Reversal of the CD4(+)/CD8(+) T-cell ratio in lymph node cells upon in vitro mitogenic stimulation by highly purified, water-soluble S3-S4 dimer of pertussis toxin

Pertussis toxin (PT), a holomer consisting of a catalytic S1 subunit and a B oligomer composed of S2-S4 and S3-S4 dimers, held together by the S5 subu nit, exerts profound effects on immune cells, including T-cell mitogenicity . While the mitogenic activity of PT was shown to reside fully within the B oligomer, it could not be assigned to any particular B-oligomer component. In this study, we purified the S3-S4 dimer to homogeneity under conditions propitious to maintenance of the native conformation. In contrast to previ ous reports which suggested that both S3-S4 and S2-S4 dimers are necessary for mitogenic activity, our preparation of the highly purified S3-S4 dimer was as strongly mitogenic as the B oligomer, suggesting that the S3-S4 dime r accounts for the mitogenic activity of the B oligomer, Moreover, in vitro stimulation of naive lymphocytes by the S3-S4 dimer resulted in reversal o f the normal CD4(+)/CD8(+) T-cell ratio from approximately 2:1 to 1:2. The reversal of the CD4(+)/CD8(+) T-cell ratio is unlikely to ire due to prefer ential apoptosis-necrosis of CD4(+) T cells, as indicated by fluorescence-a ctivated cell sorter analysis of annexin-stained T-cell subsets, or to pref erential stimulation of CD8(+) T cells. The mechanism underlying the revers al requires further investigation. Nevertheless, the data presented indicat e that the S3-S4 dimer may have potential use in the context of diseases am enable to immunological modulation.