Validation of the

The cluster structure of the neutron-rich isotope ^{10}Be has been probed via the (p,pα) reaction at 150 MeV/nucleon in inverse kinematics and in quasifree conditions. The populated states of ^{6}He residues were investigated through missing mass spectroscopy. The triple differential cross section for the ground-state transition was extracted for quasifree angle pairs (θ_{p},θ_{α}) and compared to distorted-wave impulse approximation reaction calculations performed in a microscopic framework using successively the Tohsaki-Horiuchi-Schuck-Röpke product wave function and the wave function deduced from antisymmetrized molecular dynamics calculations. The remarkable agreement between calculated and measured cross sections in both shape and magnitude validates the molecular structure description of the ^{10}Be ground-state, configured as an α-α core with two valence neutrons occupying π-type molecular orbitals.

Observation of Coulomb-Assisted Nuclear Bound State of Ξ

In an emulsion-counter hybrid experiment performed at J-PARC, a Ξ^{-} absorption event was observed which decayed into twin single-Λ hypernuclei. Kinematic calculations enabled a unique identification of the reaction process as Ξ^{-}+^{14}N→_{Λ}^{10}Be+_{Λ}^{5}He. For the binding energy of the Ξ^{-} hyperon in the Ξ^{-}-^{14}N system a value of 1.27±0.21 MeV was deduced. The energy level of Ξ^{-} is likely a nuclear 1p state which indicates a weak ΞN-ΛΛ coupling.

[Early viscoelasticity-based coagulation therapy for severely injured bleeding patients: Report of the consensus group on the consensus conference 2014 for formulation of S2k guidelines]. / Frühe viskoelastizitätsbasierte Gerinnungstherapie bei blutenden Schwerverletzten: Bericht der Konsensusgruppe über die Konsensuskonferenz 2014 zur Erarbeitung einer S2k-Leitlinie.

Although there is increasing interest in the use of a viscoelastic test procedure (ROTEM/TEG) for diagnostics and therapy guidance of severely injured and bleeding patients, currently no uniformly accepted guidelines exist for how this technology should be integrated into clinical treatment. In September 2014 an international multidisciplinary group of opinion leaders in the field of trauma-induced coagulopathy and other disciplines involved in the treatment of severely injured patients were assembled for a 2-day consensus conference in Philadelphia (USA). This panel included trauma/accident surgeons, general/abdominal surgeons, vascular surgeons, emergency/intensive care surgeons, hematologists, transfusion specialists, anesthesiologists, laboratory physicians, pathobiologists/pathophysiologists and the lay public. A total of nine questions regarding the impact of viscoelastic testing in the early treatment of trauma patients were developed prior to the conference by a panel consensus. Early use was defined as baseline viscoelastic test result thresholds obtained within the first minutes of hospital arrival, when conventional laboratory results are not yet available. The available data for each question were then reviewed in person using standardized presentations by the expert panel. A consensus summary document was then developed and reviewed by the panel in an open forum. Finally, a 2-round Delphi poll was administered to the panel of experts regarding viscoelastic thresholds for triggering the initiation of specific treatments including fibrinogen (concentrates), platelet concentrates, blood plasma products and prothrombin complex concentrates (PCC). This report summarizes the findings and recommendations of this consensus conference, which correspond to a S2k guideline according to the system of the Association of the Scientific Medical Societies in Germany (AWMF) and taking formal consensus findings including Delphi methods into consideration.

Effect of delaying same-admission cholecystectomy on outcomes in patients with diabetes.

BACKGROUND: Recent studies have suggested that same-admission delayed cholecystectomy is a safe option. Patients with diabetes have been shown to have less favourable outcomes after cholecystectomy, but the impact of timing of operation for acute cholecystitis during the same admission is unknown. METHODS: This was a retrospective analysis of patients undergoing laparoscopic cholecystectomy for acute cholecystitis between 2004 and 2010, from the American College of Surgeons National Surgical Quality Improvement Program database. Patients with no significant co-morbidities (American Society of Anesthesiologists grade I or II) were included. Propensity score matching (PSM) was used to match patients with diabetes with those who did not have diabetes, in a ratio of 1:3, to ensure homogeneity of the two groups. Logistic regression models were applied to adjust for differences between early (within 24 h) and delayed (24 h or more) surgical treatment. The primary outcome was development of local and systemic infectious complications. Secondary outcomes were duration of operation and length of hospital stay. RESULTS: From a total of 2892 patients, 144 patients with diabetes were matched with 432 without diabetes by PSM. Delaying cholecystectomy for at least 24 h after admission in patients with diabetes was associated with significantly higher odds of developing surgical-site infections (adjusted odds ratio 4.11, 95 per cent confidence interval 1.11 to 15.22; P = 0.034) and a longer hospital stay. For patients with no diabetes, however, delaying cholecystectomy had no impact on complications or length of hospital stay. CONCLUSION: Patients with diabetes who undergo laparoscopic cholecystectomy 24 h or more after admission may have an increased risk of postoperative surgical-site infection and a longer hospital stay than those undergoing surgery within 24 h of admission.

Impact of anastomotic complications on outcome after laparoscopic gastrectomy for early gastric cancer.

BACKGROUND: The effects of anastomotic complications after laparoscopically assisted gastrectomy (LAG) have not been studied widely. The aims of this observational study were to identify potential factors that predict anastomotic complications and investigate the impact of anastomotic complications in patients undergoing gastrectomy for early gastric cancer. METHODS: The study included consecutive patients with histologically proven T1 gastric adenocarcinoma treated by LAG with regional lymphadenectomy between August 1997 and March 2008, who had not received neoadjuvant chemotherapy. Anastomotic complications included anastomotic leakage, stricture and remnant gastric stasis of grade II or higher (modified Clavien classification) and were identified by clinical assessment and confirmatory investigation. Predictive factors for the development of anastomotic complications were identified by univariable and multivariable analyses. Long-term survival with or without anastomotic complications was examined. RESULTS: Anastomotic complications occurred in 37 (9·3 per cent) of 400 patients. Multivariable analysis indicated surgeon experience as the only independent predictor of anastomotic complications (hazard ratio 4·40, 95 per cent confidence interval 2·04 to 9·53; P < 0·001). Patients with anastomotic complications had a significantly worse overall 5-year survival rate than those without (81 versus 94·2 per cent; P = 0·009). CONCLUSION: Anastomotic complications after LAG lead to worse long-term survival.

Relevance of lymph node metastasis along the superior mesenteric vein in gastric cancer.

BACKGROUND: The purpose of this study was to evaluate the prognostic value of lymph node metastasis along the superior mesenteric vein (station 14v) to determine the need for 14v dissection in gastric cancer surgery. METHODS: A total of 1104 patients with gastric cancer who underwent gastrectomy including 14v dissection were enrolled. Patients were categorized into two groups: those with and those without 14v lymph node involvement by metastasis. RESULTS: Of the total study population, 73 patients (6·6 per cent) had 14v-positive gastric cancer. These patients were more likely to have advanced tumour (T), node (N) and distant metastatic (M) status, and histologically undifferentiated gastric cancers. The 3- and 5-year survival rates of patients with 14v-positive disease were 24 and 9 per cent respectively. Survival in this group was similar to that of patients who had gastric cancer with distant metastasis (M1). Multivariable analysis demonstrated that 14v status was a significant prognostic factor for gastric cancer (hazard ratio 2·13; P < 0·001). After histologically complete (R0) resection, the overall survival of 14v-positive patients with any stage of cancer was significantly worse than that for 14v-negative patients with stage IV cancer (P = 0·006). CONCLUSION: 14v status is an independent prognostic factor for gastric cancer, with 14v-positive gastric cancer having a poor prognosis, similar to that of M1 disease. The exclusion of 14v in regional lymph node dissection should be considered.

Accessory cell-T lymphocyte interactions. Antigen-dependent and -independent clustering.

Previous work documented the capacity of dendritic cells (DC) to stimulate primary immune responses and to physically cluster with the responding lymphocytes. Rapid cell-cell aggregation assays were used here to study the interaction of DC and other types of APC with T lymphocytes. Graded doses of APC were sedimented with T cells that had been primed to alloantigens, soluble proteins, or lectin, and then labeled with carboxyfluorescein diacetate. The number of clustered T cells was measured after 10 min at 4 or 37 degrees C. At 4 degrees, binding was antigen-dependent and included greater than 50% of the added T cells. Clustering was mediated by all types of APC tested, including DC, macrophages, B lymphocytes, and fresh Langerhans cells, although DC were the most effective. Specificity was evident in the findings that alloreactive T lymphoblasts bound to allogeneic but not syngeneic APC; KLH- and OVA-reactive T cells bound to syngeneic APC in the presence of specific protein: and Con A blasts needed lectin to cluster. A 30 min pretreatment with chloroquine, a drug known to inhibit APC activity, markedly blocked the specific binding of alloreactive and protein-specific T blasts at 4 degrees C. Since Lyt-2- alloreactive blasts should specifically recognize Ia, presentation of Ia seems to be altered by chloroquine. Binding assays at 37 degrees C gave similar results to those performed at 4 degrees C, with one exception. When DC were used as APC, striking antigen-independent clustering occurred. DC could efficiently cluster primed T cells in the absence of alloantigen, soluble protein, or lectin. We suggest that antigen-independent binding contributes to the distinctive capacity of DC to prime T cells in the afferent limb of the immune response, whereas antigen-dependent binding between other APC and sensitized lymphocytes is critical in the efferent limb.

Monoclonal antibodies to LFA-1 and to CD4 inhibit the mixed leukocyte reaction after the antigen-dependent clustering of dendritic cells and T lymphocytes.

T cell proliferation in response to many stimuli is known to occur in discrete clusters of dendritic cells (DC) and CD4+ helper lymphocytes. The role of lymphocyte function-associated antigen (LFA-1) and CD4 in the formation and function of these clusters has been evaluated in the mixed leukocyte reaction (MLR). By day 1 of the control MLR, most of the DC and responsive T cells are associated in discrete aggregates. Addition of anti-LFA-1 and CD4 reagents does not block DC-T aggregation but reduces the subsequent proliferative response by 80-90%. Anti-LFA-1 disassembles newly formed DC-T cell aggregates, whereas anti-CD4 inhibits blastogenesis without disrupting the cluster. Binding of DC to sensitized, antigen-specific CD4+ cells has been studied using lymphoblasts isolated at day 4 of the MLR. It has been shown previously that greater than 80% blasts rebind to DC in an antigen-specific fashion in rapid (10 min) binding assays. Antigen-dependent DC-T binding is blocked by anti-Ia but not by mAb to LFA-1 or CD4. However, the bound anti-CD4-coated lymphocytes are unable to release IL-2. Anti-LFA-1-coated T cells release IL-2 but are easily disaggregated after binding to DC. These findings lead to two conclusions. LFA-1 and CD4 are not involved in the initial steps whereby DC bind to T cells but exert an independent and subsequent role. LFA-1 acts to stabilize the DC-T cluster, while CD4 contributes to lymphocyte blastogenesis and IL-2 release. Because DC but not other presenting cells cluster unprimed lymphocytes, it seems likely that an antigen-independent mechanism distinct from LFA-1 and CD4 mediates aggregate formation at the onset of cell-mediated immunity.

Resting and sensitized T lymphocytes exhibit distinct stimulatory (antigen-presenting cell) requirements for growth and lymphokine release.

Previous studies have shown that unprimed or resting T lymphocytes will grow and release lymphokines when stimulated by dendritic cells (DC). We now have examined the stimulatory requirements for antigen-primed or blast-transformed T cells. The latter were derived from dendritic/T cell clusters that developed during the primary mixed leukocyte reaction (MLR). The specificity of the blasts was established by a binding assay in which most T cells aggregated small B lymphocytes of the appropriate haplotype within 2 h at 4 or 37 degrees C. Since unprimed T cells did not aggregate allogeneic B cells, we suggest that DC induce T lymphocytes to express additional functioning receptors for antigen. Lyt-2-T blasts did not grow or release interleukin 2 or B cell helper factors unless rechallenged with specific alloantigen, whereupon growth (generation time of 14-18 h) and lymphokine release rapidly resumed. The blasts could be stimulated by allogeneic macrophages, B cells, and B lymphoblasts, whereas the primary MLR was initiated primarily by DC. responsiveness appeared restricted to the I region of the major histocompatibility complex, and varied directly with the level of Ia antigens on the stimulator cells. The interaction of B cells and T blasts was bidirectional. The T blasts would grow and form B cell helper factors, while the B cells grew and secreted antibody. However, the efficacy of T cell-mediated antibody formation was enhanced some 10-fold by the addition of specific antigen. Therefore, responses of resting helper T cells, then, are initiated by antigen plus DC. Once sensitized, T blasts interact independently with antigen presented by other leukocytes.

An antigen-independent contact mechanism as an early step in T cell-proliferative responses to dendritic cells.

Dendritic cells bearing antigen efficiently aggregate and stimulate antigen-specific T cells. We describe an experimental model in which an initial, apparently antigen-independent binding step is followed by ligation of the TCR. The model is the polyclonal response to mAb to the CD3 portion of the TCR complex. Epidermal and thymic dendritic cells utilize low levels of Fc receptors to present the anti-CD3 mAb and induce mitogenesis. Within 3 h of coculture, most of the dendritic cells have formed clusters with the resting T lymphocytes, and these clusters are the site for subsequent DNA synthesis and cell growth. However, the binding of dendritic cells to T cells proceeds as efficiently in the absence of anti-CD3 as in its presence, and anti-FcR mAb does not block. CD3 and Fc receptors are essential for the subsequent mitogenesis response in dendritic-T cell clusters. Because an exogenous ligand for the TCR does not seem to be required for the extensive polyclonal clustering of resting lymphocytes to dendritic cells, we suggest that an antigen-independent mechanism mediates the initial interaction. This clustering seems essential for T cell growth since we do not detect, in two-chamber experiments, soluble lymphocyte-activating factors that originate from dendritic-T cell aggregates and that activate anti-CD3-coated T cells.

Direct activation of CD8+ cytotoxic T lymphocytes by dendritic cells.

Recent experiments (11-13) have shown that antigen-specific, CD8+, CD4- T lymphocytes can be induced to proliferate and become killer cells in the absence of a second population of "helper" CD8-, CD4+ cells. We have studied early events in the activation of CD4+ and CD8+ T cell subsets in the primary mixed leukocyte reaction. Dendritic cells are a major if not essential accessory cell for the activation of both subpopulations. Antigen-bearing macrophages fail to stimulate unprimed CD8+ cells, but act as targets for the sensitized cytolytic lymphocytes that are induced by dendritic cells. The initial proliferative response is comparable for CD4+ and CD8+ lymphocyte subsets. For both subpopulations, dendritic cells efficiently cluster the responding lymphocytes on the first day and induce the release of IL-2. The data indicate that CD4+ and CD8+ lymphocytes can be activated by a similar mechanism, and illustrate the special role of dendritic cells in the sensitization stage of cell-mediated immunity.

Interleukin 1 enhances T-dependent immune responses by amplifying the function of dendritic cells.

The function of exogenous murine recombinant IL-1 alpha as a T lymphocyte-activating molecule was examined. IL-1 did not induce IL-2 release or responsiveness in purified T cells regardless of their state of activation: unprimed lymphocytes, freshly sensitized lymphocytes, or memory cells derived from the blasts. Nor did IL-1 synergize with mitogens, or with antigens, to stimulate proliferation. For example the combinations of IL-1 plus Ia+ peritoneal macrophages, or IL-1 plus Con A, were less than 5% as effective in triggering T cell growth as a low dose (1%) of dendritic cells. However, when IL-1 was added at the onset of culture, the response to limiting doses of dendritic cells was increased 3- to 10-fold in several systems: the syngeneic and allogeneic MLR, Con A- and periodate-induced polyclonal mitogenesis, and T-dependent antibody formation against foreign red cells. The amplifying effect of IL-1 could be obtained if the dendritic cells but not the responding lymphocytes were exposed to IL-1 before use as accessory cells. Optimal activation of dendritic cells required a dose of 5 U/ml (50 pM) and 18 h of exposure, and was not due to carryover of IL-1 into the lymphocyte culture. IL-2, IL-3, and cachectin/TNF did not amplify dendritic cell function, while IFN-gamma diminished it. The enhanced function of IL-1-treated dendritic cells was due to an enhanced clustering with helper T lymphocytes in the first day of the MLR response. Therefore IL-1 does not seem to act as an activating factor for most peripheral T lymphocytes. Instead, IL-1 enhances the function of accessory dendritic cells and represents the first molecule that has been shown to enhance the immune response at this critical level.

Lymphokine production by murine T cells in the mixed leukocyte reaction.

Although the production of B cell stimulatory factors by cell lines and hybridomas is well established, production of specific lymphokines by normal T cells in response to antigen stimulation has not been analyzed. We have used bioassays and neutralizing mAbs to demonstrate that IL-2, IL-4, and B cell growth factors (BCGF) are produced during primary and secondary MLRs. IL-2 is detected in the first 12 h of both types of MLR. IL-4 and BCGF appear at 24-48 h in the conditioned medium of the primary MLR, and peak by 12 h in the secondary MLR. The amount of IL-4 in the primary response reaches a level that is 10% of that detected in the secondary. In contrast, BCGF production steadily increases over time in the primary MLR, and maximal production is equivalent to that made in the secondary response. Allogeneic dendritic cells and anti-Ig-activated B blasts both stimulated lymphokine production in the primary MLR, whereas small B cells were weak. In the secondary MLR, all three cell populations stimulated the production of IL-2, IL-4, and BCGF. Therefore, the release of several defined B cell stimulating factors can be detected in the conditioned media of responding primary T lymphocytes.

Dendritic cells induce T lymphocytes to release B cell-stimulating factors by an interleukin 2-dependent mechanism.

Dendritic cells (DC) are essential accessory cells for T-dependent antibody responses in culture (1). We have outlined a three-stage mechanism to explain the capacity of DC to stimulate primary antibody responses to heterologous erythrocytes. First, DC induced T cells to produce and to become responsive to interleukin 2 (IL-2). This stage corresponded to the syngeneic mixed leukocyte reaction (2) and involved the clustering of DC and T cells into discrete aggregates. Isolated clusters, representing 5-10% of the culture, were critical for IL-2 release and the production of IL-2-responsive T blasts. In the second stage, IL-2 directly triggered the responsive T cells to release B cell helper factors. This role for IL-2 was documented with a rabbit anti-IL-2 reagent, purified IL-2, and T cells that had been rendered IL-2 responsive by an initial co-culture with DC. T cell growth was not required for IL-2-mediated helper factor release, since irradiated and untreated responders produced similar levels of factor and did so within 3 h of the addition of IL-2. In the final stage, helper factors stimulated the development of antibody-secreting cells from purified B lymphocytes. The helper factors were not H-2 restricted, but for both sheep and horse erythrocytes, the response to factors was antigen dependent and specific. The IL-2 that was present in the DC/T cell-conditioned medium did not act on B cells, since helper activity was neither neutralized nor absorbed by our anti-IL-2 reagent. We conclude that the ability of the DC to induce IL-2 release and responsiveness underlies its capacity to trigger both T and B lymphocyte reactions.

Clustering of dendritic cells, helper T lymphocytes, and histocompatible B cells during primary antibody responses in vitro.

Mouse spleen suspensions generate discrete cell clusters within 1-2 d of culture. We have isolated these clusters by velocity sedimentation to study their contribution to primary antibody responses. Clusters represent approximately 5% of the starting spleen cells and consist of 20-50% B cells, 20-50% T cells, and 10-20% dendritic cells (DC). When the cultures are stimulated with thymus-dependent antigens, like heterologous red cells or dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH), the clusters are the principal site for the development of plaque-forming cells (PFC). Noncluster fractions form few PFC and only when supplemented with fresh DC. PFC responses in all cases are antigen specific. B cells cluster only in the presence of T cells and DC (1 DC/200 B-T cell mixtures) and only after encountering specific antigen. The elimination of either DC or Lyt-1+2- T cells, with monoclonal antibody and complement, ablates B cell development into PFC. PFC responses are restored with antigen-nonspecific helper factors formed in the syngeneic mixed leukocyte reaction between DC and T cells. Since PFC to DNP-KLH do not develop de novo when B cells are exposed to antigen and helper factors, anti-DNP PFC precursors must be stimulated within clusters to become responsive to helper factors. PFC development within clusters is restricted by the major histocompatibility complex (MHC). When DC and T cells are from strain P1, then P1 but not P2 B cells develop into PFC; when DC are from strain P2 and T cells from strain P1, strain P2 B cells are selected to become PFC in clusters. The entry of B cells into clusters is itself MHC restricted, since P1 DC/T cells aggregate six times as many B cells from strain P1 as strain P2. Thus, clusters are the site in which DC, B, and T cells interact to generate PFC. One can use clusters to retrieve B cells that have been selected in an antigen-dependent, MHC-restricted fashion and to show that clustering B cells become responsive to soluble, polyclonal helper factors.

Stimulation of lymphokine release from T lymphoblasts. Requirement for mRNA synthesis and inhibition by cyclosporin A.

Three-day, concanavalin A-induced T lymphoblasts have been used as a model to study lymphokine release from sensitized T cells. The blasts responded to interleukin 2 (IL-2) but did not constitutively produce this or other lymphokines. After mitogen restimulation, blast cells synthesized IL-2 as well as gamma-interferon, B cell-stimulating factor(s), and cytolytic differentiation factor(s). This production resulted from the induction of biologically active lymphokine mRNA. Cyclosporin A (CSA), a potent immunosuppressive agent, strongly inhibited synthesis of IL-2, gamma-interferon, and B cell- and CTL-stimulating factor(s), from mitogen-restimulated T blasts. In contrast, CSA did not block the cytolytic activity of the T blasts, nor modify bulk protein synthesis induced by Con A. CSA also blocked lymphokine release from a phorbol myristate acetate-stimulated thymoma cell line, EL-4. The effect of CSA was to block the induction of active lymphokine mRNA, as assayed in an oocyte translation system. This selective inhibition of lymphokine mRNA suggests that CSA may be useful in the therapy of inflammatory, lymphokine-mediated disease states.

Dendritic cells are the principal cells in mouse spleen bearing immunogenic fragments of foreign proteins.

We monitored the APC function of cells taken from the spleen and peritoneal cavity of mice that had been given protein antigens via the intravenous or intraperitoneal routes. Using the mAb 33D1 and N418 to negatively and positively select dendritic cells, we obtained evidence that dendritic cells are the main cell type in spleen that carries the protein in a form that is immunogenic for antigen-specific T cells. In vivo pulsed macrophages were not immunogenic and did not appear capable of transferring peptide fragments to dendritic cells.

Dendritic cell progenitors phagocytose particulates, including bacillus Calmette-Guerin organisms, and sensitize mice to mycobacterial antigens in vivo.

Dendritic cells, while effective in sensitizing T cells to several different antigens, show little or no phagocytic activity. To the extent that endocytosis is required for antigen processing and presentation, it is not evident how dendritic cells would present particle-associated peptides. Evidence has now been obtained showing that progenitors to dendritic cells can internalize particles, including Bacillus Calmette-Guerin (BCG) mycobacteria. The particulates are applied for 20 h to bone marrow cultures that have been stimulated with granulocyte/macrophage colony-stimulating factor (GM-CSF) to induce aggregates of growing dendritic cells. Cells within these aggregates are clearly phagocytic. If the developing cultures are exposed to particles, washed, and "chased" for 2 d, the number of major histocompatibility complex class II-rich dendritic cells increases substantially and at least 50% contain internalized mycobacteria or latex particles. The mycobacteria-laden, newly developed dendritic cells are much more potent in presenting antigens to primed T cells than corresponding cultures of mature dendritic cells that are exposed to a pulse of organisms. A similar situation exists when the BCG-charged dendritic cells are injected into the footpad or blood stream of naive mice. Those dendritic cells that have phagocytosed organisms induce the strongest T cell responses to mycobacterial antigens in draining lymph node and spleen. The administration of antigens to GM-CSF-induced, developing dendritic cells (by increasing both antigen uptake and cell numbers) will facilitate the use of these antigen-presenting cells for active immunization in situ.

Dendritic cells pulsed with protein antigens in vitro can prime antigen-specific, MHC-restricted T cells in situ.

T cells recognize peptides that are bound to MHC molecules on the surface of different types of antigen-presenting cells (APC). Antigen presentation most often is studied using T cells that have undergone priming in situ, or cell lines that have been chronically stimulated in vitro. The use of primed cells provides sufficient numbers of antigen-reactive lymphocytes for experimental study. A more complete understanding of immunogenicity, however, requires that one develop systems for studying the onset of a T cell response from unprimed lymphocytes, especially in situ. Here it is shown that mouse T cells can be reliably primed in situ using dendritic cells as APC. The dendritic cells were isolated from spleen, pulsed with protein antigens, and then administered to naive mice. Antigen-responsive T cells developed in the draining lymphoid tissue, and these T cells only recognized protein when presented on cells bearing the same MHC products as the original priming dendritic cells. In contrast, little or no priming was seen if antigen-pulsed spleen cells or peritoneal cells were injected. Since very small amounts of the foreign protein were visualized within endocytic vacuoles of antigen-pulsed dendritic cells, it is suggested that dendritic cells have a small but relevant vacuolar system for presenting antigens over a several day period in situ.