Localization of intracellular FL (Flt3L) in T lymphocytes. Two-color immunofluorescence confocal microscopy of T cells purified from PB of a healthy donor was performed after staining with anti-FL MoAb M5 followed by FITC-labeled goat antirat IgG (green) and with antibodies against giantin, ERGIC-53, transferrin receptor (TfR), lamp-1 (all mouse IgG1), and cathepsin D (rabbit IgG), followed by secondary Cy3-labeled goat antimouse IgG or goat antirabbit IgG, as appropriate (red signals). Areas of exact overlap of green FL signal with red signals of giantin or ERGIC-53 are highlighted in yellow.