TNF-α receptor 1 (R1; p55) and R2 (p75) expression. (A) Flow cytometric analysis of membrane TNF R1 and R2 in BMMCs from patients with MDS (RA, n = 4; RAEB, n = 8) and healthy controls (n = 4). Results represent the mean ratios of fluorescence intensities (RFIs) between specific antibody and isotype control antibodies (total BMMCs). (B) Histograms and scattergrams showing TNF receptor patterns for isotype control (i), R1(ii), and R2 (iii) in 2 individual cases of MDS; of note is the prominence of R1 (ii) in RA, distinctly different from RAEB, where R2 (iii) is expressed at a level similar to R1 (ii). Fields with the scattergrams are circled to highlight differences in R1 and R2 expression between RA and RAEB. (C) Ratio of TNF R1 to R2 determined as in panel A in BMMCs and CD34⁺ cells from the same patients (comparison between RA and RAEB by unpaired t test), as well as healthy controls (n = 3).