Aberrant expression of GM1 on lymph node cells of MRL/Mp-lpr/lpr mice: influences on the autoreactivities of anti-asialo GM1 antibodies.

Although changes in surface carbohydrate expression of abnormally expanded MRL/Mp-lpr/lpr (MRL/lpr) lymph node (LN) cells have previously been described, the composition and function of glycolipids present on these cells as well as the spectrum of specificity of anti-carbohydrate antibodies reactive with these cells remains obscure. Analysis of antibodies to a panel of 22 carbohydrate structures using a liposome immune lysis assay (LILA) showed that, except for anti-asialo GM2 (GA2) antibodies, marked reduction of antiglycolipid antibody levels was observed in sera from 4-mo-old MRL/lpr mice compared with these from MRL/Mp(-)+/+ (MRL/+) mice. Absorption experiments revealed that both anti-asialo GM1 (GA1) and globoside antibodies had binding capacity to MRL/lpr LN cells. To elucidate the glycolipid profiles of MRL/lpr LN cells, glycolipids were extracted from LN cells of both MRL/lpr and MRL/+ mice and analysed. A 30-fold elevation of GM1 was found in MRL/lpr LN cells compared with MRL/+ LN cells. From the results of LILA using GA1/GM1 mixed liposomes, aberrantly expressed GM1 inhibited the classical complement pathway but did not interfere with the binding of anti-GA1 antibodies to liposomal GA1. These findings suggest that a drastic GM1 increase on MRL/lpr LN cells would inhibit the action of anti-GA1 antibodies and complement on the cell surface. This may explain the escape of these cells from an activated self directed immune response.