The flow of blood to lymph nodes and its relation to lymphocyte traffic and the immune response

The migration of lymphocytes into rat popliteal lymph nodes during antigenic promotion or competition between heterologous erythrocytes

The injection of chicken and sheep red blood cells (CRBC and SRBC) into rat popliteal lymph nodes either together or sequentially 2, 4, 6, or 8 days apart resulted in an enhanced immune response when the second antigen was injected 2 or 4 days after the injection of the first antigen (antigenic promotion) or a suppressed immune response when the second antigen was injected 6 days after the injection of the first antigen (antigenic competition). The immune response to either antigen was dependent upon the time of administration of the second antigen with respect to the first antigen. Lymphocyte migration into antigenically stimulated lymph nodes was greater when the two antigens were injected sequentially rather than together. Further, the migration of lymphocytes into the lymph node was enhanced when the second antigen was injected during the inductive or suppressive phase of the immune response to the first antigen (CRBC) regardless of whether the same (CRBC) or an antigenically unrelated antigen (SRBC) was used as the second antigen. While antigenic promotion may in part be explained by the increased rate at which lymphocytes migrate into lymph nodes, lymphocyte migration is also enhanced during antigenic competition. This suggests that while suppressor cells/factors may regulate the effector phase of an immune response they do not directly modulate the migration of blood-borne lymphocytes into the lymph node.

The appearance of fluorescein-labelled lymphocytes in lymph following in vitro or in vivo labelling: the route of lymphocyte recirculation through mesenteric lymph nodes

Fluorescein isothiocyanate (FITC) has been used to study lymphocyte migration in sheep. After being labelled in vitro with FITC, lymphocytes migrated from blood into lymph at the same rate and with the same recovery as lymphocytes labelled with with the radioisotope 51chromium. The in vivo labelling of mesenteric lymph nodes (MLN) with FITC resulted in high numbers of labelled lymphocytes appearing in prescapular lymph. However, the appearance of the FITC-labelled lymphocytes in the prescapular lymph could be prevented by cannulating the main intestinal lymph duct prior to the in vivo labelling procedure. It was concluded that lymphocytes labelled in vivo within the MLN required an intact lymphatic system to reach the blood circulation and did not enter the venous circulation directly from the MLN.

The interaction of high endothelial venules with T and B cells in peripheral lymph nodes after antigenic stimulation

The influence of an ongoing immune response on the specific interaction of high endothelial venules (HEV) in peripheral lymph nodes with T and B cells was determined using short-term homing experiments and an in vitro HEV adherence assay. It was demonstrated that stimulation with various antigens did not change the receptor specificity of the HEV. However, the retention and/or the efflux of immigrant cells in the stimulated lymph nodes had changed.

Lymphatic and blood vessels of the popliteal node in sheep

Our aim was to describe the lymphatic and blood vascular pathways to and from the popliteal lymph node in sheep. The blood vessels and lymphatics were filled with Microfil, and were cleared in methyl salicylate. Afferent lymphatics divide and anastomose as they pass dorsally along the lateral saphenous vein, and 6-12 lymphatics reach the node. Each branches extensively on the surface of the node giving rise to 20-50 terminal afferents which enter the node over a roughly circular area. Most enter the subcapsular sinus, but some penetrate deeply into the node. Lymph leaves the node through numerous initial efferent lymphatics, many of which contain valves. These join forming progressively larger vessels, and 2-4 efferent trunks emerge from the hilus. The hilus varies considerably in shape, depth and location, and it is filled with fat. Either a single artery, or up to 10-12 arteries derived from an anastomotic network or circle, enter the node from the hilar fat pad. Arteries may also enter at other sites. The arteries originate from the caudal femoral, or the medial circumflex femoral artery; a single node may receive blood from both arteries. This arrangement may help to maintain blood flow especially during an immune response, and despite external pressures applied to the arteries and node during movements of the animal.

The migration of blood-borne lymphocytes into rat popliteal lymph nodes stimulated with xenogeneic red blood cells

The recruitment of radiolabelled blood-borne lymphocytes into rat popliteal lymph nodes (PLN) was investigated following the injection of varying doses of chicken (CRBC) or sheep red blood cells (SRBC) into the hind foot pad. Within the dose range tested (10(5)-10(8) RBC) an increase in the dose of injected antigen resulted in elevated levels of lymphocyte recruitment into the draining popliteal lymph node. The kinetics of lymphocyte recruitment with the same dose of CRBC or SRBC was similar even though these red cells differ in size and are antigenically non-cross-reactive. While little is known of the mechanisms which control the rate of entry of blood-borne lymphocytes into antigen-stimulated lymph nodes, the extent of lymphocyte recruitment was shown to be directly related to the quantity of antigen injected.

The entry of T and B lymphocytes into rat popliteal lymph nodes undergoing a graft-versus-host reaction

The entry of radiolabeled blood-borne T and B lymphocytes into resting popliteal lymph nodes and popliteal lymph nodes stimulated with semiallogeneic lymphocytes was investigated in rats. Thoracic duct lymphocytes separated into T- and B-lymphocyte populations on nylon-wool columns were radiolabeled with 51chromium and equal numbers of T or B lymphocytes were injected intravenously. While the ratio of T and B lymphocytes in the blood is approximately 3:1 it was found that the ratio of T to B lymphocytes migrating into lymph nodes was approximately 9 T to 1 B lymphocyte in both resting and antigenically stimulated lymph nodes. Since the ratio of T to B lymphocytes in thoracic duct lymph is similar to that of blood, there is a disparity between the number of T cells entering and leaving lymph nodes. These results suggest that some T lymphocytes may return to the blood directly and/or there is increased T lymphocyte death in lymph nodes.

The influence of gut function on lymphoid cell populations in the intestinal mucosa of lambs

The number and type of lymphoid cells in the intestinal mucosa of lambs change during the first weeks after birth. The influence of gut function on these changes was examined by comparing the evolution of lymphoid cell populations in normal ileum with that in lengths of ileum which had been isolated surgically from the functional intestinal tract of the lamb before birth. The isolated lengths of ileum had a normal blood and nerve supply and they remained healthy throughout a period of at least 2 years, although they did not have a normal histological development. In comparison with normal ileum, the villi of the isolated ileal segments were much smaller and there were many fewer intraepithelial lymphocytes; the lamina propria had significantly fewer lymphocytes than the functional ileum and only a few plasma cells. When isolated ileal segments were reconnected into the intestinal tract after having been isolated from it for 1-3 months, the histology of the mucosa reverted to that of the normal gut, with the same number and types of lymphoid cells. Radiolabelled lymphoblasts collected from intestinal lymph and injected intravenously accumulated to only a small extent in isolated segments of ileum compared with either the normal or the reconnected segments of ileum. This suggested that the paucity of lymphocytes in the mucosa of the isolated segments was due to a reduced extravasation of these cells there. The influence which the gut contents exert on the lymphoid cell population in the mucosa is probably associated with antigenic stimulation but may also be related to other factors concerned in the normal digestive functions of the gut.

Cyclic AMP reduces and cyclic GMP increases the traffic of lymphocytes through peripheral lymph nodes of sheep in vivo

Acute and chronic infusions of a lipophilic analogue of cyclic AP (dibutyryl cyclic AMP) into cannulated afferent lymphatics of popliteal lymph nodes of sheep have reduced the output of both small and blast lymphocytes into efferent lymph and have tended to reduce the volume of efferent lymph flow (collected by chronic cannulation). Similar infusions of a cyclic GMP analogue (8-bromo cyclic GMP) have increased the output of both small and blast lymphocytes into efferent lymph and the volume of efferent lymph flow. It is suggested that cyclic nucleotide metabolism of lymphocytes and of vascular endothelium may play an important role in the regulation of lymphocyte traffic through peripheral lymph nodes in vivo and that secondary alterations in cellular cyclic nucleotide levels may be a common pathway by which the many and varied agents arriving in afferent lymph may affect lymphocyte traffic.

Cyclosporin-A inhibits accumulation of lymphocytes within lymph nodes

The ability of cyclosporin-A (CS-A) to modify lymphocyte accumulation, seen in lymph nodes draining a site of antigen deposition, has been compared with the effect of other drugs known to affect lymphocytes and/or macrophages. CS-A markedly inhibited lymphocyte accumulation in a dose-related manner, whereas aspirin, BW755c (3 amino 1 [m (trifluoromethyl) phenyl] 2-pyrazoline) and hydrocortisone were without effect. Indomethacin produced inconclusive results. The time of CS-A administration was critical, the drug needing to be present before antigen inoculation, being ineffective if given 23 hr after antigen.

Redistribution of renal allograft-responding leukocytes during rejection. II. Kinetics and specificity

We investigated the traffic of allograft-responding leukocytes between the host and graft without handling of these cells in vitro. The blood flow between the host and graft was disconnected, the proliferating cells were labeled with [3H]thymidine selectively in the graft or in the host, the label was chased with cold thymidine, and the circulation was reestablished. The localization of labeled cells was quantitated by autoradiography. The first host-derived labeled cells appeared in the graft and graft-derived labeled cells in the host, already on the 1st d after transplantation. This was followed by an exponential increase in the labeled cell traffic in both directions. The peak of traffic was observed on day 4 after transplantation, whereafter the traffic rapidly declined and tapered off. This decline was not due to exhaustion of supply, as the labeled cells continued to proliferate in their original compartments, nor to a slowdown of blood circulation, which took place 2-3 d later. We consider the decline to indicate that the rejection has proceeded to a (irreversible) stage autonomous of the host lymphatic and hematopoietic system. During the exponential increase, nearly one-third of the graft-infiltrating inflammatory cells were replaced as a consequence of relocalization during each 18-h-period. All mononuclear white cell types, with the exception of granulocytes, participated in the traffic. Most lymphoid cells entrapped in the graft were descendents of recent cell divisions; most of the mononuclear phagocytes derived from a preexisting phagocyte pool. The entrapment of labeled leukocytes in a relevant graft was specific: when an allograft and an autograft were simultaneously transplanted, a more than 50-fold entrapment was observed in the allograft, compared with the autograft. Very few of the cells localized in irrelevant positions, such as the liver and lung, of the recipient.

The appearance and significance of phospholipase A2 in lymph draining tuberculin reactions

Popliteal and prefemoral lymphatics of sheep were cannulated, and lymph was collected before and during the course of responses to PPD and concanavalin A. Hyperemia-inducing activity (HIA) and phospholipase A2 (PLA2) were released into lymph in response to antigenic stimulation, whereas lymph plasma draining unstimulated lymph nodes had consistently little or no detectable HIA and PLA2 activity. HIA appeared in the lymph efferent to the stimulated node at a time when blood flow to the responding node was enhanced. While the appearance of HIA did not directly correlate with changes in lymphocyte output, lymph protein concentration, or lymph flow rates, there was, however, a statistically significant correlation between HIA and PLA2 levels in lymph plasma, suggesting that extracellular PLA2 may contribute to the vasoactivity in lymph and thereby modulate blood flow to areas of antigenic stimulation. Vasoactive lymph, injected into rabbits, induced hyperemia via an indomethacin-sensitive pathway, since the induction of hyperemia was abrogated by pretreatment of injection sites with indomethacin. The extracellular release of PLA2 in response to inflammatory stimuli may represent an amplification mechanism for the generation of high levels of prostaglandins found in lymph draining stimulated nodes.

Lymphocyte traffic through chronic inflammatory lesions: differential migration versus differential retention

Afferent lymphatics draining granulomas and efferent lymphatics from normal lymph nodes were cannulated in sheep. Cells collected from these lymphatics were radiolabelled in vitro with 111In (afferent lymph cells) and 51Cr (efferent lymphocytes) and both labelled cells were returned to the animal simultaneously by i.v. injection. The reappearance of these labelled cells in lymph, and the amount of 111In and 51Cr in normal or antigenically stimulated lymph nodes, cutaneous inflammatory sites (FCA-granulomas, NLT- and BCG-induced lesions) and blood was determined 24 hr later. As previously reported, labelled afferent cells preferentially migrated from the blood back through the granuloma into afferent lymph, and efferent lymphocytes back into efferent lymph. Forty per cent as many 111In- as 51Cr-labelled cells ;appeared in efferent lymph. This was caused by the greater migration of 51Cr-labelled cells appeared in efferent lymph. This was caused by the greater migration of 51Cr- than 111In-labelled cells out of the blood into the node. Neither cell type was selectively retained in the node, and 28% of the labelled cells that entered the node migrated on into efferent lymph in 24 hr. Similarly, there was no selective retention of either cell type in the granuloma, and equal amounts of 111In the 51Cr appeared in afferent lymph. The ratio 111In/51Cr in the blood suggested that in the lymph node the two labelled cell populations were extracted equally, while in the granuloma selectively at the level of the vascular endothelium resulted in the preferential extraction of 111In-labelled (afferent lymph) cells.

The sequence of changes in blood flow and lymphocyte influx to stimulated rat lymph nodes

The rat popliteal lymph node was studied from 1 hr to 8 days after the footpad injection of either sheep erythrocytes or syngeneic rat erythrocytes. The following were measured relative to the contralateral (unstimulated) lymph node: (i) blood flow; (ii) lymph node weight; (iii) influx of lymphocytes from the blood; (iv) [3H]-thymidine incorporation; (v) [35S]-sulphate incorporation into macromolecular form (chiefly by high endothelial venules). After the arrival of sheep erythrocytes all five quantities showed substantial increases which began in a definite sequence. The blood flow started to rise first and may have been the main factor contributing to the later increase in lymphocyte influx. Increased sulphate incorporation began later than the rise in lymphocyte influx. After the injection of rat erythrocytes a small increase in lymphocyte influx was found without a corresponding increase in blood flow. In rats irradiated before the footpad injections lymphocyte influx increased three-fold after sheep erythrocytes, rat erythrocytes or PBS, again without a corresponding increase in blood flow. Thus while variation in blood flow to high endothelial venules is one important factor in determining the supply of lymphocytes to the lymph node other factors are operative in certain situations.

Measurement of blood flow and vascular permeability changes in response to 12-O-tetradecanoyl-phorbol-13-acetate and to asbestos fibers

The hyperemia (increased blood flow) and vascular permeability changes induced in rabbit skin by the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate and by asbestos fibers have been quantitated. The resultant hyperemia, measured with radiolabeled microspheres, was inhibited in both cases by steroidal and nonsteroidal anti-inflammatory drugs. Since the inflammatory responses resulting from exposure to these agents might be important for the subsequent development of neoplasms, it is proposed that such a specific and quantitative technique be used to analyze the components of these inflammatory responses in more detail.

Specific selection of antigen-reactive lymphocytes into antigenically stimulated lymph nodes in sheep

Sheep were primed to a variety of antigens and the efferent lymphatic from a popliteal lymph node was cannulated. The cannulated node was challenged repeatedly with PPD and all the lymph and cells removed from the animal. During this time the PBL were monitored for reactivity to all antigens (purified protein derivative of tuberculin [PPD], johnin, and keyhole limpet hemocyanin [KLH]) by the vitro transformation assay. The response of these cells to PPD was found to be gradually eliminated after repeated challenge of the cannulated node with that antigen. The response to the other antigens was unimpaired. No depletion of this response to PPD occurred in cannulated sheep when the antigen was given into a noncannulated node. In vivo delayed-type hypersensitivity skin test and helper T cell assays confirmed that there is a specific selection of antigen-reactive cells from the recirculating lymphocyte pool into antigen-stimulated lymph nodes.

Lymphocyte traffic through antigen-stimulated lymph nodes. I. Complement activation within lymph nodes initiates cell shutdown

Complement activation within lymph nodes has been shown to alter lymphocyte traffic through the node. Challenge of cannulated sheep lymph nodes with either immune complexes or complement activators was found to initiate the phenomenon of cell shutdown associated with antigenic challenge of lymph nodes in primed animals.

Lymphocyte traffic through antigen-stimulated lymph nodes. II. Role of Prostaglandin E2 as a mediator of cell shutdown

Prostaglandin E2 (PGE2) can mediate changes in lymphocyte traffic through lymph nodes. By measuring PGE2 levels in efferent lymph from cannulated sheep lymph nodes it was shown that increased synthesis of PGE2 always correlated with cell shutdown; infusion of PGE2 alone induced cell shutdown and inhibition of PGE2 synthesis by the node abolished cell shutdown induced by antigen.

Morphological changes in paracortical high endothelial venules to single and repeated application of oxazolone to mouse skin

Morphological changes in paracortical high endothelial venules (HEV) have been studied after single and repeated applications of oxazolone to mouse skin. The primary response was characterized by a rapid and marked vascular dilatation, by marked increase in the cross sectional area of the vessel wall and in the size of the individual endothelial cells, as well as increased accumulation of lymphocytes in HEV walls. These changes regressed (in the more long lasting response). The transitory structural alterations may be related to increase of blood flow, increased flow of cells from the thymus to the stimulated lymph nodes as well as increased transport capacity of endothelial cells based on augmentation of their surface area. These features are closely related to other cellular events such as a prominent blastoid reaction in the paracortex as well as an associated cellular depletion of the thymus.

Feto-maternal histoincompatibility and placental blood flow

1. We have designed experiments aimed at resolving some of the controversy concerning the effect of histoincompatibility on the development of the fetus and its placenta. 2. Experiments included the generation of pregnancies in which H-2 compatible and H-2 histoincompatible embryos were simultaneously present. Genetic markers (Brachyury and Kink) were used to facilitate determination of the H-2 haplotype. Additional strain combinations were used to analyse the role of non-H-2 differences. 3. In addition to determining fetal and placental weights, blood flow to the placenta was measured by use of radioisotope-labelled microspheres introduced into the arterial circulation. 4. Under the conditions of our experiments we have failed to detect differences in fetal weight, in placental weight, or in placental blood flow. 5. Thus we support the increasingly prevalent view that histo-incompatibility does not necessarily lead to changes in placental or fetal weight, and we add the additional finding that placental blood flow also is not significantly altered as a result of feto-maternal incompatibility.

Age-related changes in cell localization and proliferation in lymph nodes and spleen after antigenic stimulation

Antigen-dependent localization of 51Cr-labelled lymphocytes, and the subsequent uptake of IUdR into lymphoid organs has been studied as a function of age. Measures of cell localization indicated that while old age can alter the patterns of entry of lymphocytes into lymph nodes and spleen, these changes are variable and probably not sufficient alone to explain decreased primary antibody responses in old animals. Proliferation of cells, however, was consistently affected in both organs and this phenomenon is discussed in terms of abnormal T-cell function.

Alveolar response to experimental Pneumocystis carinii pneumonia in the rat

In order to characterize the alveolar response to Pneumocystis carinii pneumonia, light and electron miscropy were used to trace the development of experimental infections with P carinii in rats treated with cortisone acetate and a low-protein diet. The first changes were found by the eighth day of treatment and consisted of the selective attachment of Pneumocystis organisms, mostly trophozoites, to alveolar Type 1 pneumocytes; the host cells were undamaged, and no inflammatory response was seen. After approximately one month of treatment, the seemingly innocuous host-parasite interaction was succeeded by focal necrosis of the Type 1 pneumocytes adjacent to organisms; hyperplasia of nearby Type 2 pneumocytes also occurred, to replace the dead Type 1 pneumocytes. Even at this stage, inflammatory reaction was conspicuously absent except for occasional alveolar macrophages in the diseased alveoli; in addition, all cells of the alveolar-capillary membrane other than Type 1 pneumocytes appeared entirely normal. Not only does the present study clarify the nature of alveolar injury caused by Pneumocystis carinii, but it also provides an experimental animal model in which selective injury of the alveolar lining cells occurs.

The distribution of prostaglandins in afferent and efferent lymph from inflammatory sites

Arachidonic acid labeled with (14)C was injected directly into lymph nodes that had been stimulated at various times with Escherichia coli. The efferent lymph was collected, and labeled catabolites were extracted and analyzed chromatographically. The pimary conversion product recovered was Prostaglandin E(2) (PGE(2)), with the lesser products thromboxane, prostacyclin and prostaglandin F(2alpha) (PGF(2alpha)) also detected. When the efferent lymph was analyzed by radioimmunoassay after subcutaneous injectino of E coli into the hock, PGE and PGF levels rapidly increased, reached the highest levels in the first 10 hours, and then returned to normal by 24 hours. When the afferent lymph plasma draining inflammatory sites was compared directly with efferent lymph, PGF levels were similar, but the PGE level was always several times higher in the afferent lymph. To examine the catabolism of PG, either (3,)H-PGF(2alpha) of (3)H-PGE(2) was injected into the node, and the efferent lymph plasma was analyzed. No conversion of PGF(2alpha) to other products was found. In contrast, catabolic products of PGE(2) were detected. With the use of equilibrium dialysis techniques, the binding of PGE(2) and PGF(2alpha) to proteins in lymph and to bovine serum albumin (BSA), human serum albumin (HSA), and BSA stripped of its fatty acids was established. The binding to lymph proteins correlated with the albumin concentrations in the lymph. This albumin binging probably facilitated the retention and transport of PG in the lymph. PG appears in the lymph at a time corresponding to the uptake and processing of antigen by the node and near the time when lymphokines are detected in lymph and could modulate several steps in the immune response. The PGE detectable in the lymph draining an inflammatory site may play a role in the modulation of blood flow.

Comparative histological studies of regional lymph nodes of 201 melanoma patients. (Microscopic features in relation to individual age, site, and metastatic spread)

Since May 1968 a total of 2.108 regional lymph nodes (l.n.) dissected from 201 melanoma patients (86 axillary, 107 groin, and 8 neck) have become available for study. The purpose was to detect histological differences between the l.n. of 134 patients lacking and those of 67 patients exhibiting l.n. metastases, histologically verified in 104 of 706 nodes. The main finding is a more than six-fold increase in number and an eleven-fold increase in total area (evaluated by a microscope micrometer) of germinal centers in the lymph follicles of patients with, as compared to those without, l.n. metastases (P less than or equal to 0.05). Paracortical areas were found to be diminished in 56.7% of cases with metastatic spread. Accumulations of plasma cells were mainly seen in the nodes of elderly patients (48.4%) and of those exhibiting regional metastases (47.8%). The observation of numerous and dilated blood vessels in the interfollicular regions noticeably corresponded to the occurrence of lymphatic metastases (P less than or equal to 0.01), suggesting a "tumor angiogenic factor". A negative correlation with metastatic involvement was found as to histiocytosis of marginal sinuses and with respect to the observed fibrinoid hyalinosis of pulp vessels (P less than or equal to 0.01). The marked hyperplasia of lymph node B-lymphocyte regions as opposed to diminished T-lymphocyte areas prevailing in cases with metastatic melanoma is in accord with findings of humoral immunologic blocking activity and impaired T-cell response in advanced malignant melanoma.

Regional blood flow and its relationship to lymphocyte and lymphoblast traffic during a primary immune reaction

The relationship of alterations in blood flow with changes in cell distribution has been studied in an inflammatory site and its draining lymph node during the induction of an immune reaction with oxazolone in mice. The cells which move to the site of inflammation are predominantly lymphoblasts and their increased localization in the inflamed ear is significantly correlated with increased regional blood flow to the inflamed tissue. The existence of this correlation is not antigen dependent although there is a relative increment of lymphoblasts which are specifically primed to the inflammatory agent. The localization of nonblastic (small) 51Cr-labeled lymphocytes on the other hand is substantial only in lymphoid tissue and during the induction of an immune reaction after oxazolone application, the increase in localization of these cells in the draining lymph node is positively correlated with increased blood flow to the node. Furthermore, the probability of finding 51Cr labeled lymphocytes in a particular lymph node is related to the regional blood flow which that node receives.

Arteriovenous shunting in the lymph node before and after antigenic stimulus

We have assessed the effects of antigenic stimulation on the regional blood flow of the lymph node. In seventeen New Zealand white rabbits, the regional blood flow to the popliteal lymph nodes was determined using 9 and 15 micron microspheres at 16, 40, and 144 h following antigen administration. The regional blood flow in the resting lymph node measured with 15 micron spheres was 0 . 46 +/- 0 . 07 ml g-1 min-1, with 9 micron spheres 0 . 26 +/- 0 . 03 ml g-1 min-1. There was a significant 'differential flow' (the difference in blood flow between the experimental and control nodes) measured with 15 micron spheres (P less than 0 . 05). This increase in blood flow was larger early (16 h) than late (144 h) following antigen administration (P less than 0 . 01). There was significant (P less than 0 . 05) 'shunt flow' (the difference in blood flow measured with 15 micron and 9 micron spheres) in the lymph node, with more shunting early (16 h) than late (144 h) following antigen administration. No significant shunting was seen in the kidney or thigh muscle. Thus, we have established: (1) a significant increase in blood flow following antigenic stimulus; (2) shunting of 9 micron microspheres in the resting popliteal lymph node; (3) increased shunting following antigenic stimulus; and (4) that the increase in nodal blood flow was, to a large extent, secondary to increased shunt flow. Both the increased blood flow and the shunting shortly after antigenic stimulus may be important in the evolution of the immune response.

Changes in lymphocyte accumulation and proliferation in the lymph nodes draining the pregnant uterus

Changes in weight, lymphocyte accumulation and cellular proliferation have been measured in the lymph nodes draining the uterus during inter- and intra-strain pregnancies and compared with similar effects after other antigenic stimuli. From the data obtained it was concluded that "paternal" antigenic stimulation from the conceptus initiated an immune response in these nodes. The mechanisms of the subsequent suppression of this response are discussed.

Effect of Peptichemio upon Localization of Injected Radiolabelled Lymphocytes in the Lymphatic Organs of Antigen - Stimulated Mice

Increased localization (trapping) of lymphocytes occurs in lymphoid organs following antigenic challenge. The effect of peptichemio (PTC) upon lymphocyte trapping in lymph nodes and spleen was investigated: the results demonstrate that the drug diminishes trapping in lymphatic organs. The depression of lymphocyte trapping may provide at least one mechanism whereby PTC achieves its immunosuppressive effects.