Understanding of T helper 17 lineage (T-H17) polarization has been significantly promoted by cell culture experiments that reduce the complexity of the in vivo environment. We here investigated T-H17 amplification by coating of cytokine preparations. Cytokine preparations coated to the surface compared to the same amount given in solution significantly enhanced T-H17 polarization assessed by flow cytometry and interleukin (IL)-17A, IL-17F and ROR gamma t mRNA expression. T cell proliferation and T-H1 polarization were similarly enhanced while T-REG polarization was impeded. T-H17 amplification was replicated by coating the plate with low amounts of FCS or albumin as used as carrier protein for cytokines (0.5 mu l 0.1%). It was unaltered by filtration, protein digestion and arylhydrocarbon receptor blockade, not replicated by LPS and independent of integrin stimulation. T-H17 amplification required anti-CD3 stimulation and was T cell intrinsic. Supernatants of CD4(+) cells polarized on coated cytokine preparations with carrier albumin conferred amplification to fresh splenocytes. Coating markedly elevated CD4(+) IL-22 mRNA expression and IL-22 blockade significantly reduced T-H17 amplification. Our data show T-H17 amplification by coated albumin in the low amounts present in recombinant cytokine preparations. This unexpected adjuvant like effect underscores the need for controls also for temporal and spatial factors in cell culture.