Sterile protection of monkeys against malaria after administration of interleukin-12.

An estimated 300-500 million new infections and 1.5-2.7 million deaths attributed to malaria occur annually in the developing world, and every year tens of millions of travelers from countries where malaria is not transmitted visit countries with malaria. Because the parasites that cause malaria have developed resistance to many antimalarial drugs, new methods for prevention are required. Intraperitoneal injection into mice of one dose of 150 ng (approximately 7.5 micrograms per kg body weight) recombinant mouse interleukin-12 (rmIL-12) 2 days before challenge with Plasmodium yoelii sporozoites protects 100% of mice against malaria. We report that one subcutaneous injection of 10 micrograms/kg recombinant human IL-12 (rhIL-12) 2 days before challenge with P. cynomolgi sporozoites protected seven of seven rhesus monkeys. Protection was associated with marked increases in plasma levels of interferon-gamma (IFN-gamma), and relative increases of lymphoid cell messenger RNA coding for IFN-gamma and several other cytokines. We speculate that rIL-12 protects monkeys through IFN-gamma-dependent elimination of P. cynomolgi-infected hepatocytes. This first report of rIL-12-induced protection of primates against an infectious agent supports assessment of rhIL-12 for immunoprophylaxis of human malaria.

Dipetalonema viteae (Nematoda: Filarioidea): culture of third-stage larvae to young adults in vitro.

Infective third-stage larvae of Dipetalonema viteae (Nematoda: Filarioidea) were cultured to young adults in a cell-free culture system. Third-stage larvae from the tick vector grew, developed, and molted twice in a medium containing NCTC 135 and Iscove's modified Dulbecco's medium supplemented with fetal bovine serum under a gas phase of 95 percent nitrogen and 5 percent carbon dioxide. The availability of such a culture system for filariids should facilitate studies of their immunology, biochemistry, and sensitivity to drugs.

Inducing protective immune responses against the sporozoite and liver stages of Plasmodium.

Work on vaccines against the pre-erythrocytic stages of the Plasmodium life cycle is based on the observation that immunization with irradiated sporozoites (IRR SPZ) is protective. Antibodies against several SPZ surface proteins can prevent SPZ from effectively invading hepatocytes; antibodies and cytolytic-T lymphocytes directed against at least 3 parasite proteins expressed in infected hepatocytes can kill infected hepatocytes; and cytokines can activate infected hepatocytes to kill the intracellular parasite. Work is in progress to identify additional pre-erythrocytic parasite targets and to develop methods for optimally inducing protective immunity against SPZ and infected hepatocytes. The goal is to construct a vaccine that protects by inducing antibody and cellular immune responses against multiple parasite proteins.

Drug resistance in leishmaniasis: its implication in systemic chemotherapy of cutaneous and mucocutaneous disease.

We report that in vitro sensitivity to pentavalent antimony (Sb5) of 35 Leishmania isolates as determined by the semiautomated microdilution technique (SAMT) showed an 89% and 86% correlation with clinical outcome after Pentostam and Glucantime treatment, respectively. These results suggest that in over 85% of the cases, the clinical outcome of treatment (cure or failure) could have been predicted by using the SAMT technique. Furthermore, the results clearly indicate that drug resistance is a problem, and that at least in some instances, failure to respond to treatment is due to the parasite as well as patient factors. Strains from Sb5-treated patients with American cutaneous and mucocutaneous disease who fail at least one complete course of Pentostam are as highly nonresponsive to this drug as laboratory-proven drug-resistant Leishmania strains. It was determined that some Leishmania isolates are innately less susceptible to Sb5 than others, and that moderate resistance to Sb5 exists in nature. A 10- and 17-fold increase was detected in the 50% inhibitory concentration (IC50) of Sb5 for L. mexicana and L. braziliensis isolates after subcurative treatment of the patients, when compared with the mean IC50 of seven and six isolates from the same endemic areas in Guatemala and Peru, respectively. Thus, we have correlated subcurative treatment to a decrease in drug sensitivity in at least these two cases. Collectively, these results indicate that under Sb5 pressure from undermedication, the parasites inherently most drug resistant are favored. The degree of resistance of a strain to antimony in association with host-specific factors will determine whether the clinical response to treatment with this drug is a total cure or a partial response followed by relapse(s), and possibly secondary unresponsiveness resulting in total resistance to antimony. It is evident from our in vitro test data that the SAMT is an extremely powerful and highly accurate technique for the prediction and determination of drug sensitivity of leishmanial isolates, as well as a means to screen for anti-leishmanial agents.

In vitro cultivation of third stage larvae of Wuchereria bancrofti to the fourth stage.

Third stage larvae of Wuchereria bancrofti obtained from laboratory-infected mosquitoes grew and molted to the fourth stage in vitro. The culture medium which supported the best growth and development consisted of a 1:1 mixture (v/v) of two commercially available cell culture media, NCTC 135 and Iscove's modified Dulbecco's medium supplemented with 10% human serum or plasma and an antibacterial/antimycotic mixture. Cultures were incubated at 37 degrees C in an atmosphere of either 5% or 8% CO2 in air. After 35 days of culture, 65% to 100% of the larvae were fourth stage. They were motile and in excellent morphological condition with development of the reproductive system in males and females. This culture system will provide an important tool for biochemical and immunological studies.

Detection and enumeration of Leishmania in sand flies using agar-based media.

An agar plating technique was used to determine the number of amastigotes ingested by Lutzomyia longipalpis fed on papules on Mesocricetus auratus caused by Leishmania mexicana amazonensis and on lesions on Mystromys albicaudatus caused by Leishmania braziliensis panamensis. The technique involved homogenizing sand flies after bloodfeeding on the infected animals and spreading the homogenate over the surface of agar plates. A great variation in the number of amastigotes ingested by individual sand flies was demonstrated. Not all amastigotes ingested developed anterior stomodeal infections.

Antibody response to the circumsporozoite protein of Plasmodium vivax in naturally infected humans.

The circumsporozoite (CS) protein of Plasmodium vivax consists of a central repeat region flanked by highly conserved non-repeat regions. Serum samples from 33 individuals with naturally acquired infections of P. vivax were tested for antibodies to four antigens representing the vivax CS protein. Three recombinant proteins containing different overlapping sequences in the non-repeat regions and either the entire central repeat region (vivax-1 and vivax-2) or two of the repeat sequences (vivax-3) were used as antigens in an enzyme-linked immunosorbent assay (ELISA). Antibodies to two other proteins, one (NS1(81)V20) containing the entire predominant repeat region (GDRAA/DGQPA) and the other (Pvk247) containing the variant repeat sequence (ANGAGNQPG) that was recently reported from Thailand were also measured by ELISA. Immunoglobulin G antibodies to the antigen representing the predominant repeat were present in 15% of the patients on the first day of treatment (day 0) and in 24% of the patients two weeks later (post-treatment). Six and 12% of the patients had IgG antibodies to the antigen containing the variant repeat on day 0 and post-treatment, respectively. A larger proportion of the sera had antibodies to the three antigens containing the non-repeat sequences; on the first day of treatment and two weeks later, 79 and 97% of the patients, respectively, had antibodies to vivax-1, vivax-2, and vivax-3. In this sample of Peruvians naturally infected with P. vivax, the most prevalent antibody responses were targeted to epitopes in the non-repeat region of the CS protein rather than to epitopes in the repeat region.(ABSTRACT TRUNCATED AT 250 WORDS)

Leishmania (Viannia) lainsoni: first isolation in Peru.

Surveys were conducted from 1986 through 1992 to define the etiology and geographic distribution of human leishmaniasis in Peru. Lesion aspirates and skin biopsies were obtained from clinically diagnosed cases of leishmaniasis and tested for promastigotes by standard culture techniques. The isozyme profile of the isolates was determined by the cellulose acetate electrophoresis technique. Data indicated that the isozyme profiles for Leishmania isolates from six patients were similar to that of reference strains of L. lainsoni. These results are the first reported evidence of L. lainsoni and the first association of this parasite with human cases of cutaneous leishmaniasis in Peru.

Prevalence of antibody to the variant repeat of the circumsporozoite protein of Plasmodium vivax in Peru.

Individuals living in a malaria-endemic area in northern Peru were found to have antibodies to the variant repeat sequence of the circumsporozoite (CS) protein of Plasmodium vivax. The presence of IgG antibody to the predominant repeat sequence GDRAA/DGPA represented by the recombinant protein NS1(81) V20 (V20), and the variant repeat sequence ANGAGNQPG contained in the synthetic peptide Pvk247, was determined by enzyme-linked immunosorbent assay. IgG antibodies to the repeats were present in 78 (26%) of 298 serum samples; 56% of the positive serum samples had antibodies to V20 and 60% had antibodies to Pvk247. These findings stress the importance of considering the variant epitope in designing a vaccine based on the repeat region of the vivax CS protein. In a malaria-endemic area such as the one in this study, in which exposure to the variant repeat epitope may be as frequent as exposure to the predominant repeat, a vaccine based solely on the predominant repeat epitope may be ineffective against the variant form.

Efficacy of 28-day and 40-day regimens of sodium stibogluconate (Pentostam) in the treatment of mucosal leishmaniasis.

The efficacy and toxicity of two regimens of antimony, 28 and 40 days of 20 mg of antimony/kg/day, were compared in the treatment of culture-positive mucosal leishmaniasis involving more than one anatomic site. Forty consecutive eligible Peruvians with infiltrative or ulcerative mucosal disease of the lips, nose, palate-uvula-pharynx, or larynx-epiglottis were randomized to receive either 28 days (P28) or 40 days (P40) of sodium stibogluconate (Pentostam). Treatment was prematurely terminated due to thrombocytopenia in three patients and two patients did not complete six months of follow-up. At one month post-treatment, 13% (2 of 16) of the P28 patients and 16% (3 of 19) of the P40 patients no longer had infiltrates or ulcers and were initially considered cured. During a further 11 months of follow-up, infiltrated lesions healed in eight more P28 patients and in 10 more P40 patients. The cure rate after 12 months of follow-up was therefore 63% for both groups (10 of 16 in the P28 group and 12 of 19 in the P40 group). The total of 13 patients who had infiltrates or ulcers at the 9-12-month follow-up were considered failures. All seven patients (three in the P28 group and four in the P40 group) whose lesions were culture-positive for Leishmania at some point in the 12 months after treatment, and who were thereby parasitologic failures, were also clinical failures.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffuse cutaneous leishmaniasis acquired in Peru.

A case of diffuse cutaneous leishmaniasis (DCL) acquired in Peru is described. The causative agent was Leishmania mexicana amazonensis as determined by isoenzyme analysis and species-specific monoclonal antibody binding characteristics. Histological examination of biopsy material showed a large number of intracellular and extracellular amastigotes and few lymphocytes. Treatment with meglumine antimoniate (Glucantime) administered iv at a dosage of 20 mg antimony/kg body weight/day for 60 days resulted in visible improvement of the lesions, but not in clinical or parasitological cure.

Serologic and genetic characterization of Plasmodium vivax from whole blood-impregnated filter paper discs.

The presence in the New World of a variant strain of Plasmodium vivax (VK247) containing a unique circumsporozoite (CS) repeat domain was determined by the detection of antibodies to the variant CS protein and by genetic analysis of the CS gene from field isolates. Whole blood specimens were collected on filter paper from patients infected with P. vivax in Mexico and Peru. Plasmodium vivax DNA was eluted from filter paper samples and the CS gene was amplified by the polymerase chain reaction (PCR) and analyzed for the presence of VK247 or VK210 DNA by oligoprobe hybridization. Sera eluted from a companion filter paper sample were screened for antibodies reactive with the predominant and variant repeat peptides by enzyme-linked immunosorbent assays (ELISA) and with sporozoites by the immunofluorescent antibody (IFA) test. All 24 patients were positive by PCR and oligoprobe hybridization for either VK210 (16 of 24), VK247 (3 of 24), or both (5 of 24). Mixed infections were common (5 of 7) in Peru, but were not observed in the Mexican isolates (0 of 17). All three VK247 infections from Mexico occurred in residents of the foothills above Tapachula (P = 0.02). Of patients with smear-positive P. vivax infection, 42% (10 of 24) had detectable antibodies eluted from dried blood dots that were reactive with the CS protein by IFA or ELISA. These findings establish the widespread distribution of the P. vivax variant CS protein in the New World and indicate that dried blood filter paper samples represent a valuable source of material for the serologic and molecular analysis of plasmodial infections.

Immune response of humans to the circumsporozoite protein of Plasmodium falciparum: limited T cell response to the immunodominant central repeat region.

Most adults in highly malarious areas have antibodies to the repeat region of the circumsporozoite protein of Plasmodium falciparum. To determine if a T cell epitope on the repeat region stimulated T cell help for this antibody, we used R32tet32, a recombinant construct derived from the repeat region of the circumsporozoite protein of P. falciparum, to stimulate in vitro mononuclear cells from residents of an area hyperendemic for malaria. Three groups differing in the length of time they had resided in a malarious area were studied. The percentage of individuals in each group who had positive antibody responses to R32tet32 increased with increased exposure to malaria. However, antibody positivity was not correlated with in vitro lymphocyte proliferation responses to the antigen. Lymphocytes from 79% of the individuals showing serum antibodies to R32tet32 failed to respond in a lymphocyte transformation assay, suggesting that T cell helper activity in these individuals was based upon the recognition of a T cell epitope not located within this peptide.

Geographic distribution and clinical description of leishmaniasis cases in Peru.

Studies were conducted from 1986 through 1993 to further define the geographic distribution and relative importance of different species of Leishmania as a cause of leishmaniasis in Peru. Patients with a clinical diagnosis of cutaneous and/or mucosal or diffuse cutaneous leishmaniasis were enrolled at the Naval Medical Research Institute Detachment (NAMRID) Laboratory in Lima, the Tropical Disease Clinic at San Marcos University Daniel A. Carrión, the Central Military Hospital, and a Ministry of Health hospital in Cusco, Peru. Clinical features, lesion aspirates, and biopsy tissue were obtained from each patient. All specimens were collected and assayed separately, including multiple specimens from some of the same patients for Leishmania parasites by inoculating aliquots of either aspirates or biopsy tissue suspensions onto Senekji's blood agar medium. Stocks of Leishmania isolates were used to prepare promastigotes to produce extracts for identifying the Leishmania species by the cellulose acetate electrophoresis enzyme technique. A total of 351 isolates of Leishmania were obtained from 350 patients who were infected primarily in the low and high jungle of at least 15 different Departments of Peru. Of the 351 isolates, 79% were identified as L. (V.) braziliensis, 7% as L. (V.) guyanensis, 10% as L. (V.) peruviana, 2% as L. (V.) lainsoni, and 1.7% as L. (L.) amazonensis. The clinical form of disease varied depending on the species of Leishmania, with L. (V.) braziliensis being associated most frequently with cutaneous, mucosal ulcers and mixed cutaneous and mucosal disease, and L. (V) peruviana, L. (V.) guyanensis, L. (V.) lainsoni with cutaneous lesions. Leishmania (L.) amazonensis was isolated from six patients, three with cutaneous lesions, one with mucosal lesions, and two with diffuse cutaneous lesions. Among all of the leishmaniasis cases, males were affected more frequently, and cases occurred among patients less than 10 to more than 51 years of age. These data further defined the geographic distribution and the relative frequency of Leishmania species associated with different clinical forms of leishmaniasis in Peru.

Plasmodium vivax VK247 and VK210 circumsporozoite proteins in Anopheles mosquitoes from Andoas, Peru.

Anopheles mosquitoes captured in Andoas, Peru, a Plasmodium vivax-endemic area in the Peruvian Amazon region, contained both VK210 and VK247 P. vivax circumsporozoite (CS) proteins. Approximately 0.9% of the 4,403 mosquitoes tested by enzyme-linked immunosorbent assay were positive; 28% and 72% of the positive mosquitoes contained VK210 and VK247 CS proteins, respectively. These findings correlate strongly with a recent report of the presence of antibodies in residents of this area that recognize the VK210 and VK247 repeats, clearly indicating that both P. vivax CS protein polymorphs are common in the region.

In vitro cultivation of Dipetalonema viteae third-stage larvae: evaluation of culture media, serum, and other supplements.

Third-stage larvae of Dipetalonema viteae obtained from the tick vector developed to the fourth stage in several cell-free culture systems. Survival and development of larvae in a number of commercially available cell culture media, supplemented with serum and other defined and undefined components, were compared. All cultures were gassed with 5% carbon dioxide in nitrogen. Best survival, growth and development were obtained in stationary cultures containing 1:1 (v/v) mixtures of NCTC 135, either RPMI 1640 or Iscove's Modified Dulbecco's Medium, and a supplement of 20% non-heat-inactivated fetal bovine serum. The importance of the medium composition and physical environment of the culture system, for the survival, growth and development of D. viteae was demonstrated.

In vitro cultivation of Dipetalonema viteae third-stage larvae: effect of the gas phase.

The effect of the gas phase on the in vitro growth and development of Dipetalonema viteae (Nematoda: Filarioidea) third-stage larvae obtained from the tick vector and 3 day infections of jirds was examined. Measurements of the oxygen (pO2) and carbon dioxide (pCO2) tensions and the pH in the medium were made for each gas phase. In cultures gassed with 5% carbon dioxide in nitrogen the pO2 was between 32 and 50 mm Hg, the pCO2 ranged from 25 to 40 mm Hg and the pH was between 7.2 and 7.4. This gas phase resulted in the best growth and development of third-stage larvae to the fourth-stage. Survival and development of larvae were decreased in cultures with oxygen tensions less than 20 mm Hg and greater than 50 mm Hg.

Evaluation of medium supplements for in vitro cultivation of Wuchereria bancrofti.

Third-stage larvae (L3) of Wuchereria bancrofti molt to the fourth stage in an in vitro culture medium composed of NCTC 135 and Iscove's modified Dulbecco's medium (1:1; v/v) supplemented with 10% human serum and a mixture of anti-bacterial and anti-mycotic agents. In the present investigation this culture medium was used to examine the effects of different concentrations of human serum, medium supplements, and serum replacements on larval growth, development, and molting. Several medium supplements and serum replacements were evaluated including hemin, Nutridoma, and a mixture of soybean lipids, bovine serum albumin, and transferrin. The supplements tested could not support larval growth and development in the absence of serum and they did not have an enhancing effect on larval growth and development in combination with human serum. A medium supplement of 30% human serum resulted in molting of 80-94% of L3s and optimum growth to the mid to late fourth stage. This culture system provides an excellent alternative to experimentally infected animals as a source of larvae undergoing the third molt and fourth-stage larvae for screening potential anti-filarial compounds and for immunologic and biochemical studies.

Antibody response of humans to the circumsporozoite protein of Plasmodium vivax.

We studied the interaction of sera from residents of an area in northern Peru where vivax malaria is endemic with four recombinant DNA-derived circumsporozoite (CS) proteins of Plasmodium vivax. The antigens used in the enzyme-linked immunosorbent assay included one Escherichia coli-produced and three Saccharomyces cerevisiae-produced recombinant proteins. Three of the proteins (NS1(81)V20, Vivax-1, and Vivax-2) contain the entire central repeat region of the P. vivax CS protein, and one protein (Vivax-3) contains only two repeat sequences. Vivax-1, Vivax-2, and Vivax-3 contain different lengths of sequences flanking the repeats. A higher percentage of the sera had antibodies to Vivax-2 and Vivax-3, the two proteins containing the longest nonrepeat sequences, than to NS1(81)V20 or Vivax-1. Children less than 5 years of age did not have immunoglobulin G antibodies to NS1(81)V20; however, they had antibodies to Vivax-1, Vivax-2, and Vivax-3. The finding that individuals living in a malaria-endemic area produce antibodies to peptides containing nonrepeat regions of the CS protein emphasizes the need to characterize the immune response to these regions in naturally exposed and experimentally immunized humans.