SUMMARY1. Experiments have been performed in sheep to determine the contribution of lymph formed within a lymph node to the total protein output in lymph leaving the node.2. The lymphatic duct leaving the popliteal lymph node was cannulated and the protein and lymphocyte output in efferent lymph determined. The afferent lymph flow to the popliteal node was then diverted and lymph formed only within the lymph node collected from t~he efferent cannula. It appeared from the results that the popliteal lymph node forms lymph at the rate of approximately 1 ml. per hour and may contribute 30-50% of the protein output observed in efferent lymph.3. The importance of lymph formation within the lymph node varied between nodes found in different regions of the body. This was due in part to the different protein concentrations in the afferent lymph to the different nodes.4. A positive correlation was found between the protein and lymphocyte concentrations in efferent lymph from the popliteal lymph node in seven out of eleven sheep and in lymph formed within the popliteal lymph node in two out of three sheep. It is suggested that this relationship may be due to an increased transfer of plasma proteins through the post-capillary venules in the lymph node accompanying the continual traffic of lymphocytes across the wall of these vessels. The results indicated that the protein transfer across the post-capillary venules was not an indiscriminate transfer of plasma per se but a selective transport from the blood plasma compartment based on molecular size.

SummaryA technique has been described for the collection of thoracic duct lymph from the young milk-fed calf. The establishment of a recirculating lymphatico-venous shunt permitted the repeated sampling of lymph from three calves for periods of 9-17 days, during which the animals remained in good health.The pattern of absorption oflipid was studied by determining the changes in the output of lipid in lymph of the calves fed whole milk either twice or once daily. When the calves were fed twice daily it was found that the mean hourly flow of lymph and output of neutral lipid, free fatty acid, and phospholipid changed relatively little with time after feeding, compared with a definite pattern of change observed over the first 12 hr after feeding when the calves were fed once daily.With once daily feeding the flow of lymph reached a peak 4-5 hr after feeding. The concentration of neutral lipid was at its lowest level at this time but subsequently increased sharply to reach its highest level at about 10 hr. The output of neutral lipid, free fatty acid, and phospholipid also reached their highest levels at about 10 hr after feeding. There was a sharp decrease in the output of the lipids between 10 and 12 hr with relatively constant values over the 12-24-hr period after feeding. The mean hourly output of lipid in the lymph over this latter period was found to be similar to that in the first 12-hr period, emphasizing the continuous nature of lipid absorption.The ingestion of approximately 140-190 g/24 hr of longer-chain fatty acid (> C12) in one or two feeds of milk resulted in the transport of an estimated 100-160 g/24 hr of neutral lipid fatty acid in the thoracic duct lymph. Since the concentrations of neutral lipid and triglyceride were found to be similar, the estimate for the output of neutral lipid would represent approximately the output of chylomicron triglyceride. The lipid composition of the lymph was found to be similar for samples collected before feeding and at the time of maximum lipid absorption.

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An acute pain stimulus resulted in elevated lymph flow and output of cells from the popliteal lymph node of the sheep in the first 15 min after the stress. Efferent lymph flow increased by an average of 93 % above the mean resting flow and cell output rose by an average of 170% during this period, but by 30 min after the stress, values for both lymph flow and cell output had returned to normal. The cell content of the efferent lymph was significantly higher in the first 15 min after the acute stress and it is suggested that there is a sizeable pool of lymphocytes within the resting popliteal node which can be mobilized into the lymph by an acute stress. A single intravenous injection of 1 mg adrenaline increased the efferent lymph flow in all the sheep examined but gave rise to an increased cell output in only 50 % of the sheep. This indicated that there may be other factors, possibly hormonal, involved in the movement of the pool oflymphocytes out of the regional lymph node following acute stress.Both acute pain stress and adrenaline resulted in an increased afferent popliteal lymph flow and output of cells from the regional tissues in the first 15 min after administration. The results are suggestive of a small pool of lymphocytes in the regional tissues which may be readily mobilized by either acute stress or adrenaline.Part of the increases in efferent and afferent lymph flow observed following acute stress and adrenaline appeared to be due to an increased lymph formation, presumably as a result of an increased capillary pressure. Nevertheless, it is considered that the greater part of the increased flow of lymph from both regions resulted from an accelerated movement of performed lymph.The lymphatic system acts as an important transport system in man and animals, for fluid and protein and also for recirculating lymphocytes. Physiological factors affecting the lymphatic system are thus likely to alter the recirculation of lymphocytes and this in turn could influence processes involved in the immune response. While the process of lymphocyte recirculation [cf.. Gowans, 1966] and its presumed importance in initiating responses to antigen [Gowans, McGregor, Cowan and Ford, 1962; Hall and Morris, 1963;Gowans. and McGregor, 1965;Sprent, Miller and Mitchell, 1971] have been known for some time, little attention has focussed on physiological factors that might alter the cellular traffic in lymph. Previous work in this area has shown the effect of corticotrophic and corticosteroid hormones on the recirculation of lymphocytes [Spry, 1972;Shannon and Jones, 1974] and indicates the need for further work on physiological interactions in the lymphatic system. Moreover, the importance of factors influencing the recirculation of lymphocytes can be inferred from recent work by Zatz and Gershon [1975] which suggests that the regulation of lymphocyte traffic may provide a mechanism for the control of immune responses in vivo.

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