Plasmodium falciparum: sporozoite boosting of immunity due to a T-cell epitope on a sporozoite vaccine.

Plasmodium falciparum: Sporozoite boosting of immunity due to a T-cell epitope on a sporozoite vaccine. Experimental Parasitology 64, 64-70. The impact of a malaria sporozoite vaccine may be enhanced if protective immunity elicited by the vaccine is boosted by natural exposure to sporozoites. For this to occur, a helper T lymphocyte epitope present on the vaccine must be shared by sporozoites. These studies show that T cells from mice immunized with R32tet32, the Plasmodium falciparum sporozoite vaccine candidate, recognize an epitope of less than or equal to 7 amino acids derived from the circumsporozoite protein repeat region of R32tet32, as well as an epitope on the tet32 fusion protein tail of R32tet32. Exposure of R32tet32 immunized animals to P. falciparum sporozoites elicits a significant secondary antibody response which suggests that humans who are immunized and respond to this vaccine may be boosted by field exposure to sporozoite infected mosquitoes.

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.

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%).