A diagnostic ELISA for visceral leishmaniasis, based on antigen from media conditioned by Leishmania donovani promastigotes.

Leishmania donovani promastigotes were cultured in a protein-free medium for 3-5 days and the spent medium used to prepare antibody-detection ELISA plates. When the plates were used to test 29 Kenyan and 16 Nepalese patients with visceral leishmaniasis (VL; kala-azar), all the sera collected at diagnosis were found to have high levels of parasite-specific IgG. The levels of these antibodies dropped 6-12 months post-initiation of antileishmanial therapy in all but one of the patients. Although the levels in sera from 59% of the treated patients fell to those measured in sera from healthy controls, those in sera from 17% of the patients did not drop below those seen at diagnosis. The antigen used did not cross-react with sera from patients with parasitological diagnosis of malaria, filariasis, African trypanosomiasis or echinococcosis. Antibodies to antigens in the spent medium were detected, by western blot, in all the sera from Nepalese patients with VL. Promastigote-conditioned media could be the source of cheap antigen for the immunodiagnosis of leishmaniasis.

Safety and immunogenicity of a Plasmodium falciparum sporozoite vaccine: boosting of antibody response in a population with prior natural exposure to malaria.

Recombinant sporozoite vaccine or placebo were administered once to 25 volunteers from an area endemic for malaria. Antibody to R32tet32 rose in 9 of 15 receiving vaccine and remained elevated in 6 for 6 months. Mean absorbance increase was 0.43 +/- 0.40 with vaccine, 0.01 +/- 0.23 with placebo, and 0.72 +/- 0.19 in responders. Six non-responders had significantly lower pre-immunization levels (0.07 +/- 0.05) than responders (0.39 +/- 0.25). There was an association between an increase in immunofluorescence (n = 4) and an increase in absorbance (n = 9) among vaccine recipients (n = 15). Vaccine-induced increase in antibody to natural circumsporozoite antigen was indicated by increases in immunofluorescence and by increases in circumsporozoite precipitation score in 2 of the 5 responders with highest antibody increase measured by enzyme-linked immunosorbent assay. Response to subunit sporozoite vaccine paralleled response to prior natural sporozoite exposure and was significant and prolonged in a population with prior natural exposure to malaria.