Biomedical subjects

E M Riley

Publications and source records attributed to E M Riley.

At least 73 records · Page 4Linked to original sources

PubMed1990

Number of cells from Plasmodium falciparum-immune donors that produce gamma interferon in vitro in response to Pf155/RESA, a malaria vaccine candidate antigen.

Secretion of gamma interferon (IFN-gamma) in response to stimulation of Plasmodium falciparum-primed T cells by specific antigens may be a useful indicator of cellular immunity to malaria. An enzyme-linked immunospot (ELISPOT) assay designed to detect IFN-gamma at the single-cell level was used to study IFN-gamma-producing cells from P. falciparum-primed donors from The Gambia after in vitro stimulation with various malarial antigens. IFN-gamma secreted into the culture supernatant was measured by conventional enzyme-linked immunosorbent assay (ELISA). There was a good correlation in individual donors between the level of IFN-gamma secreted into the culture supernatant and the number of IFN-gamma-secreting cells. However, the ELISPOT assay was apparently more sensitive in demonstrating low levels of IFN-gamma production than the ELISA was. Thus after stimulation with crude P. falciparum antigen from infected erythrocytes, 72% of the primed donors responded positively in the ELISPOT assay but only 55% responded positively in the ELISA. When stimulated with synthetic peptides representing immunodominant epitopes of the malarial antigen Pf155/RESA, a vaccine candidate, 31 to 55% responded in the ELISPOT assay and 21 to 36% responded in the ELISA. Unprimed Europeans did not respond positively to these antigens in either of the assays, and background in antigen-free controls was generally low. These results indicate that measurement of IFN-gamma by the ELISPOT assay or ELISA should have wide applications in large-scale epidemiological studies of malaria immunity. In addition, the ELISPOT assay makes it possible to analyze the T cells responding to malarial antigens in terms of both numbers and functional heterogeneity.

Adult↗

PubMed1989

T and B cell responses of Plasmodium falciparum malaria-immune individuals to synthetic peptides corresponding to sequences in different regions of the P. falciparum antigen Pf155/RESA.

The C-terminal (3') amino acid repeat region of the Plasmodium falciparum Ag Pf155/RESA, a vaccine candidate, contains immunodominant T and B cell epitopes. In order to identify additional T cell epitopes in the molecule, synthetic peptides corresponding to the centrally (5') located repeat region, as well as to four nonrepeated regions, were synthesized. T cells from 46 P. falciparum-primed individuals living in a holoendemic area of The Gambia where malaria transmission is seasonal were tested for their responsiveness to the peptides by thymidine incorporation and IFN-gamma release. There was a considerable variation in the response to different peptides. Proliferation and IFN-gamma release were not correlated in individual donors, underlining the importance of measuring both activities when screening donor populations for total T cell responsiveness to a given Ag. Whereas 72% of the donors responded with proliferation and/or IFN-gamma release to the intact protein the mean % responders to the peptides was 40%. The most frequent responses (up to 60%) were induced with peptides from the 3'- and 5'-repeat region of the protein. Analysis of some closely related sequences in the 3'-repeat region indicated that they contained at least two epitopes that were either distinct or cross-reacting in different donors, suggesting difference in the genetic control of these responses. When the same peptides were investigated for reactivity with antibodies, the best T cell inducing sequences also displayed the best antibody reactivities. However, in individual donors, T and B cell responses were not correlated. T cell responses were shown to persist after a period with no P. falciparum transmission, whereas antibody concentrations tended to decrease, suggesting differences in the requirements of boosting at the T and B cell levels, respectively.

Amino Acid Sequence↗

PubMed1989

Human T cell recognition of polymorphic epitopes from malaria circumsporozoite protein.

Lymphocytes obtained from forty individuals living in a malaria endemic area of West Africa were tested for in vitro proliferative responses to peptides representing variant regions of the immunodominant T cell domain of the circumsporozoite protein (amino acids 326 to 345, referred to as Th2R, and 361 to 380, referred to as Th3R) from three distinct strains of Plasmodium falciparum. A total of 83% of the individuals responded to at least one of the six peptides tested, confirming that these epitopes are immunodominant. A much greater number of individuals than expected by chance (32% of the responders to Th2R and 27% of the responders to Th3R) reacted to all three of the variant peptides for that epitope, indicating interdependency of the T cell responses, suggestive of cross-reactivity. Nevertheless, some subjects' T cells were clearly able to distinguish each variant peptide from the others. Using EBV transformed B cells, lymphocytes from 10 of the individuals were HLA typed. In this small group, HLA DRw13 was associated with a positive response to any of the peptides, whereas there was a negative association between DQw3 and response to any of the peptides. These results, although limited by the small sample size, suggest that recognition of T epitopes may be Ir gene linked. Our findings suggest that it may be possible to broaden the immunogenicity of an anti-sporozoite malaria vaccine.

Adult↗

PubMed1989

Can implanted cyst pieces of Echinococcus granulosus regenerate?

Small piece of ovine hydatid cysts devoid of brood capsules and protoscoleces, and half or quarter pieces of secondary sterile murine cysts of equine origin failed, over a six-month period, to regenerate when passaged into the peritoneal cavity of BALB/c mice. The majority of similar pieces placed in microdiffusion chambers prior to insertion into mice also failed to regenerate, suggesting that the passage of cyst pieces may not be totally reliable in the assessment of the viability of germinal layer tissue after chemotherapy.

Animals↗

PubMed1989

Suppression of in-vitro lymphoproliferative responses in acute malaria patients can be partially reversed by indomethacin.

In-vitro lymphoproliferative responses to malaria antigens are suppressed in patients with acute Plasmodium falciparum infection. Studies with other parasitic diseases have suggested that monocyte/macrophage-derived prostaglandins may be responsible for immunosuppression. Since acute malaria infection is characteristically associated with fever it is likely that prostaglandin E production will also be enhanced in these patients. In this study, indomethacin, a cyclooxygenase inhibitor which blocks the synthesis of prostaglandins, was added to the culture medium during assays of lymphoproliferative responses to malaria antigens and other soluble proteins. Responses to several antigens were enhanced in the presence of indomethacin, indicating that prostaglandins may have a generalized immunosuppressive role in malaria-infected individuals. However, responses to malaria antigens were particularly enhanced by indomethacin, suggesting that malaria-specific T-cells are especially sensitive to the effects of prostaglandin, possibly due to prior activation in vivo by circulating malaria antigens.

Animals↗

PubMed1989

Plasmodium falciparum schizont sonic extracts suppress lymphoproliferative responses to mitogens and antigens in malaria-immune adults.

Cellular immune responses to malaria antigens are suppressed during acute Plasmodium falciparum infection, and evidence from both murine and human studies suggests that parasite-derived factors may be directly immunosuppressive. In this study we have shown that P. falciparum schizont sonic extract will suppress in vitro lymphoproliferative responses to purified malaria antigens and other soluble antigens. The degree of suppression appears to correlate with the level of the lymphoproliferative response to the schizont preparation and is correspondingly more marked in malaria-immune donors than in nonimmune individuals. The effect can be transferred with primed mononuclear cells and is partially abrogated by removal of CD8+ lymphocytes. The suppressive component of the schizont preparation is nondialyzable and partially heat labile and comigrates with hemoglobin-derived proteins in the molecular mass range 10 to 20 kilodaltons.

Adult↗

PubMed1989

CD8+ T cells inhibit Plasmodium falciparum-induced lymphoproliferation and gamma interferon production in cell preparations from some malaria-immune individuals.

Infection with Plasmodium falciparum induces marked disturbances in normal immunoregulatory functions. Antigen-specific immunosuppression is a feature of acute malaria and has been linked to activation of CD8+ T suppressor cells. Among immune adults, cell-mediated immune responses to malaria antigens are extremely variable when measured in vitro, and there is no obvious relation between responsiveness and resistance to clinical disease. In this study, when CD8+ cells were removed from peripheral blood mononuclear cell preparations obtained from individuals who responded poorly to a soluble malaria antigen preparation, both lymphoproliferation and gamma interferon production were significantly enhanced, but responses to other soluble antigens and mitogen were unaffected. No effect of CD8+ cell depletion was seen in individuals whose undepleted mononuclear cells gave a high response to the malaria antigen. This suggests that for some malaria-exposed individuals, CD8+ cells activated in vitro by exposure to malaria antigens suppress other cellular responses and may obscure the presence of potentially protective immune mechanisms.

Adult↗

PubMed1989

Suppression of cell-mediated immune responses to malaria antigens in pregnant Gambian women.

In malaria endemic areas, pregnancy predisposes previously immune women to clinical and subclinical malaria infection. While parameters of humoral immunity do not seem to be affected by pregnancy, suppression of cellular immunity has been demonstrated for a number of antigens. In this study of women from a rural area of the Gambia where falciparum malaria is holoendemic, we show that lymphoproliferative responses to Plasmodium falciparum antigens are depressed in pregnant women compared to parity matched non-pregnant women, and that this effect is particularly marked in primigravidae. The data also indicate that malaria antigen induced gamma-interferon production may be depressed in pregnant women. There was no significant difference in antimalarial antibody titers between the 2 groups.

Animals↗

PubMed1988

T cell reactivity of defined peptides from a major Plasmodium falciparum vaccine candidate: the Pf155/RESA antigen.

Several immunodominant B-cell epitopes of the P. falciparum antigen blood stage Pf155/RESA, a major vaccine candidate antigen, are located in the molecular regions containing amino acid repeats. We started to map Pf155/RESA for T cell reactive epitopes. For this purpose, short synthetic peptides corresponding to the 3'- and 5' repeat regions of the molecule as well as to non-repeated sequences outside these regions were prepared. T cells from P. falciparum primed donors from two highly endemic areas of Africa were tested for their responsiveness to the peptides by thymidine incorporation and/or interferon gamma (IFN-gamma) release. There was a considerable variation in the response to the different peptides. However, the strongest and most frequent responses were seen with a few peptides from the 3'- and 5'-repeat regions. Thus, the immunodominant B cell epitope regions of Pf155/RESA, contain several T cell epitopes. Since the repeat regions are known to be conserved in different P. falciparum strains, the T cell epitopes reported here may be suitable constituents of a P. falciparum subunit vaccine.

Animals↗

PubMed1988

Determination of the minimum time of praziquantel therapy required for the in vitro treatment of protoscoleces of Echinococcus granulosus.

Ovine and equine protoscoleces of Echinococcus granulosus were cultured for 26 days with our without praziquantel and viability assessed, by eosin exclusion, for cultures in various drug concentrations (50, 250 and 500 micrograms/l) and periods of exposure (1, 3 or 7 days (d] before removing/'rescuing' to drug-free medium. Drug efficacy was proportional to drug concentration and to length of exposure. At higher drug concentrations shorter exposures were required to produce the effect of continuous drug treatment, 1d therapy at 500 micrograms/l killing 96% ovine protoscoleces by day 14 whereas 7d therapy at 50 micrograms/l was required to produce a similar effect. Equine protoscoleces appeared marginally less susceptible than those of ovine origin. The relevance of the results in the need for peri-operative prophylaxis against spilled protoscoleces in man is discussed.

Animals↗

PubMed1988

Echinococcus granulosus: the effects of praziquantel, in vivo and in vitro, on the ultrastructure of equine strain murine cysts.

Praziquantel (500 mg/kg) administered orally to BALB/c mice with secondary equine E. granulosus daily for 21, 30 or 30 + 30 days without the drug resulted in the majority of cysts, using bench criteria of turgidity and eosin exclusion, being assessed as 'alive'. Ultrastructural examination of 54 of these 'alive' cysts did not support this conclusion. They all showed increased vesiculation of the germinal layer leading, in many, to the loss of its integrity. Increased mitochondrial numbers occurred frequently. The longer drug treatments appeared to have greater effects on the germinal layer of 'alive' cysts and there was no detectable reestablishment of structural organization within 30 days after drug withdrawal. Subjectively, there was no substantial difference between cysts from 4-month and 9-month infections or between affected peritoneal and hepatic cysts. Tissue from collapsed cysts was necrotic. Peak serum levels of praziquantel (6430-6136 micrograms/l) occurred 5-10 min after drug administration (500 mg/kg) and dropped rapidly to less than 10 micrograms/l at 3 h. In an in vitro study at praziquantel concentrations of 1000 and 5000 micrograms/l over a 10-day period, most cysts were judged 'alive' by bench criteria but showed ultrastructurally a time- and concentration-dependent loss of integrity identical to that seen in vivo. Turgidity and eosin exclusion therefore underestimate the effect of praziquantel and the results indicate that in vitro experiments can fulfil a legitimate preliminary role in a hydatid chemotherapy programme.

Animals↗

PubMed1988

Human T-cell recognition of the circumsporozoite protein of Plasmodium falciparum: immunodominant T-cell domains map to the polymorphic regions of the molecule.

The definition of human T-cell antigenic sites is important for subunit vaccine development of a peptide immunogen if the goal is to allow antibody boosting during infection or to stimulate antibody-independent T-cell immunity. To identify such sites on the circumsporozoite (CS) protein of Plasmodium falciparum, 29 overlapping synthetic peptides spanning the entire CS protein were made and tested for their ability to stimulate peripheral blood lymphocytes from 35 adults living in a P. falciparum malaria-endemic region of West Africa. Three immunodominant domains were located outside the repetitive region. These domains, however, occurred in the polymorphic regions of the molecule, suggesting that parasite mutation and selection has occurred in response to immune pressure from T cells. Such polymorphism may impose an obstacle for vaccine development.

Adult↗

PubMed1988

Cell-mediated immune responses to Plasmodium falciparum antigens in adult Gambians.

Peripheral blood mononuclear cells from clinically immune Gambian adults were assayed for in vitro proliferation in response to crude and partially purified Plasmodium falciparum antigens. Lymphoproliferative responses to malaria antigens, lectin mitogens and Candida albicans were compared with those of control donors with no previous exposure to malaria. Cells of malaria-immune individuals were significantly more responsive to conconavalin A, and less responsive to phytohaemagglutinin, than cells from the control donors in both non-immune human serum and autologous serum. Cells from a proportion of immune donors proliferated in response to soluble malaria antigens but a substantial minority did not. Young adults and women were over-represented in the non-responding population. Responses to soluble malaria antigens were depressed in autologous serum compared with normal human serum. Both immune and control cells produced low levels of gamma-IFN when stimulated with crude P. falciparum schizont antigens. Approximately half the immune donors, and none of the controls, produced significant levels of gamma-IFN in response to purified soluble malaria antigen or malaria parasite culture supernatant. There was no direct correlation between lymphoproliferation and gamma-IFN production.

Adolescent↗

PubMed1988

Cellular immune responses to Plasmodium falciparum antigens in Gambian children during and after an acute attack of falciparum malaria.

Peripheral blood mononuclear cells from 63 Gambian children with acute Plasmodium falciparum malaria were examined for lymphoproliferation and interferon-gamma (IFN) production in response to stimulation by mitogens, malaria antigens and other soluble antigens. Mitogen or Candida-induced proliferation was not depressed during acute infection but was enhanced 2 to 4 weeks after treatment. Responses to partially purified soluble P. falciparum antigens were minimal or absent in all children in the acute phase but approximately 50% of the children responded by proliferation or IFN-gamma production during the 2 to 8 week convalescent period. These proliferative responses were severely depressed in the presence of the patient's own serum. Nine children with significant convalescent phase proliferative responses were re-examined several months after acute infection. Of these, four remained responsive for at least 8 months in the probable absence of reinfection.

Acute Disease↗

PubMed1988

Studies on the effect of short term, high dose praziquantel treatment against protoscoleces of ovine and equine Echinococcus granulosus within the cyst, and in vitro.

Protoscoleces of Echinococcus granulosus were subjected to high concentrations of praziquantel (10-1000 micrograms/ml medium or cyst fluid) for a short, 10 min duration in vitro or in situ within cysts. Drug efficacy was then monitored either by in vitro culture in drug-free medium and/or by passage into rodents. The in vitro test of effectiveness suggested that ovine-derived protoscoleces were more sensitive than those of equine origin, and that the in vitro method of treatment was more successful than that performed in situ. However, the subsequent passage of treated protoscoleces, whether immediately after in situ or in vitro exposure or after culture in drug-free medium, indicated that the in situ administration was as effective as the in vitro treatment. Both methods reduced cyst burdens in rodents to 9-15% of control infections.

Animals↗

PubMed1987

Experimental Echinococcus granulosus infection in mice: immunocytochemical analysis of lymphocyte populations in local lymphoid infections during early infection.

The influence of subcutaneous infection with protoscoleces of Echinococcus granulosus on the distribution of lymphocyte subsets in draining lymph nodes has been evaluated by immunocytochemical labelling of lymphocyte surface antigens. These studies reveal marked expansion of paracortical Thy-1+, Lyt-1+ cells and moderate proliferation of surface immunoglobulin-bearing B-cells immediately after infection. The Lyt-1+:Lyt-2+ ratio decreases rapidly during the first 21 days post-infection and remains below unity until at least 12 weeks post-infection due to severe depletion of Lyt-1+ cells in draining lymph nodes and a significant increase in the percentage of Lyt-2+ cells. The potential role of these Lyt-1-,2+ (putative T-suppressor) cells in regulation of the anti-parasite immune response and mediation of generalized immunosuppression is discussed in the light of evidence of inhibition of anti-parasite immunity in infected mice.

Animals↗

PubMed1986

Echinococcus granulosus infection in mice: host responses during primary and secondary infection.

The reaction of Balb/c mice to primary and secondary subcutaneous infection with Echinococcus granulosus protoscoleces (PSC) is described. From 3 to 14 days following primary exposure to PSC, draining lymph nodes increase in weight and there is expansion of T and B lymphocyte populations, enhancement of in vitro lymphocyte transformational responses and production of PSC-specific IgM and IgE antibodies. Despite the persistence of viable PSC in host tissues, lymphocyte responses decline to pre-infection values over the period 3-8 weeks post-infection. Secondary exposure to PSC immediately induces lymphoproliferation, enhancement of transformational responses, production of IgE antibody and encapsulation of PSC by inflammatory cells. Although specific antibody levels remain high until at least 8 weeks after challenge infection, lymphocyte activity begins to decline after 4 days and is profoundly suppressed by 10 days. Parasite viability appears to be significantly reduced in secondary, as opposed to primary, infection and is associated with the accumulation of large numbers of eosinophils, mast cells and macrophages in infected tissues.

Animals↗

PubMed1985

The immune response to Echinococcus granulosus: sequential histological observations of lymphoreticular and connective tissues during early murine infection.

This paper describes the organ weight changes and the early (0 to 56 days) histological and ultrastructural changes in the lymphoid structures and injection sites after subcutaneous infection of Balb/c mice with Echinococcus granulosus protoscolices (psc). Local lymph nodes enlarged markedly, reaching maximal weight 5 to 14 days after infection (pi). Expansion of the thymus-dependent areas of draining lymph nodes was first recognized at 3 days pi and reached a maximum between 14 and 21 days pi. Lymphoproliferation within B-cell-dependent areas was less extensive and of shorter duration. Comparable, but diminished, changes were seen in contralateral lymph nodes and spleen. Lymphoid cell depletion was observed in T-dependent areas of lymphoid organs by 56 days pi. Local inflammatory reactions to psc, at the site of injection, were intense, involving neutrophils, eosinophils, macrophages and mast cells. Viable psc were present until at least 6 weeks pi. The central role of the T-lymphocyte in recognition of, and response, to E. granulosus psc is discussed.

Animals↗