Figure 3.

LPS directly induces CD4⁺ CD25⁺ proliferation through TLR-4. (a and b) Proliferative responses of CD4⁺ CD25⁺ cells to LPS are APC independent. Sort-purified CD4⁺ CD25⁺ from B6 animals were maintained in culture for 3 d in the presence of anti-CD3 (a) or not (b) and supplemented or not with APC (solid or open bars). For each culture condition, proliferative responses induced by either LPS or IL-2 are compared. (c) Purified CD4⁺ CD25⁺ cells were cultured for 3 d in the absence of APC in medium supplemented with various doses of LPS. (d and e) TLR-4–deficient CD4⁺ CD25⁺ cells do not proliferate in response to LPS. CD4⁺ CD25⁺ were sort purified from TLR-4–competent animals B6 (d) and C3H/HeN (e; open bars) or TLR-4–deficient B10ScCr (d) and C3H/HeJ (e) mice (solid bars) and maintained for 3 d in culture without APC nor anti-CD3. The medium was supplemented with LPS, IL-2, or both, as indicated. Each assay has been performed at least twice on independent cell samples and with similar results.