Endogenous CD4⁺ T cells in MBP/R⁺ mice prevent both spontaneous EAE and homeostatic proliferation. (A) In MBP/R⁺ mice, T cells expressing TCRs encoded by endogenous TCR genes protect from EAE. 3 × 10⁷ CD4⁺ T cells purified from H-2^d/u MBP/R^– (n = 5) or MBP/R⁺ (n = 7) mice were transferred into nontransgenic H-2^d/u RAG-1^–/– recipient mice, and the incidence and severity of EAE in the recipients were monitored. (B) In MBP/R⁺ mice, T cells expressing TCRs encoded by endogenous TCR genes prevent the homeostatic proliferation of OVA-specific T cells. 3 × 10⁷ CD4⁺ T cells purified from H-2^d/u MBP/R^– (n = 4) or MBP/R⁺ (n = 3) mice were transferred into nontransgenic H-2^d/u RAG-1^–/– recipient mice. Thirty days after the first transfer, recipient mice were transferred with 1 × 10⁷ CFSE-labeled splenocytes from H-2^d/u OVA/R^– mice. Twelve days after the second transfer, single-cell suspensions of lymph node cells from the recipient mice were made and stained with anti-CD4 and anti–OVA TCR clonotypic antibody KJ1.26 for FACS analysis. Shown is the CFSE dilution of gated CD4⁺KJ1.26⁺ cells. Filled histogram: representative recipient of MBP/R⁺ T cells; open histogram, representative recipient of MBP/R^– T cells.