A murine IL-4 receptor antagonist that inhibits IL-4- and IL-13-induced responses prevents antigen-induced airway eosinophilia and airway hyperresponsiveness.

The closely related Th2 cytokines, IL-4 and IL-13, share many biological functions that are considered important in the development of allergic airway inflammation and airway hyperresponsiveness (AHR). The overlap of their functions results from the IL-4R alpha-chain forming an important functional signaling component of both the IL-4 and IL-13 receptors. Mutations in the C terminus region of the IL-4 protein produce IL-4 mutants that bind to the IL-4R alpha-chain with high affinity, but do not induce cellular responses. A murine IL-4 mutant (C118 deletion) protein (IL-4R antagonist) inhibited IL-4- and IL-13-induced STAT6 phosphorylation as well as IL-4- and IL-13-induced IgE production in vitro. Administration of murine IL-4R antagonist during allergen (OVA) challenge inhibited the development of allergic airway eosinophilia and AHR in mice previously sensitized with OVA. The inhibitory effect on airway eosinophilia and AHR was associated with reduced levels of IL-4, IL-5, and IL-13 in the bronchoalveolar lavage fluid as well as reduced serum levels of OVA-IGE: These observations demonstrate the therapeutic potential of IL-4 mutant protein receptor antagonists that inhibit both IL-4 and IL-13 in the treatment of allergic asthma.

A T-cell-selective interleukin 2 mutein exhibits potent antitumor activity and is well tolerated in vivo.

Human interleukin 2 (IL-2; Proleukin) is an approved therapeutic for advanced-stage metastatic cancer; however, its use is restricted because of severe systemic toxicity. Its function as a central mediator of T-cell activation may contribute to its efficacy for cancer therapy. However, activation of natural killer (NK) cells by therapeutically administered IL-2 may mediate toxicity. Here we have used targeted mutagenesis of human IL-2 to generate a mutein with approximately 3,000-fold in vitro selectivity for T cells over NK cells relative to wild-type IL-2. We compared the variant, termed BAY 50-4798, with human IL-2 (Proleukin) in a therapeutic dosing regimen in chimpanzees, and found that although the T-cell mobilization and activation properties of BAY 50-4798 were comparable to human IL-2, BAY 50-4798 was better tolerated in the chimpanzee. BAY 50-4798 was also shown to inhibit metastasis in a mouse tumor model. These results indicate that BAY 50-4798 may exhibit a greater therapeutic index than IL-2 in humans in the treatment of cancer and AIDS.

A murine skeletal muscle ischemia-reperfusion injury model: differential pathology in BALB/c and DBA/2N mice.

Ischemia-reperfusion injuries can occur with diseases such as myocardial infarction and stroke and during surgical procedures such as organ transplantation and correction of aortic aneurysms. We developed a murine model to mimic abdominal aortic aneurysm repair with cross-clamping of the aorta distal to the renal artery. After model development, we compared the normal complement BALB/c mouse with the C5-deficient DBA/2N mouse. To assess quantitative differences, we measured neuromuscular function up to 72 h after ischemia with a subjective clinical scoring system, as well as plasma chemistries, hematology, and histopathology. There were significant increases in clinical scores and creatine phosphokinase, lactate dehydrogenase, and muscle histopathology scores in BALB/c mice compared with those in DBA/2N mice and sham-surgery mice. Muscle histopathology scores of the cranial tibialis and quadriceps correlated well with clinical signs, creatine phosphokinase, and lactate dehydrogenase, and indicated the greatest pathology in these muscle groups. We developed a murine model of skeletal muscle ischemia-reperfusion injury that can utilize the benefits of murine genetic and transgenic models to assess therapeutic principles of this model. Additionally, we have shown a significant reduction in clinical signs, plasma muscle enzyme concentrations, and muscle pathology in the C5-deficient DBA/2N mouse in this model.

Expression of vascular cell adhesion molecule-1 by vascular endothelial cells in immune and nonimmune inflammatory reactions in the skin.

Expression of VCAM-1 was compared with that of E-selectin in cytokine-induced lesions and in delayed-type hypersensitivity reactions to tuberculin purified protein derivative (PPD) in pig skin. Lumenally expressed Ags were quantified by measuring localization in skin of i.v. injected (111)In-mAb 10.2C7 (anti-vascular cell adhesion molecule-1 (anti-VCAM-1), (125)I-mAb 1.2B6 (anti-E-selectin), and (99m)Tc-MOPC21 (control IgG1). Anti-VCAM-1 mAb uptake was greater following intradermal (i.d.) injection of TNF-alpha than following injection of IL-1, while the two cytokines induced similar uptake of anti-E-selectin. In immunologically naive pigs there was no detectable increase in anti-VCAM-1 after i.d. injection of PPD, although anti-E-selectin uptake was increased at 3 and 6 h. In contrast, i.d. injection of PPD in sensitized pigs led to increased uptake of both anti-VCAM-1 and anti-E-selectin at 6, 8, 24, and 48 h, each of which was significantly greater than the uptake of control IgG1 into the same lesions (each p < 0.01). Anti-TNF-alpha mAb abolished the increased uptake of anti-VCAM-1 3 and 8 h following i.d. injection of PPD in sensitized pigs and significantly inhibited uptake at 24 h (p = 0.0025), but did not significantly reduce uptake of anti-E-selectin. We conclude that in this delayed-type hypersensitivity model 1) E-selectin expression by endothelial cells follows sequential Ag nonspecific and immune-specific phases, 2) increased VCAM-1 expression by endothelial cells is only seen in sensitized animals, and 3) expression of VCAM-1 appears to be relatively more dependent on TNF-alpha than E-selectin. Differential expression of E-selectin and VCAM-1 may influence the leukocytic infiltrate during the course of nonspecific and immune-specific inflammatory reactions.

Endothelial activation in monosodium urate monohydrate crystal-induced inflammation: in vitro and in vivo studies on the roles of tumor necrosis factor alpha and interleukin-1.

OBJECTIVE: There is relatively little direct evidence for the roles of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) in activating endothelium in vivo. The aim of this study was to use in vitro and in vivo models to investigate the contribution of these cytokines to both E-selectin expression and the recruitment of polymorphonuclear cells (PMN) in monosodium urate monohydrate (MSU) crystal-induced inflammation. METHODS: MSU crystals were incubated with freshly isolated mononuclear cells, after which the harvested supernatants were tested for their ability to induce E-selectin expression during coculture with human umbilical vein endothelial cells. Subsequent experiments were performed with the addition of neutralizing anticytokine antibodies/antisera. The role of TNF alpha was then studied in an MSU crystal-induced monarthritis model, in the presence or absence of anti-TNF alpha (5 mg/kg intravenously). 99mtechnetium (99mTc)-labeled PMN cells and (111)indium (111In)-labeled anti-E-selectin monoclonal antibody (MAb) 1.2B6 were intravenously administered 4 hours after intraarticular injection to quantify PMN recruitment and E-selectin expression in inflamed joints. RESULTS: MSU crystals were a potent stimulus for IL-1 and TNF alpha production by monocytes in vitro, and these cytokines fully accounted for MSU crystal-stimulated, monocyte-mediated endothelial activation. In the MSU crystal-induced monarthritis model, TNF alpha blockade was very effective in suppressing both E-selectin expression and PMN emigration into the inflamed joints, as judged by gamma-camera image analysis and postmortem tissue counting following the intravenous injection of 99mTc-PMN and 111In-anti-E-selectin MAb. CONCLUSION: IL-1 and TNF alpha appear to be the only factors released by monocytes following incubation with MSU crystals, which induce E-selectin expression in vitro. Anti-TNF alpha is effective in suppressing endothelial activation and PMN recruitment in vivo E-selectin imaging can be used to assess the endothelial response to therapy and may prove useful for clinical studies.

The interaction of alpha 1-proteinase inhibitor and tissue kallikrein in controlling allergic ovine airway hyperresponsiveness.

We reported previously that the development of airway hyperresponsiveness (AHR) 24 h after antigen challenge in allergic sheep was associated with increased tissue kallikrein activity (TK) and decreased alpha-1-proteinase inhibitor (alpha 1-PI) activity in bronchoalveolar fluid (BAL). The inverse correlation between TK and alpha 1-PI in these experiments suggested that administration of alpha 1-PI might reduce TK activity and block AHR. To test this hypothesis, airway responsiveness, as determined by calculating the cumulative carbachol breath units (BU) that increased specific lung resistance by 400% (PC400), was measured before and 24 h after aerosol challenge with Ascaris suum antigen in seven sheep hypersensitive to this antigen. On the next day, 30 min before the 24 h PC400 measurement, the sheep were treated with either aerosol alpha 1-PI (Prolastin, 10 mg/5 ml) or denatured (DN) prolastin (10 mg/5 ml), which had only 10% of its original activity. BAL was also performed before and 24 h after challenge for the measurement of TK and alpha 1-PI activity. Treatment with DN-Prolastin at 24 h after antigen challenge did not block antigen-induced AHR: PC400 fell from a baseline (mean +/- SE) of 26.0 +/- 3.2 BU to 11.2 +/- 1.5 BU after challenge (p < 0.05). This AHR was associated with increased TK (363%, p < 0.05) and decreased alpha 1-PI activity (65%, p < 0.05). Prolastin treatment at 24 h blocked the AHR: PC400 was 21.0 +/- 2.8 before and 23.2 +/- 3.7 after challenge (p < 0.05 versus DN-Prolastin) and the changes in BAL TK (28% increase) and alpha 1-PI activities (15% increase) were not different from baseline (both p < 0.05 versus DN-Prolastin). There was a significant inverse correlation between alpha 1-PI activity and TK activity in BAL, as well as the changes between baseline and 24 h in alpha 1-PI activity and TK activity in BAL Pretreatment (30 min before antigen challenge) with Prolastin also protected against the antigen-induced AHR. The effect of Prolastin was also seen against aerosol challenge with high-molecular-weight kininogen (HMWK), a substrate of TK. HMWK caused bronchoconstriction which was blocked by Prolastin (p < 0.05), and the bradykinin B2 antagonist, NPC-567 (indicating that kinins were generated), but not DN-Prolastin or the elastase inhibitor, ICI 200, 355. Although the negative association between alpha 1-PI activity and TK activity identified in this study does not prove cause and effect, our findings do raise the possibility that in vivo alpha 1-PI may regulate TK activity and allergen-induced AHR.

IL-4 induced leucocyte trafficking in cynomolgus monkeys: correlation with expression of adhesion molecules and chemokine generation.

BACKGROUND: Interleukin-4 (IL-4) is an immunoregulatory cytokine which has a wide variety of effects on immune cell function. In addition, recent studies suggest that IL-4 may have effects on other cells including endothelial cells in terms of the regulation of adhesion molecule expression and leucocyte extravasation from the vascular space to sites of tissue inflammation. Consequently, IL-4 may have an important role in the pathogenesis of allergic inflammation and disease. OBJECTIVE: The purpose of this study was to learn more about the potential role of IL-4 in inflammatory disease, specifically in regard to the potential of IL-4 to induce the expression of adhesion molecules on vascular endothelial cells and promote the adherence and transmigration of circulating leucocytes to sites of tissue inflammation. METHODS: Single subcutaneous injections of human IL-4 were administered to cynomolgus monkeys and tissue biopsy samples were obtained and analysed for adhesion molecule expression on vascular endothelium and inflammatory cell infiltrates. In another series of experiments, multiple subcutaneous injections of human IL-4 were administered (bid on four consecutive days) and the effects on peripheral blood leucocytes and plasma levels of various cytokines and chemokines were examined. RESULTS: Intradermal injection of IL-4 induced the expression of vascular cell adhesion molecule-1 (VCAM-1) on cutaneous vascular endothelium that was present at 8 hr and persisted out to 24 h post injection. The expression of VCAM-1 was associated with an inflammatory cell infiltrate comprised of granulocytes and mononuclear cells. Multiple injections of IL-4 resulted in a dose-related decrease in the relative percentage and total number of circulating lymphocytes and an increase in circulating neutrophils (4.6 +/- 1-2.1 +/- 0.2 x 10(6)/mL and 1.7 +/- 0.3-7.0 +/- 1 x 10(6)/mL, respectively). Analysis of cell surface markers by flow cytometry revealed a transient decrease in the number of CD4+T lymphocytes and a sustained decrease in CD16+ cells. In addition, IL-4 administration resulted in a large increase in plasma MCP-1 concentration. CONCLUSION: This is the first study to demonstrate an acute effect of IL-4 consistent with lymphocyte trafficking out of the vascular space, the induction of VCAM-1 expression on vascular endothelium and increases in plasma levels of MCP-1 in vivo. We suggest that IL-4 may be involved in the early recruitment of mononuclear cells to sites of tissue inflammation by the upregulation of VCAM-1 expression on vascular endothelium and the generation and release of potent chemoattractants.

Thromboxane-blocked swine as an experimental model of severe intravascular inflammation and septic shock.

The cardiopulmonary response elicited by intravenous bacteria or endotoxin is well characterized in swine and has two major components. The first represents the acute pulmonary and broncho-constrictive phase (0-2 h) and the second phase (3-8 h) represents increased microvascular permeability, hypotension, and enhanced leukocyte-endothelial adhesion. The pulmonary vasoconstriction and bronchoconstriction of phase 1 results in acute pulmonary hypertension and airway dysfunction, which may result in rapid mortality. Because this acute pulmonary response may not mimic the development of human septic shock, we sought to block this early phase and examine the role of tumor necrosis factor in the latter septic phase (3-8 h). Employing a thromboxane A2 (TXA2) receptor antagonist (BAY U 3405) in the presence of LD100 Escherichia coli challenge, we blocked the acute pulmonary hypertensive phase and prevented early mortality, however, TXA2 blockade did not affect the latter development of septic shock and death. This latter lethal phase, characterized by prolonged leukopenia, was blocked in a dose-dependent manner by tumor necrosis factor monoclonal antibody. We conclude that the TXA2-blocked E. coli-challenged swine may provide a novel animal model in which to investigate the pathophysiology of acute septic shock.

The onset and recovery from airway hyperresponsiveness: relationship with inflammatory cell infiltrates and release of cytotoxic granule proteins.

Previous studies from our laboratory have demonstrated a temporal relationship between eosinophil influx into the airways and the onset of airway hyperresponsiveness to inhaled methacholine. The purpose of the present study was to extend this observation by evaluating changes in airway cellular composition and measuring the levels of granulocyte-derived mediators recovered in BAL fluid during the onset and recovery from antigen-induced airway hyperresponsiveness. Airway cellular composition, airway responsiveness to inhaled methacholine and the levels of BAL fluid EPO and MPO were monitored over a 32 day study in eight adult male Ascaris suum sensitive cynomolgus monkeys. Repeated Ascaris suum inhalation (nine challenges during days 0-21) resulted in a selective, sustained airway eosinophilia that was temporally related with the onset and maintenance of airway hyperresponsiveness (r = 0.67, P less than 0.001). The level of BAL eosinophil-derived EPO was increased and remained elevated concurrent with the increase in airway eosinophils and airway responsiveness. During the recovery phase (days 22-32) the actual number of eosinophils remained elevated, while BAL EPO levels were significantly decreased. The recovery phase was also associated with a transient increase in the number of BAL neutrophils and MPO concentration. We conclude that the number and state of activation of airway eosinophils directly correlate with the onset and maintenance of airway hyperresponsiveness. Recovery from airway hyperresponsiveness is associated with a decrease in eosinophil activation and a transient increase in the number of activated neutrophils.

Acidic polyamino acids inhibit human eosinophil granule major basic protein toxicity. Evidence of a functional role for ProMBP.

Eosinophil granule major basic protein (MBP), a potent toxin for helminths and mammalian cells in vitro, is a single polypeptide chain rich in arginine. MBP has been localized on damaged helminths and tissues in hypersensitivity diseases including bronchial asthma. The MBP cDNA indicates that MBP is translated as a slightly acidic preproprotein with an acidic propart. To test the hypothesis that the acidic pro-part of proMBP inhibits the toxicity of mature MBP, acidic polyamino acids (aa) were used as antagonists of MBP toxicity to K562 cells and guinea pig tracheal epithelium and used as antagonists of MBP airway hyperresponsiveness in primates. The acidic poly aa inhibited MBP toxicity and MBP airway hyperresposiveness. The acidic poly aa inhibited MBP toxicity in a charge-dependent manner similar to that proposed for proMBP, suggesting that the acidic pro-part of proMBP functions to mask mature MBP toxicity. This inhibition was not limited to MBP, but also applied to polyarginine and eosinophil cationic protein. These acidic poly aa may be useful to inhibit the actions of a number of cationic toxins released by the eosinophil in numerous hypersensitivity diseases.

Effect of erythrocytes on alveolar macrophage cytostatic activity induced by bleomycin lung damage in rats.

Bleomycin (BLM) has been successfully used to treat a number of human neoplasms. The main toxicity associated with BLM therapy is an acute pulmonary inflammation that can culminate in diffuse chronic fibrosis. The effect of BLM-induced pulmonary inflammation on the cytostatic activity of alveolar macrophages (AM) was investigated using AM obtained from rats that had been previously treated with BLM. Bronchoalveolar lavage fluid was collected at selected time intervals following a single fibrogenic dose of intratracheally administered BLM (3.6 mg/kg). AM obtained 12 to 72 h following intratracheal BLM (BLM-AM) caused cytostasis of murine leukemia L1210 cells in co-culture, whereas AM obtained from saline-treated controls were not cytostatic. These results indicate that the growth-inhibitory activity of the AM was related to the pulmonary inflammation. Cytostatic activity in control AM could be induced by in vitro exposure to lipopolysaccharide (5 micrograms). When RBC were added to the AM-L1210 co-culture, the cytostatic activity of the BLM-AM was abrogated. The fact that chemical treatment of the RBC with sodium nitrite and potassium cyanide or N-ethylmaleimide did not alter the ability of the RBC to abrogate AM cytostatic activity suggests that the RBC is not acting as a scavenger of oxygen radicals. In contrast, the addition of FeSO4 to the AM-L1210 co-culture mimicked the effect of RBC addition. Aconitase, an iron-sulfur-containing enzyme necessary for mitochondrial respiration, is decreased in L1210 cells that have been co-cultured with BLM-AM but not when the co-cultures also contain RBC. These results suggest that (a) pulmonary inflammation induces cytostatic activity in AM, (b) the alteration of iron homeostasis plays an important role in this cytostatic process, and (c) RBC can prevent this cytostatic activity.

Repeated antigen inhalation results in a prolonged airway eosinophilia and airway hyperresponsiveness in primates.

The effects of repeated antigen inhalation on airway cellular composition and airway responsiveness were examined in primates. Airway cellular composition was assessed by bronchoalveolar lavage (BAL), and airway responsiveness was measured as the bronchoconstrictor response to cumulative methacholine dose-response determinations over the course of a 10-wk study. Control animals, exposed to repeated vehicle inhalation challenges, were tested in parallel with the antigen-challenged group. Repeated antigen inhalation resulted in a prolonged inflammatory reaction characterized by a large increase in airway eosinophils (3 +/- 1 to 59 +/- 15%, P less than 0.01). Airway eosinophilia was associated with an increase in airway responsiveness as indicated by a leftward shift in the methacholine dose-response curves, an increase in the slope of the dose-response curves, and a decrease in PC100 values (the dose of methacholine required to cause a 100% increase in lung resistance). The number of BAL eosinophils and the level of eosinophil major basic protein in BAL correlated significantly with methacholine PC100 values (r = 0.61, P less than 0.01 and r = 0.64, P less than 0.01, respectively). Histological examination of lung biopsy samples taken at week 10 of the study demonstrated a striking infiltration of eosinophils in the antigen-challenged animals. These results support earlier observations that demonstrated an association between increases in airway eosinophils and increases in airway responsiveness and suggest that eosinophils are involved in the pathogenesis of hyperresponsive airways.

Intercellular adhesion molecule-1 (ICAM-1) in the pathogenesis of asthma.

Airway eosinophilia, epithelial desquamation, and hyperresponsiveness are characteristics of the airway inflammation underlying bronchial asthma. The contribution of intercellular adhesion molecule-1 (ICAM-1) to eosinophil migration and airway responsiveness was studied. ICAM-1 partially mediated eosinophil adhesion to to endothelium in vitro and was upregulated on inflamed bronchial endothelium in vivo. ICAM-1 expression was also upregulated on inflamed airway epithelium in vitro and in vivo. In a primate model of asthma, a monoclonal antibody to ICAM-1 attenuated airway eosinophilia and hyperresponsiveness. Thus, antagonism of ICAM-1 may provide a therapeutic approach to reducing airway inflammation, hyperresponsiveness, and asthma symptoms.

Antigen-coated sepharose beads induce airway eosinophilia and airway hyperresponsiveness in cynomolgus monkeys.

A method of inducing sustained airway eosinophilia and airway hyperresponsiveness in primates has been developed. Our method utilizes a series of intratracheal instillations of Ascaris suum-coated sepharose 4B beads (3 x 10(5] administered once a week for four weeks. Five cynomolgus monkeys (Macaca fascicularis) demonstrating a naturally occurring skin and respiratory sensitivity to Ascaris suum extract were studied. Airway cell composition was measured by bronchoalveolar lavage (BAL), and airway responsiveness was determined as the bronchoconstrictor response to inhaled methacholine. Ascaris suum bead administration resulted in a transient increase in total cells recovered by BAL (2.4 +/- 0.4 to 8.7 +/- 2.5 x 10(5) cells/ml, p less than 0.05) and a selective increase in BAL eosinophils (17 +/- 6 to 916 +/- 158 x 10(3) cells/ml, p less than 0.05). Increases in airway responsiveness were concurrent with the increase in airway eosinophils. These observations show that airway eosinophilia is associated with airway hyperresponsiveness in primates. Furthermore, this new model is a novel experimental system in which the underlying mechanisms in the pathogenesis of airway hyperresponsiveness can be investigated.

In vitro cellular cytotoxicity for a human colon cancer cell line by mucosal mononuclear cells of patients with colon cancer and other disorders.

In vitro cellular cytotoxicity of mononuclear cells of intestinal mucosa and peripheral blood for a colon cancer cell target was measured in patients with colon cancer and other disorders requiring resection. Four- and 24-hour cytotoxicity assays were conducted using selenium 75 (75Se)-labeled RPMI-4788 human colon cancer target cells grown in culture. In the cancer group mean cytotoxicity was 30.4% at 24 hours for peripheral blood effectors and 8.0% for effectors from normal mucosa. Values in patients with Crohn's disease were 10.4% for blood and 17.2% for effectors from normal mucosa, and 13.6% and 18.5%, respectively, for blood and abnormal mucosa. Values in patients with other diseases were 25% for blood and 14.7% for mucosa. Mean cytotoxicity at 4 hours did not exceed 6.4% for any group, and assays in autologous serum gave results similar to tests in calf serum. In additional studies, K 562 chronic leukemia cells were somewhat more sensitive to lysis than RPMI-4788 by blood mononuclear cells, but there was no lysis of K 562 by mucosal populations that were cytotoxic for RPMI-4788. There was no competitive inhibition by either target cell for the other. It was concluded that 75Se RPMI-4788 colon cancer cells are suitable targets for evaluating in vitro cytotoxicity by intestinal mucosal cells and that mucosal cytotoxicity in patients with colon cancer is depressed compared to cytotoxicity by peripheral blood effectors.

Comparative studies of mononuclear phagocyte function in patients with Crohn's disease and colon neoplasms.

Phagocytosis and cellular cytotoxicity by mononuclear phagocytes of blood and intestinal mucosa were studied in patients with Crohn's disease and large bowel neoplasms. Antibody coated sheep erythrocytes were used for phagocytic assays and cellular cytotoxicity in vitro was measured by 24 hour isotope release from 75Selenium methionine-labelled RPMI 4788 human cancer cell cultures in the presence of mononuclear phagocyte-enriched effector populations. The mean percent of mononuclear phagocytes in Ficoll-Hypaque purified mononuclear cell suspensions of blood of healthy controls was 25.9 compared with 44.6 in patients with Crohn's disease, 45.6 in patients with colon neoplasms and 11.6 in intestinal mucosa. Phagocytic indices were similar in all groups, but the phagocytic capacity of mucosal macrophages was twice that of blood monocytes. Mean cytotoxicity of monocytes of patients with Crohn's disease was 12.8% compared with 22.9% for monocytes from normal controls, and 29.4% for patients with colon tumours. Mean cytotoxicity by mucosal macrophages was 18.0% compared with 13.2% by mucosal lymphocyte populations. Exposure of monocytes of Crohn's disease patients to bacterial lipopolysaccharide modestly increased cytotoxicity, but exposure did not alter phagocytosis by monocytes of patients or controls. The results indicate that monocytes of patients with Crohn's disease exhibit subnormal in vitro cytotoxicity. Mucosal macrophages from patients with various diseases show enhanced phagocytosis compared with blood monocytes, and they can mediate cellular cytotoxicity in vitro.

Depressed spontaneous cell-mediated cytotoxicity in Crohn's disease.

Cytotoxicity of peripheral blood mononuclear cells of 30 patients with Crohn's disease (CD) and 30 matched controls was assayed by measuring isotope release from 75Se-L-methionine labelled RPMI 4788 human colon cancer cells. Effector populations were studied with and without monocyte depletion after 4 and 24 hr incubations in 10% fetal calf serum or autologous serum or plasma. Cytotoxicity was negligible at 4 hr. Twenty-four hour cytotoxicity was consistently lower in CD patients than in healthy controls, mean values ranging from 13.6 +/- 2.7% (s.e.m.) to 19.5 +/- 3.7% in patients and from 27.2 +/- 4.1% to 33.6 +/- 5.3% in controls. Cytotoxicity of disease controls was not significantly different from that of healthy subjects. Cytotoxicity was reduced by monocyte depletion, was weakly and inversely related to disease activity, was relatively stable for up to 24 months and was not HLA restricted. Cell lysis was attributable to spontaneous cell-mediated cytotoxicity. Antibody-dependent cellular cytotoxicity and antibody-complement-dependent cytotoxicity were not detected.