Inhibition of p38 MAPK activity with SB203580 impairs DP-to-SP differentiation in FTOC.

Thymic lobes from day 16 fetuses were cultured for 4 days in the absence (control) or in the presence of 30 μmol/L SB203580, and analyzed by flow cytometry for surface marker expression. A, Contour plots of CD4/CD8 expression. Numbers indicate the percentage of cells in each quadrant. B, Histograms represent expression of the indicated surface molecule on DP (thick solid line), CD4⁺CD8^lo (dotted line) and CD4⁺CD8⁻ (thin solid line) cells gated as shown in CD4/CD8 plots. Percentages of cells within the marked region are given for CD4⁺CD8⁻ cells. For CD4 expression, mean fluorescence intensity (MFI) values for DP (top), CD4⁺CD8^lo (middle), and CD4⁺CD8⁻ (bottom) cells are shown to appreciate the difference in CD4 levels in the subpopulations. C, Mean cell recovery per lobe (5 experiments) for DN, DP, CD4 SP, and CD8 SP cells (as defined by quadrants in A) from control (white bars) and SB203580-treated (black bars) FTOCs. In each case, SEM did not exceed 15% of the mean.