Biomedical subjects

H Perlmann

Publications and source records attributed to H Perlmann.

At least 37 records · Page 2Linked to original sources

PubMed1995

Asymptomatic malaria parasitaemia and seroreactivities to Plasmodium falciparum antigens in blood donors from Ibadan, south-western Nigeria.

Malaria parasite rates, parasite densities and seroreactivities to two Plasmodium falciparum antigens (Pf155/RESA and circumsporozoite protein) were investigated in a random sample of 416 blood donors attending the Blood Transfusion Unit of the University College Hospital in Ibadan, south-western Nigeria: 224 in October-November 1991 and 192 in March 1992. The incidence of malaria parasitaeia observed in 1991 was significantly higher than that seen in 1992 (41% v. 19%; P < 0.001). In contrast, the geometric mean parasite density in 1992 was significantly higher than in 1991 (440 v. 191) parasites/microliters blood; P < 0.001). Although parasite rates were highest in the group aged 25-31 years in both surveys, there was no apparent correlation between age of donor and parasite density in either survey. Parasite density was significantly higher in AA- than in AS-haemoglobin individuals only in the 1992 survey (P = 0.050). All the blood donors were seropositive for antibodies to crude parasite antigens, indicating heavy exposure to malaria infection. Seroreactivity to Pf155/RESA was similar in the two surveys but that to circumsporozoite protein (CSP) was significantly higher in 1991 than in 1992 (P < 0.001). The seropositivity rates were generally similar to malaria-positive and -negative blood donors. In 1992, however, all the blood donors with high reactivities to Pf155/RESA, as detected by erythrocyte membrane immunofluorscence, were negative for malaria parasites, indicating that this group was relatively protected against malaria parasitaemia. It is recommended that blood samples from prospective blood donors be examined for malaria parasites and that recipients of malaria-infected blood samples be given a curative regimen of antimalarials.

Adolescent↗

PubMed1995

Antibodies to Pf155/RESA and circumsporozoite protein of Plasmodium falciparum in paired maternal-cord sera from Nigeria.

Paired maternal-cord serum samples were analysed for antibodies to the Pf155/RESA and circumsporozoite protein (CSP) antigens of Plasmodium falciparum. Malaria parasites were found in 2.6% (3/117) of cord blood and 22.4% (26/116) of maternal samples. Immunofluorescence assays detected P. falciparum-specific IgG antibodies in all paired samples while P. falciparum-specific IgM was detected in 5.8% (7/121) of cord samples. The positivity rates for antibodies to Pf155/RESA and (NANP)6 but not (EENV)6, a C-terminal repeat sequence of Pf155/RESA, were significantly higher in maternal as compared with cord samples. Seropositivity rates to Pf155/RESA and (EENV)6 were not related to maternal parity group while positivity rates to the (NANP)6 peptide were higher in primiparae and multiparae of > or = 4 parity. These data confirm the transplacental transfer of P. falciparum-specific antibodies and the higher incidence of malaria parasitaemia in primiparae. The presence of P. falciparum-specific IgM in some cord samples suggests intrauterine sensitization of the foetus to malarial antigens.

Adolescent↗

PubMed1995

Surface display compared to periplasmic expression of a malarial antigen in Salmonella typhimurium and its implications for immunogenicity.

Two different expression systems were investigated for the production of an 80 amino acid polypeptide, M3, from the C-terminus of the Plasmodium falciparum blood stage antigen Pf155/RESA in an attenuated Salmonella typhimurium vaccine strain. Upon expression, the malarial polypeptide was targeted either to the periplasm as a soluble fusion protein containing two IgG-binding domains (ZZ) from the staphylococcal protein A or, to the bacterial surface as an insert within a chimeric outer membrane protein A (OmpA) derived from Escherichia coli and Shigella dysenteriae. Both the ZZM3 and the OmpAM3 proteins were stably expressed in the periplasm or on the surface of Salmonella, respectively. The ZZ expression system yielded 10-100 times more malarial immunogen than did the OmpA system. Live recombinant Salmonella expressing ZZM3 or OmpAM3 were used to immunize mice intraperitoneally. Both the ZZM3 and OmpAM3 genes persisted for up to three weeks in bacteria isolated from different lymphoid organs. Bacteria expressing ZZM3 induced antibodies to M3, ZZ and to the Pf155/RESA antigen whereas, bacteria producing OmpAM3 induced similar levels of antibodies reactive with M3 but not with Pf155/RESA. Both recombinants induced a memory response of antibodies reactive with both M3 and Pf155/RESA. The high levels of M3 produced by the ZZ expression system make it suitable for the expression of heterologous antigens in Salmonella. Nevertheless, in spite of the quantitative difference in M3 expression, the ZZ and OmpA constructs elicited comparable immune responses to M3.

Animals↗

PubMed1995

Cellular mechanisms in the immune response to malaria in Plasmodium vinckei-infected mice.

Infection of mice with the malaria parasite Plasmodium vinckei vinckei is 100% lethal. However, after two infections followed by drug cure, BALB/c mice develop a solid immunity which is antibody independent but mediated by CD4+ T cells. To elucidate the mechanisms of this immunity, spleen cells from immune mice were challenged in vitro with lysates of P. vinckei-infected or uninfected erythrocytes. The parasite antigen induced proliferation of T cells from immune mice but not from nonimmune mice. When gamma interferon production by cells from immune mice was assayed at the single-cell level, 1 to 3 cells per 1,000 cells were found to release this cytokine when exposed to antigen. In contrast, the numbers of interleukin 4 (IL-4)-producing cells from both immune and control mice were < or = 4 per 10(6) cells, regardless of antigen exposure. Investigation in a bioassay showed that P. vinckei antigen induced the release of IL-4 from spleen cells of immune mice but not from those of control mice. Nevertheless, that IL-4 is of minor significance in this system is also suggested by the absence of elevation of immunoglobulin E levels in blood samples from these mice, in contrast to what is seen with P. chabaudi infection, in which IL-4-producing Th2 cells are of major importance for immunity during later phases of infection. Taken together, the present results indicate that immunity to P. vinckei is a Th1 response, with gamma interferon being an important protective factor. Whether or not the Th1 response, through overproduction of tumor necrosis factor alpha, is also responsible for pathology and death in this infection remains to be clarified.

Animals↗

PubMed1994

IgE elevation and IgE anti-malarial antibodies in Plasmodium falciparum malaria: association of high IgE levels with cerebral malaria.

In the course of studying immunoregulation in human Plasmodium falciparum malaria we have investigated IgE levels and IgE anti-plasmodial antibodies in children and adults from areas of high malaria endemicity in both Africa and Asia. On average, 85% of all donors had significantly elevated levels of total IgE. A fraction of the IgE had anti-plasmodial activity as revealed by ELISA with lysates of infected erythrocytes as antigen. Using synthetic peptides representing antigenic regions of two major plasmodial blood stage antigens, IgE antibody concentrations ranged from 5 to 15 ng/ml serum for each of the peptides. On average, the concentrations of the corresponding IgG antibodies were x 500-1000 higher. Immunoblotting of parasite lysates showed that most donors had IgE antibodies against one or several of a restricted number of plasmodial polypeptides, with antibodies against an antigen of mol.wt 45 kD already being present in all donors at an early age. Donors having IgE antibodies to particular antigens also frequently had corresponding IgG4 antibodies, reflecting underlying IL-4-dependent cellular mechanisms controlling formation of these isotypes. As infection with other parasites such as helminths is known to induce IgE elevation, the results do not prove that plasmodial infections were the primary cause of IgE induction. However, the importance of plasmodial infection for IgE elevation was supported by the finding of significantly higher levels of IgE, but not of IgG, in children with cerebral malaria compared with patients with uncomplicated disease.

Adolescent↗

PubMed1994

A longitudinal study of seroreactivities to a major blood stage antigen (Pf155/RESA) of the malaria parasite Plasmodium falciparum in an endemic area of Thailand.

We have performed a longitudinal study of the formation of antibodies to Plasmodium falciparum in an area of Thailand where malaria transmission is moderate and seasonal. The study population comprised 118 subjects living in two villages 230 km southeast of Bangkok. All subjects included in this study were seropositive for antibodies to the blood stages of P. falciparum but only approximately 80% had antibodies to the blood stage antigen Pf155/RESA when assayed by erythrocyte membrane immunofluorescence (EMIF) or peptide ELISA during the period of maximal transmission. The reduced capacity to form these antibodies in a significant fraction of subjects living under comparable environmental and socio-economic conditions may reflect a genetic but antigen specific non-responsiveness. Both seropositivity and mean antibody titers to Pf155/RESA and its B-cell epitopes tended to be slightly higher during the rainy than during the dry season but the seasonal variations were slight and statistically not significant. Parasite rates were significantly higher in the rainy than in the dry season in both the EMIF positive and the EMIF negative groups. However, during the rainy season, the parasite rates in subjects with no or low titered antibodies to Pf155/RESA were significantly higher than those in subjects having such antibodies. The results suggest that antibodies to Pf155/RESA and some of its defined epitopes may be of importance for controlling parasitemias.

Adolescent↗

PubMed1994

Characterization of regulatory T-cell responses in humans induced by the P. Falciparum blood stage antigen Pf155/RESA.

T-cells have a major role both as helper cells for efficient antibody production and as inducers and effector cells in antibody-independent malaria immunity. Thus, antigens to be included into a subunit vaccine must contain T-cell epitopes to become effectively immunogenic. The P. falciparum blood stage vaccine antigen Pf155/RESA has been shown to contain T-helper epitopes inducing T-dependent anti-malarial antibodies in vitro. We have also shown that synthetic peptides representing sequences from the amino-acid repeat regions of Pf155/RESA stimulate T-cells from P. falciparum primed donors to proliferate, to release IFN-gamma and/or IL-4. In individual donors there was no correlation between these different activities. Rather, they were frequently negatively associated. However, IL-4 secretion could be induced in T-cells from donors who had elevated concentrations of serum antibodies to the same peptide as used for T-cell activation. Taken together the results support the occurrence of malaria-specific CD4+ T-cell subsets (e.g. TH1 and TH2) in humans similar to what has been found in mice and suggest the involvement of TH2-type helper cells in the induction of some important P. falciparum specific antibodies. CD4+ T-cells recognize the antigen in the context of MHC class II molecules. However, in human outbred populations no consistent MHC restrictions of anti-Pf155/RESA immune responses could be demonstrated. This is not surprising in view of the extensive polymorphism of the HLA system. Neither were there any obvious MHC class II restrictions seen when antibody- and t-cell responses were measured in naturally primed monozygotic twins.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1993

Enzyme-linked staining method for light microscopic detection of antibodies to parasite antigens on the membrane of Plasmodium falciparum infected erythrocytes.

Indirect erythrocyte membrane immunofluorescence (EMIF), a standard method for detection of antibodies to the P. falciparum blood stage vaccine candidate antigen Pf155/RESA, has been adapted to light microscopy by enzyme-linked immunostaining of the erythrocyte membrane, using alkaline phosphatase and chromogenic substrate. This method gives a dark blue staining of the membranes of ring infected erythrocytes. Results obtained with 70 African sera in EMIF and in enzyme immunostaining correlated well although the enzyme based method sometimes resulted in higher antibody titers and appeared to be slightly more sensitive. Similar results were obtained when comparing immunofluorescence with enzyme immunostaining for detection of antibodies to intraerythrocytic parasite antigens. The enzyme linked immunostaining described is simple and fast and does not require expensive equipment and should, thus, be well suited for use in laboratories with limited resources or under field conditions.

Animals↗

PubMed1992

Seroepidemiologic studies of humoral immune response to the Plasmodium falciparum antigens in Thailand.

We have investigated seroreactivity against Plasmodium falciparum crude parasite antigens, the P. falciparum ring-infected erythrocyte surface antigen (Pf155/RESA), as well as against two synthetic peptides (EENV)6 and (EENVEHDA)3 that represent important epitopes of Pf155/RESA. The study population consisted of 421 children and adult Thais living in an area with moderate malaria transmission. We related these serologic findings to some important epidemiologic baseline data collected in the study area. The parasite rate in study subjects was 18.76%. Sixty-two percent were seropositive to crude P. falciparum antigens, 30.3% to the Pf155/RESA antigen, 23.05% to (EENV)6, and 20.17% to (EENVEHDA)3. Antibody responses to crude P. falciparum antigens and to Pf155/RESA were age dependent and increased with exposure. There was evidence that Pf155/RESA antibodies might play a role in protective immunity in this population. Since Pf155/RESA is a potential vaccine candidate antigen, the information obtained from these field studies will provide some seroepidemiologic baseline data for subsequent vaccine trials.

Adolescent↗

PubMed1991

Studies on Pf155/RESA and other soluble antigens from in vitro cultured Plasmodium falciparum.

Spent culture medium from in vitro cultures of Plasmodium falciparum was used as the source for immunoadsorbent enrichment of soluble parasite antigens. IgG obtained from P. falciparum-hyperimmune Liberian serum was used as the ligand in the immunoadsorbent. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the immunoadsorbent isolated material revealed the presence of at least 15 antigenic and parasite-derived polypeptides. Immunoblotting after SDS-PAGE showed greater than 20 antigenic polypeptides in the molecular weight range of 15-250 kDa. Several of these were heat-stable (100 degrees C for 5 min), and six of them were detected even after heating for 60 min. Among the latter antigens was Pf155/RESA, a merozoite antigen deposited in the erythrocyte membrane at invasion. Pf155/RESA can be detected using a modified erythrocyte membrane immunofluorescence (EMIF) assay. Inhibition of EMIF with heated parasite material showed that the antigenic activity was intact after heating for up to 30 min. The immunofluorescence-inhibitory activity was separated into two fractions, one containing Pf155/RESA and one containing polypeptides with molecular weights of 135 and 120 kDa. All three of these antigenic polypeptides bound selectively, albeit nonspecifically, to aminoethyl-BioGel resins.

Animals↗

PubMed1991

Failure to detect MHC class II associations of the human immune response induced by repeated malaria infections to the Plasmodium falciparum antigen Pf155/RESA.

Available evidence suggests that human T and B cell responses to a major Plasmodium falciparum malaria antigen (Pf155/RESA) in individuals primed by repeated infections are genetically regulated. In the present study we have attempted to establish whether these regulations reflect genetic restrictions imposed on the immune response by class II molecules of the donor's MHC system. T cell activation (proliferation and IFN-gamma release in vitro) and antibody activity (ELISA) were assayed with synthetic peptides corresponding to major Pf155/RESA epitopes. To associate T cell and antibody responses with the donors' MHC class II genotypes, leukocytes from 145 donors living in holo- or hyperendemic regions of Africa (Liberia, Gambia, Madagascar) were used for genomic HLA class II typing of their DRB-DQA and DQB genes by means of restriction fragment length analysis (RFLP). No associations between T cell responses and HLA-DR or -DQ alleles or DRB-DQA-DQB haplotypes were seen among the West Africans even when the donors were divided into high, medium or low responders. This was also true for a small group of HLA class II identical Malagasy donors including three pairs of twins. However, while the T cell responses between the twin pairs varied, those within the pairs were similar. Very similar findings were made with antibodies binding to Pf155/RESA peptides. Our data imply that the impact of MHC class II gene products on specific immune responses to Pf155/RESA epitopes is weak and hard to demonstrate in outbred human populations naturally primed by infection. This may be due to genetic regulations by other, non-HLA class II coded factors superimposed on possible HLA class II restrictions.

Adult↗

PubMed1991

Longitudinal study of seroreactivities to Pf155/RESA and its repetitive sequences in small children from a holoendemic area of Liberia.

The seroreactivities to Pf155/RESA antigen and to three oligopeptides (EENV)2, EENVEHDA and K(DDEHVEEPTVA)2, which constitute repeat subunits of the RESA molecule, were investigated between 1980 and 1986 in two cohorts of children (n = 114) with and without monthly chemosuppression (pulsed reduction of parasite load) against malaria from six months to five years of age during development of protective immunity. Serum samples were collected first at half-yearly and then yearly intervals. Positive immunofluorescence against Pf155/RESA (EMIF) was only found in 24% of the samples. The children with chemosuppression were more often seropositive (30%) than the non prophylactic children (17%). This was in contrast to the seroreactivity against crude parasitic antigens which was highest in the non prophylactic children. In these children, there was a general decrease of EMIF titres around two years of age. Immunosuppression by chronic parasitaemia may be suggested as a reason for this. ELISA seroreactivity was found against one, two or three oligopeptides in all children with high EMIF titres (greater than 250) although (EENV)2 appeared to best correlate (92%) with the EMIF seropositivity. While EMIF seropositivity only showed partial correlation to immunoprotection against patent parasitaemia in the non prophylactic children, the individual profiles of the seroreactivities to the different specific epitopes of the Pf155/RESA molecule and their relevance with regards to protective immunity to malaria need to be investigated further.

Amino Acid Sequence↗

PubMed1991

Passive immunization of Aotus monkeys with human antibodies to the Plasmodium falciparum antigen Pf155/RESA.

In order to assess the protective effects of anti-Pf155/RESA antibodies of different specificities in vivo, passive immunizations of Aotus monkeys were performed. Antibodies reactive with the Pf155/RESA repeat sequences (EENV)2 and EENVEHDA were isolated from the immunoglobulin G (IgG) fraction of a pool of plasmas from Liberia by affinity chromatography on synthetic peptides. The two fractions of antibodies differed in specificity but displayed similar capacities to inhibit merozoite invasion in Plasmodium falciparum in vitro cultures. Four groups of monkeys (named groups I to IV) were injected with (i) 160 mg of total control IgG, (ii) 2 mg of IgG affinity purified on (EENV)2, (iii) 2 mg of IgG affinity purified on EENVEHDA, and (iv) 160 mg of total immune IgG, respectively. The monkeys were then challenged with P. falciparum-infected erythrocytes, and the levels of parasitemia and hematocrits as well as other serological parameters were determined daily. Although all groups developed parasitemia, groups II and IV tended to show lower mean daily levels. Three monkeys of group II and two monkeys (each) of groups III and IV self cured the infections, but so did one monkey from the group treated with control IgG (group I). The serum levels of transfused antibodies were low at the peak of parasitemia, suggesting that clearance of parasites was mediated by immune responses mounted by the monkeys. The results indicate that antibodies to epitopes formed by repeats of Pf155/RESA may depress P. falciparum parasitemias and thus that immunogens based on such repeats should be suitable components in a subunit vaccine against asexual stages of P. falciparum.

Adult↗

PubMed1991

A longitudinal study of seroreactivities to Plasmodium falciparum antigens in infants and children living in a holoendemic area of Liberia.

Investigators studied 348 children age 0-10 years, living in a holoendemic area of Liberia, for parasitological, serological and clinical parameters. The age-specific parasite rate increased towards the 7-10 year-old age group in which it was 86.8%. The geometrical mean parasite density decreased from the 3-4 year-old age group, in which fewer episodes of clinical malaria were observed. Antibodies to crude Plasmodium falciparum parasite antigens were detected in all children. The (EENV)6 seropositive rate was a maximum of 67.9% in the 3-11 month-old age group. It declined to a minimum of 31.7% in the 5-6 years age group after which it increased slowly in the 7-10 years age group. Antibodies to the synthetic peptide (NANP)6 showed a steady seropositive rate after the age of 3 months, between 30.0% and 39.3% in all the age groups up to 10 years. No statistically significant correlation was found between seropositivity to (EENV)6 and malarial parasitemia. In contrast, a statistically significant positive correlation was found between seropositivity to (NANP)6 and parasite rates. The antibody response for the individual child was transient to both Pf155/RESA, measured by immunofluorescence, and to (EENV)6 and (NANP)6, measured by ELISA, especially in the younger age groups of this study population. Parasitological and clinical immunity developed before a stable antibody response to these defined malaria antigens was established. These antibodies may still contribute to the immune protection against malaria, but they were not reliable parameters for protective immunity in the population we studied.

Amino Acid Sequence↗

PubMed1991

Plasmodium falciparum reinfection in children from a holoendemic area in relation to seroreactivities against oligopeptides from different malaria antigens.

The rate and densities of Plasmodium falciparum reinfections were investigated in children five to 14 years old from one village in Tanzania with a high transmission rate. Initial parasitemias were eradicated by a curative treatment with quinine, a drug with a short elimination half-life, to minimize the effects of residual drug on reinfection. The seroreactivities to seven oligopeptides, representing T and B cell epitopes from the ring erythrocyte surface antigen (Pf155/RESA), the clustered arginine-rich protein antigen (CARP), and the circumsporozoite (CS) proteins were determined in the children at the start of the study and after 28 days. All children were reinfected within 42 days (mean 27 days). The geometric mean maximum parasite density at reinfection was 308 parasites per microliter (range 4-13, 920). The antipeptide antibody levels showed high interindividual variation, with a significant mean decrease (16%) between days 0 and 28 for the blood stage antigens, but not for the (NANP)6 peptide from the CS protein. This suggests that the absence of blood stage antigenic stimulation had already influenced the antibody levels within this short period of time. The mean reinfection day was not influenced by the levels of antibodies to any of the peptides. However, the children with higher antibody levels to (EENVEHDA)2(EENV)2 developed significantly lower parasitemias than those with lower antibody levels (P less than 0.05). This suggests that this subunit of the Pf155/RESA molecule is an important B cell epitope for protective antiparasitic immunity.

Adolescent↗

PubMed1990

Characterization of regulatory T cell responses to defined immunodominant T cell epitopes of the Plasmodium falciparum antigen Pf155/RESA.

Several immunodominant B and T cell epitopes of the P. falciparum blood stage antigen Pf155/RESA, a vaccine candidate, are located in the central (5') and C-terminal (3') invariant repeat regions of the molecule. Here we have attempted to functionally analyze human T cell responses to some of the T cell epitopes. For this purpose short synthetic peptides corresponding to these epitopes were used to study the induction of in vitro expression of IL-4 mRNA, IFN-gamma secretion, proliferation and B cell help for antibody production. In individual malaria immune donors these different T cell activities were not correlated. The findings emphasize the importance of examining multiple parameters of T cell activation when estimating the total proportion of individuals responding to a defined antigen. IL-4 mRNA was expressed in activated T cells of donors who had elevated serum concentrations of antibodies to the peptide used for T cell activation. These results suggest the involvement of IL-4 producing T helper cells in the induction of Pf155/RESA specific antibody production in individuals in which immunity has been induced by natural infection. Taken together, these findings also suggest that functionally distinct CD4+ T cells occur in humans similarly to what has been described in mice. In further experiments, we have also attempted to establish MHC class II restriction of the immune response to these epitopes at the level of the donor populations. When studying monozygotic twins, antibody responses to Pf155/RESA derived peptides and some of the T cell responses could be paired within the twin pairs, indicating a genetic regulation of their B cell responses. Whether or not this regulation reflects MHC class II restriction, or other factors needs to be elucidated.

Amino Acid Sequence↗

PubMed1990

Production by activated human T cells of interleukin 4 but not interferon-gamma is associated with elevated levels of serum antibodies to activating malaria antigens.

T cells play a crucial role in antibody-mediated and antibody-independent immunity against Plasmodium falciparum malaria. Therefore, a vaccine immunogen should include parasite-derived B- and T-cell epitopes capable of giving rise to protective responses in both systems. The P. falciparum antigen Pf155/ring-infected erythrocyte surface antigen (RESA), a vaccine candidate, contains immunodominant T- and B-cell epitopes located in the central (5') and C-terminal (3') invariant repeat regions of the molecule. To relate Pf155/RESA-peptide-specific responses of T cells to function, T cells from P. falciparum immune donors were activated with peptides corresponding to these immunodominant regions. Activation was measured as induction of interferon-gamma secretion, T-cell proliferation (DNA synthesis), or transcription and translation of interleukin 4 (IL-4) mRNA. Peptides from both regions were shown to induce interferon-gamma, IL-4, proliferation, or any combination. In individual donors, there was no correlation between these different activities. Rather, they were negatively correlated, demonstrating the importance of examining multiple parameters of T-cell activation when estimating the proportion of individuals responding to a given epitope. However, IL-4 mRNA and intracellular IL-4 could be induced in T cells of donors who had elevated concentrations of serum antibodies to the same peptide that was used for T-cell activation. These results suggest that a causal relationship exists between the activation of IL-4-producing T-cell subsets and production of the anti-Pf155/RESA-specific antibodies in individuals in which immunity has been induced by natural infection. This finding has implications that should be considered for the selection of immunogens to be included in a future P. falciparum subunit vaccine and for vaccine development in general.

Adult↗

PubMed1990

Consecutive determinations of seroreactivities to Pf 155/RESA antigen and to its different repetitive sequences in adult men from a holoendemic area of Liberia.

Sera from 32 adult men residing in a malaria holoendemic area of Liberia were investigated for seroreactivities to different asexual blood-stage malaria antigens on five consecutive occasions from 1984 to 1986. The seroreactivities to crude parasitic antigens and to Pf 155/RESA (EMIF) were determined by immunofluorescence and to repetitive sequences of Pf 155/RESA by enzyme-linked immunosorbent assay (ELISA). All sera were highly reactive against the crude parasitic antigens with reciprocal titres varying from 5000 to 100,000. The EMIF titres showed a wider variation from negative (less than 10) to 25,000, and when the same individuals were re-examined on subsequent surveys similar EMIF titres were found. The ELISA seroreactivities to three different repetitive sequences of Pf 155/RESA also showed different individual profiles which were rather consistent on consecutive surveys. High EMIF titres appeared to be correlated mainly to one of the peptide sequences, namely (EENV)2. The consistent individual profiles of the seroreactivities to Pf 155 and its repetitive sequences suggest genetic restriction of the humoral immune response. Although no significant correlation was found between EMIF titres and parasitic densities in the adult hyperimmune men the specific peptides, however, offer new possibilities of further investigating protective capacities of different immune responses to specific epitopes of the malaria parasite.

Adolescent↗