Mycobacterial Suppression of Delayed Hypersensitivity in Experimental Allergic Encephalomyelitis

Abstract

The mechanism of prevention of experimental allergic encephalomyelitis (EAE) by mycobacteria was studied. Guinea pigs were challenged with encephalitogenic homologous myelin basic protein (BP) in complete Freund''s adjuvant. When the amount of mycobacteria was increased from the usual 0.1 mg to 2. 5 mg., the guinea pigs had diminished EAE (1 out of 10 instead of 12 out of 15) and markedly depressed delayed hypersensitivity to BP (skin test). EAE and delayed hypersensitivity to BP could also be prevented by pretreatment with a single injection of mycobacterial adjuvant. Serial bleedings from all animals were tested for anti-BP antibody by direct radioimmunoelectro-phoresis. No animals in the present series developed such antibodies. Thus, active induction of EAE which is known to correlate with delayed hypersensitivity does not correlate with circulating antibody to myelin BP. Suppression of EAE by pretreatment with mycobacteria or by high levels of mycobacteria in the adjuvant is not accomplished through immune deviation or formation of protective antibodies but by suppression of delayed hypersensitivity to the encephalitogenic protein by some other means.