Protection Against Experimental Allergic Encephalomyelitis in Guinea Pigs by Bacterial Lipopolysaccharide

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Abstract
Protection against experimental allergic encephalomyelitis (EAE) was studied in guinea pigs. Antibody titers to bovine myelin basic protein (BP), measured by means of passive hemagglutination on day 12 or 13 after sensitization with bovine spinal cord (BSC) in complete Freund’s adjuvant (CFA), were higher in animals which recovered later from mild EAE than in those which showed severe EAE. The effect of bacterial lipopolysaccharide (LPS), a B lymphocyte stimulator, on the suppression of EAE was examined. Pretreatment of guinea pigs with LPS 3 days prior to the sensitization with BSC-CFA at the same sites resulted in marked attenuation of both clinical and histologic EAE. The protective effect of LPS against EAE, however, depended upon the times and sites of its use; LPS suppressed EAE only when it was given 3 days prior to the sensitization with BSC-CFA at the same sites. Intraperitoneal injection of LPS, even if given 3 days prior to sensitization, failed to suppress EAE. In the group of guinea pigs protected against EAE by pretreatment with LPS, delayed hypersensitivity skin reactions to BP were depressed and humoral antibody titers to BP were increased several days earlier than in the control group although their peak titers were not significantly different. The ratio of T to B lymphocytes, as assessed by rosette formation, was diminished in the draining lymph nodes of guinea pigs protected against EAE, indicating an increased proliferation of B lymphocytes. These results suggested that the stimulation and proliferation of B lymphocytes themselves or their products, antibodies to BP, could inhibit T lymphocytes and suppress EAE.