Nonrandom migration of CD4+, CD8+, and gamma delta+T19+ lymphocyte subsets following in vivo stimulation with antigen

We report here the results of experiments in which the migration of three T cell subsets (CD4+, CD8+, and gamma delta+T19+ cells) through antigen-stimulated lymph nodes and subcutaneous granulomas has been compared with that through normal skin and resting lymph nodes. The percentage of gamma delta+T19+ lymphocytes was halved and the percentage of CD8+ lymphocytes was doubled in lymph draining stimulated compared with control tissues, and all lymphocyte subsets except gamma delta+T19+ lymphocytes had higher hourly outputs in lymph draining antigen-stimulated compared with control tissues. Antigen also resulted in a higher percentage of CD8+ lymphoblasts and a lower percentage of gamma delta+T19+ lymphoblasts in efferent lymph draining antigen-stimulated lymph nodes. The data indicate that lymphocyte subsets leave the blood with differing efficiencies in different vascular beds and raise the possibility that antigen can influence the rate at which tissues extract individual T cell subsets from the blood.     

CD73-generated adenosine restricts lymphocyte migration into draining lymph nodes

After an inflammatory stimulus, lymphocyte migration into draining lymph nodes increases dramatically to facilitate the encounter of naive T cells with Ag-loaded dendritic cells. In this study, we show that CD73 (ecto-5'-nucleotidase) plays an important role in regulating this process. CD73 produces adenosine from AMP and is expressed on high endothelial venules (HEV) and subsets of lymphocytes. Cd73(-/-) mice have normal sized lymphoid organs in the steady state, but approximately 1.5-fold larger draining lymph nodes and 2.5-fold increased rates of L-selectin-dependent lymphocyte migration from the blood through HEV compared with wild-type mice 24 h after LPS administration. Migration rates of cd73(+/+) and cd73(-/-) lymphocytes into lymph nodes of wild-type mice are equal, suggesting that it is CD73 on HEV that regulates lymphocyte migration into draining lymph nodes. The A(2B) receptor is a likely target of CD73-generated adenosine, because it is the only adenosine receptor expressed on the HEV-like cell line KOP2.16 and it is up-regulated by TNF-alpha. Furthermore, increased lymphocyte migration into draining lymph nodes of cd73(-/-) mice is largely normalized by pretreatment with the selective A(2B) receptor agonist BAY 60-6583. Adenosine receptor signaling to restrict lymphocyte migration across HEV may be an important mechanism to control the magnitude of an inflammatory response.     

In vivo differentiated cytokine-producing CD4(+) T cells express functional CCR7

Chemokines and their receptors fulfill specialized roles in inflammation and under homeostatic conditions. CCR7 and its ligands, CCL19 and CCL21, are involved in lymphocyte recirculation through secondary lymphoid organs and additionally navigate lymphocytes into distinct tissue compartments. The role of CCR7 in the migration of polarized T effector/memory cell subsets in vivo is still poorly understood. We therefore analyzed murine and human CD4(+) cytokine-producing cells developed in vivo for their chemotactic reactivity to CCR7 ligands. The responses of cells producing cytokines, such as IFN-gamma, IL-4, and IL-10, as well as of subsets defined by memory or activation markers were comparable to that of naive CD4(+) cells, with slightly lower reactivity in cells expressing IL-10 or CD69. This indicates that CCR7 ligands are able to attract naive as well as the vast majority of activated and effector/memory T cell stages. Chemotactic reactivity of these cells toward CCL21 was absent in CCR7-deficient cells, proving that effector cells do not use alternative receptors for this chemokine. Th1 cells generated from CCR7(-/-) mice failed to enter lymph nodes and Peyer's patches, but did enter a site of inflammation. These findings indicate that CD4(+) cells producing effector cytokines upon stimulation retain the capacity to recirculate through lymphoid tissues via CCR7.     

Recirculatory and sessile CD4+ T lymphocytes differ on CD45RC expression

CD4+ T cell subsets are unequally distributed in rat secondary lymphoid organs. Those with the memory phenotype CD45RClow Thy-1- L-selectin- are present at a higher frequency in Peyer's patches (PP) than in lymph nodes and spleen, and increase in numbers with age in all three tissues, particularly in the PP. Homing experiments revealed that CD4+ T cells that recirculate through secondary lymphoid organs are mainly CD45RChigh. It was also apparent that the ability of recirculating cells to enter different lymphoid organs varies; less cells enter PP than the spleen or lymph nodes. Our results also reveal the existence of a nonrecirculating population of CD4+ T cells in secondary lymphoid organs, which are predominantly, if not exclusively, CD45RClow. Our results show that secondary lymphoid organs differ in their CD4+ T cell subset composition as a consequence of having different ratios of recirculatory:nonrecirculatory CD4+ T cells, and these cells display a different CD45RC phenotype.     

Random recirculation of small T lymphocytes from thoracic duct lymph in the mouse

The migration of ⁵¹Cr-labeled nylon-wool separated mouse thoracic duct T cells has been followed in order to determine whether there is a circulation of small (nondividing) T cells through the small intestine. Approximately 6% of the injected dose of T-TDL localized in the small intestine (minus Peyer's patches). Experiments revealed that this gut-localizing cell population consisted almost entirely, if not exclusively, of lymphoblasts present in mouse T-TDL. When lymphoblasts and small lymphocytes from mouse T-TDL were separated by velocity sedimentation, and the migration of separated fractions was studied, we found large cells (66% blasts) migrated well to the gut but poorly to the lymph nodes, whereas small cells (2% blasts) showed minimal migration to the gut but localized randomly in lymph nodes and spleen. The in vivo distribution of small cells from T-TDL was similar to that of T-PLN. Furthermore, the recirculatory patterns of both ⁵¹Cr-labeled T-TDL and T-PLN were found to be identical as accessed by their rate of recovery in the thoracic duct lymph of recipient mice. These results support the notion that the vast majority of T-TDL and T-PLN are part of a common pool of recirculating T cells which recirculate randomly through lymph nodes and spleen and not the small intestine.     

Most B cells in non-lymphoid tissues are naïve

The current view of lymphocyte migration states that na?ve lymphocytes re-circulate between the blood and the lymph via the lymph nodes, but are not able to access non-lymphoid tissues. We examined B lymphocytes in peripheral tissues and found that the majority were phenotypically similar to na?ve B cells in lymphoid tissues and were located within the parenchyma, not associated with blood vessels. The mutation rate within the Vh region of these cells was substantially less than the rate attributed to somatic hypermutation and was identical to that observed in na?ve B cells isolated from the lymph nodes, showing the presence of na?ve B cells in the non-lymphoid organs. Further, using FTY720-treated mice, we showed that na?ve B cells migrate through the peripheral tissues and, using pertussis toxin, that the entry of B cells was not controlled by chemokine-mediated signalling events. Overall, these results show that na?ve B lymphocytes constitute the majority of the total B-cell population in non-lymphoid tissues and suggest that these cells may re-circulate through the periphery as part of their normal migration pathway. This has implications for the current view of the role of na?ve B cells in priming and tolerance.     

Natural killer cell activity in the rat. V. The circulation patterns and tissue localization of peripheral blood large granular lymphocytes (LGL)

Large granular lymphocytes (LGL) and T cells were separated from blood by centrifugation on discontinuous gradients of Percoll, were labeled with [3H]uridine or [111In]oxine, and were injected i.v. into syngeneic euthymic or athymic nude rats. The tissue distribution of these labeled cells was monitored for up to 24 hr after transfer by scintillation counting of tissue homogenates and autoradiography of tissue sections. In normal euthymic rats, the main sites of LGL localization were the alveolar walls of the lungs and spleen red pulp; however, they were not detectable in the major traffic areas of T lymphocyte recirculation, the spleen white pulp, and lymph nodes. Furthermore, the density of labeled LGL was very low in the small intestine, thymus, kidney, and liver, although on a per-organ basis, about 10% of the injected radioactivity was found in the liver by 24 hr post-injection. When 111In-labeled LGL were injected i.v. into rats with an indwelling thoracic duct cannula, they completely failed to enter the thoracic duct lymphocyte (TDL) population over an observation period of 6 days. This finding was markedly different from the results obtained with T cells and was consistent with the lack of natural killer and antibody-dependent cellular cytotoxicity activity observed among TDL, even in rats pretreated with the biological response modifier, poly I:C. LGL in athymic nude rats also failed to recirculate between blood and lymph. However, in contrast to normal euthymic animals, a significant increase in the localization of radiolabeled LGL to lymph nodes was observed in nude rats between 30 min and 24 hr. Taken as a whole, these findings define the areas within the lungs and spleen in which blood LGL normally localize, and clearly demonstrate that LGL do not normally recirculate between blood and lymph.     

Overlapping and selective roles of endothelial intercellular adhesion molecule-1 (ICAM-1) and ICAM-2 in lymphocyte trafficking

The integrin LFA-1 interacts with a variety of ligands termed ICAMs. ICAM-1 and ICAM-2 are both expressed on endothelium and serve as counterreceptors during lymphocyte trafficking. In this study, we analyzed their relative contribution to lymphocyte recirculation through lymph nodes and to recruitment into lung and inflamed skin by blocking mAbs against ICAM-1 and ICAM-2 and mice deficient for ICAM-1. The entry of lymphocytes into peripheral and mesenteric lymph nodes was found to be unaffected by the functional deletion of either ICAM-1 or ICAM-2. However, when both pathways were blocked, recirculation through lymph nodes was strongly reduced. Trapping of lymphocytes in the lung after i.v. injection is partly mediated by LFA-1/ICAM interactions; the data presented in this study show an exclusive role of ICAM-1 in LFA-1-dependent lung trapping. Similarly, ICAM-1, but not ICAM-2, was required for the migration of T effector cells into the inflamed skin. These results indicate that ICAM-1 and ICAM-2 have redundant functions in lymphocyte recirculation through lymph nodes, but ICAM-1 is unique in supporting migration into inflamed sites and trapping within the lung.     

The kinetics of antigen-reactive cells during lymphocyte recruitment

Lymphocyte recruitment, the increased traffic of lymphocytes from blood to lymph which occurs within antigenically stimulated lymph nodes, was monitored in the efferent lymph of single lymph nodes in sheep after immunization with allogeneic lymphocytes or purified protein derivative. Specific antigen-reactive cells were assayed by their ability to proliferate in vitro in the presence of the priming antigen. During lymphocyte recruitment such cells were no longer detected in the efferent lymph draining either the immunized node or a nonstimulated node remote from the region of antigen administration. These results probably reflect the selective removal of specific lymphocytes from the recirculating pool. Alternatively, the findings could involve a state of specific unresponsiveness of the cells.     

Signaling through L-selectin mediates enhanced chemotaxis of lymphocyte subsets to secondary lymphoid tissue chemokine

L-selectin functions as an important adhesion molecule that mediates tethering and rolling of lymphocytes by binding to high endothelial venule (HEV)-expressed ligands during recirculation. Subsequent lymphocyte arrest and transmigration require activation through binding of HEV-decorated homeostatic chemokines such as secondary lymphoid tissue chemokine (SLC; CCL21) to its counterreceptor, CCR7. Importantly, L-selectin also functions as a signaling molecule. In this study, signaling induced by ligation of L-selectin using mAb or endothelial cell-expressed ligand significantly enhanced the chemotaxis of murine T cells and B cells to SLC but not to other homeostatic chemokines. Consistent with the expression levels of L-selectin in different lymphocyte subsets, L-selectin-mediated enhancement of chemotaxis to SLC was observed for all naive lymphocytes and effector/memory CD8(+) T cells, whereas only a subpopulation of effector/memory CD4(+) T cells responded. During in vivo mesenteric lymph node migration assays, the absence of L-selectin on lymphocytes significantly attenuated both their ability to migrate out of the HEV and their chemotaxis away from the vessel wall. Notably, ligation of L-selectin and/or CCR7 did not result in increased CCR7 expression levels, internalization, or re-expression. Pharmacologic inhibitor studies showed that L-selectin-mediated enhanced chemotaxis to SLC required intact intracellular kinase function. Furthermore, treatment of lymphocytes with the spleen tyrosine kinase family inhibitor piceatannol reduced their ability to migrate across the HEV in peripheral lymph nodes. Therefore, these results suggest that "cross-talk" in the signaling pathways initiated by L-selectin and CCR7 provides a novel mechanism for functional synergy between these two molecules during lymphocyte migration.     

Divergent actions of monomeric, dimeric, and tetrameric concanavalin A on lymphocyte traffic

The autoradiographic analysis of the localization of [³H]adenosine-labeled cells exposed to concanavalin A (Con A) in vitro has confirmed that the altered migration of Con A-treated lymphocytes is a consequence of their slower rate of migration and delay in normal areas of traffic (5, 6). The mechanisms through which Con A alters cell migration were further investigated by studying the effects of several derivatives of Con A on the distribution of ⁵¹Cr-labeled lymph node cells. The results obtained show that the monomeric and dimeric forms of Con A were unable to modify cell traffic, a condition that was partially reversed when succinyl Con A-treated cells were exposed to divalent antibodies to Con A. This suggests that Con A may alter lymphocyte recirculation by actively modifying the membrane fluidity or the surface lateral transport of the lymphocyte. Whatever the exact mechanisms responsible for the altered migration are, they probably involve complex active processes that can be related to the heterogeneity of Con A receptors, the existence of subsets of cells with different reactivities to the lectin, or simply the result of a passive phenomenon dependent on the presence of Con A on the cell surface.     

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 ¹¹¹Inlabeled 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.     

The activatory receptor 2B4 is expressed in vivo by human CD8+ effector alpha beta T cells.

The membrane receptor 2B4 is a CD2 family member that is involved in lymphocyte activation. A fraction of human CD8+ alphabeta T cells up-regulate 2B4 in vivo, and here we demonstrate that this correlates with the acquisition of effector cell properties such as granzyme B and perforin expression, rapid IFN-gamma production, and down-regulation of the lymph node homing chemokine receptor CCR7. In PBLs from healthy donors, cytomegalovirus-specific effector T cells were 2B4 positive, whereas naive melanoma Ag (Melan-A/melanoma Ag recognized by T cells-1)-specific T cells were 2B4 negative. In melanoma patients, Melan-A-specific T cells up-regulated 2B4 in parallel with in vivo differentiation. This occurred in PBLs after vaccination with Melan-A peptides and in tumor-infiltrated lymph nodes, likely through disease-associated activation of Melan-A-specific T cells. Thus, 2B4 expression correlates with CD8+ T cell differentiation in vivo.     

Alterations in lymphocyte homing patterns within mice exposed to ultraviolet radiation

This report presents the results of an investigation designed to establish whether exposure of mice to ultraviolet radiation (UVR) is capable of influencing the factors that control the distribution of lymphoid cells in vivo. We found that such exposure resulted in a dramatic and long-lasting increase in the tropism of peripheral lymph nodes for circulating lymphoid cells. Termination of UVR exposure did not result in a reversal of this phenomenon. Since an increase in lymphocyte migration into the lymph nodes of UVR-exposed mice was apparent within 2 hr of infusion of the radiolabeled cells, we conclude that the homing assay data reflect a relatively increased binding of circulating lymphocytes to high endothelial venules (HEV) within the lymph nodes of irradiated animals. A histologic analysis of skin from UVR-exposed mice established that the dermal microvasculature had expanded in terms of size and number of vessels, a condition that also does not completely reverse after the termination of treatments. In spite of the increase in dermal microvasculature, very few inflammatory cells were detected in the irradiated skin site. These observations support our conclusion that the enhanced traffic of lymphocytes into peripheral lymph nodes of UVR-exposed mice occurs primarily via lymphocyte-HEV interactions rather than afferent drainage of the irradiated skin.     

Human lymphocyte-high endothelial venule interaction: organ-selective binding of T and B lymphocyte populations to high endothelium

We wished to determine whether human lymphocytes, like their murine counterparts, show organ-specific interactions with high endothelial venules (HEV). Functional HEV-binding ability was measured by an in vitro assay of lymphocyte adherence to HEV in frozen sections of human lymphoid tissues which was adapted from rodent systems. It was found that human lymphocytes bind selectively to HEV and that, whereas mature T lymphocytes bind preferentially to HEV in peripheral lymph nodes and tonsils, B lymphocytes show preferential binding to HEV in GALT. Moreover, by analyzing the binding characteristics of T4+ and T8+ T cell populations, it was found that T8+ cells adhere preferentially to HEV in GALT and mesenteric lymph nodes and tonsil, and that T4+ cells bind slightly better to HEV in peripheral lymph nodes. The above findings indicate that organ--specific lymphocyte-endothelial cell recognition mechanisms exist also in humans, and suggest that these mechanisms play an important role in normal and pathologic lymphocyte traffic.     

Physiology of B cells in mice with X-linked immunodeficiency. I. Size, migratory properties, and turnover of the B cell pool

In terms of certain immune functions and density of surface IgM, B cells from xid mice are often viewed as the equivalent of the immature (Lyb-5-) B cell subset of normal adult mice. In this paper we examine xid B cells with regard to certain physiologic functions, including homing to the lymphoid tissues, recirculation, and turnover. Xid mice were found to possess about one-third of the total number of B cells found in normal mice. This applied irrespective of whether one examined the spleen, lymph nodes, or outputs of B cells in thoracic duct lymph. In terms of migration to spleen, lymph nodes, and Peyer's patches, capacity to recirculate from blood to thoracic duct lymph, and turnover, xid B cells proved to be indistinguishable from normal spleen or thoracic duct B cells. Within these parameters, most xid B cells closely resemble the normal mature long-lived population of B cells residing in the recirculating pool of normal mice. Because xid B cells are functionally quite different from normal mature B cells, it seems reasonable to view xid B cells as an abnormal population not represented in normal mice.     

Effect of sublethal ionizing radiation on rat Peyer's patch lymphocytes

After sublethal doses of ionizing radiation, rat Peyer's patch lymphocytes regenerated significantly more slowly than lymphocytes from spleen, thymus, and peripheral lymph nodes. Long Evans rats were exposed to 150 rad (40 rad/min) of whole-body irradiation from a 60Co, gamma-emitting source. On Days 1-20 postirradiation, single cell suspensions of lymphocytes from thymus, spleen, peripheral lymph nodes, and Peyer's patches were stained with mouse monoclonal antibody reagents specific for rat lymphocyte subpopulations (Ia+ cells, non-helper T-cell subsets, and helper T-cell subsets). Cells were then counterstained with Texas Red-conjugated, goat anti-mouse IgG and, at the same time, were also stained with fluorescein diacetate to determine viable lymphocytes. The stained lymphocytes were analyzed using a dual-laser, fluorescent-activated cell sorter (Becton-Dickinson FACS-II) from which the percentage of each lymphocyte subpopulation was determined. From our studies, we found that all subpopulations of lymphocytes were affected similarly by irradiation. In addition, we observed that viable lymphocyte subpopulation in thymus, spleen, and peripheral lymph nodes from irradiated animals returned to normal (nonirradiated control animals) levels 5-12 days postirradiation, while viable lymphocyte subpopulations in Peyer's patches from irradiated animals remained suppressed up to 20 days postirradiation. These results suggest that either the lymphocytes or, more likely, the microenvironment of Peyer's patches is more greatly damaged by ionizing radiation than that observed in other lymphoid tissue.     

Lymphocyte migration during the development of regional lymph node anergy in experimental tumor growth

The development of lymph node anergy in Wistar rats to growing Walker carcinoma 256 was studied in vitro using the 51Cr-release cytotoxicity assay. Cell-mediated cytotoxicity to the tumor peaked in draining lymph nodes 11 days after tumor transplantation. By 14 days, the regional lymph node had become anergic to the tumor at a time when cell-mediated cytotoxicity was still increasing in the more distal contralateral lymph node. Lymphocyte migration into resting, cytotoxic, and anergic lymph nodes was analyzed to determine if altered cell migration into the regional lymph node was associated with the development of anergy. Lymphocyte migration was found to be enhanced in both cytotoxic and anergic regional lymph nodes of tumor-bearing animals. It is concluded that lymph node anergy in this experimental tumor system is not related to changes in lymphocyte migration patterns; rather, it is the result of alterations in the microenvironment of the lymph node which prevents the expression of cytotoxic effector cells.     

Expression of low levels of peripheral lymph node-associated vascular addressin in mucosal lymphoid tissues: possible relevance to the dissemination of passaged AKR lymphomas

Lymphoid tumors display a wide variety of growth patterns in vivo, from that of a solitary extralymphoid tumor, to a general involvement of all lymphoid organs. Normal lymphocytes are uniquely mobile cells continuously recirculating between blood and lymph throughout much of their life cycle. Therefore, it is reasonable to propose that disseminating malignant lymphocytes may express recirculation characteristics or homing properties consistent with that of their normal lymphoid counterparts. Trafficking of lymphocytes involves the expression and recognition of both lymphocyte homing receptors and their opposing receptors on endothelium, the vascular addressins. These cell surface elements direct the tissue-selective localization of lymphocyte subsets in vivo into organized lymphoid organs and sites of chronic inflammation where specific binding events occur between lymphocytes and the endothelium of specialized high endothelial venules (HEV). In a recent murine study of 13 lymphoma lines, we found that lymphomas that bind well to high endothelial venules, in the Stamper-Woodruff in vitro assay (an assay of lymphocyte binding to venules in frozen sections of peripheral lymph nodes or Peyer's patches), spread hematogenously to all high endothelial venule bearing lymphoid organs, whereas non-binding lymphomas did not. In some cases lymphomas that bound with a high degree of selectivity to peripheral lymph node (PLN) high endothelial venules exhibited only limited organ preference of metastasis, involving the mucosal lymphoid organs Peyer's patches (PP) in addition to the peripheral lymph nodes of adoptive recipients. Here we demonstrate that Peyer's patch high endothelial venules express a low but functional level of peripheral lymph node addressin (MECA-79) that can be recognized by lymphomas expressing the peripheral lymph node homing receptor (MEL-14 antigen).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for an accessory role of LFA-1 in lymphocyte-high endothelium interaction during homing

In a variety of lymphocyte interactions, lymphocyte function-associated antigen-1 (LFA-1) plays an important role as an accessory mechanism mediating cell adhesion. We tested the possibility that LFA-1 could also be involved in the specific binding of lymphocytes to high endothelial venules (HEV) during homing. Antibodies against LFA-1 but not against various other cell surface molecules (except the putative gp90 homing receptor defined by the MEL-14 antibody) were found to inhibit in vitro adherence of lymphocytes to HEV in frozen sections of lymph nodes. Binding of T cell lines to HEV was also inhibited by anti-LFA-1 antibody. Using sublines selected for differential expression of the MEL-14 antigen, MEL-14 high cells (which bind well to HEV) were less susceptible to inhibition by anti-LFA-1 than poor binders with low levels of the homing receptor, supporting the model of LFA-1 being an accessory mechanism strengthening weak interactions between cells. Parallel results were found in vivo where anti-LFA-1 antibodies reduced the migration of normal lymphocytes into lymph nodes and Peyer's patches by 40 to 60%. Localization in the lung, especially of activated lymphocytes, was also impaired, although to a lesser extent. These findings suggest that LFA-1 plays an accessory role in cellular interactions relevant for lymphocyte migration.