Suppression of IgE response induced by phytohemagglutinin (PHA) inoculation near the time of immunization is studied. Donor spleen cells injected with PHA on day - 1 before transfer were either depleted from Lyt 1 + or Lyt2 + T cells and inoculated to isogenic recipients. Animals were immunized with ovalbumin in aluminum hydroxide gel 1 h later. IgE response was determinated by passive cutaneous anaphylactic (PCA) reaction and ELISA. Results show that suppression of the IgE response caused by PHA only affects PCA reaction. In contrast, IgE response measured by ELISA is not modified. Depletion of Lyt 1 + T cell abolished the PHA effect. Thus, as a provocative notion, we propose the generation of an IgE suppressor factor which inhibited the PCA reaction. It was present in the sera of treated animals. IgM and/or IgG production was not affected.
