The immunosuppressive activity of chemically modified lipopolysaccharide of Shigella sonnei

In the present investigations we aimed to study the effect of Shigella sonnei lipopolysaccharide (LPS) on delayed type hypersensitivity (DTH) to non-bacterial antigen in CBA mice. These experiments showed that intraperitoneal injection of phenol–water extracted LPS and avirulent S. sonnei did not affect the level of DTH. However, an injection of avirulent bacteria and LPS treated with 2-mercaptoethanol reduced significantly the levels of DTH. Gel filtration of redox-reactivated LPS through Sephadex G-200 shows that LPS contains three immunosuppressive components: ∼800 kDa and higher, 150–200 and 50–70 kDa. These components differed by their specificity and heat-sensitivity.