CD4⁺ T cells can acquire MHC II in vivo.

(A) Freshly isolated CD4⁺ T cells from DO11.10 TCR-transgenic mice were stained with PE-conjugated anti–H2-A^d and FITC-conjugated anti-CD4 immediately following isolation or after 24 hours in medium. The level of H2-A^d on DO11.10 cells gated for CD4 expression is shown. These data have been reproduced in 3 animals. (MFI of whole CD4⁺ T cells: freshly isolated = 11.12; after 24 hours' culture = 5.59.) (B) CD4⁺ T cells, either the whole preparation or purified naive cells, from BALB/c mice were triple-stained with PE-conjugated anti–H2-A^d, cy-chrome–conjugated anti-CD4, and FITC-conjugated anti-CD3 or anti-CD44. Only the CD4⁺ population was gated for analysis. (C) CD4⁺ T cells from DO11.10 transgenic mice were transferred to BALB/c mice. Some mice were immunized with CFA plus OVA peptide or with CFA alone. T cells were recovered from the draining lymph node one day after immunization. The cells were then triple-stained with PE-conjugated anti–H2-A^d, FITC-conjugated anti-CD4, and cy-chrome–conjugated DO11.10 TCR clonotypic antibody (KJ1-26). Included in each group were 3 mice. CD4⁺ KJ1-26⁺ and CD4⁺KJ1-26⁻ cells were analyzed separately as indicated on the figure. Representative mice from each group are shown.