The lymphatic system in the dorsal skinfold chamber of the Syrian golden hamster in vivo.

The lymphatic network contributes to maintaining tissue homeostasis and immunological function by transporting fluid, plasma protein and cells from peripheral tissue via the lymph nodes into the blood vascular system. In contrast to the blood circulatory system, little is known about the lymphatic system. In particular, suitable animal models are lacking. Therefore, the dorsal skinfold chamber model was used to investigate the existence of a lymphatic system. To analyze the lymphatic network Syrian golden hamsters (n=12) fitted with titanium chambers were used. FITC-dextran of different concentrations (5% or 25%) and different molecular weights (4, 40 or 150 kDa) was used to contrast lymphatic vessels and measure initial lymph flow velocity. Intravital fluorescence microscopy enabled the quantification of diameter, velocity and branching order. Histology and electron microscopy supported the in vivo findings. Immediately after intradermal injection of FITC-dextran the lymphatics including valves were visible. The diameters of the lymphatic vessels (n=189) ranged from 133+/-5.4 microm (branching order 1) to 26+/-4.0 microm (branching order 5). Using different molecular weights of FITC-dextran, no significant differences in velocity were measured (327+/-157 microm/s with 4 kDa, 391+/-126 microm/s with 40 kDa, and 378+/-175 microm/s with 150 kDa). Blood and lymphatic vessels could not be differentiated clearly by H&E staining. However, endothelial cells of vessels with an irregularly shaped lumen containing no erythrocytes in cross section showed a weaker signal for CD31 staining as compared to endothelial cells of vessels containing erythrocytes. Moreover, transmission electron microscopy identified the dye-containing vessels as lymphatics after intradermal injection of Berlin Blue. In conclusion, a lymphatic network was characterized in the dorsal skinfold chamber model of the Syrian golden hamster. Thus, this well-established animal model for intravital microscopy provides the opportunity to elucidate the physiological and pathological function of the lymphatic vascular system.