruses in restimulating freshly isolated CD4+ and CD8+ T cells. The bias towards a higher frequency of IFN-gamma-producing CD8+ T cells in contacts rather than patients may indicate a protective role for CD8+ cells in human tuberculosis.
Adult↗
Human T- and B-cell reactivity to the 16kDa alpha-crystallin protein of Mycobacterium tuberculosis.
The attributes of immunodominance, predominant expression during mycobacterial dormancy and restriction to the Mycobacterium tuberculosis complex make the 16 kDa protein an important candidate for the study of the immune response in humans. We therefore investigated the relationship between T- and B-cell reactivity to the recombinant antigen and disease in a total of 127 subjects. The percentage of T-cell responders towards both the intact antigen and its permissively recognised peptide 16p91-110 was highest in healthy bacillus Calmette-Guérin (BCG)-sensitized controls (96% and 68%, respectively) and lowest in those with extensive untreated tuberculosis (26% and 18%) (P < 0.001). By contrast, antibody levels (ABT50 > 100) were highest in patients with extensive disease (46-50%) (P < 0.005). There was significantly higher production of IFN-gamma in the BCG-sensitized controls by comparison with untreated patients (P < 0.05), but complete antituberculous chemotherapy abolished this deficit in patients. The significance of these findings to immunodiagnosis and protective immunity is discussed.
Antigen Presentation↗
Peptide-specific T cell response to Mycobacterium tuberculosis: clinical spectrum, compartmentalization, and effect of chemotherapy.
The T cell repertoire of 59 patients with untreated tuberculosis was compared with that of 46 bacille Calmette-Guérin-vaccinated controls by assaying the proliferative responses to six permissively recognized peptides from the 16-, 19-, and 38-kDa molecules of Mycobacterium tuberculosis. A trend from higher to lower reactivity following this order: vaccinated controls > lymph node disease > localized extrapulmonary > pulmonary > pleural was seen for 4 of the peptides (P < .03). The decreased response of blood lymphocytes from patients with pleural tuberculosis was partially accounted for by sequestration of peptide-responsive cells within the pleural fluid. Chemotherapy "reversed" the depressed proliferative responses of patients with pulmonary and pleural tuberculosis depending on the peptide origin, being greatest for peptides of 16 kDa, transient for those of 19 kDa, and least for those of 38 kDa. These data demonstrate antigen specificity in the decreased responsiveness of patients with tuberculosis.
Adolescent↗
The treatment of falciparum malaria in African children.
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Adolescent↗
Host resistance to malaria runs into swampy water.
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Adult↗
Severe anaemia in children living in a malaria endemic area of Kenya.
Severe anaemia is an important cause of morbidity and mortality in African children, but the causes, particularly falciparum malaria, are difficult to determine. We assessed the contribution of falciparum malaria to anaemia in Kenyan children by clinical examination and measurement of parasitaemia and haemoglobin (Hb) concentration in 559 children in the community and in 2412 children admitted to Kilifi district hospital during a 2-year period. We also attempted to characterize severe malarial anaemia by examining the causes and pathophysiology of anaemia in 101 children admitted with Hb concentration < or = 50 g/l during a 1-year period. Plasmodium falciparum infection was associated with reduced Hb concentration in children in the community and in those admitted to hospital irrespective of diagnosis. Falciparum malaria was the primary cause in 46 cases (46%) of severe anaemia admitted to hospital. There was no difference in the frequency of haemolysis or dyserythropoiesis in the children with malarial anaemia and those with anaemia from other causes, such as iron deficiency or sickle cell disease. The mortality rate in the children with severe malarial anaemia was 8.6% compared with 3.6% in children with severe anaemia due to other causes. Falciparum malaria does not present with a characteristic clinical or haematological picture, but is a major cause of the morbidity and mortality in children with severe anaemia who live on the Kenyan coast, a malaria endemic area.
Anemia↗
Evaluation of the recombinant 38-kilodalton antigen of Mycobacterium tuberculosis as a potential immunodiagnostic reagent.
The diagnosis of infection caused by Mycobacterium tuberculosis is of increased public health concern following increases in the number of cases in developed countries and major increases in developing countries associated with the spread of human immunodeficiency virus (HIV) infection. The specificity of purified protein derivative skin testing for the detection of infection is compromised by exposure to environmental mycobacteria. Examination of sputum detects the most infectious patients, but not those with extrapulmonary disease. The 38-kDa antigen of M. tuberculosis contains two M. tuberculosis-specific B-cell epitopes. We overexpressed the gene for this antigen in Escherichia coli and evaluated the recombinant product in in vitro assays of T-cell function and as a target for the antibody response in humans. The sensitivity and specificity of the antigen as a skin test reagent were also assessed in outbred guinea pigs. We found that 69% of healthy sensitized humans recognize the antigen in vitro, as manifested by both cell proliferation and the production of gamma interferon. Untreated patients initially have a lower frequency of response (38%); this recovers to 72% during therapy. A total of 292 patients (20 with HIV coinfection) and 58 controls were examined for production of antibody to the 38-kDa antigen by using a commercially available kit. The sensitivity of the test in comparison with that of culture was 72.6%, and the specificity was 94.9%. The antigen was also tested for its ability to induce skin reactions in outbred guinea pigs sensitized by various mycobacterial species. The antigen provoked significant skin reactions in M. tuberculosis-, M. bovis BCG-, and M. intracellulare-sensitized animals. The significance of these findings and the usefulness of this antigen in immunodiagnosis are discussed.
AIDS-Related Opportunistic Infections↗
Malaria and resistance genes--they work in wondrous ways.
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Anemia, Sickle Cell↗
Plasmodium falciparum lacks sialidase and trans-sialidase activity.
Sialic acid on the red cell surface plays a major role in invasion by the malaria parasite Plasmodium falciparum. The NeuAc(alpha 2,3) Gal motif on the O-linked tetrasaccharides of the red cell glycophorins is a recognition site for the parasite erythrocyte-binding antigen (EBA-175). Consequently, the interaction of P. falciparum and the red cell might share homology with that of the influenza virus. The cellular interactions of P. falciparum were examined for their sensitivity to 4-guanidino-2,3-didehydro-D-N-acetyl neuraminic acid (4-guanidino Neu5Ac2en), a potent inhibitor of influenza virus sialidase. Parasite invasion and subsequent development was unaffected by the sialidase inhibitor. The inhibitor did not affect rosette formation of parasite-infected erythrocytes with uninfected cells nor their cytoadherence to C32 melanoma cells. Furthermore, we were unable to confirm the presence of a previously reported parasite sialidase using sensitive fluorometric or haemagglutination assays, neither was any malarial trans-sialidase identified. We conclude that P. falciparum possesses neither sialidase nor trans-sialidase activity and that an inhibitor of influenza virus sialidase has no effect on important cellular interactions of this parasite.
Animals↗
T cell responses to a mixture of Mycobacterium tuberculosis peptides with complementary HLA-DR binding profiles.
The T cell response to a mixture of eight peptides derived from sequences of the Mycobacterium tuberculosis 16-, 19- and 38-kD antigens (MTBmix-8) has been studied. The peptides were selected on the basis of complementary binding to nine HLA-DR molecules (HLA-DR1 to DR9). MTBmix-8 at 6.25 and 50 micrograms/ml gave rise to significant stimulation (P < 0.05) of peripheral blood mononuclear cells (PBMC) from healthy tuberculin-positive and both untreated and treated diseased subjects, but not in any of a control group of healthy tuberculin-negative subjects. MTB-mix-8 stimulated proliferation of PBMC from healthy tuberculin-positive individuals at lower concentrations than the individual component peptides. However, the maximal stimulation achieved was only slightly higher than that achieved with individual peptides. MTBmix-8 also stimulated the production of interferon-gamma (IFN-gamma) in vitro. Using the mean +/- 2 s.d. of the values for IFN-gamma production in the tuberculin-negative population as a cut-off, MTBmix-8 at 6.25 micrograms/ml was able to detect infection with a sensitivity of 100% in untreated patients, 87% in treated patients, and 82% in tuberculin-positive controls. The corresponding figures for the most potent single peptide (16p91-110) were: 66% in untreated patients, 71% in treated patients and only 42% in controls. Thus, using the IFN-gamma-based assay, which has the additional advantages of speed and does not require radioactivity, the mixture of peptides is more sensitive than single peptides in diagnosing infection.
Adult↗
Antigen-driven shedding of L-selectin from human gamma delta T cells.
Activation of lymphocytes leads to the modulation of a number of surface molecules. We have investigated the expression of one such molecule. L-selectin, following activation of gamma delta T cells with Mycobacterium tuberculosis. L-selectin is modulated during lymphocyte entry into lymph nodes; this modulation reflects the recirculation and homing potential of lymphocytes. We find that stimulation of gamma delta T cells by M. tuberculosis antigens results in shedding of L-selectin from gamma delta T cells. Re-expression of L-selectin occurs on removal of antigen suggesting that the regulation of expression is controlled by the presence or absence of antigen. The gamma delta T-cell receptor (TCR)-positive, L-selectin negative population of peripheral blood lymphocytes appears to be resting cells, as assessed by forward- and light-scatter analysis. We further find that gamma delta T cells isolated from a site of infection, the pleural fluid of a tuberculosis patient, are L-selectin negative, and that L-selectin is re-expressed following culture of the pleural fluid gamma delta T cells in the absence of antigen. These results demonstrate that, in addition to stimulation with polyclonal mitogens, antigen stimulation can also promote the surface shedding of L-selectin and that gamma delta T cells have the potential to home to sites of infection supporting their role in the immunological defence against infectious micro-organisms.
Antigens, Bacterial↗
Mechanism of regulation of malarial invasion by extraerythrocytic ligands.
Invasion of red cells by Plasmodium falciparum in vitro was inhibited by a range of extracellular ligands, none of which block the major receptors for merozoites. Most effective, in terms of dose response, were two monoclonal antibodies against the Wrb antigen on glycophorin A; wheat germ agglutinin which also binds to glycophorin, and an anti-band 3 monoclonal antibody, caused inhibition of invasion at higher levels of saturation, while concanavalin A, which binds to band 3, was without effect. All the ligands except concanavalin A, increased the rigidity of the host cell membrane. The anti-Wrb antibodies generated the highest dose response effect, but no correlation between invasion and shear elastic modulus of the membrane could be established. All ligands, with the exception of concanavalin A, caused a reduction in the translationally mobile fractions of band 3 and glycophorin, as revealed by fluorescence recovery after photobleaching (FRAP). Invasion diminished with loss of mobile band 3, engendered by bound wheat germ agglutinin or anti-band 3, falling precipitately when the mobile fraction fell below 40% of that in unperturbed membranes. Both anti-Wrb antibodies suppressed invasion completely at concentrations insufficient to affect significantly either membrane rigidity or intramembrane protein diffusion. A univalent anti-glycophorin A (Fab) fragment, the parent antibody of which was previously shown to inhibit invasion strongly, had only a modest effect on invasion and induced a correspondingly small change in the mobile fraction of band 3.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Human T cell responses to peptide epitopes of the 16-kD antigen in tuberculosis.
The 16-kD protein constituent of the Mycobacterium tuberculosis complex has been known mainly for its prominent serological immunogenicity and species specificity in tuberculous infection. In this study, we evaluated the T cell immune repertoire in 27 sensitized healthy subjects and 46 patients with active tuberculosis using 14 overlapping 20mer peptides spanning the entire sequence of this protein. Four of the tested peptides individually stimulated proliferation of blood mononuclear cells from more than 50% of healthy controls. Tuberculosis patients reacted to a narrower peptide range and with a 17-27% lower rate of responses to the four most immunogenic peptides, but these differences do not distinguish in any simple way between the T cell repertoire of patients and sensitized healthy subjects. The most immunogenic peptide (91-110) was recognized by 67% of healthy subjects and by 50% of tuberculosis patients. Importantly, several non-responders to this peptide were stimulated with the other three most permissive peptides with sequences of 111-130, 71-91 and 21-40, resulting in an overall response rate to at least one of these four peptides of 93% in healthy controls and 74% in tuberculosis patients. In view of this additive effect between the most immunogenic peptides, their combined use may achieve sufficient sensitivity in a test aimed at the specific discrimination between infected and non-infected healthy subjects. The major interest in testing with these peptides rests in their species specificity, which is not achieved using purified protein derivative (PPD).
Amino Acid Sequence↗
Recent advances in tropical medicine.
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HIV Infections↗
Streptococcal toxic shock-like syndrome: evidence of superantigen activity and its effects on T lymphocyte subsets in vivo.
Toxic shock-like syndrome is a serious complication of invasive streptococcal disease. The syndrome is believed to be the consequence of exposure to exotoxins produced by the infecting organisms which behave as superantigens. We describe two patients who fulfilled clinical criteria for this syndrome, one of whom died. Streptococci isolated from both patients were found to produce a mitogen specific for the V beta 2+ T lymphocyte subset in vitro, which had the characteristics of a superantigen. The phenotype and function of lymphocytes collected from both patients during the acute phase of their illness demonstrated a marked reduction in circulating CD4+ ('helper') and CD45RA+ ('naive') T lymphocytes expressing the V beta 2 chain, and an increase of those expressing CD8, CD45RO and the V beta 2 chain. This effect resolved within 4 weeks in the patient who survived. Proliferation assays demonstrated no T cell anergy in either patient. Stimulation of lymphocytes by superantigen in these clinical situations does not appear to cause permanent deletion of T cell subsets, as has been observed in animal models.
CD4-Positive T-Lymphocytes↗
Epitope specificity and isoforms of the mycobacterial 19-kilodalton antigen.
The topography and specificity of B- and T-cell stimulatory epitopes from the 19-kDa protein of Mycobacterium tuberculosis were investigated by using overlapping synthetic peptides. Murine antisera identified two cryptic epitopes (residues 11 to 30 and 61 to 80) and one species-specific immunodominant epitope (residues 140 to 159). Immunoglobulins G1 and G2a antibody isotypes varied for the respective peptide immunogens but without relationship to the T-cell cytokine profiles which were characterized by high gamma interferon and low interleukin 5 levels. Antisera to recombinant M. tuberculosis 19-kDa protein (rGST-19) cross-reacted with homologous proteins of similar size from organisms of the Mycobacterium avium-intracellulare complex. Two-dimensional gel electrophoresis revealed differences in the number, relative mobility, and charge of isoforms of the 19-kDa protein, possibly reflecting posttranslational modifications. The immunodominant T-cell epitope from the M. tuberculosis 19-kDa protein (residues 61 to 80) and the corresponding peptide sequence from Mycobacterium avium subsp. intracellulare (residues 64 to 83), differing at five residues, were both recognized in a genetically permissive manner. Peptides 61-80 and 64-83 stimulated cross-reactive responses in BALB/c (H-2d) mice, while in the C57BL/10 (H-2b) strain, responses to peptide 61-80 were species specific. In purified protein derivative-positive healthy individuals, the M. avium subsp. intracellulare peptide stimulated stronger responses than did the M. tuberculosis peptide, whereas patients with active tuberculosis had enhanced in vitro T-cell responses to both peptides.
Amino Acid Sequence↗
Severe falciparum malaria: predicting the effect of exchange transfusion.
The rationale for exchange transfusion (ET) in severe Plasmodium falciparum malaria is to lower the parasite burden rapidly, to replenish unparasitized cells and to correct severe anaemia. In addition, parasite antigens or 'toxins' may be removed. Despite reports of successful ET in the treatment of malaria since 1974, it remains controversial and its role and technique have been poorly defined. We present a mathematical model of ET which relates volume of exchange to reduction in parasitaemia and change in haemoglobin concentration. This model fits published and unpublished clinical data well, and should facilitate standardization of ET in future.
Blood Volume↗