EXPRESSION OF CD45RB AND CD27 IDENTIFIES SUBSETS OF CD4(-CELLS WITH DIFFERENT CAPACITIES TO INDUCE B-CELL DIFFERENTIATION() MEMORY T)

The capacity of four subsets of CD4(+) memory T cells, defined by expr ession of CD45RB and CD27, to provide help for B cells was examined. L arger amounts of Ig were induced by CD45RB(dim)CD27(-) cells compared with the CD45RB(dim)CD27(+) population, whereas CD45RB(bright)CD27(+) or CD27(-) cells were poor inducers of Ig synthesis. Mitomycin C treat ment, which prevents suppressive activity, markedly enhanced Ig produc tion supported by each subset except for CD45RB(bright)CD27(-) cells. Mitomycin C-treated CD45RB(dim) cells remained the most efficient indu cers of Ig production, but no difference was detected between CD27(+) and CD27(-) cells. The subsets also differed in their ability to proli ferate and secrete cytokines, but these differences did not explain va riations in the capacity to provide help for B cells. Both CD27(-) sub sets exhibited decreased proliferation and uniquely secreted IL-4, wit h the CD45RB(dim)CD27(-) subset producing the greatest quantities of I L-4. No differences in IL-2 and IFN-gamma production were found. IL-10 secretion increased with the acquisition of the CD45RB(dim) phenotype and, within the CD45RB(dim) cells, with the loss of CD27. Staining fo r cytoplasmic cytokines indicated that individual populations of CD27( -)CD4(+) helper T cells produced either IL-4 or IFN-gamma, whereas mor e than half of the IL-4 producers also synthesized IL-2. Finally, the different abilities of CD4(+) memory T cell subsets to support B cell differentiation did not relate to variations in the expression of CD40 ligand. These results indicate that within the CD4(+) memory T cell p opulation an increase of helper activity associates with the shift fro m a CD45RB(bright) to a CD45RB(dim) phenotype. Within the CD45RB(dim) subset, the loss of CD27 is associated with a reduction of suppressive activity.