A PEG-ELISA for the detection of Leishmania donovani antigen in circulating immune complexes.

Leishmanial antigen in circulating immune complexes (CIC) from sera of cotton-rats experimentally infected with Leishmania donovani and visceral leishmaniasis patients (VLP) was detected using a polyethylene glycol (PEG) enzyme-linked immunosorbent assay (PEG-ELISA). The immune complexes were precipitated in the cold with 12% PEG (average M(r) 6000) and then dissociated with glycine-HCl buffer. The dissociated antigen bound to the plate was then detected by peroxidase-labelled rabbit antibody raised to either amastigotes or to CIC. Serum samples from either controls or patients infected with heterologous organisms were used to define the sensitivity and specificity of the test. Leishmanial antigen was detected in the CIC from all experimentally infected animals (100% sensitivity) and in 22 of 25 of the CIC from VLP (88% sensitivity), using either conjugate. Immunoblotting of PEG-precipitated CIC from infected animals with both rabbit antisera revealed multiple antigen components. Antigens of 40, 42 and 45 kDa appeared to be specifically recognized by both antibodies; the components of 40 and 42 kDa were common to amastigote extracts and CIC from infected animals.