The effect of the canine popliteal node on the composition of lymph

The composition of afferent lymph draining into the canine popliteal lymph node was compared with that of the efferent lymph leaving the node. Both the protein and cellular composition were studied. In twenty-five greyhounds the protein concentration of efferent lymph was greater than that of afferent lymph collected from the same limb. Although the absolute level of protein varied greatly between dogs, in a particular animal there was a constant ratio between the protein content of afferent and efferent lymph. The concentration of protein in efferent lymph was approximately double that of afferent lymph. Chromatographic analysis of lymph and the use of radio-iodinated canine albumin indicated that the reason for the increased level of protein in the efferent lymph is that the popliteal node concentrates the protein in afferent lymph. Afferent lymph contained less than 3 X 10(3) cells/ml; efferent lymph contained between 0.5 X 10(6) and 4.3 X 10(6) cells/ml, 98% of which were lymphocytes. In different dogs there was no correlation between efferent lymphocyte density and afferent or efferent protein concentration; however, when an afferent lymphatic was perfused with solutions of different protein concentration, the lymphocyte number in the efferent fluid became greater as protein concentration in the afferent perfusate was increased. The concentrating effect of the node is discussed in terms of its significance to both fluid balance and immunological surveillance.