Recirculating lymphocytes (RL) 1 are long-lived small lymphocytes which migrate continuously from blood to lymph, predominantly at specialized traffic sites in lymph nodes (LN) (1, 2). In individual LN, recirculation of lymphocytes accounts for over 95% of the cell output (3). In LN undergoing an immune response, where the cell output may increase by as much as 10-fold over the first 48 h after antigen, the migration of RL from blood to lymph still accounts for over 95% of the cell output (3-5).The observation that increased numbers of intravenous (i.v.)-injected ~lCr-labeled lymphocytes are present in LN after antigen stimulation has been attributed to a failure of RL to leave LN, as a direct consequence of antigen priming (6, 7). The transient fall in cell output in the efferent lymph of an antigen-stimulated LN was originally considered by Hall and Morris as possibly reflecting a temporary reduction in the entry of RL into the LN (8). Hall (9) has since reported that lymphocytes are entering a LN from the bloodstream during a period when the output of cells from an antigen-stimulated LN is decreased.Thus, at present, the effect of antigen on the migration of RL through LN is interpreted in two contradictory ways. According to one view, antigen provokes an increase in the input of lymphocytes from the blood into LN but is assumed to prevent those same lymphocytes from leaving the LN (6, 7). According to the other view, antigen provokes both an increased input of lymphocytes from blood into LN and an increased output of the same lymphocytes into the efferent lymph (3-5).Recently, by infusing i.v. ~Cr-labeled autologous RL obtained from efferent lymph draining single lymph nodes, we have demonstrated (10) that the majority of RL required about 30 h to pass from the bloodstream through a single resting LN and reach the efferent lymph. The present experiments were designed to decide between the conflicting opinions on immune response traffic changes and to examine the effects of antigenic stimulation on the migration of RL through single LN. In particular, to determine how the presence of antigen ~Abbreviations used in this paper: BCG, Bacille Calmette-Gu~rin; HRBC, horse red blood cells; i.v

Afferent lymph vessels entering popliteal lymph nodes of sheep were infused with [3H]acetyl-labelled hyaluronan of high Mr (4.3 x 10(6)-5.5 x 10(6)) and low Mr (1.5 x 10(5)). Analysis of efferent lymph and of residues in the nodes showed that hyaluronan presented by this route is taken up and degraded by lymphatic tissue. Labelled residues isolated in node extracts by gel chromatography and h.p.l.c. included N-acetylglucosamine, acetate, water and a fraction provisionally identified as N-acetylglucosamine 6-phosphate. Between 48 and 75% of the infused material was unrecovered, and had been presumably eliminated through the bloodstream as diffusible residues. Rates of degradation reached as high as 43 micrograms/h in a node of 2 g wt. infused with 56 micrograms/h. Some HA passed into efferent lymph and some was detected in the nodes, but fractions of Mr greater than 1 x 10(6) were not found in either. It is concluded that the amounts and Mr values of hyaluronan released from the tissues into peripheral lymph can be significantly underestimated by analysis of efferent lymph, i.e. lymph that has passed through lymph nodes. A substantial role in the normal metabolic turnover of at least one major constituent of intercellular matrix and connective tissue may now be added to the established functions of the lymphatic system.

The surface phenotypes (CD1, CD4, CD5, CD8, SBU-T19, MHC class I, MHC class II, and sIg) of cells in blood, lymph nodes, and lymph were determined to examine simultaneously the distribution of lymphocyte subsets circulating in blood, afferent lymph, and efferent lymph of a peripheral lymph node. Marked differences in the percentage of certain lymphocyte subsets were apparent within the compartments examined, suggesting that lymphocyte subsets leave the blood with differing efficiencies. Lymphocyte subsets also appeared to be extracted from the blood at different rates by lymph node as opposed to subcutaneous vascular endothelium. Endothelial cells in different vascular beds may express different numbers of molecules complementary to a set of migration-related cell surface molecules specific for each lymphocyte subset. Accordingly, the vascular endothelium would be the key factor in regulating nonrandom cell migration.

A pronounced asymmetry in the recirculation from blood to lymph of resting small recirculating T lymphocytes is described. When 51Cr-labeled small T-recirculating lymphocytes (TRL) from intestinal lymph were infused intravenously their relative recovery in intestinal lymph was about twice that in nodal lymph. In contrast, the relative recovery in nodal lymph of 51Cr-labeled nodal TRL was twice that in intestinal lymph. Intestinal TRL migrated in large numbers through the small intestine. Nodal TRL did not. It is proposed that the pool of recirculating small T lymphocytes consists of two major subdivisions, an intestinal pool and a nodal pool. The nodal circulation comprises small TRL which traverse PCV in all lymph nodes (LN) but not the small intestine. The intestinal circulation comprises small TRL which do not traverse PCV in LN, but which do recirculate through the small intestine from which they pass via afferent lymphatics to the mesenteric LN and subsequently via the thoracic duct into the blood. It is suggested that the intestinal circulation is present in the fetus and that its initial development is independent of extrinsic antigen.

Human lymph was collected from patients with leaking lymph vessels after thoracic surgery. Ovine lymph was obtained from the mesenteric, lumbar, popliteal and prescapular lymph ducts by cannulation. The concentration of hyaluronate varied considerably (between 0.2 and 50 mg/l) and the highest concentrations were found in mesenteric lymph. The Mr of the polysaccharide showed a great polydispersity and variation between individuals and in different regions of the lymphatic system. High-Mr hyaluronate (greater than 10(6) was present in lymph both from man and sheep. Hyaluronate was also isolated by affinity chromatography in 70-80% yield from human serum and plasma obtained from healthy individuals and patients with rheumatoid arthritis and primary biliary cirrhosis. The weight (Mw)- and number (Mn)-average relative molecular masses were roughly the same in the three groups [(1.4-2.7) X 10(5) and (2.1-5.7) X 10(4) respectively]. The low Mr of hyaluronate in blood compared with that in lymph is explained by a preferential uptake of the large molecules by the liver endothelial cells.