Recent applications of the Dot-ELISA in immunoparasitology.

The dot enzyme-linked immunosorbent assay (Dot-ELISA) is a highly versatile solid-phase immunoassay for antibody or antigen detection. The assay uses minute amounts of reagent dotted onto solid surfaces such as nitrocellulose and other paper membranes which avidly bind proteins. After incubation with antigen-specific antibody and enzyme-conjugated anti-antibody, the addition of a precipitable, chromogenic substrate causes the formation of a colored dot on the solid phase which is visually read. The Dot-ELISA has been used extensively in the detection of human and veterinary protozoan and metazoan parasitic diseases, including amebiasis, babesiosis, fascioliasis, cutaneous and visceral leishmaniasis, cysticercosis, echinococcosis, malaria, schistosomiasis, toxocariasis, toxoplasmosis, trichinosis, trypanosomiasis and even ixodid tick infestation. The technique is rapid, easy to perform and interpret, reagent conservative, cost effective and field portable. In addition, the Dot-ELISA may be configured to detect antibodies or parasite antigen in either microtiter plates for large-batch testing or with dipsticks for small numbers of determinations. A slight modification of the Dot-ELISA procedure allows the determination of infection rates of vectors such as ticks and sandflies with parasites.

Discontinuous polyacrylamide gradient agarose gels resolve a wide range of restriction fragments and optimize the efficiency of nucleic acid transfer.

A vertical electrophoresis procedure utilizing a discontinuous polyacrylamide gradient agarose gel was developed to resolve DNA fragments ranging in size from over 50 kb to less than 300 bp in length. The gel consisted of a polyacrylamide plug at the base of the gel followed by a gradient of agarose ranging from 0.3 to 0.9%. Restriction fragments migrated shorter distances than in a comparable polyacrylamide-0.3% agarose gel, and small fragments were retained. Southern transfer of DNA fragments from the gradient gel onto nitrocellulose was more efficient than transfer of fragments using a nongradient gel.

Determination of IgM and IgG antibodies to Toxoplasma using the IFA test, ELISA, and Dot-ELISA procedures.

The dot enzyme-linked immunosorbent assay (Dot-ELISA) and the enzyme-linked immunosorbent assay (ELISA) were compared with the immunofluorescent antibody test (IFA) for detection of IgM- and IgG-specific antibodies to human toxoplasmosis. Reciprocal titers were determined in all three assays using sera from 56 patients with suspected toxoplasmosis or with symptoms and diseases requiring exclusion of toxoplasmosis and control sera from 56 healthy persons. Using the Dot-ELISA, six patient sera (10.7%) were positive at titers of greater than equal to 1024 for IgM antibodies (titer range 1024-16 384) and 47 sera (84%) were positive for IgG antibodies (titer range 16-262 144) at a titer of greater than or equal to 16. One control serum was reactive for IgM (titer 1024) and 10 control sera (18%) were positive for IgG in the Dot-ELISA. In the ELISA, at titers of greater than or equal to 128, five sera (9%) were reactive for IgM (titer range 128-512) and 52 sera (92.8%) were reactive for IgG (titer range 32-8192) at a titer of greater than or equal to 32; no control sera gave positive reactions for IgM while 10 sera (18%) were positive for IgG in the ELISA. Using the IFA test at reciprocal titers of greater than or equal to 16, four sera (7.1%) were positive for IgM (titer range 32-512), and 51 sera (91%) were positive for IgG (titer range 16-8192). None was reactive for IgM, and eight sera (14%) were positive for IgG (titer range 32-128) in the IFA test. The Dot-ELISA correlated well with the IFA test (correlation coefficient = 0.895) and the ELISA correlated slightly higher with the IFA test (correlation coefficient = 0.910) for detection of IgG antibodies to Toxoplasma gondii.

Dot-ELISA for the rapid serodiagnosis of human hydatid disease.

We studied the serodiagnosis of human hydatid disease using the dot-enzyme-linked immunosorbent assay (dot-ELISA) and the indirect hemagglutination assay (IHA). Hydatid cyst fluid antigens from sheep were highly reactive against a battery of positive human sera. Moose-derived antigen was less reactive, whereas human- and camel-derived antigens showed nonspecific false-positive reactions. Sensitivity of the Dot-ELISA was 96% using sheep-derived antigen and 45 human sera from 43 surgically proven cases of hydatidosis disease caused by Echinococcus granulosus, E. multilocularis and E. vogeli. The IHA test reacted with 100% of patient sera (P = N.S.). Specificity of the dot-ELISA was 98%; one false-positive reaction was observed in the dot-ELISA when 52 sera from healthy subjects were assayed. Cross-reactions were observed with sera from patients with cysticercosis, filariasis, toxocariasis, trichinosis, visceral larval migrans, and liver cirrhosis. Of 204 sera tested in duplicate, 191 (94%) did not vary more than one twofold titer dilution. The dot-ELISA is rapid and as sensitive as the IHA test in the diagnosis of hydatidosis. In addition, unlike other currently performed tests for hydatid disease, this rapid and economical enzyme immunoassay is very antigen-conservative, requiring only nanogram quantities of parasite antigen, and very serum conservative, needing only 50 microliter of diluted patient serum.

Evaluation of complement fixation procedures for the diagnosis of visceral leishmaniasis.

Three complement fixation (CF) procedures were evaluated for their ability to detect serum antibodies to visceral leishmaniasis. These tests differ in their use of buffers, volumes of complement and sensitized erythrocyte concentrations, incubation times and percentage haemolysis endpoints. Freeze-thawed sonicates of Leishmania donovani promastignotes were used as antigen. Test sensitivity was determined using sera from 46 Kenyans with parasitologically proven leishmaniasis. The frequencies of positive reactions in all three tests were 96-97% and positive antibody titres ranged from 1:16 to 1:4096. Specificity was determined with 20 sera from healthy individuals with no known exposure to leishmaniasis. The frequencies of false positive reactions were 0-10% in the control sera, with titres up to 1:16. No cross-reactions were observed with sera from patients with bacterial, fungal and other parasitic diseases. In replicate experiments, 99-100% of the sera tested were within one titre dilution of each other. All three CF procedures provide very good sensitivity, specificity and low cross-reactivity and are statistically similar in their capacity to diagnose visceral leishmaniasis.

Reduced false positive reactions in the Dot-enzyme-linked immunosorbent assay for human visceral leishmaniasis.

Specificity of the Dot-enzyme-linked immunosorbent assay (Dot-ELISA) for visceral leishmaniasis was significantly improved through the use of enzyme-conjugated antisera specific for IgG heavy chains. Of sera from Kenyans with visceral leishmaniasis, 97% (29/30) were positive using horseradish peroxidase (HRP)-conjugated anti-IgG (heavy and light chain specific) which detected bound IgG and IgM. False positive reactions occurred in 80% of sera from both trypanosomiasis-infected patients (8/10) and apparently healthy Africans (24/30). HRP-conjugated anti-IgG (heavy chain specific), which detected only bound IgG, significantly reduced false positive reactions among trypanosomiasis-infected (2/10, P less than 0.02) and healthy Africans (6/30, P less than 0.001), without reducing test sensitivity in leishmaniasis patients. No false positives occurred when either HRP-conjugated antiserum was used to assay sera from 30 North Americans. Application of enzyme-conjugated antisera specific for IgG improves the serodiagnostic value of the Dot-ELISA for individual patient evaluation and epidemiologic investigations.

Rapid serodiagnosis of leptospirosis using the IgM-specific Dot-ELISA: comparison with the microscopic agglutination test.

The dot enzyme-linked immunosorbent assay (Dot-ELISA) was compared to the microscopic agglutination test (MA test) for the diagnosis of human leptospirosis. Of 177 sera from 68 soldiers who trained in the Republic of Panama, 102 sera were positive in the MA test and 93 of these sera were positive in the IgM-specific Dot-ELISA. Incidence of infection was 50 of 68 patients with the MA test and 48 of 68 in the IgM Dot-ELISA. Five MA test-positive sera were reactive only in the IgG-specific Dot-ELISA, suggesting previous exposure. All 21 infecting serovars of Leptospira interrogans, as determined by positive reactions in the MA test or culture of blood and urine specimens, were reactive in the Dot-ELISA. Of 75 sera negative in the MA test, 61 were nonreactive in the Dot-ELISA. However, 9 of these 14 Dot-ELISA-positive/MA test-negative sera were acute samples from patients whose later sera were MA test-positive. Positive reactions in the IgM Dot-ELISA occurred in 2 of 30 control, 4 of 10 Lyme disease, 1 of 11 relapsing fever, and 1 of 8 yaws sera; 10 syphilis patient sera were nonreactive. The IgM-specific Dot-ELISA appears to be sensitive and specific for the serodiagnosis of acute leptospirosis. In addition, this rapid test is inexpensive, simple to perform, utilizes minute volumes of killed leptospiral antigen and is easily adaptable to field use.

Fluorogenic substrate detection of viable intracellular and extracellular pathogenic protozoa.

Viable Leishmania promastigotes and amastigotes were detected by epifluorescence microscopy with fluorescein diacetate being used to mark living parasites and the nucleic acid-binding compound ethidium bromide to stain dead cells. This procedure is superior to other assays because it is faster and detects viable intracellular as well as extracellular Leishmania. Furthermore, destruction of intracellular pathogens by macrophages is more accurately determined with fluorescein diacetate than with other stains. The procedure may have applications in programs to develop drugs and vaccines against protozoa responsible for human and animal disease.

Human cutaneous leishmaniasis acquired in Texas.

Four cases of autochthonous human cutaneous leishmaniasis have been identified in south-central Texas since 1980. The patients presented with chronic ulcerating papules on the face, earlobe, and lateral thigh. In two patients, the infections healed without treatment. In the other two patients, the lesions healed following treatment with intramuscular sodium stibogluconate or topical antimony potassium tartrate. Serologic testing of family members, using four different techniques, indicates that asymptomatic infections may occur. These are the first reported cases of cutaneous leishmaniasis acquired in Texas since 1974. Organisms isolated from patients in 1974 and 1980 belonged to the Leishmania mexicana complex when tested by the isoenzyme technique. Although no animal reservoir or insect vector has been identified, six species of sand flies belonging to the genus Lutzomyia do inhibit this part of Texas. Accumulated evidence strongly suggests that cutaneous leishmaniasis is endemic in south-central Texas.

Standardization of the dot enzyme-linked immunosorbent assay (Dot-ELISA) for human visceral leishmaniasis.

The Dot-ELISA, a rapid, visually read micro enzyme immunoassay for visceral leishmaniasis utilizing minute volumes of antigen "dotted" on nitrocellulose filter discs and precipitable chromogenic substrate, was analyzed under a variety of experimental parameters. Raising assay incubation temperatures from 23 degrees C to 28 degrees C resulted in titer increases in three of five leishmaniasis patient sera; at 37 degrees C, all five patient sera and one of five normal human sera showed titer increases. The amount of antigen used could be reduced 50% by incubating patient serum overnight at 4 degrees C. Antigen discs stored at - 20 degrees C were optimally reactive with leishmaniasis sera over a 270-day period. Antigen discs stored at 4 degrees C and 23 degrees C showed reproducible titer decreases at 90 days. Aging either peroxidase-conjugated antibody or substrate for up to 28 days at 4 degrees C did not adversely affect titers of positive and negative control sera and reagent controls. Activated substrate stored at 23 degrees C was optimally reactive in the assay for at least 24 hours. No changes in titers of positive and negative control sera or nonspecific reactions in reagent controls occurred when using different brands of microtiter plates. The long shelf lives and stabilities of Dot-ELISA antigen and reagents indicate this test should prove useful both in the laboratory and in the field.

Leishmania mexicana: purine metabolism in promastigotes, axenic amastigotes, and amastigotes derived from Vero cells.

Leishmania mexicana mexicana promastigotes, axenic amastigotes, and amastigotes derived from Vero cells were examined for de novo purine synthesis and mechanisms of purine salvage. Both promastigotes and axenic amastigotes were incapable of de novo purine synthesis, as shown by the lack of [14C]formate and [14C]glycine incorporation into purine nucleotide pools. However, the ready incorporation of [14C]hypoxanthine, [14C]adenine, and [14C]guanine suggested that purine salvage pathways were operating. In addition, a significant percentage (greater than or equal to 60%) of the total label from these purine precursors was associated with adenylate nucleotides. Nucleotide pool levels of axenic amastigotes were consistently greater but the specific activities were less than those of promastigotes, suggesting a slower rate of purine metabolism in the axenic amastigote form. Similar results were obtained from amastigotes isolated from infected Vero cells.

Immune complex decomplementation of canine sera for use in a complement-fixation test for diagnosis of visceral leishmaniasis.

Canine sera frequently become anti-complementary when heat-inactivated at 56 degrees C for 30 min, and generally cannot be used in standard complement-fixation (CF) assays. Therefore, a procedure was developed for decomplementing canine sera by absorption with particulate immune complexes consisting of sheep erythrocyte stroma optimally sensitized with anti-sheep erythrocyte antibody (hemolysin). Canine sera incubated for 20 min at 30 degrees C with sensitized stroma consistently showed less than 10% residual complement and were not anti-complementary. This decomplementation procedure was applied in a complement-fixation (CF) test for detection of serum antibodies during canine visceral leishmaniasis. Two groups of German shepherd dogs were injected intravenously with Leishmania donovani or L. donovani chagasi amastigotes, and the course of infections was followed for 12 weeks. Using freeze-thaw sonicate preparations of L. donovani parasites as antigen, reciprocal CF antibody titers above 24 were detectable in sera 7 weeks after infection and gradually increased to a maximum titer of 775 at 12 weeks. Sera from control dogs had mean titers of 24. This improved methodology enhances the potential of the CF test in the serodiagnosis of canine leishmaniasis.

Dot enzyme-linked immunosorbent assay (Dot-ELISA): comparison with standard ELISA and complement fixation assays for the diagnosis of human visceral leishmaniasis.

The dot enzyme-linked immunosorbent assay (Dot-ELISA), standard ELISA and the complement fixation (CF) tests were compared in the serodiagnosis of African visceral leishmaniasis (kala-azar). Assay sensitivity was determined using sera from 44 patients with parasitologically confirmed kala-azar. Using the Dot-ELISA, 42 of 44 patients (95%) were positive at a reciprocal titer of greater than or equal to 32 (titer range 512-524 288). In the standard ELISA technique, 43 of 44 patients (98%) were positive (titer range 32-32 768). At a reciprocal titer of greater than or equal to 8 in the CF test, 35 patients (80%) were positive, 1 (2%) was negative and 8 patients (18%) showed anticomplementary (AC) activity (titer range 8-2048). Specificity, determined using 33 sera from healthy individuals not living in endemic areas, was 97% in both the Dot-ELISA and the standard ELISA (32 of 33 sera); in he CF test, all sera were negative except 1 (3%) which showed AC activity. Sera from patients with Chagas' disease cross-reacted in the dot-ELISA up to a titer of 512. In the standard ELISA, cross-reactions occurred mainly using sera from patients with Chagas' disease, malaria and syphilis, and to a lesser extent with sera from amebiasis, schistosomiasis and trichinosis patients. Overall titer agreement in replicate experiments was highest in the Dot-ELISA (89%), followed by the standard ELISA (80%) and the CF test (72%).

Dot enzyme-linked immunosorbent assay (Dot-ELISA): a micro technique for the rapid diagnosis of visceral leishmaniasis.

A micro enzyme-linked immunosorbent assay utilizing antigen dotted onto nitrocellulose filter discs (Dot-ELISA) was developed for the rapid diagnosis of visceral leishmaniasis. Leishmania donovani promastigotes applied to filter discs in volumes of 1 microliter were placed in 96-well microtiter plates, blocked with bovine serum albumin, then incubated with 4-fold dilutions of patient sera. After incubation with peroxidase-conjugated anti-human antibody, washing and addition of precipitable substrate, positive reactions appeared as blue dots on a white background which were easily read by eye. The procedure is performed at room temperature, takes about 2 h and is economical. At a reciprocal diagnostic titer of greater than or equal to 32, 41 of 42 (98%) leishmaniasis patients were positive, and positive titers ranged from 512 to 524,288. Control sera from healthy individuals showed 1 of 50 (2%) false positive reactions. Sera from patients with African trypanosomiasis, Chagas' disease, and lupus erythematosus were cross-reactive in the Dot-ELISA. No cross-reactivity was noted with sera from patients with amebiasis, coccidioidomycosis, cutaneous leishmaniasis, viral hepatitis, hydatidosis, malaria, schistosomiasis, syphilis, toxoplasmosis or trichinosis. In replicate experiments, 90% of 167 sera tested did not vary in titer. This rapid and inexpensive test should prove to be an important field diagnostic technique for visceral leishmaniasis.

Evaluation of promastigote and amastigote antigens in the indirect fluorescent antibody test for American cutaneous leishmaniasis.

Leishmania braziliensis panamensis promastigotes, temperature-induced in vitro-cultivated amastigotes, Vero cell-derived amastigotes, and rodent lesion-derived amastigotes were evaluated as antigens in the indirect immunofluorescent antibody (IFA) test for American cutaneous leishmaniasis. Test sensitivity was determined using sera from 34 U.S. soldiers with leishmaniasis diagnosed by demonstrating parasites in their skin lesions. Sera were collected from 3 to 24 months after exposure to Leishmania. Positive IFA reactions among patient sera were 82% with promastigotes or lesion amastigotes, 79% with in vitro amastigotes, and 76% with Vero cell amastigotes (P = N.S.). Positive titers ranged from 1:8 to 1:128 using all antigens. Test specificity was determined with 30 sera from healthy individuals. False positive reactions ranged from 0-5% depending on the antigen and all titers were less than or equal to 1:8. Test cross-reactivity was assessed with 47 sera from patients with other diseases. Depending on the antigen, cross-reactions occurred with sera from patients with Chagas' disease, lupus erythematosus, malaria, toxoplasmosis and amebiasis. None of the antigens cross-reacted with sera from patients with viral hepatitis, coccidioidomycosis, syphilis, schistosomiasis, and trichinosis. In replicate experiments, 99-100% of the sera varied no more than +/- 1 titer dilution. As sensitivity, specificity, cross-reactivity, and reproducibility of the four antigens were statistically similar, promastigotes, which can be easily and economically cultured in large numbers in vitro are recommended for use in the IFA test for American cutaneous leishmaniasis.

Infection and replication of Leishmania tropica in mouse peritoneal macrophages elicited by sterile inflammatory agents and BCG.

C3HeB/FeJ peritoneal exudate macrophages elicited with a variety of sterile inflammatory agents or with Mycobacterium bovis strain BCG were exposed to Leishmania tropica amastigotes in vitro. The percentages of L. tropica-infected macrophages were similar in resident and inflammatory macrophage populations over 72 hours in culture. Inflammatory macrophages supported intracellular replication of L. tropica in excess of that by resident macrophages. These macrophages also failed to demonstrate cytotoxicity to tumor cells in vitro, a defined nonspecific effector function of activated macrophages. However, macrophages from BCG-treated mice were significantly more resistant to initial infection with L. tropica, killed intracellular amastigotes by 72 hours in culture and were cytotoxic to tumor cells, indicating full immunologic activation. The inability of inflammatory macrophages to kill L. tropica parasites suggests that inflammation may actually contribute to the pathogenesis of leishmaniasis.