MURINE MALARIA - ANTIERYTHROCYTIC ANTIBODIES RECOGNIZE N-ACETYL NEURAMINIC ACID RESIDUES

A cell-ELISA was developed using monolayers of glutaraldehyde-fixed no rmal as well as Plasmodium berghei-infected mouse erythrocytes for qua ntification and characterization of anti-erythrocytic autoantibodies i n murine malaria. Testing normal (NMS) and peak parasitaemic sera (PPS ) on erythrocyte monolayers treated with trypsin, sodium meta periodat e, neuraminidase or heat, and competitive inhibition of antibodies wit h 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 l evels of antibodies to NANA covalently conjugated to bovine serum albu min (BSA) were detectable in PPS. Such antibodies could be significant ly absorbed out by preincubation of PPS with mouse erythrocytes (MRBC) . Antibodies in PPS, when affinity-purified on a column of Fetuin-Agar ose, were found to be reactive to normal as well as parasitized erythr ocyte monolayers. Immunoglobulin isotyping and IgG subgroup typing rev ealed that most of the anti-erythrocytic autoantibodies in NMS were Ig M and IgA, while in PPS there was an appreciable increase in IgG2a and IgG3. Affinity-purified anti-NANA antibodies reacted with DNA when te sted in an ELISA. There was a significant positive correlation between anti-erythrocytic antibody and DNA-binding levels in NMS as well as P PS. The DNA-binding antibodies in PPS could be effectively absorbed ou t by preincubation of sera with fresh MRBC. Affinity determination of anti-erythrocytic antibodies eluted from MRBC revealed binding charact eristics in the following order: MRBC>single-stranded DNA>double-stran ded DNA.