The life-span and recirculation of marrow-derived small lymphocytes from the rat thoracic duct

Mathematical modeling reveals kinetics of lymphocyte recirculation in the whole organism

The kinetics of recirculation of naive lymphocytes in the body has important implications for the speed at which local infections are detected and controlled by immune responses. With a help of a novel mathematical model, we analyze experimental data on migration of 51Cr-labeled thoracic duct lymphocytes (TDLs) via major lymphoid and nonlymphoid tissues of rats in the absence of systemic antigenic stimulation. We show that at any point of time, 95% of lymphocytes in the blood travel via capillaries in the lung or sinusoids of the liver and only 5% migrate to secondary lymphoid tissues such as lymph nodes, Peyer's patches, or the spleen. Interestingly, our analysis suggests that lymphocytes travel via lung capillaries and liver sinusoids at an extremely rapid rate with the average residence time in these tissues being less than 1 minute. The model also predicts a relatively short average residence time of TDLs in the spleen (2.5 hours) and a longer average residence time of TDLs in major lymph nodes and Peyer's patches (10 hours). Surprisingly, we find that the average residence time of lymphocytes is similar in lymph nodes draining the skin (subcutaneous LNs) or the gut (mesenteric LNs) or in Peyer's patches. Applying our model to an additional dataset on lymphocyte migration via resting and antigen-stimulated lymph nodes we find that enlargement of antigen-stimulated lymph nodes occurs mainly due to increased entrance rate of TDLs into the nodes and not due to decreased exit rate as has been suggested in some studies. Taken together, our analysis for the first time provides a comprehensive, systems view of recirculation kinetics of thoracic duct lymphocytes in the whole organism.

The function and pathways of lymphocyte recirculation

The early work on lymphocyte recirculation assumed that all recirculating lymphocytes composed a common pool and that the composition of this pool could be inferred from studies on thoracic duct lymph. These propositions are examined in the light of more recent evidence, particularly from experiments on the traffic of lymphocytes through the lamina propria of the small intestine. There has been little speculation on the functional significance of lymphocyte recirculation apart from the suggestion that it increases the efficiency of regional immune responses by allowing antigen-induced selection of precursors from pool larger than that accommodated by the regional nodes alone. In addition, the mounting of a local immunity is dependent on a peripheral recirculation through the tissues, notably in the case of the secretory immune system of the intestine.

Recruitment and proliferation of CD4+ T cells in synovium following adoptive transfer of adjuvant-induced arthritis

Adjuvant-induced arthritis can be transferred to naive Dark Agouti (DA) strain (DA.CD45.1) rats by thoracic duct (TD) lymphocytes. Disease can be re-induced in convalescent rats by further transfer of arthritogenic cells, suggesting that resolution of the adoptive disease is not due to active regulation. To examine whether resolution is due to exhaustion of effector cells, we transferred the disease to DA.CD45.1 recipients, using CD4+ T cells from DA.CD45.2 donors. At the height of the adoptively transferred disease, donor cells comprised only 5-10% of recirculating CD4+ T cells but they accounted for approximately 40% of the CD4+ T cells in synovium-rich tissues of the hind paws. Approximately 65% of the donor cells in the synovium expressed a marker of proliferation (Ki-67 antigen). Division of CD4+ T cells continued in shielded paws after suppression of the recirculating pool of lymphocytes by selective irradiation. Intravenously injected CD4+ TD T lymphoblasts from arthritic donors were recruited to normal paws and, in greater numbers, to paws of animals with existing arthritis. Survival of the [125I]iodo-deoxyuridine-labeled lymphoblasts was greater in animals with existing arthritis. We conclude that effector CD4+ T cells in target tissues can proliferate in response to autoantigens and exhibit enhanced survival. However, without a continuous supply, adoptively transferred effector cells do not produce autonomous local disease, due to limits to their lifespan and ability to replicate indefinitely.

Quantification of proliferating lymphocyte subsets appearing in the intestinal lymph and the blood

Lymphocyte emigration from the intestinal wall via lymphatics is necessary to maintain gastrointestinal immunity and also to connect the different parts of the mucosal immune system. In the present study the numbers and time kinetics of proliferating lymphocyte subsets leaving the gut wall via intestinal lymphatics were analysed in mesenteric lymph node adenectomized minipigs (n = 8). After cannulation of the major intestinal lymph duct, afferent lymph was collected under non-restraining conditions. In four pigs lymphocytes taken from the intestinal lymph and blood were incubated in vitro with the thymidine analogue bromodesoxyuridine (BrdU) to label all lymphocytes in the S-phase of the cell cycle. The other four pigs received a single i.v. injection of BrdU 1 week after cannulation. The initial percentage of BrdU+ lymphocyte subsets in the intestinal lymph 15 min after BrdU injection was comparable to that after the in vitro labelling (1.5 +/- 0.7% in T cells, 10.6 +/- 1.6% in IgM+ cells and 30.0 +/- 11.9% in IgA+ cells). From this level onwards, the percentage of in vivo labelled BrdU+ lymphocyte subsets reached a maximum at 12 h after BrdU application. A different pattern of BrdU+ subsets was seen in the blood. After an early peak at around 3-4 h, the frequency of BrdU in vivo labelled cells decreased. Each subset had a maximum between 12 h and 48 h after BrdU application (maximum of BrdU+ CD2+ T cells at 12 h, 4.6 +/- 1.5%; IgM+ BrdU+ at 48 h, 8.8 +/- 3.3%). The present results provide a basis to determine the time necessary for induction of specific intestinal immunity during oral vaccination studies.

Acute graft-versus-host reaction in SCID mice leads to an abnormal expansion of CD8+ V beta 14+ and a broad inactivation of donor T cells followed by a host-restricted tolerance and a normalization of the TCR V beta repertoire in the chronic phase

The persistence and selection of allogeneic CBA/J T lymphocytes were studied during graft-versus-host (GvH) reaction in immunodeficient C.B-17 SCID (SCID) mice. After neonatal injection the donor cells primarily migrated to the spleen plus lymph nodes (SL) and the thymus of the recipients. Thirteen days post engraftment, CD8+ cells in SL had increased five times in cell number with an 18-fold increase of CD8+ V beta 14+ cells, paralleled by clinical signs of GvH disease (GvHD). Donor lymphocytes from these mice were proliferative unresponsive to allogeneic Balb/c or C57Bl/6 SL cells, whereas 8 weeks post injection the tolerance was confined to H-2d specific donor cells. Here, spleens had a total cell content similar to untreated SCID mice but the average percentage of donor cells had reached 25%. Moreover, the CD4/CD8 cell ratio in the donor population in SL and thymus had changed to normal and the TCR V beta repertoire was similar to that of the originally injected cells. Following secondary transfer into syngeneic CBA/Ca nu/nu recipients donor cells regained a significant but reduced response to H-2d stimulators indicating that the antigen specific tolerance of allogeneic donor cells in the SCID mice was due, at least in part, to a reversible state of anergy.

Competition for follicular niches excludes self-reactive cells from the recirculating B-cell repertoire

Two different approaches to follow clones of B lymphocytes in a diverse preimmune repertoire reveal a new process for eliminating self-reactive cells in the periphery which depends on competition between cells with different specificities. A key feature of this censoring mechanism is the selective exclusion of self-antigen-binding B cells from the normal migration route into lymphoid follicles, resulting in their premature death. This is a striking example of homeostasis by cellular competition for limiting niches and may explain the paradoxical association between immunodeficiency and autoimmunity.

Studies on the participation of different T cell subsets in rat liver allograft rejection. Comparison of liver with heart graft

In this study, we investigated which subsets of rat T cells (CD8+ vs. CD4+) are involved in the rejection of liver allografts by the in vivo administration of monoclonal antibody (OX-8 or OX-38, and W3/25 MAb) into thymectomized recipient Lewis (RTI(l)) rats prior to DA (RTI(a)) liver transplantation. We also compared the results of allograft survival of liver and heart transplants under the same experimental conditions. In order to deplete either CD8+ T cells or CD4+ T cells from recipient animals, 0.4 ml of OX-8 (ascitic form) or a 0.8 ml cocktail of MAb W3/25 and OX-38 (0.4 ml each) was injected into thymectomized recipient rats, respectively. Untreated Lewis rats consistently rejected donor DA liver grafts between 9 and 11 days (n = 7, 9.8 days +/- 1.1 days). In contrast, anti-CD8 MAb pretreatment extended the survival times of DA liver grafts for up to 40 days (n = 5, 26.8 days +/- 8.4 days). Furthermore, survival of DA liver grafts was significantly prolonged in Lewis rats that had been pretreated with anti-CD4 MAb (n = 7, 35.6 days +/- 17.9 days). Two out of seven recipient animals survived for more than 60 days. For heart transplantation, untreated Lewis rats rejected DA heart grafts between 6 and 8 days after operation (n = 6, 6.5 days +/- 1.2 days). Anti-CD4 MAb treatment prolonged heart graft survival for more than 60 days in all cases (n = 3, > 60 days). However, there was virtually no effect of anti-CD8 MAb treatment on heart graft survival (n = 4, 7.0 days +/- 0.9 days). These results suggested that when whole MHC disparity prevailed between donor and recipient, both subsets of T cells were required for the rejection of liver allografts and that class II reactive T cells predominantly mediated liver graft rejection. Furthermore, CD8+ T cells played a differential role in the rejection of rat liver and heart allograft.

Migration of 99mTc-labelled syngeneic lymphocytes in the rat. Biological and theoretical models predict radiation damage and poor scintigraphic detectability

The possibility of obtaining useful scintigrams of secondary lymphoid organs after infusion of syngeneic lymphocytes labelled with technetium-99m (99mTc) was explored in a rat model. Thoracic duct lymphocyte (TDL) accumulation in various organs was measured with both 99mTc and 51Cr labelled cells, the latter processed with a method that has been shown not to damage lymphocytes. 99mTc labelled TDL did not localize properly in the lymph nodes and spleen. We could not visualize lymph nodes in scintigrams, neither could we demonstrate any difference between normal and hyperplastic spleens. Our conclusion is that radiation from the 99mTc label readily influences lymphocyte migration so that useful scintigraphy in rats and other small experimental animals becomes impossible. This was supported by results from culture experiments with 99mTc labelled, radiosensitive mouse haemopoietic progenitor cells. Theoretical considerations, including the calculations of lymphocyte self-irradiation and signal/noise ratios during scintigraphy of rat tissues, supported our conclusion that scintigraphy in small animals, to disclose the physiological migration of lymphocytes, may be impossible with the present sensitivity of gamma cameras.

Accumulation of bromodeoxyuridine-labeled cells in central and peripheral lymphoid organs: minimal estimates of production and turnover rates of mature lymphocytes

Daily lymphocyte production in both central and peripheral lymphoid organs was evaluated by associating in vivo incorporation of bromodeoxyuridine (BrdUrd) with cell surface labeling and multi-parameter flow analysis. At least 10% of mature T and B lymphocytes are generated every 24 h. The kinetic behavior of these cell populations differs, however, in that mature B cells are generated predominantly in the precursor compartments of the bone marrow, while most mature T cell generation occurs at the periphery. Therefore, peripheral expansion is the major mechanism of mature T cell production in the adult mouse. By following the accumulation of BrdUrd-labeled cells in peripheral lymphoid organs we found that the progeny of the daily lymphocyte production was sufficient to renew 30%-40% of all peripheral T and B cells every 48 h, demonstrating a high turnover rate of mature lymphocytes. We also examined the conditions of BrdUrd labeling of cycling cells in vivo. We found that while greater than 90% of bone marrow and thymus cells in S phase were labeled with a single injection of BrdUrd, in peripheral lymphoid compartments 70% of T and B cells in S failed to incorporate BrdUrd. Particular schedules of BrdUrd administration were required to overcome the low labeling efficiency of mature cells in vivo. Prolonged BrdUrd administration, however, had toxic effects on resident cells. The low labeling efficiency of BrdUrd incorporation by mature cells, as well as its potential toxicity during prolonged administration, may explain controversial results obtained by the different strategies used to study lymphocyte population dynamics.

Lymphocyte homing

The phenomenon of "homing" is discussed with respect to patterns of lymphocyte circulation and the molecules on the surface of both endothelium and lymphocytes that mediate this process. In addition, the data are analysed in the context of a model for lymphocyte homing.

Blood transit and recirculation kinetics of lymphocyte subsets in normal rats

Thoracic duct lymphocytes (TDL) were labelled with fluorescein isothiocyanate (FITC) and injected into normal, unanaesthetized rats with either a central venous catheter or a thoracic duct cannula. The blood transit time and the appearance in the lymph was calculated and then the percentages of B, T, T helper, and T suppressor lymphocytes were determined with monoclonal antibodies (Ox12, Ox19, W3/25, and Ox8, respectively). The blood transit time of all subsets was about 30 min. However, the percentage of B lymphocytes from 5 min after injection onwards is reduced (14.5 +/- 1.9%) compared to the injected TDL (32.7 +/- 1.7%). These cells are not in the lung vascular pool. The recovery of FITC-labelled TDL in the thoracic duct within 48 h is much higher (56.8 +/- 5.3% of the injected lymphocytes) than in previous studies using radioactive markers. B lymphocytes appear later and in a reduced number in the thoracic duct. The mean transit time is 26 h and the recovery 31.5 +/- 4.2% in contrast to T lymphocytes (18 h and 66.3 +/- 6.5%, respectively). The technique of combining FITC in vitro labelling with surface staining after completion of migration does not interfere with lymphocyte migration. It can therefore be used to study the migration of lymphocyte subsets in normal, untreated animals.

T and B cells have similar recirculation kinetics in sheep

T and B cells continually migrate around the body by recirculating between blood and lymph via lymphoid tissues. This is an important way of fostering the cell-cell interactions required for the initiation of an immune response. Data from previous studies of T and B cell recirculation, based on relatively complex approaches, have been interpreted as evidence that the recirculation of B cells is more sluggish than for T cells. We have shown from a study in sheep that this is not the case. Lymphocyte migration through both the intestine and the prescapular lymph node was analyzed by cannulating efferent lymphatics. The lymph cells were labeled in vitro with Hoechst 33342, or other fluorochromes, then injected i.v., and the rate of their recirculation into the lymph was determined by fluorescence microscopy. A multicolor immunofluorescence assay was used to classify each recirculated cell as either a T or B cell. This established that the T and B cells from intestinal lymph and from prescapular lymph recirculate with similar kinetics. The recovery of i.v. injected T and B cells was the same in prescapular lymph, but fewer injected B cells than T cells were recovered in intestinal lymph. Thus, although the recirculation kinetics are the same for T and B cells, the two populations are handled differently in intestinal tissues and a lymph node remote from the gut.

Newly produced virgin B cells migrate to secondary lymphoid organs but their capacity to enter follicles is restricted

The migration of recirculating B cells was compared with that of newly produced virgin B cells following passive cell transfer between congenic strains of rats differing in their kappa immunoglobulin light chain (kappa) allotype. The number and location of donor B cells in the secondary lymphoid organs was determined at intervals following transfer by immunohistology using monoclonal antibodies specific for rat kappa allotypes. Recirculating B cells were obtained from thoracic duct lymph while bone marrow from rats depleted of recirculating cells was used as a source of newly produced virgin B cells. B cells from both sources gained immediate access to extrafollicular areas of secondary lymphoid organs rich in interdigitating cells and T cells. However, in lymph nodes extrafollicular B cells were found adjacent to lymphatics and not in the central paracortex. By 8 h after transfer most B cells from thoracic duct lymph were found in follicles. However, the capacity of the bone marrow B cells to enter follicles was very limited. These results are interpreted in relation to previous observations concerning (a) the timing of virgin B cell recruitment into T cell-dependent antibody responses, and (b) the role of B cells in antigen presentation.

Cyclosporine-induced autoimmunity. Conditions for expressing disease, requirement for intact thymus, and potency estimates of autoimmune lymphocytes in drug-treated rats

These studies explore the phenomenon of cyclosporine-induced autoimmunity in irradiated Lewis rats. We show that (a) the presence of a thymus is required, and autoimmune precursors develop in and exit from this organ to the peripheral lymphocyte pool within a 2-wk period after the initiation of cyclosporine treatment; (b) adoptive transfers of drug-induced autoimmunity to irradiated secondary recipients can be accomplished with relatively few cells of the Th subset, and these transfers of autoimmunity can be blocked by cotransfer of normal lymphoid cells; and (c) potency estimates, using popliteal lymph node assays in syngeneic and F1 recipients indicate similar levels of auto- and alloreactivity by cells from drug-induced autoimmune donors. These various findings indicate that this particular animal model may be useful for studies of the onset and control of autoimmunity, and they raise the possibility that the lack of autoimmunity in normal animals and its induction with cyclosporine may involve similar cellular mechanism as have been found to be operative in GVH reactions and specifically induced immunologic resistance to GVHD.

Lymphocyte migration and differentiation in a large-animal model: the sheep

The size and docility of the sheep permit various surgical interventions and repeated collections of biological samples. Development of lymphatic cannulation techniques in this species enabled the investigation of the kinetics of lymphocyte migration in single lymph nodes of not only postnatal animals but also of fetuses at various stages of gestation. It was first demonstrated in the sheep that lymphocyte recirculation commences in the fetus without any exogenous antigenic stimulus. Using these cannulation techniques, it is also possible to investigate humoral events such as the secretion of lymphokines taking place in single lymph nodes with regard to the regulation of lymphopoiesis and the immune response. An extracorporeal perfusion system has been used successfully to investigate the emigration of cells from various lymphoid organs in the sheep. This apparatus enables cells to be labelled in their normal microenvironment with radioisotopes and/or fluorescent probes without destroying the normal tissue architecture. In studies with outbred animals such as the sheep, an investigation in which an individual animal is studied as a case history over a long time often provides much more information than studies based on single-point examinations of many animals and is much closer to the clinical study of immunological problems in individual humans. The recent development of an array of monoclonal antibodies against lymphocyte surface antigens in sheep will help to further dissect the complexity of immunological phenomena. Therefore, the sheep is a useful animal model to study physiological events taking place in the lymphoid system, and in vivo studies in this species will continue to offer a great potential for research of biological relevance and supplement the research done on the in vitro manipulation of cells and biological products related to the immune system.

Antigen-driven selection of virgin and memory B cells

This review has summarized the evidence indicating that far more B cells are produced in adult bone marrow than are required to maintain B cell numbers in the periphery. It is shown that most if not all these newly-formed B cells have the potential to become mature peripheral B cells. However, to do this they need to receive an appropriate signal in secondary lymphoid organs. Cells failing to receive such a signal die after a brief period. Two separate situations have been identified which result in recruitment of newly-formed virgin B cells into the peripheral B-cell pool: Following activation by antigen. When the peripheral B-cell pool has been depleted. It is proposed that the first of these signals requires T help and is initiated by antigen presented on interdigitating cells in extrafollicular areas of secondary lymphoid organs. This process seems to be confined to periods immediately following administration of antigen and does not continue in established immune responses to thymus-dependent antigens. It seems probable that continued B cell activation, occurring during long term antibody responses, takes place in the follicles of secondary lymphoid organs and is driven by antigen presented on follicular dendritic cells. Indirect evidence is cited which suggests that somatic mutation in rearranged immunoglobulin V-region genes occurs mainly following B-cell activation in follicles and not during primary B lymphopoiesis. It is suggested that this may involve a hypermutation process which is switched on in activated B cells in germinal centers. Evidence is presented suggesting that plasma cells generated from B cells activated early in immune responses have an average life-span of less than 3 d. However, plasma cells generated in established responses appear to have an average life-span in excess of 20 d. Later sections in the review consider how B-cell recruitment in thymus-independent antibody responses differs markedly from recruitment during thymus-dependent responses. The possible role of splenic marginal zone B cells in some thymus-independent antibody responses is discussed and the evidence indicating that SIgM + ve, IgD-ve marginal zone B cells develop as a distinct population from recirculating SIgM + ve, IgD + ve B cells is summarized.

The roles of interdigitating cells and natural killer cells in the rapid rejection of allogeneic lymphocytes

The fate of radiolabeled allogeneic thoracic duct lymphocytes injected into congenitally athymic, nude rats was followed by autoradiography and electron microscopy. The allogeneic cells entered the host lymphoid organs at a normal rate, but once inside the lymphoid tissue they were rapidly phagocytozed by interdigitating cells (IDC) situated in the lymph node paracortex and the splenic periarteriolar lymphoid sheaths. Neither host nor donor T cells were required to initiate phagocytosis, as purified donor B cells were also avidly ingested by the athymic host IDC. Compared with fully allogeneic cells phagocytosis of semiallogeneic donor cells was much less efficient. When natural killer cell activity was blocked by preinjecting the recipients with antibodies against natural killer cells (anti-asialo GM1 or MRC OX-8) phagocytosis of the allogeneic cells was strongly reduced. As IDC did not bind these antibodies, the finding indicates that natural killer cells were needed to discriminate between own and foreign lymphocytes and to kill the allogeneic cells, which were then ingested by surrounding IDC. This was further supported by the observation that dendritic, constitutively Ia+ cells from peripheral lymph, phenotypically identical to IDC, did not lyse or phagocytoze allogeneic lymphocytes in vitro.

Immunogenicity and crossreactivity of specificity-associated markers on alloreactive T cells. Confirmation based on the model of tolerance abolition by adoptive transfer

Syngeneic or parental strain T cells adoptively transferred into hybrid rats tolerant of third party alloantigens (L/DA tolerant of BN), in numbers insufficient to abolish tolerance, induce instead an active resistance to tolerance abolition with larger, usually effective dosages of donor cells. Of particular interest is the finding that immunization with T cells from one parental strain donor (e.g., DA) inhibited the tolerance-abolishing alloreactivity (anti-BN) of subsequently transferred T cells from the same (DA) and the other (L) parental strain donor. We conclude that anti-MHC receptors on T cells from different genetic backgrounds reactive to the same third party alloantigens share the same conserved immunogenic specificity-associated markers (SAM). The nonpolymorphism of anti-MHC receptors shown here in the transplantation tolerance model is a confirmation of the same conclusion drawn from earlier studies with the GVHD-resistance model, and it therefore suggests that these two models of T cell MHC interactions involve very similar mechanisms of T cell idiotypic regulation.

Prolonged survival in vivo of unprimed B cells responsive to a T-independent antigen

Despite earlier evidence to the contrary, it has recently been claimed that most B lymphocytes, including lymph node (LN) and thoracic duct B cells, are short-lived cells of recent marrow origin. To seek direct information on this question, we transferred unprimed LN or thoracic duct B cells from normal mice to xid mice, i.e., mice unresponsive to the T-independent antigen, trinitrophenyl (TNP)-Ficoll. At varying periods after B cell transfer the recipients were challenged with TNP-Ficoll; anti-TNP plaque-forming cells were assayed in the spleen 6 d later. The results showed that the B cell recipients retained responsiveness to TNP-Ficoll for at least 3 mo after transfer. Responsiveness increased within the first 3 wk but then remained relatively constant. These findings imply that, at least for TNP-Ficoll-reactive cells, B cells residing in LN and thoracic duct lymph are not short-lived cells of recent marrow. Indeed, the data suggest that once the pool of recirculating B cells is fully formed in adult mice, further input of newly formed cells from the marrow into the recirculating pool is very limited.

B-cell production and differentiation in adult rats

The B-cell development in a group of rats was suppressed for the first 45 days of life by serial administration of rabbit anti-rat IgM and IgD antibody. Total or near total suppression of B lymphopoiesis was achieved. At 45 days, suppression was stopped by injection of IgM and IgD rat paraproteins. The sequence of B-cell and plasma cell development following suppression was assessed by immunohistological analysis of spleen lymph nodes and small intestinal lamina propria. The main findings are listed below. Complete reconstitution of B-cell numbers occurs within 8 days, at which stage germinal centres are also present. B lymphopoiesis in the red pulp of the spleen differs from that reported for bone marrow. Cells develop expressing surface sIgM and sIgM with IgA, but not sIgD. sIgD-positive cells first appear in splenic follicles 2 days after stopping suppression, but their appearance in lymph nodes is delayed until after 3 days. At this stage, sIgD-positive cells become apparent in the splenic red pulp. IgM plasma cells appear from day 4. IgA plasma cells in the gut appear in small numbers at day 6, and gradually increase to normal numbers by day 14. sIgG2c expression in the splenic marginal zone did not approach normal levels, even 2 weeks after suppression was stopped.

Localization of lymphocyte subpopulations in peripheral lymphoid organs: directed lymphocyte migration and segregation into specific microenvironments

The distribution of lymphocytes in the peripheral lymphoid organs is controlled by recirculatory and microenvironmental factors. Specific interactions between recirculating lymphocytes and high endothelial venules in various lymphoid organs determine the presence and proportions of the various lymphoid sets and subsets in those organs. Separate endothelial determinants on peripheral node and Peyer's patch endothelium along with complementary lymphocyte receptors mediate this organ specificity. B and T cells also exhibit nonrandom organization within lymphoid tissues; after entry via high endothelial venules they segregate into their respective domains, which appear to be determined by distinct types of nonlymphoid stromal cells. Antigenic stimulation results in changes in lymphocyte phenotype as well as in the lymphoid microenvironment. The response to most complex antigens is the formation of germinal centers (GC) composed primarily of proliferating B cells; the phenotype of the few T cells therein is supportive of the GC as a site of B-T interaction. The phenotype of the B cells in GCs suggest a role for GCs in immunoglobulin class switching and the determination of subsequent homing specificity.

Repopulation of the gut lamina propria with IgA-containing cells by lymphoid cells isolated from the gut lamina propria

Migration and lodging properties of IgA cells and their precursors of the gut lamina propria (GLP) were studied by transfer of highly purified GLP lymphoid cells between immunoglobulin allotype-congenic mice (CB-20 to BALB/c). The donor IgA-containing ( cIgA ) cells appeared in the GLP of the recipients at day 1, peaked at days 12-15 (late repopulation peak) and persisted up to day 20 after cell transfer. An additional peak at day 3 (early repopulation peak) was seen only when large numbers of GLP B cells were transferred. Few cIgA cells appearing in spleen and mesenteric lymph nodes were seen mainly at days 12-15. The early repopulation peak was probably formed by the differentiation and accumulation of IgA blasts, recirculating IgA-bearing cells and some IgA precursors. The former 2 cell types homed directly back, while the later homed indirectly via spleen to the GLP. The late repopulation peak was possibly formed by the homing and differentiation of Peyer's patch IgA precursors arriving in the GLP with membrane immunoglobulins unchanged. These GLP IgA precursors migrated first to the spleen and later back to the GLP, where they differentiated into IgA plasma cells.

Restoration of allograft responsiveness in B rats. IV. The divergent migratory behavior of lymphocyte populations mediating cardiac allograft rejection

The T lymphocyte-deprived (B) rat, produced by X-radiation and bone marrow reconstitution of adolescent thymectomized animals, exhibits a true immunological deficit and are unable to reject histoincompatible heterotopic cardiac allografts. A comprehensive survey of lymphocyte traffic in B recipients was performed to correlate the differential potency of specifically sensitized lymphocyte populations mediating re-establishment of immune responsiveness toward the graft, with their migratory and recirculatory behavior. 111In-oxine-labeled thoracic duct lymphocytes (TDL) were retained in the peripheral blood and migrated from nonlymphoid organs to lymph nodes of B recipients in higher proportion than any other lymphoid population, particularly splenic lymphocytes (SL). Although all cell groups but TDL were sequestered in the spleen in equal and relatively large numbers, no differences were found between the lymphocyte populations tested in their capacity to accumulate in the grafts. In contrast, an increased avidity in the allograft of 125IUdR-labeled TDL and lymph node (LNL) lymphoblasts, as compared to 125IUdR-labeled SL, resembles closely the results of functional studies of the differential potency of adoptively transferred cells. We assume that specific cellular interactions induced by the accumulated 125IUdR-labeled cells invoke nonspecific mechanisms for the recruitment of other uncommitted 111In-labeled lymphocytes which recirculate between blood and lymph and localize indiscriminately in the allograft amplifying its rejection. The latter lymphocytes can be "armed" by adherent cells residing in the lymphoid organs of graft recipients, particularly spleen, and subsequently increase the penetration of the foreign tissue. When radiolabeled lymphocytes were traced in B recipients experiencing rejection of their allografts following transfer of sensitized cells plus lymphokine, their migration patterns as well as blastogenic response in B hosts were similar to those observed during acute rejection of cardiac allografts in unmodified hosts. Thus the similarities between the rejection network brought by alloimmune cells into otherwise unresponsive animals and immunocompetent animals able to reject their grafts are stressed.

Recirculating and sessile B cell populations in normal and CBA/N mice

Chromosomally distinguishable syngeneic mice were parabiosed and the resultant chimerism was followed for 6 weeks in the lymphoid organs, by culturing their cells with polyclonal mitogens, lipopolysaccharide (LPS) for B cells and phytohemagglutinin (PHA) for T cells. As expected of a recirculating population, the T cells equilibrated completely. The B cells in lymph nodes (LN) and Peyer's patches (PP) also equilibrated completely, suggesting that they too are recirculating. B cells in the spleen and blood, however, did not equilibrate over this period. After separation of parabiosed mice, the percentage of partner cells in both the recirculating T and B lymphocyte populations declined steadily, but it continued to rise in the LPS-responsive populations in spleen and peripheral blood suggesting that they were derived from precursor populations which were themselves chimeric. Injection of lymphocytes into CBA/Ca or CBA/N mice showed that LPS-responsive populations in LN and spleen localized differently. These results have been interpreted as demonstrating two major populations of LPS-responsive B lymphocytes in the mouse, one recirculating and the other sessile. The recirculating population appears to be the only LPS-responsive population in LN and PP. In the spleen, however, the recirculating cells constitute about a quarter of the LPS-responsive cells, while the rest are sessile cells. The relationship between these two populations has yet to be clarified. CBA/N mice are deficient in both populations but the sessile one appears to be more severely depleted.

Macrophages and interdigitating cells; their relationship to migrating lymphocytes in the white pulp of rat spleen

The pathway of lymphocyte migration through the white pulp of rat spleen and the relationship of migrating cells to the accessory cells (marginal zone macrophages and interdigitating cells, IDCs) of the white pulp compartments were analysed. Donor lymphocytes were obtained from lymph nodes, enriched for T lymphocytes and labeled in vitro with 5-(3H)uridine. They were injected intravenously into syngeneic recipients from which samples of spleen were taken at short intervals from 3 to 300 min after injection. Autoradiographs of semithin and ultrathin sections showed that, in the internal layer of the marginal zone (MZ), lymphocytes tended to accumulate within some regions in close proximity to marginal-zone macrophages before migrating into the periarteriolar lymphoid sheath (PALS). The lymphocytes enter PALS between protrusions of the accessory cells located in the peripheral area of the sheath. During migration towards the central area of PALS, a close contact between both cell types was noted. In the central area of PALS, preferential accumulation of lymphocytes around IDCs was observed. Labeled lymphocyte distribution within PALS and the rate of cell migration through the white pulp seem to depend on lymphocyte-IDC contact. A common feature of accessory cells which may affect the migration of lymphocytes in both MZ and PALS is the presence of Birbeck granules.

The incidence of B cell leukaemia and lymphopenia in B cell neoplasia in adults: a study using the Kiel classification of non-Hodgkin's lymphoma

The incidence of B cell leukaemia in 186 consecutive untreated patients with histologically defined B cell neoplasms is described. The lymphomas were classified by the Kiel convention. B cell leukaemia in the context of this paper refers to the situation where a neoplastic clone of B cells in the blood greatly outnumbers normal blood B cells. It is defined as an absolute blood B cell count greater than 0.75 X 10(9)1(-1) where either greater than 90% B cells express kappa immunoglobulin light chains or greater than 80% express lambda light chains. This was found in several patients where the total blood lymphocyte count was within normal limits. All patients with diffuse lymphocytic lymphoma with the histological appearances of B cell chronic lymphocytic leukaemia (ML-BCLL) were found to have B cell leukaemia. However, more than half these patients had blood B cell counts less than 10 X 10(9)1(-1). B cell leukaemia was also a feature in approximately 33% of patients with follicle centre cell tumours and 33% of those with lymphoplasmacytoid tumours. B cell leukaemia was not detected in 34/35 patients with myelomatosis. The 35th patient had plasma cell leukaemia. Only 3/22 patients with high grade lymphoma had B cell leukaemia. In the three principal tumour types associated with B cell leukaemia mu + delta was the most common immunoglobulin heavy chain phenotype. Spontaneous mouse red cell rosette formation also characterised leukaemic B cells in these three groups but high proportions of mouse rosetting cells were seen only in association with ML-BCLL. None of 4 cases of prolymphocytic leukaemia showed mouse red cell rosetting. HLA-DR alpha chain was found on the leukaemic cells of all patients except one with ML-BCLL. B cell lymphopenia was a frequent finding in all histological groups in those patients who did not have B cell leukaemia.

The in-vivo kinetics of lymphoblast localization in the small intestine

We have studied the in-vivo kinetics of the accumulation of 125I-UdR labelled mesenteric lymphoblasts in the small intestine of mice. The efficiency with which the labelled cells were extracted from the blood and retained by the intestine was quantified by examination of the accumulations observed over the first 4 hr after cell transfer. The kinetic parameters for the uptake and retention of lymphoblasts determined from these early times were found to provide a good approximation to the entire time course of accumulation observed from 1 hr to 22 hr after cell transfer. For normal mice, approximately 1% of lymphoblasts delivered by the blood stream at any given time gained entry to the small intestine and were retained with an average half-time of 6.5 hr. We also studied the accumulation of lymphoblasts in the small intestine of mice undergoing a self-limited enteric infection with the nematode, Trichinella spiralis. There was a greater accumulation of lymphoblasts in the small intestine of these animals. This was the consequence of a prolongation of the half-time for retention of lymphoblasts within the intestine to 15 hr, rather than increased uptake of lymphoblasts from the blood. During a secondary infection with T. spiralis, the half-time for retention of lymphoblasts in the intestine was decreased to 3 hr. These studies show that viewing the accumulation of lymphoblasts as the result of a series of first order kinetic processes provides a suitable model for the migration of lymphoblasts to the small intestine.

Disappearance and reappearance of high endothelial venules and immigrating lymphocytes in lymph nodes deprived of afferent lymphatic vessels: a possible regulatory role of macrophages in lymphocyte migration

Interruption of the afferent lymphatic vessels of the popliteal lymph node resulted in the disappearance of high endothelial venules (HEV) and immigrating lymphocytes within 3 weeks. HEV showed several characteristic morphological changes: the endothelial cells became flattened and less pyroninophilic, the chromatine became condensed and protein synthetizing and secretory cell organelles became scarce. At the same time the number of macrophages in the lymph node was severely reduced. Injection of sheep red blood cells into such lymph nodes, 6 weeks after operation, resulted in reappearance of HEV and immigrating lymphocytes, and development of many plasma cells and some germinal centres. Injection of lipopolysaccharide into the operated lymph nodes resulted in the appearance of many plasma cells and a few poorly developed germinal centres; HEV and immigrating lymphocytes, however, remained almost absent. The results show a relationship between the immigration of lymphocytes and the activity of the endothelial cells in the HEV. The activation of the latter may occur by mediators released by antigen-stimulated macrophages and T cells. Moreover, the morphological features of the HEV are independent of the presence of recirculating lymphocytes.

The recirculation of T and B lymphocytes in the athymic, nude rat

The recirculation of lymphocytes through the tissues and their return to the blood were compared in nude and euthymic rats. Three approaches were used: the organ distribution of 15Cr-labelled lymphocytes from nude or euthymic donors at 24 h after injection; the compartmental distribution of B and T lymphocytes as assessed by autoradiography of the spleen, lymph nodes, and Peyer's patches; and the tempo of recirculation from blood to thoracic duct lymph as estimated by counting timed fractions of lymph from a recipient of labelled lymphocytes. The following conclusions were drawn: (1) The distribution of lymphocytes between organs and within organs is very similar in nude and euthymic recipients. In particular, B lymphocytes proceed normally to the follicular areas in the absence of T cells. (2) The recirculation from blood to lymph is delayed in nude rats. (3) For equal numbers of B and T cells injected intravenously about half as many B cells as T cells enter mesenteric and cervical lymph nodes, but approximately equal numbers of B and T cells enter the spleen and Peyer's patches.

Labeling of human lymphocytes with 99mTc by means of stannous pyrophosphate. Scintigraphic applications

An original 99mTc-labeling method applied to human lymphocytes is described. This technique is based on the use of stannous pyrophosphate to reduce sodium pertechnetate. The proposed procedure has two main advantages: firstly, the labeling process takes place in a neutral and buffered medium which prevents any cellular aggregation; secondly, the labeling yield obtained is compatible with scintigraphic studies in man. The influence of each parameter on the labeling quality had been studied as well as the binding stability of the technetium fixed on cells. A systematic study of lymphocyte surface markers, before and after labeling, has led to the suggestion that the labeling process seems to affect cellular membranes, probably because of the technetium binding. Finally, scintigraphic results are presented, the study being performed on eight healthy volunteers. These results are compared with those published by other authors who used either a different radioisotope or a different labeling method.

Cells of the marginal zone of the spleen are lymphocytes derived from recirculating precursors

The origin of the B cells of splenic marginal zones was studied using transfer experiments in rats depleted of marginal-zone cells. Cyclophosphamide given as a single dose of 500 mg/m2 was used to deplete the marginal zones. Approximately 90% depletion was still apparent 10 days after treatment. Fetal liver cells did not induce rapid repopulation of the marginal zone. Also bone marrow cells from rats depleted of recirculating lymphocytes were inefficient in this respect. Conversely, thoracic duct lymphocytes and bone marrow cells from normal rats were efficient at restoring marginal-zone cell numbers in cyclophosphamide-treated rats. Thoracic duct cells passaged through an irradiated intermediate host and collected from that host's thoracic duct were also efficient at achieving marginal-zone reconstitution. In rats receiving 1000 rd whole body irradiation, which were protected with fetal liver cell transfer, marginal zones did repopulate at about 3 weeks. It is concluded that marginal-zone B cells, after leaving primary lymphoid organs, enter the recirculating pool for a period of at least several days before settling in the marginal zone. The turnover rate of marginal-zone cells was assessed using tritiated thymidine infusion. Most marginal-zone cells were not labeled after 5 days continuous labeling suggesting that the marginal-zone B cells are not rapidly dividing.

A repopulation assay for B and T lymphocyte stem cells employing radiation chimaeras

The repopulation of the peripheral lymphoid compartment of lethally-irradiated rats reconstituted with lymphopoietic stem cells was studied. Cell lineages were traced by using genetic markers of cell surface molecules: immunoglobulin allotype for B lymphocytes and peripheral T cell alloantigen for T lymphocytes. Provided the markers had been bred on to a genetic background congenic with the hosts, they conferred neither an advantage nor disadvantage in competition with unmarked cells. The degree of chimaerism measured the lymphopoietic activity of the restorative inoculum. The most potent activity was found in foetal liver and spleen; next was infant spleen and bone marrow; then young adult bone marrow. Peripheral lymphoid tissues showed very little activity and thymus cells were inert. This tissue distribution, the stability of the chimaerism and the substantial expansion of numbers from the injected cells all point to the assay measuring an early stem cell. The overlap of subpopulations of lymphocytes in the rat thoracic duct was studied. A method for the conjugation of fluorescein to antibodies while they are attached to immuno-adsorbent affinity columns is also described.

Induced tolerance in F1 rats to anti-major histocompatibility complex receptors on parental T cells. Implications for self tolerance

The immunogenicity of cell surface markers associated with specific anti-major histocompatibility complex (MHC) alloreactivity of rat peripheral T lymphocyte subpopulations has been demonstrated in the past by the ability of such cell populations to induce a profound and specific resistance to systemic graft-vs.-host (GVH) disease in adult rats. Our studies demonstrate that these specificity-associated anti-MHC parental strain T cell markers are also tolerogenic; if small numbers of parental strain T cells are administered to newborn F1 rats, they result in the specific inability to induce GVH resistance later on in adult life. Moreover, unlike normal animals, these F1 rats are extremely sensitive to systemic GVH disease caused by T cells from the original donor parental strain.

Role of the popliteal lymph node in infection with Mycobacterium marinum of the hind footpad of the mouse, and source of the cells that characterize the process

We examined the possibility that the popliteal lymph node serves as the source of the lymphocytes that, together with macrophages, characterize the lesion produced by infection with Mycobacterium marinum in the hind footpad of the mouse. Naïve mice were partially protected against challenge with M. marinum in the hind footpad by intravenous infusion of lymphocytes harvested from the popliteal nodes of donor mice infected with M. marinum 7 days earlier. Lymphocytes harvested from the popliteal nodes of infected donors, labelled in vitro with 3H-uridine, and infused intravenously into naïve mice that were immediately challenged in the hind footpads with M. marinum, localized in the popliteal nodes of the recipient mice but not in the footpad lesions. Lymphocytes harvested from the spleens of naïve donors and labelled in vitro appeared to home to the popliteal node draining the M. marinum-infected footpad. Thus, the primary role of the popliteal lymph node appeared to be passive trapping of the lymphocytes brought to it by the circulation or afferent lymphatics. We then tried to locate the sources of both lymphocytes and macrophages that characterize the lesion. Temporary occlusion of the abdominal aorta prevented labelling by intravenously infused 3H-thymidine (3H-TdR) of the mononuclear cells of both footpad lesion and popliteal node. Temporary occlusion of the left common iliac artery during 3H-TdR infusion prevented immediate labelling on the ipsilateral side. After 24 and 48 h, however, small numbers of labelled lymphocytes were found in the left hind footpad lesion. Amputation of the right leg at the hip joint, but not right popliteal lymphadenectomy, performed immediately after re-establishment of patency of the left common iliac artery, prevented the late influx of labelled lymphocytes into the lesion of the left hind footpad. Thus, the chief source of both the lymphocytes and the macrophages of the footpad lesion appeared to be the lesion itself.