Murine malaria: anti-erythrocytic antibodies recognize N-acetyl neuraminic acid residues.

A cell-ELISA was developed using monolayers of glutaraldehyde-fixed normal as well as Plasmodium berghei-infected mouse erythrocytes for quantification and characterization of anti-erythrocytic autoantibodies in murine malaria. Testing normal (NMS) and peak parasitaemic sera (PPS) on erythrocyte monolayers treated with trypsin, sodium meta periodate, neuraminidase or heat, and competitive inhibition of antibodies with soluble sialic acid, revealed that some anti-erythrocytic antibodies (which increase during the parasitaemic phase of infection) recognize N-acetyl neuraminic acid (NANA) residues on host erythrocytes. High levels of antibodies to NANA covalently conjugated to bovine serum albumin (BSA) were detectable in PPS. Such antibodies could be significantly absorbed out by preincubation of PPS with mouse erythrocytes (MRBC). Antibodies in PPS, when affinity-purified on a column of Fetuin-Agarose, were found to be reactive to normal as well as parasitized erythrocyte monolayers. Immunoglobulin isotyping and IgG subgroup typing revealed that most of the anti-erythrocytic autoantibodies in NMS were IgM and IgA, while in PPS there was an appreciable increase in IgG2a and IgG3. Affinity-purified anti-NANA antibodies reacted with DNA when tested in an ELISA. There was a significant positive correlation between anti-erythrocytic antibody and DNA-binding levels in NMS as well as PPS. The DNA-binding antibodies in PPS could be effectively absorbed out by preincubation of sera with fresh MRBC. Affinity determination of anti-erythrocytic antibodies eluted from MRBC revealed binding characteristics in the following order: MRBC > single-stranded DNA > double-stranded DNA.