Abstract
The lymphocytosis-promoting factor (LPF) was found to suppress the formation of circulating antibody in mice at various immune stages.
The primary immune response of mice to sheep red cells (SRC) was suppressed to a marked extent when LPF was inoculated 1, 2 or 3 days before the antigen. Not only the formation of both 2-mercaptoethanol-sensitive and -resistant serum hemagglutinins was delayed but also the peak titers were reduced. The smaller the dose of the antigen to immunize the LPF-pretreated mice, the more pronounced was the effect. Some data suggested that the pretreatment with LPF one day prior to the antigen was the most effective, but the results were not consistent.
The primary immune response to tetanus toxoid was also suppressed. When LPF was administered 3, 4 or 6 days prior to the antigen, the suppression was significantly greater than when it was given 1 or 2 days before the antigen.
The secondary antibody production to SRC was also delayed and the titer was lower than that of control.
The mice deprived of the primary response to SRC by the LPF pretreatment did not show the secondary type response to a subsequent inoculation of SRC. This shows that no immunological memory was conferred by the primary inoculation of the antigen.
The mechanism of the immunosuppression by LPF is discussed on the basis of these findings as well as in light of the current views concerning the mechanism of antibody formation.
