Treatment with non-toxic monophosphoryl lipid A (MPL), derived from a polysaccharide deficient heptoseless Re-mutant of Salmonella typhimurium was found to inactivate suppressor T cell activity as evidenced by a decrease in the degree of low-dose immunological paralysis expressed and an increase in the magnitude of the antibody response to Type III pneumococcal polysaccharide (SSS- III). The effect produced, which could not be attributed to the polyclonal activation of immune B cells by MPL, were dependent upon the dose of MPL used, as well as the time when MPL was given relative to low-dose priming or immunization with SSS-III. Neither amplifier nor helper T cell activity was decreased by treatment with the same--or larger--doses of MPL.
