The kinetics of antigen-reactive cells during lymphocyte recruitment

Cell recruitment and cytokines in skin mice sensitized with the vaccine adjuvants: saponin, incomplete Freund's adjuvant, and monophosphoryl lipid A

Vaccine adjuvants are substances associated with antigens that are fundamental to the formation of an intense, durable, and fast immune response. In this context, the use of vaccine adjuvants to generate an effective cellular immune response is crucial for the design and development of vaccines against visceral leishmaniasis. The objective of this study was to evaluate innate inflammatory response induced by the vaccine adjuvants saponin (SAP), incomplete Freund’s adjuvant (IFA), and monophosphoryl lipid A (MPL). After a single dose of adjuvant was injected into the skin of mice, we analyzed inflammatory reaction, selective cell migration, and cytokine production at the injection site, and inflammatory cell influx in the peripheral blood. We found that all vaccine adjuvants were able to promote cell recruitment to the site without tissue damage. In addition, they induced selective migration of neutrophils, macrophages, and lymphocytes. The influx of neutrophils was notable at 12 h in all groups, but at other time points it was most evident after inoculation with SAP. With regard to cytokines, the SAP led to production of interleukin (IL)-2, IL-6, and IL-4. IFA promoted production of tumor necrosis factor (TNF)-α, interferon (IFN)-γ, IL-6, IL-17, IL-4, and IL-10. We also observed that MPL induced high production of IL-2, TNF-α, and IFN-γ, in addition to IL-6, IL-17, and IL-10. In peripheral blood, values of certain cell populations in the local response changed after stimulation. Our data demonstrate that the three vaccine adjuvants stimulate the early events of innate immune response at the injection site, suggesting their ability to increase the immunogenicity of co-administered antigens. Moreover, this work provides relevant information about elements of innate and acquired immune response induced by vaccine adjuvants administered alone.

Finding a way out: lymphocyte egress from lymphoid organs

The egress of lymphocytes from the thymus and secondary lymphoid organs into circulatory fluids is essential for normal immune function. The discovery that a small-molecule inhibitor of lymphocyte exit, FTY720, is a ligand for sphingosine 1-phosphate (S1P) receptors led to studies demonstrating that S1P receptor type 1 (S1P1) is needed in T cells and B cells for their egress from lymphoid organs. S1P exists in higher concentrations in blood and lymph than in lymphoid organs, and this differential is also required for lymphocyte exit. Transcriptional and post-translational mechanisms regulate S1P1 and thus the egress of lymphocytes. In this review we discuss the body of evidence supporting a model in which lymphocyte egress is promoted by encounter with S1P at exit sites. We relate this model to work examining the effects of S1P receptor agonists on endothelium.

Lymphoid organ development: from ontogeny to neogenesis

The development of lymphoid organs can be viewed as a continuum. At one end are the 'canonical' secondary lymphoid organs, including lymph nodes and spleen; at the other end are 'ectopic' or tertiary lymphoid organs, which are cellular accumulations arising during chronic inflammation by the process of lymphoid neogenesis. Secondary lymphoid organs are genetically 'preprogrammed' and 'prepatterned' during ontogeny, whereas tertiary lymphoid organs arise under environmental influences and are not restricted to specific developmental 'windows' or anatomic locations. Between these two boundaries are other types of lymphoid tissues that are less developmentally but more environmentally regulated, such as Peyer's patches, nasal-associated lymphoid tissue, bronchial-associated lymphoid tissue and inducible bronchial-associated lymphoid tissue. Their regulation, functions and potential effects are discussed here.

A novel mechanism of immune regulation: interferon-gamma regulates retention of CD4 T cells during delayed type hypersensitivity

The local immune response is characterized by an increase in the rate of entry of lymphocytes from the blood into regional lymph nodes and changes in the output of cells in lymph. While significant data are available regarding the role of inflammation-induced vascular adhesion processes in regulating lymphocyte entry into inflamed tissues and lymph nodes, relatively little is known about the molecular processes governing lymphocyte exit into efferent lymph. We have defined a novel role for lymphatic endothelial cells in the regulation of lymphocyte exit during a delayed type hypersensitivity (DTH) response to mycobacterial purified protein derivative (PPD). Soluble, pro-adhesive factors were identified in efferent lymph concomitant with reduced lymphocyte output in lymph, which significantly increased lymphocyte binding to lymphatic endothelial cells. While all lymphocyte subsets were retained, CD4+ T cells appeared less susceptible than others. Among a panel of cytokines in inflammatory lymph plasma, interferon (IFN)-gamma alone appeared responsible for this retention. In vitro adhesion assays using physiological levels of IFN-gamma confirmed the interaction between recirculating lymphocytes and lymphatic endothelium. These data demonstrate a new level of immune regulation, whereby the exit of recirculating lymphocytes from lymph nodes is selectively and sequentially regulated by cytokines in a manner equally as complex as lymphocyte recruitment.

Evidence of CXC, CC and C chemokine production by lymphatic endothelial cells

Although production of chemokines by vascular endothelial cells has been documented, there is only limited information regarding the expression of chemokines by the lymphatic endothelium. Here we used lymphatic endothelial cells (LEC) derived from experimentally induced murine lymphangiomas to investigate the pattern of chemokine expression by these cells. Histological analysis of the lymphatic hyperplasia revealed the presence of leucocytes in the tissues surrounding the lesions, suggesting the presence of chemoattractant activity. A functional chemotactic assay on human polymorphonuclear cells and on purified subpopulations of murine leucocytes using culture supernatants from LEC primary cultures confirmed the presence of chemoattractant activity. The identity of different cytokines of the CXC, CC and C subfamilies was investigated by reverse trancriptase-polymerase chain reaction on total endothelial cell RNA. Amplified fragments corresponding to KC, IP10, Mig-1, BCL, MIP-2, SLC, RANTES, MCP-1, C10, and Lptn were obtained, and confirmed by Southern blot and sequencing. In contrast, MIP-1alpha, MIP-1beta, and MIP-1gamma were not detected. Higher levels of expression were revealed by Northern blot analysis for Mig-1, MCP-1 and C10. The lymphatic endothelium-restricted production of these chemokines was also confirmed by in situ hybridization. The presence of high C10 mRNA expression levels in LEC was particularly unexpected, because the production of this molecule has been previously identified only in cells of the haematopoietic lineage. These observations represent the first detailed analysis of chemokine production by lymphatic endothelial cells and may account, in part, for the mechanism of leucocyte recruitment into the lymphatics, and of lymphocyte recirculation within the lymphatic system.

Quantitative studies on the movement of fluid and lymphocytes through periodontal tissue and into the draining lymph

Chronic lymph drainage techniques in sheep have been used to map the pathways and to quantify the fluid and cell traffic through periodontal tissues. The continuous collection of cervical and prescapular lymph has demonstrated that 65% of labelled protein tracer injected into the periodontal tissues could be found in lymph over a period of 7.5 hours. Nearly 90% of the total radioactivity could be accounted for between the lymph and the tissue site. When silk was impregnated with radiolabelled albumin and a tooth ligated, the kinetics of the subsequent appearance of the tracer in lymph emphasized the ease with which macromolecules surrounding the teeth gain access to the lymphatics, regional lymph nodes, and immune apparatus. Animals were primed with BCG and then tuberculin (delayed hypersensitivity) lesions were simultaneously induced in the skin, bowel, and periodontium. When T cells were labelled with radioisotopes and their migration from blood to lymph measured, the periodontal tissue traffic pattern was distinct from the traffic pattern through DTH in the skin and also distinct from the pattern through the small intestine. This indicates that the lymphocyte traffic through the inflamed periodontium has unique features. This tissue specificity was not apparent when lesions were induced with TNFalpha. The static assessment of lymphocyte subsets within the tissues was also assessed with immunohistochemistry.

Local immune responses to influenza antigen are synergistically enhanced by the adjuvant ISCOMATRIX

The peripheral (draining) lymph node, as the primary site of immune induction, determines the course of systemic responses to an injected antigen. Lymphatic duct cannulation procedures in sheep were used to investigate local immunoreactivity to human influenza virus antigen (Flu ag) admixed with the adjuvant ISCOMATRIX (IMX). Compared to Flu ag or IMX alone, the co-administration of Flu ag and IMX (Flu ag+IMX) synergistically enhanced a number of immunological responses (lymphocyte and blast migration from the node, antigen-specific antibody levels and IL6 output in efferent lymph, and antigen-induced proliferation in cultured efferent lymph cells). Together, these results demonstrate that IMX is an immune modulator, and that lymphatic duct cannulation procedures may be used to evaluate antigen/adjuvant combinations for vaccine development.

Stochastic regulation of cell migration from the efferent lymph to oxazolone-stimulated skin

The systemic immune response is a dynamic process involving the trafficking of lymphocytes from the Ag-stimulated lymph node to the peripheral tissue. Studies in sheep have demonstrated several phases of cell output in the efferent lymph after Ag stimulation. When skin contact sensitizers are used as Ag, the efferent lymph cell output peaks approximately 96 h after Ag stimulation and is temporally associated with the recruitment of cells into the skin. To investigate the relative contribution of this high-output phase of efferent lymphocytes to lymphocytic inflammation in the skin, we used a common contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone (oxazolone) to stimulate the skin and draining prescapular lymph node of adult sheep. The efferent lymph ducts draining the Ag-stimulated and contralateral control lymph nodes were cannulated throughout the experimental period. The lymphocytes leaving the lymph nodes during the 72-h period before maximum infiltration were differentially labeled with fluorescent tracers, reinjected into the arterial circulation, and tracked to the site of Ag stimulation. Quantitative tissue cytometry of the skin at the conclusion of the injection period (96 h after Ag stimulation) demonstrated more migratory cells derived from the Ag-stimulated lymph node than the contralateral control (median 18.5 vs 15.5 per field; p < 0.05). However, when corrected for total cell output of the lymph node, the Ag-stimulated migratory cells were 3.8-fold more prevalent in the skin than the contralateral control cells. These results suggest that the in situ immune response generally mirrors the frequency of recruitable lymphocytes in the peripheral blood.

The discovery of T cell help for B cell antibody formation: a perspective from the 30th anniversary of this discovery

Thirty years ago, Miller and Mitchell described the bone-marrow origin of antibody-forming cells and the thymic origin of the help needed to activate the bone-marrow-derived antibody formation. Since then, there has been a continuous stream of discovery in Australia, from Zinkernagel and Doherty's description of MHC-restricted antigen recognition to Goodnow's dissection of the maturation and tolerization of antigen-specific B cells. All of these discoveries, and many more described in the text, contribute to the modern synthesis in immunology.

Cerebral spinal fluid lymphocytes are part of the normal recirculating lymphocyte pool

We have investigated the migration of lymphocytes from blood into the central nervous system (CNS) under normal physiological conditions. Using sheep as our model, we simultaneously sampled blood, lymph and cerebral spinal fluid (CSF). Normal, nonactivated, recirculating lymphocytes can migrate into the CSF in similar concentrations as found in subcutaneous lymph and there is no difference in the temporal appearance between them. Lymphocytes infused into the CNS could be found in cervical lymph nodes. These data suggest that lymphocytes found in the CNS are part of the recirculating lymphocyte pool and do not require activation to enter the CSF.

Reduction in peripheral nerve allograft antigenicity with warm and cold temperature preservation

Lymphocyte migration into fresh and preserved peripheral nerve allografts was assessed to determine the effects of preservation time, preservation temperature, and graft harvest technique on the immunologic response to the peripheral nerve allograft. Peroneal nerve was harvested from either live or cadaveric (tissue) donors and stored as 1.5-cm segments at 5 degrees C or 37 degrees C for 1, 3, 5, or 7 days. Each of nine outbred ewes then received multiple segments of peroneal autograft, fresh allograft, and preserved nerve allograft implants. Lymphocyte migration was studied 7 days after implantation by intravenous injection of autologous 111In-labeled lymphocytes and quantified by gamma counter. Lymphocyte migration into fresh allografts (7212 +/- 1575) increased an average of 4.1 times over fresh autograft tissue (1758 +/- 421; p < 0.05). Short-term preservation (24 hours) at both temperatures enhanced lymphocyte migration into pretreated allograft tissue (12684 +/- 2575 at 5 degrees C, 8751 +/- 1577 at 37 degrees C) as compared with fresh allograft (7212 +/- 1575). Conversely, 7 days of pretreatment at both 5 degrees C (3586 +/- 1421) and 37 degrees C (1570 +/- 414) resulted in migration values not significantly different from autograft. No statistically significant difference was seen between grafts harvested from live (5710 +/- 1651) versus cadaveric (tissue) donors (4013 +/- 832) after 5 days of cold preservation.

Antigen-induced exclusion from follicles and anergy are separate and complementary processes that influence peripheral B cell fate

Anergic self-reactive B cells competing within a polyclonal B cell repertoire fail to migrate into primary follicles and die after 1-3 days residence in T cell zones. Transfer of anergic HEL-specific B cells to recipients lacking HEL autoantigen and continuous bromodeoxyuridine labeling in mixed bone marrow chimeras confirms that follicular exclusion and cell death in 1-3 days is not an intrinsic characteristic of anergic cells but results from competition with B cells bearing other specificities together with continued binding of autoantigen. When naive (nontolerant) HEL-specific B cells were transferred into mice expressing HEL autoantigen, they were also excluded from follicles and their lifespan was dramatically shortened, although they became activated to express CD86 (B7-2/B70). In the presence of helper T cells, activated B cells but not anergic B cells were rescued from death and formed large extrafollicular foci to autoantibody-secreting cells. Antigen-induced exclusion from follicles is therefore an independent process from anergy that prevents self-reactive B cells from recirculating in the long-lived repertoire and may foster interactions with T cells during immune responses. By contrast, anergy prevents self-reactive B cells from collaborating with helper T cells and secreting autoantibody while trapped in the T zone.

Coordinate expression of beta 1 and beta 2 integrin "activation" epitopes during T cell responses in secondary lymphoid tissue

The monoclonal antibodies (mAb) 15/7 and 24 recognize unique activation-dependent, conformational epitopes on beta 1 and beta 2-integrins, respectively. The expression of both of these epitopes closely correlates with the ligand binding ability of their respective integrins, and thus serves as indicators of functional integrin "activation". Here, we have used six-parameter flow cytometry to examine the expression of these epitopes and conventional beta 1- and beta 2-integrin epitopes during human T cell activation in secondary lymphoid tissues in vivo, focusing particularly on the virgin to memory/effector cell transition. Fresh tonsil lymphocytes were stained with mAb against conventional or activation-dependent integrin epitopes, followed by staining with mAb against CD3, CD45RA, and CD45RO, thus allowing the determination of integrin epitope expression on virgin (CD3+) T cells (CD45RA+/RO-to+/-), memory/effector (CD45RA-/RO++) T cells, and T cells undergoing the virgin to memory/effector transition: transition region-1 (T1; CD45RA+to++/RO+); -2 (T2; CD45RA++/RO++); and -3 (T3; CD45RA+/RO++). Conventional beta 1- and beta 2-integrin epitopes progressively increase during the virgin to T3 stages of the transition in tonsil, in keeping with the generally higher levels of these adhesion molecules on memory/effector vs. virgin T cells. Expression of both the beta 1 (15/7)- and beta 2 (24)-integrin activation epitopes first appears on transitional T cells, and is maintained on a relatively constant number of cells (averaging 25-30%) throughout the T1-T3 stages. These epitopes are also noted on a subset of activated memory/effector T cells. Importantly, on both transitional and activated memory/effector T cell subsets, the expression patterns of the 15/7 and 24 epitopes vs. a variety of T cell activation antigens are identical, and the expression of these epitopes relative to each other is linearly correlated, findings strongly supporting the coordinate activation of beta 1 and beta 2 integrins during T cell activation in vivo. These results provide the first evidence of integrin activation during an in vivo immunologic response, and demonstrate the usefulness of mAb recognizing conformational epitopes and multiparameter flow cytometry in delineating the dynamic interplay of adhesion molecules during complex physiologic processes.

Altered patterns of T cell migration through lymph nodes and skin following antigen challenge

Antigen challenge has profound effects on a regional lymph node (LN); it leads to an increase in blood flow to the node, and a marked increase in lymphocyte output through the efferent lymphatics. We used the isolated LN model developed in the sheep to see if antigen challenge in a LN resembled inflammation in peripheral tissues. Following stimulation with an antigen (purified protein derivative of tuberculin), lymphocyte output from the LN showed the typical periods of "lymphocyte shutdown" and "recruitment". The shutdown phase, when cell numbers in efferent lymph dropped by approximately 80%, affected almost exclusively the naive-type (adhesionlo, L-selectin+) T cell population. The large increase in T cell traffic through the node during the recruitment phase was mostly due to CD4+ memory-type T cells and, moreover, the majority of these T cells were L-selectin-, indicating that these cells were crossing from the blood by a molecular mechanism other than L-selectin interaction with its ligand, the "lymph node vascular addressin" (MECA-79). Examination of LN high endothelial venules revealed the presence of vascular cell adhesion molecule-1 (VCAM-1), an endothelial adhesion molecule which has been reported to bind preferentially memory-type T cells in inflammatory lesions. Within the skin, antigen challenge also induced the rapid expression of VCAM-1 on vascular endothelium. It was purely memory-type T cells (beta 1+, L-selectin+/-) that collected in lymph draining from this tissue. However within chronically inflamed skin, the MECA-79 determinant appeared on vascular endothelium, and a small proportion of T cells draining from chronically inflamed skin were of naive-type. The present results illustrate that there are similarities in the cellular and molecular events that characterize antigen stimulation of a LN and inflammation in a peripheral tissue.

Early changes in lymphocyte traffic between distant lymph nodes following regional antigenic stimulation

Regional labeling of mice by injection of cytidine-3H ([3H]CR) into the footpad of the left hind leg was used to evaluate lymphocyte traffic from the left regional nodes to the right popliteal lymph node (PLN) within a 24-h period, with or without concomitant primary or secondary stimulation of the right PLN with fluid tetanus toxoid. Results indicate that 1) in the case of primary antigen injection the relative contribution of lymphocytes from the left regional nodes to the small lymphocyte population present in the stimulated right PLN 24 h after labeling was slightly, but not significantly, greater than in non-stimulated controls; 2) a booster injection of antigen into the right hind leg footpad resulted in a significantly smaller relative contribution of lymphocytes from the previously primed left regional nodes to the small lymphocyte population in the right PLN, 24 h after injection of [3H]CR and secondary stimulation, as compared with controls or animals given a primary stimulation to the receiver node; and 3) in contrast to controls and mice subjected to primary stimulation only, the right PLN 24 h after booster contained a significant number of large lymphoid cells which, or whose precursors, had migrated to this site from contralateral nodes within a day, possibly also in the form of small lymphocytes. These findings are discussed in relation to the problem of lymphocyte recruitment and divergent behavior of non-committed lymphocytes as compared with memory cells in the initial phase after primary or secondary antigenic stimulation.

The response of the pregnant ewe to challenge with foetal and paternal lymphocytes

The efferent lymph from the popliteal lymph nodes of pregnant ewes challenged between 93 and 127 days with specific paternal or foetal lymphocytes was examined. There was an increased efflux of lymphocytes and blast cells from the challenged node, similar to that observed during the response of normal, non-pregnant ewes to allogeneic cells. Additionally, there was a decrease in the mixed lymphocyte and mitogen responsiveness of the efferent lymphatic cells that was comparable with that evoked by challenge of non-pregnant sheep. While cytotoxic cells could not be detected in the lymph after challenge of normal or pregnant animals, specific cytotoxic antibody was invariably produced in both instances. The present observations that the immune responsiveness of the pregnant ewe to foetal lymphocytes remains normal are consistent with an earlier report on the antifoetal reactivity of maternal cells in vitro. It is inferred that the in vitro reactivity of maternal lymphocytes was a valid reflection of the capacity of these cells in the intact ewe.

The response of the foetal lamb to maternal lymphocytes

Foetal lambs were inoculated with either maternal or third-party lymphocytes. Of foetuses transfused in the first half of pregnancy (from 49 to 73 days), one quarter survived until the fifth month. Examination of the immunological reactivity of these survivors revealed that all rejected skin grafts from the lymphocyte donors and manifested normal mixed lymphocyte reactivity. In two instances, responsiveness of the transfused lambs to normal lymphocyte transfer was reduced. Foetal lambs transfused with large numbers of maternal lymphocytes in the last third of pregnancy could survive provided the donor ewe had not been sensitized against foetal or paternal determinants. Following intravenous challenge with maternal lymphocytes, cells collected over a prolonged period from the thoracic duct of the foetal recipient exhibited depression of anti-maternal reactivity in mixed lymphocyte culture.

Transfer of memory cells into antigen-pretreated hosts. II. Influence of localized antigen on the migration of specific memory B cells

Following i.v. injection, 2,4,6-trinitrophenol (TNP)-primed memory cells localized in recipient lymph nodes draining a footpad injection of TNP-hemocyanin (TNP-KLH) in greater numbers than in contralateral nodes draining a p-azobenzenearsonate-coupled KLH injection. Such hapten-specific, unilateral memory B cell localization was still observed in immunosuppressed mice when antigen injections were given as long as 4 days prior to the memory cell transfer. The memory cells could be challenged to form plaque-forming cells by footpad injections of TNP-labeled Brucella abortus at 5 days, but not one day, after cell transfer. The present studies further clarify some parameters of this adoptive memory, as a model for the study of persistent local memory. Measures that promoted the unilateral lymph node retention of 125I-labeled antigen also facilitated unilateral accumulation of TNP-specific memory cells. Such measures included pretreatment of the recipients with cyclophosphamide, rather than gamma irradiation, injection of anti-carrier antibody the day before antigen, or use of small doses of preformed immune complexes instead of antigen alone. In general, a high ratio of lymph node-to-spleen and lymph node-to-blood concentration of antigen in recipients appeared crucial for unilateral localization of memory B cells. Splenectomy of recipients prior to cell transfer enhanced the difference in plaque-forming cell responses between draining and contralateral nodes, but decreased their difference when performed 1 day after cell transfer, suggesting that the spleen may have served as a trap for memory cells. I.v. injection of antigen at the time of B cell transfer also interfered with unilateral localization. The results demonstrate that in the presence of persisting depots of antigen within lymph nodes (and absence of significant amounts of antigen elsewhere), memory B cells can be retained locally without activation into antibody-secreting cells. This mechanism may, therefore, by responsible for the phenomenon of local, humoral, immunological memory.

Heart and spleen twin grafts in rats. II. Delayed host splenectomy

Simultaneous auxiliary transplantation of the spleen has been shown to delay and attenuate the rejection of cardiac grafts in rats. In the experiments reported here, 144 such twin grafts in Lewis and ACI rats were explored in an attempt to determine whether removal of the host's spleen would further facilitate graft survival in this model. Thus, 87 rats were submitted to host splenectomy at various time intervals after implantation of the twin grafts. After considerable technical problems were overcome, it was found that this additional maneuver induced permanent (greater than 5 months) survival in 64% of Lewis-to-ACI twin grafts. The important requirement for this success was timing; delaying host splenectomy for 3 to 5 days after implantation of the twin graft was mandatory.

Clonotype patterns of antibodies released by single lymph nodes

Experimental primary, secondary and tertiary stimulation with streptococcal vaccine of isolated lymph nodes in vivo in the sheep model induces largely persistence of anti-group polysaccharide antibody clonotype patterns with the rare occurrence of additional clonotypes demonstrable after secondary stimulation persisting during the tertiary stimulus. It is not clear whether these additional clonotypes are the products of mutants or whether they pre-existed and were demonstrable only after a secondary stimulus, because of threshold concentrations required for identification. Further, isolated contralateral popliteal and prescapular lymph nodes of individual sheep share completely overlapping clonotype patterns during experimental primary anti-polysaccharide antibody responses indicating an identical repertoire of specific clonotypes under this condition of responsiveness.

Migratory behavior of lymphocytes with specific reactivity to alloantigens. II. Selective recruitment to lymphoid cell allografts and their draining lymph nodes

A dual-antigen, dual-isotope assay has been used to monitor the migratory behavior of selectively labeled antiallogeneic lymphocytes in mice challenged subcutaneously in all four foot pads with semiallogeneic spleen cells. 3H-labeled anti-C3H and 14C-labeled anti-C57BL lymphocytes of DBA/2J origin were pooled and adoptively transferred to multiple groups of previously challenged DBA/2J recipients. In some of the studies, separate groups of recipients were challenged with either CDF or BDF spleen cells in all four paws, whereas in others CDF spleen cells were used to challenge the right paws of each mouse in the group and BDF spleen cells to challenge the left paws of each mouse in the group. At intervals varying from 24 to 96 h after challenge, a subgroup of four mice from each appropriate group was sacrificed and the relative numbers of anti-C3H and anti-C57BL lymphocytes present in the challenged paws, draining lymph nodes, and other tissues of each mouse were inferred from the mean 3H/14C ratios of the respective tissues of that subgroup. The results of these studies firmly establish that specific antiallogeneic lymphocytes are selectively recruited to the paws and draining lymph nodes of mice challenged subcutaneously in the foot pads with semiallogeneic spleen cells and are deleted from their circulating blood and nondraining lymph nodes. A mechanism for antigen-induced selective recruitment and its possible functional significance in tumor immunology are discussed.

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

The blood flow to individual lymph nodes of sheep and rabbits has been determined with 85Sr-labeled microspheres. A popliteal node of the sheep received 0.014% of the cardiac output and a comparable node in the rabbit 0.011%. A sheep lymph node weighing 1 g received an average of 24 ml/h of blood. It was calculated that there was a highly selective removal of lymphocytes by the node and that an equivalent to one in every four lymphocytes that entered a normal lymph node migrated out of the blood, through the substance of the node, and into the efferent lymph. During the immune response to either allogeneic lymphocytes or tuberculin, the blood flow to sheep lymph nodes, even without considering the increase in node weight, increased an average of fourfold. During the primary immune response in the rabbit to keyhole limpet hemocyanin, the blood flow increased threefold. The increase in blood flow preceded the antigen-induced increase in lymphocyte traffic recorded in the efferent lymph. The early phase of increased blood flow was considered to be due to hyperemia, whereas the latter phase had a significant angiogenesis component. It was calculated that an equivalent to 60% of the entire mobilizable pool of lymphocytes could pass through an average lymph node in the blood during an immune response lasting 5 days.

Studies on the glycolipids of sheep thymus and of normal and concanavalin A-stimulated sheep peripheral lymphocytes

The neutral glycolipids and gangliosides of sheep thymus and of sheep peripheral lymphocytes were compared. The patterns of both of these major classes of glycolipids were more complex in thymus than in the lymphocytes. The incorporation of radioactivity from D-[1-14C]galactose into the individual glycolipids of control and concanavalin A-stimulated sheep peripheral lymphocytes was also studied. A marked enhancement of incorporation into trihexosylceramide and an alteration of the pattern of incorporation into gangliosides were noted in the mitogen-treated cells. The results suggest that significant alterations of glycolipid composition and metabolism may occur during at least certain stages of lymphocyte differentiation.

The effects of antigen on the migration of recirculating lymphocytes through single lymph nodes

The increased input of RL into LN starts within 3 h after antigenic stimulation and is due to an increase in the number of RL passing through a LN. It is not associated with an altered transit time through a LN of the majority of RL and it cannot occur in the absence of high endothelial PCV. The immediate decrease in the output of RL from an antigen-stimulated LN is due to a delay in the exit from that LN of RL which had entered the LN before antigen was given. The decrease in cell output from a LN after antigen administration affects blast cells produced within the LN as well as small lymphocytes and is not specific for RL. There are at least two distinct mechanisms controlling the migration of RL through an antigen-stimulated LN. The first controls the increased input of RL which occurs only through high endothelial PCV. The second controls the immediate decrease in cell output, which although it does not occur at the level of the high endothelial PCV, can only occur in organized lymphoid tissue. The increased input of RL into an antigen-stimulated LN and the decreased cell output from the LN can occur independently and are possibly controlled by different mechanisms.

Antipolysaccharide antibodies of restricted heterogeneity secreted by a single lymph node

Immune responses which give rise to the synthesis of antibodies of restricted heterogeneity can be reproducibly induced in rabbits and mice by streptococcal polysaccharide antigens (1,2). While these reports have demonstrated clonotype restriction in the immune serum of rabbits and mice, they give little information with respect to the clontype restriction in a single reaction site of organized lymphoid tissue, for example a single lymph node. The kinetics of immune responses in lymph nodes in situ have been studied in sheep using a variety of antigens (3-6), and a substantial body of information is available on the changes in cell output, cell type, and the number of antibody-secreting cells which occur within the efferent lymph of antigen-stimulated lymph nodes. However, there is no information with respect to the amount and the heterogeneity of antibody that is secreted by the lymph node or cells within the efferent lymph. In the present report we have examined the temporal sequence of clonal restriction in the efferent lymph of individual sheep popliteal lymph nodes undergoing an immune response to the streptococcal group A-variant polysaccharide (Av-CHO).