Suppression of the Primary Immune Response induced by Phytomitogen

Abstract

FOLLOWING Nowell's observation that in the presence of extracts of navy bean, mammalian lymphocytes can transform in vitro into primitive blast-like cells¹, there have been numerous reports of studies concerning the mechanisms by which this agent may act. Nonetheless, it is not clear whether the ability of the active component, phytohaemagglutinin (PHA), to induce such a change is caused by antigenicity of the compound itself (for cells derived from specifically sensitized individuals undergo identical morphological alterations on exposure to homologous antigen) or whether it relates to other mechanisms. Additional studies have suggested that the blast is capable of differentiation into a cell which can secrete antibody². Pokeweed mitogen (PWM), another plant derivative, has a similar transforming effect³. In view of these data, PHA would be expected to enhance immune responsiveness in vivo. Concordant with this, it was demonstrated that spleens which were excised from animals pretreated with PHA could develop a primary immune response in organ culture, but if PHA was omitted no such response resulted⁴. These findings contrast with in vivo experiments of Jennings and Gates in which pretreatment for 72 h with phytohaemagglutinin before administration of heterologous erythrocytes produced depression of agglutinin titres at the sixth day⁵.