The regulatory role of macrophages in antigenic stimulation. Part Two: symbiotic relationship between lymphocytes and macrophages

Dendritic cells from human rheumatoid synovial inflammatory tissue and peripheral blood as accessory cells in mitogen stimulation of T lymphocytes

Dendritic cells (DC) were purified from the peripheral blood (PB) of normal individuals and from the synovial fluid (SF) and synovial tissue (ST) of patients with rheumatoid arthritis. These cells are strongly HLA-DR positive and lack B-cell, T-cell, and monocyte markers as well as Birbeck granules. The DC were compared with monocytes and non-T cells from PB for their ability to act as accessory cells for T-cell responses to concanavalin A (Con A) and phytohaemagglutinin (PHA). DC from PB, SF and ST were much more efficient accessory cells for the mitogenic responses than autologous monocytes from PB. The mean PHA responses in cpm obtained with DC from the various compartments were 4-20 times greater than the responses obtained with monocytes from PB. The Con A responses obtained when the various DC populations were used as accessory cells were 3-13 times greater than those obtained with monocytes from PB. The mitogenic responses seen with monocytes were very low. The non-T cells, which comprise a mixture of cells obtained after removal of T cells, also gave low T-cell responses to PHA and Con A compared with DC as accessory cells.

Expression of HLA-DR antigens on epithelium associated with lymphoid tissue in the human gastrointestinal tract

Mucosa from human stomach, terminal ileum, appendix, and colon was studied for epithelial HLA-DR expression using an immunoperoxidase technique with a monoclonal antibody that detects HLA-DR antigens in paraffin embedded tissues. Expression of HLA-DR by epithelial cells was studied with particular reference to the effect of adjacent lymphoid tissue or surrounding chronic inflammation. In the stomach, epithelial HLA-DR appeared to be induced by chronic inflammation. Where lymphoid nodules were present only that epithelium directly adjacent to the lymphoid tissue expressed HLA-DR. Expression was independent of cell type. Epithelium adjacent to normal lymphoid tissue in the terminal ileum, appendix, and colon also expressed HLA-DR, the relationship between expression and proximity to lymphoid tissue being remarkably precise. Expression of HLA-DR by gastrointestinal epithelium appears to be an effect of adjacent lymphocytes, whether part of an inflammatory response or normal tissue. This must be taken into account when assessing HLA-DR expression by gastrointestinal epithelium.

Dysfunction of Ia-positive antigen-presenting cells in autoimmune mice

Antigen-presenting activity of spleen macrophages for T-cell activation was studied in vitro using autoimmune prone MRL/Mp-lpr/lpr (MRL/l) mice, and their normal counterparts, MRL/Mp-+/+ (MRL/n) mice. In vitro induction of trinitrophenyl (TNP)-specific proliferative T-cell response in lymph node lymphocytes from picryl chloride-painted mice was markedly impaired in MRL/l mice. The presenting activity of TNP-hapten by spleen macrophages for proliferative T cells was also impaired in MRL/l mice. The impairment of both T-cell and antigen-presenting macrophage activities was marked in older MRL/l mice, but not in younger ones. The impaired antigen-presenting activity of macrophages was not due to the development of suppressor macrophages. In accordance with the impaired antigen-presenting activity of macrophages the population of Ia-positive cells in spleen macrophages and the production of interleukin 1 by spleen macrophages were also reduced in older MRL/l mice. These results suggest that Ia-positive macrophages are impaired in autoimmune prone mice and that the dysfunction of Ia-positive macrophages plays an important role in the pathogenesis of autoimmune diseases.

Expression of Ia-antigens on guinea pig Kupffer cells. Studies with monoclonal antibodies

The expression of the Ia-antigen on guinea pig Kupffer cells was studied employing two monoclonal antibodies against two different determinants of the Ia-molecule. The study was performed in situ on liver sections and on isolated highly purified Kupffer cells kept in culture up to 6 days. The influence of guinea pig hepatocyte culture supernatant and of supernatants of phytohemoagglutinin (PHA)-stimulated human peripheral blood lymphocytes (PBL) on the Ia expression was measured. Immunofluorescence staining of cryostat sections revealed that the monoclonal antibodies used are able to detect Ia-antigens on liver macrophages in situ. The in vitro studies strongly suggest that all Kupffer cells are able to express Ia-antigens. The expression of Ia-antigens on Kupffer cells decreased during the culture time and was no longer detectable on day 5. At this time, incubation of the cell cultures with PBL conditioned medium induced the reexpression of Ia-antigens. Supernatants from guinea-pig hepatocyte cultures did not have any negative influence on the expression of the Ia-antigen on Kupffer cells in vitro. These data support the hypothesis that liver macrophages have the potential to behave immunologically as accessory cells and might contribute to local immune responses in acute as well as chronic states of liver diseases.

Requirements for growth of immature thymocytes from fetal and adult mice in vitro

We report here defined culture conditions that allow reproducibly the growth of the majority of immature thymocytes from both fetal (14-15 days of gestation) and adult mice. The combination of phorbol myristate acetate (PMA), ionomycin and recombinant interleukin 2 (IL2) is both sufficient and necessary to induce growth of about 1/6.2 (range 1/3-1/9) and 1/4.3 (range 1/2-1/7) immature thymocytes from adult and fetal mice, respectively, in serum-free cultures. Several other combinations tested (e.g. PMA + IL2, concanavalin A + IL2) were poorly or not active. None of the agents tested alone (PMA, ionomycin, concanavalin A, pokeweed mitogen, IL2) had any effect. We found no evidence for a role of IL1 and IL3 on growth of these cells. The growth of activated immature thymocytes from either fetal or adult mice was inhibited by a monoclonal antibody against mouse IL2 receptors. Under the same conditions that stimulated growth of most immature thymocytes, they did not mature into cells expressing Lyt-2, L3T4 or T cell antigen receptor (KJ16) after 7 to 15 days of continuous proliferation in culture. Nor did they give rise to cells with cytolytic activity after 7-9 days of culture. In some but not all experiments cultures of immature thymocytes from adult mice but not from fetal mice generated cells (1 out of 120-310) with helper function for B lymphocytes. While we confirmed here that approximately 50-70% freshly isolated immature thymocytes express receptors for IL2, our results indicate that these cells need to be activated (by e.g. PMA + ionomycin) to respond to IL2. A possible mechanism to account for the expression of nonfunctionally competent IL2 receptors is proposed and our results concerning the maturation of immature thymocytes in vitro are discussed.

Activated macrophage hybridomas secreting a cytotoxic factor

Stable activated macrophage hybridomas were generated by somatic cell fusion between Propionibacterium acnes-induced peritoneal exudate cells and NS-1 myeloma cells. Five cell lines were obtained and each was cloned by limiting dilution; 59 clones were obtained. The cells of 2 clones (MP4-4 and MP4-8) which adhered to the culture dishes were selected for further analysis. These hybridomas exhibited non-specific esterase and beta-galactosidase intracellularly, and asialo GM1, Mac-1, Ia antigens and Fc-receptors on their cell surface. They did not, however, show phagocytic activity or secrete lysozyme. These hybridomas (MP4-4 and MP4-8) secreted the cytotoxic factor without any stimulation. Furthermore strong cytotoxic activity was found in ascites and sera from nude mice inoculated with these hybridomas. These activated macrophage hybridomas should be very useful in studies on cancer immunology and the physiology of macrophages.

Modulation of Ia and photoreactive antigen on antigen-presenting cells: fun with a photoprobe

To identify the antigen-specific recognition complex containing elements from T cells and antigen-presenting cells (APC), a photoactivatable antigen system was developed which could potentially crosslink the complex during the specific cellular responses. In this paper we describe the development of this system using murine T-cell hybridomas responding to stimulator cells chemically conjugated with N-hydroxysuccinimidyl 4-azidobenzoate (HSAB) and genetically restricted by I-Ad. In initial experiments it was found that several I-Ad-positive B-cell lines were nonstimulatory when coupled with HSAB, but that I-Ad-positive P388D1 macrophage-like cells were efficient stimulators of HSAB-specific T-cell responses. These results suggested that the relevant HSAB coupled surface structure was not likely I-Ad. To substantiate this point, Ia-positive or Ia-negative P388D1 cells were initially coupled with HSAB and the expression of Ia was modulated by the addition and withdrawal of Con A-stimulated spleen cell supernatant fluid through several days of culture. Under these conditions, efficient stimulation was only observed when Ia was expressed, although the HSAB antigen was continuously present. In other experiments it was found that exposure of HSAB-coupled APC to light selectively eliminated their stimulatory capacity for HSAB-specific T hybridomas, suggesting that the light-induced crosslinking by HSAB directly eliminates the antigenic determinant. This antigen system allows a unique opportunity to manipulate the antigen during specific cellular interactions, and to introduce covalent crosslinking of the specific antigen recognition complex that may allow its isolation and characterization.

Differences between intra- and extracellular interleukin-1

The intracellular (IC) and extracellular (EC) pools of interleukin 1 (IL-1) of human monocyte cultures were found to differ in their molecular size and charge characteristics. EC activity was found by Sephadex G-75 chromatography to consist mainly of a single peak in the 15,000-17,000 mol. wt range. In contrast, IC activity was distributed in four peaks (mol. wts of approx. 15,000, 26,000, 45,000 and greater than 70,000). Treatment of a pool of the IC 26,000, 45,000 and greater than 70,000 mol. wt species with CHAPS, a zwitterionic detergent, yielded a large amount of the 15,000 mol. wt species, thus suggesting that a portion of the larger species consists of aggregates of the 15,000 mol. wt molecule. Both IL-1 pools were found by isoelectrofocusing to be composed of three molecular species with pIs of 5.5, 6.7. However, the proportions of these species differed markedly between the EC and IC pools. The large majority of IC activity (approximately 90%) was found at pI 5.5, while 55-60% of EC activity had a pI of 6.7 and 35-40% had a pI of 5.5. The differences in their biophysical properties support the notion that the IC and EC pools of IL-1 also differ in their functions.

Growth inhibition of Babesia bovis in culture by secretions from bovine mononuclear phagocytes

Bovine blood mononuclear phagocytes from babesia-free cattle were cultured in vitro. Cell monolayers were treated with culture-derived soluble Babesia bovis exoantigens, immune complexes, and bovine anti-B. bovis immune serum. Subsequently, the monolayers were washed free of the reagents and allowed to develop further in the presence of standard culture medium. Transfer of supernatant media from these cultures to those of B. bovis revealed the presence of growth-inhibiting factors. These factors were thermostable, nondialyzable, and were degraded by freeze-thawing, and their action was concentration dependent. Supernatants from antigen- and immune complex-treated monolayers demonstrated greater inhibitory effects than did supernatants from antibody-treated or untreated monolayers. Erythrocytes incubated with supernatant medium from antigen-treated monolayers did not support growth of B. bovis as well as did erythrocytes incubated with supernatants from untreated monocyte monolayers. This result suggests that the mechanism of action of soluble factors could be through some modification of the erythrocyte such as the blockage of active transport of essential nutrients.

Reduced function of HLA-DR-positive monocytes in patients with systemic lupus erythematosus (SLE)

Accessory function of monocytes for T-cell activation was studied in patients with systemic lupus erythematosus (SLE). Nylon column-purified T cells alone were not activated to proliferate by stimulation with concanavalin A (Con A), but the addition of dish-adherent monocytes restored the T-cell response in a dose-dependent manner (accessory function). This accessory function is mediated by HLA-DR-positive monocytes. This accessory function of monocytes was markedly impaired in SLE patients. The dysfunction of monocytes was marked in an active stage of SLE but not in an inactive stage of SLE. Furthermore, SLE T cells were not fully activated with Con A in the presence of normal monocytes, suggesting that both monocyte and T-cell functions were impaired in SLE patients. The dysfunction of SLE monocytes was due to neither the development of suppressor monocytes nor the overproduction of prostaglandins, because SLE monocytes did not suppress the accessory function of normal monocytes and indomethacin did not restore the dysfunction of SLE monocytes. The percentage of HLA-DR-positive cells in a monocyte population was markedly decreased in active SLE patients and moderately decreased in inactive SLE patients. Thus, the impairment of accessory function of monocytes in SLE patients seems to be derived from a decrease in HLA-DR-positive monocytes. These results suggest that the dysfunction of HLA-DR-positive monocytes plays an important role in the pathogenesis of SLE.

Mammalian nitrate biosynthesis: mouse macrophages produce nitrite and nitrate in response to Escherichia coli lipopolysaccharide

Escherichia coli lipopolysaccharide (LPS)-induced nitrate biosynthesis was studied in LPS-sensitive C3H/He and LPS-resistant C3H/HeJ mice. Intraperitoneal injection of 15 micrograms of LPS led to a temporary 5- to 6-fold increase in blood nitrate concentration in the C3H/He strain. Levels of nitrate excreted in the urine were also increased. In contrast, no increase was observed in the C3H/HeJ strain with LPS injections up to 175 micrograms. Furthermore, thioglycolate-elicited peritoneal macrophages from C3H/He, but not from C3H/HeJ mice, produced nitrite (60%) and nitrate (40%) when cultured with LPS (10 micrograms/ml). T-lymphocyte addition/depletion experiments showed the presence of T cells enhanced this response. However, LPS did not cause nitrite or nitrate production in cultures of spleen lymphocytes from either strain. LPS-induced nitrate synthesis was also observed with nude mice and CBA/N mice, indicating that neither functional T lymphocytes nor LPS-responsive B lymphocytes were required for the response in vivo. This was consistent with the in vitro results showing macrophages alone were competent. Mycobacterium bovis infection of C3H/He and C3H/HeJ mice resulted in a large increase in nitrate production over the course of the infection for both strains, suggesting T-lymphocyte-mediated activation of macrophages as a potent stimulus for nitrate biosynthesis. The synthesis of nitrite is significant in that it can directly participate in the endogenous formation of nitrosamines and may also be involved in some aspect of the chemistry of cytotoxicity.

Lymphocyte activation in rheumatoid arthritis synovial fluid in vivo

Monoclonal antibodies were used in avidin-biotin-peroxidase complex staining for activation marker analysis of rheumatoid synovial fluid cells. Although Ia expression indicates T cell activation, cells displaying receptors for interleukin 2 (Tac)-and transferrin receptor (T9)- positive proliferating cells were relatively few. Similarly, activated terminal effector cells of suppressor/cytotoxic nature were scarce in rheumatoid synovial fluid, as suggested by a low expression of Tac and 4F2 markers. The in vivo situation in the rheumatoid arthritic (RA) joint does not seem to be due to the inability of synovial fluid lymphocytes to become activated, because mitogen stimulation in vitro, in spite of a low proliferative response, induced expression of all the activation markers studied. The relevance of the present observations to the down-regulation of the active, inflammatory-immune response in situ is speculative, but the data show that in spite of T-cell activation and Ia expression, activated terminal effector cells of suppressor/cytotoxic nature are few in the RA joint in vivo.

Ia-associated invariant chain is fatty acylated before addition of sialic acid

The murine invariant chain (Ii) was found to incorporate radioactive palmitic acid. This binding of fatty acid inhibits the formation of interchain S-S bonds, probably because the cysteine residue in the transmembrane region of the Ii chain is palmitylated. The inhibition of fatty acylation by cerulenin blocks further posttranslational maturation of the invariant chain as shown by two-dimensional gel electrophoresis of Ii immunoprecipitates. In particular, the addition of sialic acid residues is blocked. Thus, it appears that fatty acylation is essential for carbohydrate processing of the Ii chain.

Role of macrophages as modulators but not as autonomous accessory cells in primary antibody response

The role of macrophages (M phi) in the in vitro primary antibody response of murine lymphocytes to sheep erythrocytes was investigated. Peritoneal M phi were activated to express Ia antigens either in vitro or in vivo. Nonactivated Ia- M phi were also examined. We observed that only Ia- M phi but also Ia+ M phi failed to trigger the antibody response, in contrast with splenic dendritic cells (DC) which served as potent and autonomous accessory cells, but that M phi modulated the level of response which was dependent primarily on the DC content of culture. The modulation appeared to incline to suppression rather than enhancement, when M phi were allowed to remain throughout the culture period for 4 days. A highly enhancing capacity of M phi, however, could be revealed by removing M phi 2 days after the initiation of culture, indicating that M phi exerted their suppressive effect more strongly in the late phase than in the early phase of in vitro antibody response. The modulatory activity seemed higher in Ia+ M phi than in Ia- M phi.

Visceral leishmaniasis in congenic mice of susceptible and resistant phenotypes: T-lymphocyte-mediated immunosuppression

This paper continues a comparative study (A. D. Nickol and P. F. Bonventre, Infect. Immun. 50:160-168, 1985) describing immune responses exhibited by congenic, Lshs mouse strains C57B1/10 (cure) and B10.D2 (noncure) during the course of disseminated leishmaniasis. We report that sublethal whole-body irradiation of B10.D2 mice before challenge with Leishmania donovani converted the noncuring mice to a curing phenotype. Splenic lymphocytes from L. donovani-infected B10.D2 mice failed to proliferate in response to parasite antigen stimulation in vitro. Splenic lymphocytes from irradiated, cured B10.D2 mice regained the capacity to respond to the parasite antigen stimulus. Transfer of T cells but not B cells from L. donovani-infected B10.D2 mice prevented the acquisition of immunity and recovery from infection in X-irradiated mice. In addition, a splenic T-cell population from L. donovani-infected B10.D2 mice suppressed the proliferation in vitro of parasite antigen-stimulated lymphocytes of irradiation-cured B10.D2 mice. Suppressor T cells were not demonstrable in the spleens of spontaneously cured C57B1/10 mice. Splenic lymphocytes from infected B10.D2 mice were deficient in the production of macrophage-activating factor (MAF) upon stimulation by L. donovani antigens in vitro. Deficient MAF production was specific for parasite antigen stimulation, because MAF production subsequent to concanavalin A stimulation of splenic lymphocytes from infected B10.D2 mice was not suppressed. The data suggest that a genetically based immunological defect in B10.D2 mice prevents the acquisition of effective cell-mediated immunity and subsequent elimination of L. donovani from tissue macrophages. The immunological deficit, not apparent in the curing C57B1/10, appears to be caused by the development of parasite antigen-specific suppressor T cells during the course of the disseminated leishmaniasis.

Self-regulation of procoagulant events on the endothelial cell surface

Interleukin 1 (IL-1) is a potent mediator of inflammatory and immunologic phenomena. In addition, IL-1 may be intimately involved in the regulation of hemostasis, since interaction of IL-1 with endothelial cells has been reported to induce tissue factor activity. We demonstrate that perturbation of the endothelial cell induces augmented IL-1 release. Human umbilical vein endothelial cells perturbed by treatment with lipopolysaccharide produced enhanced amounts of IL-1 activity. IL-1 activity from lipopolysaccharide-treated endothelial cell supernatants could be absorbed by an antibody to IL-1 coupled to Sepharose. Elaboration of IL-1 activity was dependent on the dose of lipopolysaccharide and occurred in a time-dependent manner. Addition of cycloheximide blocked generation of IL-1 activity. A physiological vessel wall perturbant, the coagulation enzyme thrombin, induced comparable amounts of IL-1 activity in endothelial cell cultures. This effect was specific for the enzyme, since active site-blocked thrombin and prothrombin had no effect on IL-1. In addition, IL-1-containing supernatants from thrombin-stimulated endothelial cells induced tissue factor procoagulant activity in fresh endothelial cell cultures. Thus, in contrast to the multiple, known inhibitory mechanisms that block thrombin procoagulant activity, these data suggest a circle of interaction in which thrombin induces endothelial cell elaboration of IL-1, a mediator of endothelial cell procoagulant activity. Endothelial cell production of IL-1 in response to perturbation allows these cells to play an integral role in the regulation of the inflammatory and coagulation systems.

Binding of immunogenic peptides to Ia histocompatibility molecules

Most cellular interactions essential for the development of an immune response involve the membrane glycoproteins encoded in the major histocompatibility gene complex. The products of the I region, the class II histocompatibility molecules (Ia molecules), are essential for accessory cells such as macrophages to present polypeptide antigens to helper T cells. This interaction, antigen presentation, is needed for T-cell recognition of the antigen and its consequent activation. How the Ia molecules regulate the immune response during antigen presentation is not known, although it is commonly thought to result from their association with the presented antigen. Recent studies, including the elucidation of the structure of the T-cell receptor, favour recognition of a single structure, an antigen-Ia complex. Here we report attempts to determine whether purified Ia glycoproteins have an affinity for polypeptide antigens presented by intact cells in an Ia-restricted manner. We first identified the epitope of a peptide antigen involved in presentation. Several laboratories have shown that globular proteins are altered (processed) in intracellular vesicles of the antigen-presenting cell before antigen presentation. A major component of the T-cell response is directed toward determinants found in the unfolded or denatured molecule, and our laboratory has shown that the determinant of the hen-egg lysozyme protein (HEL), presented in H-2k mice to T cells, is a sequence of only 10 amino acids. This portion resides in an area of the native molecule partially buried inside the molecule, in a beta-sheet conformation. To be presented, intact or native HEL must first be processed in acidic intracellular vesicles. Having isolated the peptide responsible for T-cell recognition of HEL, we sought a physical association of this peptide with purified, detergent-solubilized I-Ak molecules from B-hybridoma cells. We have found such an association, which may explain the role of the Ia glycoproteins in cellular interactions.

Dextran as a modulator of immune and coagulation activities in trauma patients

Low Mr dextran has been utilized as a prophylactic therapy in treatment of coagulopathy. There is evidence that monocyte dysfunctions are important contributors to hypercoagulability episodes, as well as to immunoincompetence post-trauma. Dextran is a known monocyte modulator. Consequently, we evaluated the efficacy of dextran infusion in moderating immune dysfunction, monocyte aberrations, and hypercoagulability episodes. Twenty-eight trauma patients were randomly divided into two groups. One group of 15 received dextran at 1 g/kg wt/24 hr for 5 days in addition to standard resuscitation and treatment. The control or nontreated patient group received only standard treatment. Trauma patients in the two groups were retrospectively matched by injury severity score (ISS) to ensure comparability. Blood samples were collected daily for some studies and at 3-day intervals for other assays. In vivo coagulation status was evaluated by assessing the changes in intravascular fibrinopeptide A (FPA). Immune reactivity to the mitogen phytohemagglutinin (PHA) was also evaluated. Both monocyte production of plasminogen activator (PA) and monocyte production of procoagulant activity (PCA) have been shown to correspond to and be augmented by monocyte-T lymphocyte interactions. Consequently, monocyte production of plasminogen activator and procoagulant activity were assessed as measures of monocyte immune activity as well as indicators of monocyte function in controlling the balance between fibrinolysis and coagulation. Only patients with ISS of greater than 25 experienced significant immune, coagulation, or monocyte aberrations. Of those having an injury severity score (ISS) score of 25-35, all of the control and two of the dextran patients had significant perturbations in their immune and monocyte functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigen presentation of myoglobin: profiles of T cell proliferative responses following priming with synthetic overlapping peptides encompassing the entire molecule

Recently, the regions of myoglobin, which are recognized by T cells (T sites), were localized by a comprehensive synthetic strategy in which uniform synthetic overlapping peptides encompassing the entire protein chain were examined for stimulation of T cell proliferative activity. In this study, we report about the proliferative response to these peptides, as well as to the native protein, of lymph node cells from mice primed with the overlapping peptides either individually or in a mixture. Some, but not all, of the T site-containing peptides were effective in priming for an anti-myoglobin T cell response. Further, several peptides, which were highly immunogenic as free synthetic peptides, were not associated with any of the known T sites in this protein. Thus, the pattern of T cell recognition following priming with the overlapping peptides differs from the pattern observed when the native protein is the priming antigen. If antigen processing proceeds via fragmentation, then only those regions containing T sites would be expected to be effective in priming for a T cell response to the intact protein and, conversely, highly immunogenic peptides would correspond to T sites of the protein. Therefore, these findings indicate that the current concept of antigen fragmentation as a prerequisite for its presentation must be reappraised. We suggest that, in the presentation of a protein antigen, the protein is recognized predominantly intact and that the crucial aspects of presentation are determined by interaction with the cell membrane which trigger cellular activating events.

Antigen-dependent increase in cytosolic free calcium in specific human T-lymphocyte clones

Calcium has been implicated as an intracellular messenger in the cellular response to various external stimuli. Exposure of lymphocytes to various mitogens and lectins results in rapid transmembrane calcium fluxes and increased cytoplasmic calcium concentrations ([Ca2+]i). It is not clear, however, whether the mechanisms by which these non-physiological stimuli activate cells are related to those involved in antigen-specific activation. We have now used antigen-specific T-cell clones to study changes in [Ca2+]i associated with specific activation and show here that these cells respond specifically in the presence of antigen and antigen-presenting cells (APC) with increased [Ca2+]i and that this increased [Ca2+]i shows the same genetic restrictions as are seen in the proliferation assay. The kinetics of the [Ca2+]i response to antigen indicate that antigen undergoes a time-dependent processing step as a prerequisite for recognition by T cells, as has been shown for T-cell proliferative responses, but that the [Ca2+]i response to processed antigen is extremely rapid. The close correlation between changes in [Ca2+]i and cell activation resulting in proliferation suggests that Ca2+ may act as an intracellular messenger in antigen-specific responses.

Functional analysis of macrophage hybridomas. III. Inhibition of lymphocyte blastogenesis and tumor proliferation

Four cloned macrophage hybridoma cells prepared by fusion of splenic adherent cells with a P388D1 macrophage tumor markedly inhibited the growth of lymphocytes and tumor cells. Macrophage clones 5, 8, 63, and 64 are strong inhibitors of B-cell blastogenesis, T-cell blastogenesis, and tumor proliferation, while the P388D1, tumor line and clones 13, 59, and 67 demonstrated little inhibitory activity in all three systems. The inhibitory effect of macrophage hybridomas can be detected within 8 hr, although greater inhibition was noted following longer incubation. The correlations among these three assay systems suggest that similar mechanisms may be involved. The data indicate that the inhibition of cell proliferation was not due to cell lysis. Furthermore, the inhibition of lymphocyte proliferation in Con A-stimulated cultures was not accompanied by inhibition of lymphokine production in the same cultures. Neither prostaglandins nor hydrogen peroxide appear to be primarily responsible for growth inhibition. The inhibitory properties of these macrophage hybridoma lines represent a stable phenotype and provide a homogeneous source of cells for further analysis of the phenomenon.

Regulation of lymphocyte reactivity by plasma fibronectin: cellular requirements

Purified rat plasma fibronectin (Fn) induces significant inhibition of rat lymph node T cell reactivity to PHA in the presence of enriched populations of macrophage accessory cells. The pattern of inhibition is similar whether macrophages are obtained from peritoneal exudates or spleen. Maximal inhibition by Fn is effected at macrophage concentrations higher (2-3% of the T cell number) than that required for optimal lymphocyte proliferation (0.5-1.0%), however significant inhibition was also demonstrated at these optimal concentrations. Fn-pulsed adherent macrophages, when used as accessory cells, are capable of inducing significant inhibition of T cell reactivity to PHA although to a lesser degree than when Fn is continuously present throughout the culture period. Pulsing purified T cells with Fn has no effect on the proliferative response. Nondialyzed supernatants from 24 hour cocultures of peritoneal exudate macrophages and Fn fail to influence the T cell proliferative response when compared to supernatants from macrophages cultured in medium only or with added rat serum albumin. Thus, the inhibitory effect evoked by Fn appears to be mediated at the accessory cell membrane and not by the enhanced production of soluble inhibitors released as a result of the Fn-macrophage interaction.

Different populations of rheumatoid adherent cells mediate activation versus suppression of T lymphocyte proliferation

Adherent cells from synovial tissue of rheumatoid arthritis patients were fractionated on Percoll density gradients and analyzed to determine phenotypes, effects on allogeneic T lymphocyte proliferation, and production of prostaglandin E2 (PGE2). Cells expressing HLA-DR predominated in all fractions, and esterase-positive cells were enriched in light fractions. Heavy cells were potent stimulators in the mixed lymphocyte reaction and produced little PGE2, whereas light cells suppressed the mixed lymphocyte reaction and produced a large quantity of PGE2. These results suggest that macrophage-like synovial cells that suppress T helper lymphocyte activity are generated secondary to synovial lymphocyte activation in rheumatoid arthritis.

Evidence for a mouse mesangial cell-derived factor that stimulates lymphocyte proliferation

The functions of the glomerular mesangium are served by at least two populations of cells--a cell bearing microfilaments that regulates blood flow, and a phagocytic cell bearing Ia determinants and Fc receptors. We provide evidence that mouse mesangial cells (bearing microfilaments) produce a factor(s) that stimulates spleen cell proliferation. The factor(s) appears to act via monocytes/macrophages, since its stimulatory activity is abrogated by prior depletion of the responding mononuclear cell population of monocytes/macrophages. Confirmation of its action on macrophages was documented by experiments that showed that medium from macrophages incubated with mesangial cell supernatant contained greater amounts of a factor that stimulated [3H]thymidine uptake by macrophage-depleted spleen cell populations. By the cothymocyte proliferation assay, it could be shown that mesangial cell supernatant induced splenic macrophage production of interleukin-1-like activity. Preliminary characterization reveals the factor to have a molecular weight greater than 100,000. Thus, a novel function is delineated for this mesangial cell type that appears capable of modulating the local immune response by providing an amplification signal.

Class II antigen expression and gamma interferon modulation of monocytes and retinal pigment epithelial cells from patients with retinitis pigmentosa

Monocytes from retinitis pigmentosa patients express diminished amounts of class II (HLA-DR) antigens in comparison to normal individuals, normal siblings of retinitis pigmentosa patients, glaucoma patients, and macular degeneration patients. This observation is correlated with a subnormal production of IFN-gamma, a potent regulator of class II antigen expression. When monocytes from retinitis pigmentosa patients are treated with IFN-gamma, the decreased expression of HLA-DR on the cell surface is restored to levels found on monocytes from normal individuals. HLA-DR antigens were detected on the surfaces of human retinal pigment epithelial cells grown in vitro and the expression of these antigens can be enhanced following IFN-gamma treatment. These data demonstrate an altered expression and regulation of class II, HLA-DR, antigens in a human eye disease. Since class II antigens and IFN-gamma are currently known to be necessary regulating proteins for efficient immune reactivity, these findings may indicate an immune disturbance in retinitis pigmentosa patients. Alternatively, this alteration may have nonimmune implications. For example, these studies may demonstrate an imbalance in systemic regulatory control systems and hence raise the possibility that these or related regulatory proteins and cell surface receptors may be instrumental in maintaining retinal integrity.

Selective activation of immunoregulatory T-cell circuits by an Ia+ antigen-presenting cell line

ORA I-a, a cloned Ia+ monocyte tumor line, interacts with distinct immunoregulatory T-cell subsets. ORA cells present soluble and alloantigen to primed lymph node T cells and alloantigen to antigen-activated T-cell clones. However, they induce dose-dependent suppression during primary mixed lymphocyte cultures. Activation of a mixed lymphocyte response (MLR) suppressor pathway is mediated by Ly 1+ T cells. This T-cell subset proliferates in response to ORA when Ly 2+ cells are depleted. Furthermore, once activated, Ly 1+ T cells induce effectors of suppression within fresh T-cell populations. These studies indicate that antigen presentation to distinct T-cell subsets during different stages of an immune response may be mediated by unique antigen-presenting cell subpopulations. Immune homeostasis may thus be controlled not only by regulatory T cells, but also by unique antigen-presenting cells which are responsible for their selective activation.

Transient deficiency of peripheral blood accessory cells in supporting T cell mitogenesis in patients suffering from chronic idiopathic thrombocytopenic purpura after intravenous gammaglobulin treatment

Mitogenic response of blood lymphocytes to phytohemagglutinin (PHA) and to OKT3 monoclonal antibodies was investigated in 7 patients suffering from chronic idiopathic thrombocytopenic purpura (ITP) before, during and after high-dose intravenous (i.v.) immunogammaglobulin (IgG) infusion. The platelet count rose above the pre-treatment values during infusion therapy in all patients but one. Five out of seven patients presented elevated platelet-associated IgG (PA-IgG) levels at the time of the first infusion; four of these showed an increase in platelet count and a transient reduction or normalization of PA-IgG after IgG infusion. Five out of seven patients showed an impairment of T lymphocyte mitogenic response to PHA and OKT3 before therapy. All patients responded to IgG therapy with a transient deficiency of FcR mediated monocytes (Mo) in supporting T cell mitogenesis induced by both mitogens during and after IgG infusion. This reduced cooperative capability of Mo disappeared at various times after the end of therapy (range 3-12 days). The transient alteration of Mo function, possibly due to a modification in the surface number or in the affinity of Fc-receptors, can explain in part, the increase in platelet count during and after IgSRK infusion.

Immunization against experimental murine salmonellosis with liposome-associated O-antigen

Partially delipidated Salmonella typhimurium (O-1,4,5,12) lipopolysaccharide was incorporated into small multilamellar liposomes composed of either naturally occurring or synthetic phospholipids. Vaccination of mice with the liposome-lipopolysaccharide complexes induced a cellular response specific for O-1,4,5,12 determinants, as determined by the development of a delayed-type hypersensitivity reaction. The liposome-lipopolysaccharide vaccines were significantly more effective, compared with other nonviable vaccines tested, in protecting mice against a lethal intravenous challenge infection with virulent S. typhimurium. Protection afforded by the liposome-lipopolysaccharide vaccines was comparable to that conferred by a live S. typhimurium vaccine. Results suggest that liposome-induced modulation of the host immune response in favor of cell-mediated immunity may be more efficacious in preventing diseases in which cell-mediated immunity is of prime importance.

Functional capacity of solid tissue transplants in the brain: evidence for immunological privilege

The capacity of the mammalian brain to support the physiological function of allografts was assessed in parathyroidectomized Fischer strain rats bearing either isografts or immunogenic DA allografts of parathyroid glands implanted in their cerebral cortices. Established isografts and allografts survived indefinitely in the brain, maintaining normal serum calcium levels, with equal numbers of spontaneous failures (18-21%) in each group. Similarly, both MHC-compatible and incompatible skin allografts survived and were 'functional' at 40-50 days postgrafting as assessed by: continued formation of keratin; the presence of differentiated hair follicles and sebaceous glands; and frequent mitotic figures. No serum alloantibodies were induced by either MHC-incompatible parathyroid glands or skin in this site. However, both types of allografts were promptly rejected or failed to become established in the brains of specifically presensitized hosts. Furthermore, when Fischer hosts with long-established intracerebral DA parathyroid grafts received orthotopic DA skin grafts, their parathyroid grafts were rejected along with first-set rejection of the skin grafts. The tempo of this cellular immune response and the primary alloantibody response that accompanied it indicate that although the intracerebral grafts failed to induce detectable host sensitization or suppression, they remained susceptible to immune effectors. Thus, by using strongly immunogenic, adult tissues, we have established that the rat cerebral cortex is an immunologically privileged site, and the privilege is not dependent on lack of graft immunogenicity or alterations in host responsiveness. Furthermore, Ia+ (possible antigen-presenting) cells were rare in the cortical parenchyma sites used for transplantation though numerous in the choroid plexus of the ventricles and in certain areas of white matter. Therefore, privilege probably reflects deficient graft antigen presentation related to the paucity of Ia+ cells as well as to the brain's poor lymphatic drainage.

Functional analysis of macrophage hybridomas. II. Antibody-independent tumor cytotoxicity and its dissociation from IL-1 production and Ia expression

Cloned macrophage hybridoma cells derived from fusions between splenic adherent cells of CKB mice and the drug-marked P388D1 cell line were studied to further understand macrophage-mediated tumoricidal activity at the clonal level. Most of the macrophage hybridomas were specifically activated by a combination of lymphokine and lipopolysaccharide (LPS), but were not activated by either agent alone. There is no apparent correlation between macrophage-mediated tumor cytotoxicity and the ability of LPS to induce interleukin 1 (IL-1) secretion or of concanavalin A (Con A) supernatants containing interferon-gamma to increase H-2 and Ia expression. Thus, one hybridoma clone which was unable to kill tumor cells was still sensitive to LPS and lymphokine activation by the latter criterion.

Macrophage-derived soluble factors mediate suppression induced by 2,4-dinitrophenyl-conjugated mouse IgG in hybridoma cells

Our laboratory has established that 2,4-dinitrophenyl-conjugated mouse IgG (DNP-MGG) can specifically suppress proliferation, antibody synthesis, and secretion in vivo in two anti-DNP secreting cell lines: hybridoma 35-12 and myeloma MOPC-315. In the present study an in vitro system was used to further analyze the mechanism of suppression of hybridoma 35-12 cells (HC) by DNP-MGG. It was found that DNP-MGG-induced suppression of HC requires macrophages (M phi) and occurs only in eclipsed HC which are mainly small, nonsecreting cells. The M phi-mediated suppression is DNP specific, requires no M phi-HC cell contact, and does not involve killing of eclipsed HC. M phi culture supernatant alone cannot mediate suppression, but supernatants obtained by culturing M phi with either HC or supernatant from HC culture can mediate suppression of eclipsed HC in the presence of DNP-MGG. DNP-MGG is not required for the generation of effective M phi factors, but it is required for suppression of HC in the presence of M phi factors. Indomethacin cannot reverse M phi-mediated suppression, suggesting prostaglandins may not be the M phi factors. These data suggest that M phi-derived factors which are not prostaglandins in nature may play a role in B-cell regulation and in B-cell suppression induced by tolerogenic forms of antigen.

Immunobiological function of normal rabbit synovial cells

The ability of enzyme-dissociated primary cultures of synovial cells (Sy) to present antigen was investigated. Adult rabbits were immunized in foot pads with bovine serum albumin (BSA) in complete Freund's adjuvant (CFA) or with CFA alone. Four to six weeks later draining popliteal lymph node cells (LNC) and synovial cells were obtained. Synovial cells were cultured overnight with or without antigen. About 20% of these synovial cells had Fc receptors and 15% C3 receptors. As a positive control splenic adherent cells (SAC) were similarly treated. Next day, autologous lymph node cells were added to the extensively washed and irradiated synovial cells or splenic adherent cells. Lymphocyte proliferation was measured by [3H]thymidine uptake. Synovial cells as well as splenic adherent cells induced mixed lymphocyte reaction (MLR) and autologous mixed lymphocyte reaction (AMLR) and effectively presented antigen for specific immune response to the priming antigen. Thus, the synovium contains macrophage-like cells that can effectively interact with lymphocytes and participate in the immune phenomena in the joints of patients with rheumatoid arthritis.

Accessory cell function of cells of the mononuclear phagocyte system isolated from mycobacterial granulomas

Epithelioid cells from BCG-induced granulomas and macrophages from Mycobacterium leprae-induced granulomas were examined for their ability to act as accessory cells for T-cell proliferation to mitogen (Con A) and antigen (PPD). The granuloma cells were separated on a FACS using monoclonal antibody specific to guinea pig macrophages. Epithelioid cells (which are Ia negative) were able to support proliferation to Con A but not to antigen. Cultures containing Ia positive granuloma macrophages from M. leprae sensitized animals did not show responsiveness to Con A or to PPD. Oil-induced peritoneal exudate macrophages from BCG or M. leprae immunized animals were able to act as accessory cells for both mitogen and antigen proliferation. The nonresponsiveness of cultures containing epithelioid cells stimulated with PPD or M. leprae granuloma macrophages stimulated with Con A was not due to suboptimal or supraoptimal accessory cell:lymphocyte ratios.

Identification of a membrane-associated interleukin 1 in macrophages

We have found a surface membrane-associated interleukin 1 (IL-1) with potent thymocyte and T-cell stimulatory activity on peptone-elicited peritoneal macrophages. The IL-1 activity was demonstrated on both fixed macrophage monolayers and on isolated membranes from unfixed macrophages. Membrane IL-1 was induced by adherence and/or by adding heat-killed Listeria monocytogenes to macrophage cultures. The macrophage membrane IL-1 was similar functionally and antigenically to soluble IL-1, but its expression could be temporally dissociated from IL-1 secretion; membrane IL-1 was induced earlier and persisted longer than IL-1 secretion during in vitro macrophage culture. Moreover, when cultured macrophages that had ceased both secretion and membrane expression of IL-1 were restimulated by adding heat-killed Listeria, substantial membrane IL-1 was induced in the absence of detectable IL-1 secretion. Membrane IL-1 appears to be an integral membrane protein since it was solubilized by detergent but was not eluted by EDTA, high salt, or low pH treatment of the membranes.

A comparison of the effects of hydrocortisone on peritoneal inflammatory exudates, the tuberculin reaction and contact sensitivity-to DNFB in the guinea pig

Hydrocortisone acetate, injected subcutaneously in five doses in a depot producing vehicle, causes prolonged suppression of the ability of guinea pigs to produce a chronic inflammatory reaction in the peritoneal cavity and also of the tuberculin reaction. This suppression of the tuberculin reaction persists for at least 65 days after the last dose of hydrocortisone. Suppression of both peritoneal exudate and the tuberculin reaction was associated with a preferential depletion of macrophages at the reaction site. A similar regime had no effect on the ability of guinea pigs to manifest contact sensitivity reactions to 2,4-dinitrofluorobenzene although there was a similar drop in macrophages in the lesion. It appears that the effect of hydrocortisone on delayed hypersensitivity reactions is not directly related to the functional contribution of macrophages in the inflammatory reactions, and may be related to the site of the inflammatory reaction in the skin.

A new surface marker on equine peripheral blood lymphocytes. II. Characterization and separation of purified blood lymphocytes with receptors for Helix pomatia A hemagglutinin (HP)

In a preceding report we have shown that the lectin Helix pomatia A hemagglutinin (HP) binds to two subpopulations of neuraminidase-treated equine peripheral blood lymphocytes (PBL), constituting about 20% and 75% of PBL, respectively. The aim of the present study was to further characterize these HP+ cells in regard to other surface markers such as receptors for guinea pig erythrocytes (GPR+ cells), membrane-bound immunoglobulins (sIg+ cells), receptors for activated complement (C3R+ cells) and receptors for IgG (Fc alpha R+ cells). This was done by double marker analysis and by lymphocyte fractionation either on columns charged with HP coupled to Sepharose beads or by rosetting with guinea pig erythrocytes. The fractions were also analysed for their proliferative response in the mixed lymphocyte tumor cell interaction (MLTC) assay and to the mitogens leucoagglutinin (La) and concanavalin A (Con A). The results revealed that the majority of GPR+ cells also expressed high avidity receptors for HP, as defined by means of direct immunofluorescence. These cells constituted a subpopulation of GPR+/HP+ cells T cells comprising approximately 20% of PBL. In contrast, about 75% of the HP+ cells in indirect immunofluorescence were GPR-. The fractionation experiments showed that HP+ and GPR+ cells were probably not B cells since they were sIg-. The C3R+ and Fc alpha R+ lymphocytes were heterogeneous in regard to HP receptors but the majority of these cells was also found in the fractions depleted of HP+ and GPR+ lymphocytes. The fractions eluted from HP columns gave a strong proliferative response in MLTC, whereas fractions depleted of HP+ cells responded poorly. However, in contrast to the GPR+-depleted fractions, those enriched in GPR+ lymphocytes responded poorly to the T cell mitogens La and Con A. The mitogenic response of the HP-column fractions to La and to Con A was variable. The results are discussed in relation to HP being a surface marker for a heterogeneous population of equine T cells.

Cellular mechanisms in in vivo production of gamma interferon induced by lipopolysaccharide in mice infected with Mycobacterium bovis BCG

Infection of mice with Mycobacterium bovis BCG sensitizes them for immune induction of interferon (IFN)-gamma by specific antigen. These mice were found also to respond to lipopolysaccharide (LPS) and concanavalin A (Con A) with high level production of IFN-gamma in the circulation, which was not observed in control mice. In this study, we compared the IFN-gamma response to LPS with that to Con A in an attempt to clarify the cellular mechanisms responsible for in vivo LPS-induced IFN-gamma production. Consequently, (i) the responses to LPS and Con A differed in the kinetics, that to LPS having a longer lag period. (ii) Spleen cells taken from infected mice produced little IFN-gamma in response to LPS, but they showed a higher IFN-gamma response to Con A than those from control mice. (iii) By treating infected mice with immunosuppressive drugs or antibodies to T and natural killer cells before challenge with the inducers, it was indicated that different cellular systems are involved in the IFN-gamma responses to LPS and to Con A.

Role of class II histocompatibility antigens in Staphylococcus aureus protein A-induced activation of human T lymphocytes

The capacity of peripheral blood monocytes and B lymphocytes to support staphylococcal protein A (SpA)-induced proliferation of autologous and allogeneic T cells, as well as the role of major histocompatibility complex (MHC) class I and II molecules in this activation process, were investigated. Highly purified peripheral T lymphocytes did not proliferate in response to SpA, but their response was reconstituted by both irradiated (or mitomycin C-treated) monocytes and B lymphocytes. The effect of B cells on the SpA-induced T-cell response could not be explained by a contamination of residual accessory cells because long-term continuous B-cell lines restored SpA-induced T-cell DNA synthesis as effectively as did monocytes. Support of SpA responsiveness by B cells could not be accounted for by polyclonal binding of SpA to cell surface immunoglobulins, since the ability of SpA-unreactive and SpA-reactive B cells was comparable. The cells from two human leukemic lines--K562 and Raji--showed the same ability in supporting the pokeweed mitogen-induced T-cell response, but the class II-positive Raji cells were much more effective than class II-negative K562 cells in restoring the T-cell responsiveness to SpA. Monoclonal antibodies specific for monomorphic determinants of MHC class II antigens, as well as their F(ab')2 fragments, consistently inhibited the SpA-induced proliferative response, whereas antibodies specific for MHC class I antigens were without effect. The antibodies specific for class II antigens appeared to act at the level of accessory cell, since pretreatment with these antibodies inhibited the ability of SpA-pulsed monocytes or Raji cells to present SpA to autologous or allogeneic T lymphocytes, respectively. These data indicate that either monocytes or normal and lymphoblastoid B cells can act as accessory cells for the proliferative response of human T cells to soluble SpA and that monomorphic determinants of MHC class II molecules play an important role in this activation process.

Antigen presentation by proliferating thymic macrophages to A (T,G)-A-L specific T cell line in an H-2 restricted manner

Long-term cultures of murine homogeneous populations of Ia-bearing thymus-derived murine macrophages were tested for their ability to present antigen to a (T,G)-A-L specific IL-2-dependent continuous T cell line. Thymus-derived macrophages, with and without pretreatment for Ia induction, triggered efficiently antigen-specific T cell proliferation in an MHC restricted way. This experimental system, consisting of two normal proliferating homogeneous populations of macrophages and antigen specific T cells, provides an ideal tool for studying the mechanism of antigen presentation to T cells and for elucidation of the role of macrophages in T-B cell collaboration for antibody production.

Interleukin-1-like activities in synovial fluids of patients with rheumatoid arthritis and traumatic synovitis

Interleukin-1 (Il-1)-like activity in biological fluids was measured by their ability to rectify the Il-1-dependent lymphokine production of highly purified T lymphocytes to a recall antigen. Il-1-like activity was found in 9 of 11 synovial fluid (SF) specimens from patients with rheumatoid arthritis (RA) but only in 2 of 11 paired RA sera. In traumatic synovitis, low Il-1-like activity was recorded in 5 of 9 SF specimens, and a similar low activity was found in sera of 4 of these patients. The Il-1-like activity was partly absorbed by an anti-Il-1 antibody. The presence of Il-1 in the SF of patients with RA suggests in vivo activation of monocytes/macrophages.

Enhanced alveolar macrophage-mediated antigen-induced T-lymphocyte proliferation in sarcoidosis

Expansion of T-lymphocyte numbers is a characteristic feature of the alveolitis of pulmonary sarcoidosis. One mechanism that may influence the numbers of T-lymphocytes in the lung is the process of antigen presentation in which alveolar macrophages, in the presence of antigen, induce T-lymphocytes to replicate. To evaluate this process in sarcoidosis, alveolar macrophages were obtained by bronchoalveolar lavage, pulsed with tetanus toxoid, and co-cultured with purified autologous T cells. Strikingly, antigen-pulsed alveolar macrophages from sarcoid patients induced more than a twofold increase in autologous T-lymphocyte proliferation compared with the response seen using cells from normal or patients with idiopathic pulmonary fibrosis (P less than 0.001), all comparisons). In contrast, when monocytes were used as the antigen presenting cell, no significant differences were observed in T cell proliferation induced by antigen among the three groups. The enhanced T-lymphocyte proliferation induced by sarcoid alveolar macrophages was not dependent on the compartment from which the T cells were derived, and was independent of the specific antigen used. One possible explanation for augmented antigen presentation seen in sarcoid is that an increased percentage of sarcoid alveolar macrophages express HLA-DR or HLA-DS surface antigens. However, most normal and sarcoid alveolar macrophages express HLA-DR and HLA-DS surface antigens, and the percentage of macrophages expressing these antigens was not significantly different in the two groups. Thus, while the mechanisms of the enhanced antigen presentation in the sarcoid lung are unknown, the process of antigen-driven, alveolar macrophage-modulated lung T cell proliferation may explain, at least in part, the expansion of lung T-lymphocyte numbers that characterizes this disease.

Langerhans cells in SLE skin. A role in lymphocyte migration and activation in situ

Langerhans cells in SLE skin and mucosa were studied by using monoclonal anti-T6 and anti-Ia antibodies and avidin-biotin-peroxidase complex staining. Langerhans cells were present in cell infiltrates of natural SLE skin lesions. In developing early skin lesions induced with test antigen, Langerhans cells were the predominant inflammatory cells, suggesting that migration of Langerhans cells into the inflammatory site in fact precedes lymphocyte migration. These findings agree with the hypothesis of the role of dendritic cells in lymphocyte circulation and antigen presentation under physiological and pathological conditions. Many of the infiltrating local T lymphocytes in both natural and test antigen induced SLE lesions were activated Ia+ cells. This suggests an active immune response in both natural and test antigen induced skin lesions in SLE. The low immunomodulatory T4/T8 ratio in situ in SLE skin lesions might suggest that T8+ cells exert immunosuppressive control on the local inflammation.