Correlation between the capacity of bacterial lipopolysaccharide to supress experimental allergic encephalomyelitis and its mitogenic activity for lymph node cells in guinea pigs.

Protection of guinea pigs from experimental allergic encephalomyelitis (EAE) was attempted using bacterial lipopolysaccharide (LPS) from 4 sources. The ability of these LPS to induce DNA synthesis in guinea pig lymph node (LN) cells in vitro was also investigated. It was found that there existed a good correlation between the capacity of LPS to suppress EAE and their degree of mitogenic activities for LN cells. LPS from Escherichia coli 0111:B4 (Ec-LPS), which was most effective in suppressing EAE and also best inducer of DNA synthesis in LN cells, enhanced the proliferation of cells forming antibody to myelin basic protein (BP) in the regional LN. These results, in addition to the previous report, suggested that at the inductive phase the proliferation of B lymphocytes or their products, antibodies to BP, could inhibit formation of T lymphocytes sensitized to BP, resulting in suppression of EAE. Lipid A but not PS fraction of Ec-LPS showed a protective activity against EAE and a mitogenic activity for LN cells although less so than whole LPS. In addition, Lipid A appeared to exert its mitogenic effect mainly on B rather than on T lymphocytes.