IL-7Rα deficiency does not affect the pumping activity of lymphatic collectors but impairs uptake and transport in lymphatic initials. IL-7Rα^−/− or WT mice (n = 7/genotype) were injected with a near-infrared dye (IRDye680) 20-kDa PEG conjugate into the hind paw and LVs in the upper and lower limb were examined under a stereomicroscope. (A) Representative images of the collecting LVs in the lower limb of an IL-7Rα^−/− and a WT mouse. White circles indicate the region of the 2 collecting vessels in which pulse rates were analyzed. (B) Representative plots of the pulse rates measured in the 2 collecting vessels of a WT and an IL-7Rα^−/− mouse. (C) Quantification of the collecting LV contractility revealed no difference in pulse rates between IL-7Rα^−/− and WT mice (n = 7 mice/genotype). (D) Representative images of normal and dysfunctional lymph flow in the dorsal paw skin (upper limb) located proximal to the dye injection site. Under normal conditions (left), only deeper collecting vessels filled with dye are visible. By contrast, lymphatic dysfunction (right) is characterized by increased dye spreading through the initial lymphatic capillaries with evidence of leakage (white arrows). (E) Quantification of normal (white) and dysfunctional (black) lymphatic drainage in the dorsal paw skin proximal to the injection site (n = 7 mice/genotype). Scale bar represents 1 mm.