Accumulation of activated CTLs expressing high levels of GrzB in FL nodes as quantified by confocal laser scanning microscopy. Tissue sections from FL or reactive lymph nodes were stained for CD8 (green), CD3 (blue), and GrzB (red). (A) Representative staining of CD3⁺CD8⁺GrzB⁺ cells in FL (top panels) or reactive (bottom panels) lymph nodes (bar = 10 μm in left panels and 5 μm in right panels). (B) Scoring of CD3⁺CD8⁺GrzB⁺ cells in the interfollicular area of 10 FL and 5 reactive lymph nodes. More than 5 fields from each of the 10 FL and of the 5 control lymph nodes were randomly scored. Statistical significance of difference between groups was evaluated by a Wilcoxon-Mann-Whitney test using STATA Version 11; P = .0024. (C) Measurement of GrzB expression in CD3⁺CD8⁺ cells in the interfollicular area of 10 FL and 5 reactive lymph nodes. Measurements for GrzB fluorescence intensity were performed as described in “Confocal Image Quantification.” More than 5 fields from each of the 10 FL and of the 5 control lymph nodes were randomly scored. Statistical significance of difference between groups was evaluated by a Student t test using STATA Version 11; P < .0001.