Single-cytokine-producing CD4 memory cells predominate in type 1 and type 2 immunity

The patterns of Ag-induced cytokine coexpression in normal, in vivo-primed CD4 memory T cells has remained controversial because the low frequency at which these cells occur has effectively prevented direct ex vivo measuremen ts, We have overcome this limitation by using two-color cytokine enzyme-lin ked immunospot assays and computer-assisted image analysis. We found CD4 me mory cells that simultaneously expressed IL-2, IL-3, IL-4, IL-5, and IFN-ga mma to be rare (0-10%), This cytokine segregation was seen in adjuvant-indu ced type 1, type 2, and mixed immunity to OVA, in Leishmania infection rega rdless of the Ag dose used or how long after immunization the assay was per formed. The data suggest that type 1 and type 2 immunity in vivo is not med iated by classic Th1 or Th2 cells but by single-cytokine-producing memory c ells.