Cutting edge: Th1 cells facilitate the entry of Th17 cells to the central nervous system during experimental autoimmune encephalomyelitis

Abstract

It has recently been proposed that experimental autoimmune encephalomyelitis, once considered the classical Th1 disease, is predominantly Th17 driven. In this study we show that myelin-reactive Th1 preparations devoid of contaminating IL-17(+) cells are highly pathogenic. In contrast, Th17 preparations lacking IFN-gamma(+) cells do not cause disease. Our key observation is that only Th1 cells can access the noninflamed CNS. Once Th1 cells establish the experimental autoimmune encephalomyelitis lesion, Th17 cells appear in the CNS. These data shed important new light on the ability of Th1 vs Th17 cells to access inflamed vs normal tissue. Because the IL-17-triggered release of chemokines by stromal cells could attract many other immune cells, allowing Th17 cells to access the tissues only under conditions of inflammation may be a key process limiting (auto)immune pathology. This has major implications for the design of therapeutic interventions, many of which are now aiming at Th17 rather than Th1 cells.

FIGURE 1

Polyclonal Th1 but not Th17 effectors initially activated in vivo induce disease upon passive transfer. Draining lymph node cells from pMOG-immunized mice were restimulated for 72 h with pMOG under Th1- or Th17-polarizing conditions. A, The proportion of CD4⁺ T cells capable of producing IFN-γ (black bars), IL-17 (open bars), or IFN-γ and IL-17 (gray bars) after 3 days of culture in the presence of pMOG and the indicated recombinant cytokines. B, EAE score in recipients of Th1- (closed circles), Th17- (open circles), or Th1- and Th17-polarized (open squares) cells. Data (n = 5-7 mice per group) are from one of three experiments giving consistent results. C, EAE score in recipients of Th1- (closed circles) and IL-6 plus TGF-β-polarized cells (open circles) or Th1- and IL-6 plus TGF-β-polarized cells (open squares) (n = 3-6 mice per group).

FIGURE 2

Th1- but not Th17-polarized effectors enter the CNS and initiate inflammation. Polyclonal Th1- (CD45.1/CD90.2) and Th17-polarized (CD45.2/CD90.1) cells generated from the draining lymph nodes of pMOG-immunized mice were transferred to CD45.2/CD90.2 hosts alone (Th1, Th17) or in combination at a 1:1 ratio (Th1:Th17). The distribution of donor cells on day 16 after transfer was assessed by FACS analysis. A, The number of Th1- (closed bars) and Th17-polarized (open bars) cells recovered from the spleen of recipient mice. B, Total number of mononuclear cells recovered from the CNS of recipient mice. C, Total number of CD4⁺ T cells recovered from the CNS (donor and host cells combined). D, Number of donor Th1 (closed bars) and Th17 (open bars) recovered from the CNS. E-H, Individual splenic populations (E and F) or pooled CNS mononuclear cells (G and H) sampled from recipient mice were stimulated overnight with pMOG, and cytokine production by donor cells originally polarized to Th1 cells (closed bars) and Th17 cells (open bars) was assayed by intracellular cytokine staining with IFN-γ (E and G) and IL-17 (F and H). Bars represent the mean ± SE of 5-7 recipient mice per group. In the cotransferred groups shown in panels E-H, the populations analyzed for cytokine production are identified with boldface type and are underlined.

FIGURE 3

Th17-polarized cells from MBP-reactive TCR transgenic mice can induce mild/delayed EAE, correlating with the in vivo appearance of IFN-γ-producing cells. Th1- and Th17-polarized populations were generated from naive Tg4 mice and transferred into B10.PL mice (A-C) or B10.PL × RAG2^-/- mice (D-F). A and D, Intracellular cytokine staining of Th1-polarized (top panels) and Th17-polarized (lower panels) Tg4 cells before transfer. B, Clinical course of EAE induced by the transfer of Th1 (upper panel) and Th17 (lower panel) cells, n = 5. C, Ac1-9 stimulated IFN-γ and IL-17 production by Th1 (upper panel) and Th17 (lower panel) donor cells recovered from the CNS as determined by intracellular cytokine staining. Graphs show the mean ± SD of cells recovered from three surviving Th1-transferred and five Th17-transferred mice. E, Th1 (closed symbols), or Th17-polarized (open symbols) Tg4 T cells (as shown in D) were transferred to B10.PL × RAG^-/- recipients (three to four mice per group). F, Ac1-9-stimulated cytokine production by CD4⁺ T cells recovered from the CNS of a representative B10.PL × RAG2^-/- recipient with a disease score of 3. Data are from two of seven experiments giving consistent results.

FIGURE 4

Th1-polarized cells are phenotypically stable. A-F, Th1-polarized (closed circles) and Th17-polarized (open circles) Tg4 cells were washed extensively and restimulated with graded concentrations of Ac1-9. Cytokine production after 72 h of culture was assessed by ELISA (A and B) or cytometric bead array (C-F). G, IFN-γ and IL-10 production by polyclonal Th1- and Th17-polarized cells derived from pMOG-primed mice as determined by ELISA. H, Signature cytokine production vs Foxp3 expression in populations of Th1 (left panel) and Th17 (right panel) Tg4 cells sampled on the day of transfer. I, Expression of T-bet (filled bars) and ROR-γt (open bars) at 72 h (expressed as fold induction over cells stimulated under neutral conditions).