CD4⁺ T cell activation, retroviral transduction, and adoptive transfer of inflammatory responses. Total cell populations from sensitized lymph nodes were cultured with OVA and subsequently transduced with retroviruses encoding EGFP. (A) We identified the transduced cell population using EGFP as a selectable marker. (C) The EGFP⁺ cells exclude propidium iodide (PI) and are thus viable. (E) The majority of the EGFP⁺ cells are CD4⁺ T cells, which demonstrates selective transduction of this cell type. (B, D, and F) Stimulation with OVA led to progressive enrichment of CD4⁺ T cells in the cultured population as well as upregulation of CD4 expression from day 1 to day 6 (compare B and D). The data from B and D are presented as histograms in F. The thin line represents the CD4 distribution in the lymph node cell population as harvested from donors on day 1. The thick line represents the CD4 distribution following lymph node culture with OVA for 6 days. The dotted line represents the isotype control. (G) Following transduction, EGFP⁺ cells were sorted by FACS, and 2 × 10⁵ cells were transferred into unsensitized recipients that were subsequently airway challenged with OVA. Controls were recipients of EGFP⁺ cells challenged with vehicle or naive animals challenged with OVA. In recipients of EGFP⁺ cells, the absolute number of lung lymphocytes was increased 5-fold, and the absolute number of BAL leukocytes was increased 3-fold compared with controls. Data are from 2 independent experiments. Error bars represent range.