Properties of a second epitope of the murine Fc receptor for aggregated IgG.

The murine macrophage and lymphocyte Fc receptor for aggregated IgG (Fc gamma R) has previously been characterized by using the anti-Fc gamma R monoclonal antibody (mAb), 2.4G2. In the studies presented here, we describe a new mAb, 6B7C, that defines a second epitope of the Fc gamma R. The tissue distribution of the 6B7C epitope is coincident with the 2.4G2 epitope. However, only the 2.4G2 epitope is accessible to mAb binding on intact primary macrophages or lymphocytes. The 6B7C epitope is not detectable on primary macrophages or lymphocytes but is exposed on a portion of B lymphocyte Fc gamma R after activation by lipopolysaccharide and on some tumor cell lines. The expression of the 6B7C epitope on the surface of B lymphoblasts and tumor cell lines seems to correlate with their ability to release soluble Fc gamma R. The 6B7C mAb has the advantage that it reacts with native as well as denatured receptor and therefore can be used for techniques such as immunoblotting.

Distribution and turnover of Langerhans cells during delayed immune responses in human skin.

The changes in distribution and turnover of T6+ Langerhans cells (LC) in the skin during delayed immune responses to tuberculin, and in the lesions of tuberculoid leprosy and cutaneous Leishmaniasis were investigated. In each situation, there was a dermal accumulation of monocytes and T cells and epidermal thickening with keratinocyte Ia expression. In the tuberculin response a dramatic change in the distribution of LC was observed. By 41 h, T6+ LC were displaced to the upper zone of the thickening epidermis followed by an almost complete loss of LC from the epidermis by approximately 72 h. After 7 d, T6+ cells started to reappear in the epidermis, which regained almost normal numbers of T6+ LC by 14 d. After antigen administration and initiation of the delayed immune response, enhanced numbers of T6+ cells appeared in association with the mononuclear cell infiltrate of the upper dermal lesions. Their numbers peaked by 72 h, were reduced at 7 d, and again enhanced by 14 d, when the epidermis was being repopulated. Similar numbers of T6+ cells were found in the chronic lesions of tuberculoid leprosy and cutaneous Leishmaniasis but not lepromatous leprosy. The cells of the dermis were identified as typical LC by the presence of Birbeck granules and surface T6 antigen at the electron microscope level. These cells were closely associated with lymphocytes. We have quantified the number of LC, evaluated their directional flux into the epidermis and dermis, determined nearest neighbors, and made predictions as to their fate.

Blockade of clearance of immune complexes by an anti-Fc gamma receptor monoclonal antibody.

Clearance of immune complexes by the mononuclear phagocyte system is important for maintaining normal host defenses against bacterial and viral assault (1), but also contributes to the pathogenesis of a variety of immune- mediated diseases . For example, removal from the circulation of IgG-coated erythrocytes and platelets by the MPS is the sine qua non of immune-mediated cytopenias (2, 3). On the other hand, abnormally decreased removal by the MPS of smaller, soluble immune complexes may play a role in the pathogenesis of immune complex-mediated tissue damage found in such autoimmune diseases as SLE (4). Although the physicochemical nature and the size of immune complexes can influence rates of clearance and sites of deposition (reviewed in 5), interactions between immune complexes and the MPS in vivo are poorly understood. The inability to directly measure binding or internalization of immune complexes by cells in the liver and spleen has made the analysis of the molecular basis of immune complex clearance very difficult . Receptors for the Fc portion of IgG (FcgammaR) and for complement (CR) undoubtedly play a role in the removal of immune complexes, but the relative importance of these receptors is not known.

Immunologic properties of purified epidermal Langerhans cells. Distinct requirements for stimulation of unprimed and sensitized T lymphocytes.

Langerhans cells (LC) are Ia+ leukocytes that account for less than 2% of the cells in murine epidermal isolates. We purified LC by cell sorting to study their capacity to stimulate antigen-specific responses from unprimed and sensitized T cells. Sorting was performed after 12 or 72 h of epidermal culture, since our earlier work had indicated that LC became immunologically active during that time interval. At 12 and 72 h, the LC were uniformly and equally rich in the Ia glycoproteins that are recognized by helper T cells. At both time points, LC were comparable in their capacity to stimulate sensitized helper T lymphocytes, and would cluster the T cells in an antigen-dependent fashion at 4 degrees C. However, 12-h LC did not sensitize T cells, as indicated by their inactivity in stimulating the primary MLR or antibody response, and they were unable to cluster T cells in an antigen-independent fashion at 37 degrees C. The latter properties were acquired during 72 h of culture. As a result, the function of 72-h LC fully resembled that of lymphoid dendritic cells. We propose that the maturation of stimulatory function within the dendritic cell lineage represents an important control point in the induction phase of cell-mediated immunity.

Local and systemic effects of intradermal recombinant interferon-gamma in patients with lepromatous leprosy.

Evidence that interferon-gamma may be a physiologic macrophage-activating factor, and that macrophage activation may be defective in lepromatous leprosy, led us to test the effects of intradermal injection of low doses of recombinant interferon-gamma in six patients with this disease. Interferon-gamma, 1 or 10 micrograms, was administered daily by jet gun for three days into a single cutaneous lesion. A biopsy specimen was taken from the injection site on the sixth study day and compared with specimens obtained previously from a site where no injection had been made or where excipient alone had been injected in the same way as the interferon. Interferon-gamma elicited local effects similar to certain features of delayed-type hypersensitivity reactions or tuberculoid leprosy, including induration, T-cell and monocyte infiltration, keratinocyte proliferation, diminution of epidermal Langerhans cells, and dermal and epidermal cell HLA-DR (Ia) antigen expression. At some of the sites of interferon-gamma injection, there was also an apparent decrease in acid-fast bacilli. Before treatment, monocytes from patients with lepromatous leprosy released 48 percent as much hydrogen peroxide as did monocytes from controls in response to phorbol myristate acetate, and 36 percent as much as those from controls in response to Mycobacterium leprae. When recombinant interferon-gamma was injected, these responses became normal. No toxic effects were observed. These observations suggest that interferon-gamma can mediate certain manifestations of delayed-type hypersensitivity or cell-mediated immunity in vivo, and that recombinant interferon-gamma should be tested for possible therapeutic effects in certain nonviral infectious diseases.

Influence of delayed immune reactions on human epidermal keratinocytes.

The epidermal changes that occur in human cutaneous immune responses have been investigated in the tuberculin reaction and in the lesions of tuberculoid and lepromatous leprosy and cutaneous leishmaniasis. In each situation, there was a dermal accumulation of monocytes and T cells, and the epidermis exhibited thickening. In the tuberculin response, the thickness of the epidermis sometimes doubled in 48-72 hr, and this was attributed to increases in both size and number of keratinocytes. In addition, the phenotype of the keratinocytes changed from Ia- to Ia+. Similar changes in keratinocyte Ia-antigen expression occurred in the epidermis overlying untreated tuberculoid leprosy and cutaneous leishmaniasis lesions, but not in lepromatous leprosy. We suggest that one or more epidermal growth factors may be generated in the course of a delayed immune reaction in the dermis.

The Thy-1-bearing cell of murine epidermis. A distinctive leukocyte perhaps related to natural killer cells.

Bone marrow-derived leukocytes of murine epidermis can express two phenotypes: typical Langerhans cells, which are Ia+ and Thy-1-, and a recently discovered second population that is Thy-1+ and Ia-. To verify that these phenotypes are expressed by two different cell types, and to help understand their lineage and function, we have studied morphology and reactivity with a large panel of antibodies. Dual antibody immunofluorescence combined with electron microscopy showed that Thy-1+ and Ia+ cells were each distributed in a regular fashion and formed adjacent dendritic systems in or close to the basal layer. Double-labeling studies with anti-Ia and a second monoclonal antibody revealed that all Langerhans cells expressed F4/80 (macrophage), Mac-1 (C3bi receptor), and 2.4G2 (Fc receptor), as well as the thymus leukemia (TL) and heat-stable (M1.69/16) antigens. A large fraction expressed S100 and all exhibited membrane ATPase and nonspecific esterase. In contrast, Thy-1+ cells lacked all these features of Langerhans cells, except that a minority were strongly reactive with 2.4G2. Thy-1+ cells also lacked differentiation antigens of most other types of leukocytes, except they were rich in asialo GM1. By electron microscopy, Thy-1+ cells had cytoplasmic granules that were similar in structure and in their aryl sulfatase content to those previously described in natural killer cells. The granules were enlarged in beige mice, suggesting a lysosomal origin, and were present in mast cell-deficient W/Wv mice, indicating no relation to mast cells. We conclude that Thy-1+ epidermal cells are thoroughly distinct from Langerhans cells. On the basis of morphology and phenotype, they may represent a type of tissue natural killer cell. Thy-1+ natural killer cells are now being identified in several nonlymphoid sites, such as gut epithelium and the livers of mice given adjuvants. If Thy-1+ epidermal cells prove to be natural killer cells, it is noteworthy that they represent a resident population regularly distributed in the basal layer of all mouse strains. The notion that Thy-1+ epidermal cells are immature natural killer cells is intriguing in light of recent evidence that Ia+ Langerhans cells are also immature with respect to accessory cell function. The epidermis may not have the functional capacities of a lymphoid organ, but it could contribute immature cells important for both natural and acquired resistance.

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.

The anatomy of peripheral lymphoid organs with emphasis on accessory cells: light-microscopic immunocytochemical studies of mouse spleen, lymph node, and Peyer's patch.

Antigen, lymphocytes, and accessory cells interact within peripheral lymphoid organs to generate immunity. Two cell types have been studied for accessory function in culture: mononuclear phagocytes and nonphagocytic Ia-rich dendritic cells. The monoclonal antibodies which have been used to study isolated murine macrophages (M phi) and dendritic cells (DC) include alpha-macrophage (F4/80, M1/70), alpha-dendritic cell (33D1), alpha-Fc receptor (2.4G2), and alpha-Ia (B21-2) reagents. In this paper, the antibodies have been used to stain accessory cells in cryostat sections of mouse spleen, lymph node, and Peyer's patch. Each organ is known to contain subregions that are rich in either macrophages, B cells, or T cells. We found that the accessory cells in each subregion had a different phenotype. 1) Macrophage-rich regions: Macrophages that lined the site of antigen delivery (marginal zone of spleen, around afferent lymphatics of node, and below the epithelium of Peyer's patch) were stained with M1/70 but not with F4/80. F4/80 was abundant on macrophages in other sites: spleen red pulp, node medulla, and around Peyer's patch efferent lymphatics. 2) B-lymphocyte-rich follicles: Follicular dendritic cells, which retain immune complexes extracellularly, are concentrated on the outer aspect of the germinal center. This region stained strongly with alpha-Fc receptor antibody 2.4G2, but not with M1/70, F4/80, or 33D1. 3) T areas: The interdigitating cells of T areas have been linked to isolated dendritic cells. Irregular Ia-rich cells were distributed uniformly in the T areas of each organ. However, staining with 33D1 was not detected and was restricted to foci of nonphagocytic cells at the spleen red/white pulp junction. F4/80, M1/70 or 2.4G2 also did not stain the T area, except for the region close to splenic central arteries. Therefore the principal surface markers and locations of the candidate accessory cells in murine lymphoid organs are M1/70+ macrophages at the site of antigen entry; F4/80+ macrophages around regions of lymphocyte efflux; germinal center dendritic cells, which may be rich in 2.4G2; and Ia-rich interdigiting cells in the T area.

The phenotype of dendritic cells and macrophages.

Several types of irregularly shaped dendritic cells have been identified, including dendritic cells and interdigitating cells in lymphoid tissues, epidermal Langerhans cells, follicular or germinal center dendritic cells, and veiled cells in lymph. All these cells exhibit phenotypic differences from monocytes and macrophages that include cytology, surface markers, endocytic activity, and capacity to adhere to tissue culture surfaces. Phenotypic differences have provided the means for separating dendritic cells from macrophages and other cell types. The precise lineage of these dendritic cells is not established. Functional studies, in which positive and negative selection procedures are used, indicated that dendritic cells are specialized stimulator cells for immune responses.

Specific antimononuclear phagocyte monoclonal antibodies. Application to the purification of dendritic cells and the tissue localization of macrophages.

3C10 and 1D9 are two related monoclonal antibodies that specifically identify human mononuclear phagocytes in a large number of sites, including blood monocytes, alveolar macrophages, and macrophages in tissue sections of spleen, lymph node, and skin. The antigen persists on monocytes cultured for greater than 4 wk, but it is not found on giant cells. The 3C10-1D9 determinant is carried by a 55 kD polypeptide, is expressed at approximately 40,000 copies per monocyte, and is protease sensitive. The antigen is clearly different from HLA-class II or Ia-like antigens that have been studied with a new monoclonal 9.3F10. The 9.3F10 antigen is found on B cells, dendritic cells and monocytes; is protease resistant, and occurs on a 33-29 kD doublet typical of class II products. The 3C10 monoclonal provides a clear distinction between human mononuclear phagocytes and dendritic cells. First, monocytes and lymphocytes can be eliminated from plastic-adherent mononuclear cells using 3C10, complement, and two previously described cytotoxic antibodies, BA-1 (anti-B cell) and Leu-1 (anti-T cell). As a result, the trace dendritic cell component of blood can be enriched to considerable purity (65-75%) and yield. Second, immunocytochemical staining of tissue sections reveals that 3C10+ macrophages are anatomically segregated from dendritic cells. Large numbers of 3C10+ cells are found in red pulp of spleen and in regions surrounding lymphatic channels of lymph node. However, 3C10+ macrophages are scarce in white pulp of spleen and the lymphocyte-rich cortex of node that are the sites where dendritic cells are localized. 3C10+ cells in skin are found in the dermis, particularly in leprosy infiltrates, but the Langerhans' cells of epidermis are 3C10-. The distinctive localization of macrophages and dendritic cells is consistent with their respective functions as effector and accessory cells in the immune response.

Dendritic cells are the principal stimulators of the primary mixed leukocyte reaction in mice.

Clone 33D1 is a mouse-rat hybridoma that secretes a specific anti-dendritic cell (DC) monoclonal antibody (14). Because the antibody kills DC in the presence of rabbit complement, it can be used to study the functional consequences of selective DC depletion. Previous data on the cell specificity of 33D1 were first extended. By cytotoxicity (rabbit complement) and indirect immunofluorescence (biotin-avidin technique), 33D1 reacted with DC but not with macrophages nor other splenocytes. In contrast, the monoclonal antibody, F4/80 (15), reacted with macrophages but not DC. The functional assay evaluated in this paper was stimulation of the primary mixed leukocyte reaction (MLR). 33D1 antibody itself did not inhibit stimulation by enriched populations of DC. In the presence of complement, 33D1 killed DC and ablated stimulatory function. The effect of 33D1 and complement on MLR stimulation by heterogenous cell mixtures was then evaluated. Removal of DC from unfractionated spleen suspensions reduced stimulatory capacity 75-90 percent, comparable to that produced with specific anti-Ia antibody and complement. Stimulation of both proliferative and cytotoxic responses was reduced. DC depletion had similar effects on MLR generated across full strain differences, or across selected subregions (H2I, H-2K/D) of the major histocompatibility complex. To further compare the functional properties of spleen DC and macrophages, MLR stimulation by adherent and nonadherent fractions of spleen were tested separately. 62 +/- 8 percent of the total stimulatory capacity of spleen was in the plastic adherent population. Activity was ablated greater than 90 percent after elimination of DC. MLR stimulation by 24-h cultures of spleen adherent cells, which contained a three- to sixfold excess of Ia(+) macrophages, was also ablated when DC were removed. Stimulation by nonadherent spleen was more resistant, but was reduced 50-75 percent by 33D1 and complement. The function of spleen cells treated with 33D1 or anti-Ia antibody and complement was restored with a small inoculum of purified DC. The latter corresponded to 0.5 percent of total stimulator cells and were enriched by previously described techniques that did not require the 33D1 antibody. We conclude that the DC, a trace component of mouse spleen, is the principal cell type required for stimulation of the primary MLR. Because other cells are not immunogenic, but do express Ia and H-2 alloantigens, DC likely represent the critical accessory cell required for the induction of lymphocyte responses.

A monoclonal antibody specific for mouse dendritic cells.

Dendritic cells (DC) are a small subpopulation of lymphoid cells with distinctive cytologic features, surface properties, and functions. This report describes the DC-specific antibody (Ab) secreted by clone 33DI. Rat spleen cells immune to mouse DC were fused to the P3U myeloma. Hybrid culture supernatants were screened simultaneously against DC, a macrophage (M phi) cell line, and mitogen-stimulated lymphoblasts. 33DI Ab specifically killed 80-90% of DC from spleen and lymph node, but no other leukocytes, including Ia+ and Ia- M phi (Ia, I-region-associated antigen,). Quantitative binding studies with 5H-labeled 33D1 Ab showed that DC had an average of 14,000 binding sites per cell. Binding to DC was inhibited with Fab fragment of 33D1 Ab but not with a panel of other monoclonal antibodies, including anti-Ia Ab. Adherence and flotation procedures that enriched for DC enriched for 3H-labeled 33D1 Ab binding in parallel. 33D1 antigen was not detectable on: M phi from spleen, peritoneal cavity, and blood; three M phi cell lines; lymphocytes; granulocytes; platelets; and erythroid cells. DC continued to express the 33D1 antigen after 4 days in culture, whereas M phi and lymphocytes did not acquire it. Quantitative and autoradiographic studies confirmed that spleen and lymph node suspensions contain less than 1% DC. We conclude that 33D1 Ab detects a stable and specific DC antigen and can be used to monitor DC content in complex lymphoid mixtures.

Studies of the cell surface of mouse dendritic cells and other leukocytes.

The surface of dendritic cells (DC) has been analyzed by means of monoclonal antibodies (Ab) and lactoperoxidase (LPO)-mediated radioiodination. Antigens and other exteriorily disposed polypeptides of purified spleen DC were compared with those of tissue macrophages (Mphi), monocytes, and other bone marrow-derived elements. Quantitative binding studies and autoradiography with (125)I-Ab established that DC expressed high levels of I-A and H-2D, 2 x 10(5) and 1 x 10(5) Ab binding sites per cell, respectively. DC from conventional, germ-free, and specific pathogen-free mice were all rich in Ia. Expression of Ia on B cells was 5-10 percent of that on DC and increased fivefold during lipopolysaccharide mitogenesis. More than 70-90 percent of purified Mphi and monocytes from specific pathogen-free mice were Ia negative, but increased levels of Ia were noted on cells from mice reared under conventional conditions. Thus large amounts of Ia on DC is a constitutive trait, whereas the expression of Ia by other cell types may be governed by the environmental and immunological status of the host. The 2.4G2 Fc receptor Ag was not detected on DC. Peritoneal and spleen Mphi had 10(5) 2.4G2 binding sites/cell, whereas monocytes and lymphocytes were less reactive (1 x 10(4)-3 x 10(4) binding sites/cell). Four other Mphi-related antigens were evaluated. Each had a distinctive tissue distribution and none bound exclusively to Mphi and monocytes. Neither 1.21J (Mac-1) nor F4/80 reacted with DC. Immunoprecipitation studies of externally ((125)I) and biosynthetically ([(35)S]methionine)dabeled cells confirmed the binding data. Sensitive binding assays with (125)I-Ab confirmed previous observations that DC lack Ig and Thy-1. Lyt-1 was also not found on DC, but 5-12 percent of the cells in purified DC preparations expressed both Lyt-2 and Ia. All DC expressed the leukocyte common antigens at levels similar to other leukocytes. The spectrum of surface polypeptides labeled by LPO-mediated iodination was different on Mphi, DC, and lymphocytes. Polypeptides migrating at molecular weights of 155,000, 85,000, and 62,000 appeared to be restricted to DC. These observations establish that the cell surface of DC differs considerably from other leukocytes, including the blood monocyte, and suggest that the DC is part of a unique Ia-rich leukocyte differentiation pathway.

Lymphokine enhances the expression and synthesis of Ia antigens on cultured mouse peritoneal macrophages.

Soluble products from antigen stimulated Trypanosoma cruzi-immune spleen cells enhanced the expression of Ia antigens on proteose-peptone-elicited mouse peritoneal macrophages (M phi). Acquisition of Ia paralleled M phi activation, previously shown to be mediated by this same source of lymphokine (LK). Expression of Ia and four other plasma membrane antigens was monitored by quantitative binding and radioautographic studies with 125I-monoclonal antibodies. Immune LK selectively enhanced expression of Ia and, to a lesser extent, H-2D relative to control LK from antigen-stimulated noninfected spleen. The levels of three other non-major histocompatibility complex (MHC) antigens, including the trypsin-resistant Fc receptor, were similar in cells exposed to both sources of LK. As little as 1% immune LK induced one-half maximal expression of Ia. Kinetic studies revealed that much of the Ia on freshly explanted peritoneal M phi was lost during the 1st d of culture. In the continued presence of immune LK, Ia was re-expressed on virtually all M phi by the 2nd and 3rd d. Alternatively, > 95% Ia negative populations were obtained by culturing the cells 3 d; then, addition of LK induced Ia on most cells within 1 d. Once induced, Ia persisted on the M phi surface for at least 2 d. [35S]methionine radiolabeling indicated that immune LK selectively increased radiolabeling of M phi Ia, again with other non-MHC-linked plasma membrane polypeptides as controls. LK-induced Ia-bearing M phi were tested as primary mixed leukocyte reaction stimulators. 1 x 10(5)-2 x 10(5) M phi did not stimulate 4.5 x 10(6) responding T cells, whereas 10(4) dendritic cells induced strong responses, as previously described. Because Ia-positive M phi do not actively sensitize T cells in a model immune response, we propose that M phi MHC products serve primarily as recognition sites for previously sensitized T cells, thereby enhancing T cell-mediated M phi activation.

Identification of a novel cell type in peripheral lymphoid organs of mice. V. Purification of spleen dendritic cells, new surface markers, and maintenance in vitro.

Dendritic cells (DCs; 1) have been purified from mouse spleen in good yield. Spleen cell suspensions were floated on dense bovine plasma albumin (BPA) columns, and the low density fraction was adhered to glass (2). The adherent cells consisted of DCs and immature macrophages most of which eluted in a viable state from the culture dish after overnight incubation. The macrophages were then removed by selective rosetting with opsonized erythrocytes and recentrifugation on dense BPA. This protocol resulted in a purified DC fraction, containing 1--3 X 10(5) DCs/spleen, which was homogeneous and distinctive in its properties. All cells exhibited the phase contrast and transmission electron microscopy (EM) cytologic features that were previously described for freshly isolated adherent DCs. By scanning EM, most purified DCs exhibited a remarkable array of bulbous protrusions of varying length and shape, unlike any other lymphoid cell. All DCs expressed surface Ia and other major histocompatibility complex (MHC)-linked alloantigens. DCs, however, lacked surface Ig and T-cell antigens, and did not bind or interiorize opsonized erythrocytes. Purified DCs have been maintined in vitro for 3 days. Recovery of cultured purified cells was 70% or more of starting cell numbers. When [3H]uridine-tagged DCs were mixed with nonlabeled heterogeneous spleen cells, 70--80% of the labeled DCs were recovered as viable cells 2--3 days later. Purified DCs did not readhere to tissue culture surfaces and did not proliferate, even when cultured with mitogenic doses of concanavalin A and lipopolysaccharide. Finally, DCs did not change their cytologic or surface properties after 3 days of culture. These observations extend the evidence that DCs are a novel cell type and provide useful properties and techniques for their further study.

Lymphoid dendritic cells are potent stimulators of the primary mixed leukocyte reaction in mice.

Dendrite cells (DCs) are a new cell type initially identified in mouse lymphoid organs. Recently, DCs have been purified from mouse spleen. This paper demonstrates a functional role of DCs: they are potent stimulators of the primary mixed leukocytes reaction (MLR). As few as 300-1000 DCs doubled the proliferative activity of 5 X 10(6) allogeneic responder spleen cells, while 0.3-1.0 X 10(5) DCs induced a maximal stimulation of 30- to 80-fold. Between these extremes, the log of the MLR response increased linearly with the log of DC numbers. This dose-response assay was then used to compare the potency of purified DCs with that of other heterogeneous lymphoid populations, many of which gave dose-response curves with similar slopes. The potency of purified DCs as MLR stimulators was 100-300 times greater than that of unfractionated spleen cells. When spleen cells were fractionated by simple physical techniques, MLR-stimulating capacity in the subpopulations correlated closely with DC numbers. Removal of splenic B or T lymphocytes, by anti-immunoglobulin or anti-brain serum plus complement, did not reduce MLR-stimulating capacity. Finally, several populations, enriched in mononuclear phagocytes but lacking in DCs, stimulated weakly if at all. We conclude that DCs are a potent stimulating cell and are at least 100 times more effective than other major cell subclasses--i.e., B and T lymphocytes and macrophages.