TLR2 expression in relation to IL-6 and IL-1beta and their natural regulators production by PMN and PBMC in patients with Lyme disease

Recently, it has been reported that TLR2 on macrophages plays a unique role in the inflammatory response and host defense to infection with Borrelia burgdorferi (Bb) which is an etiologic agent of Lyme disease. Experimental studies show that PMNs also play an essential role in infection control by Bb. However, there is no available data about TLR2 expression on PMN in the course of Lyme disease. In the present study, TLR2 expression and production of IL-1beta and IL-6 as well as their natural regulators (sIL-1RII, IL-1Ra and sIL-6Ralpha, sgp130, resp) by PMN of peripheral blood in patients with Lyme disease were examined. For the purpose of comparison, the same activity of autologous peripheral blood mononuclear cells (PBMCs) was estimated. An effect of rhIL-15 on TLR2 and cytokine secretion was also studied. Increased TLR2 expression in unstimulated neutrophils suggests an important role of these cells in mechanism recognition of B burgdorferi in patients with Lyme disease. The relationship between IL-1beta and IL-6 as well as their regulators by unstimulated PMN and PBMC, observed in the present study, may lead to enhanced IL-6- and to inhibition of IL-1beta-mediated reactions in this patient group. Changes in the TLR2 expression after rhIL-15 stimulation appear to have a favorable effect on mechanism recognition of Bb. The relations between IL-6 and its regulators (sIL-6Ralpha and sgp130) as well as between IL-1beta and its regulators (IL-1Ra and sIL-1RII) after rhIL-15 stimulation may lead to enhanced IL-1beta- and IL-6-mediated inflammatory reactions in the course of Lyme disease.     

Soluble IL-1RII and IL-18 are associated with incipient upper extremity soft tissue disorders

Previous studies suggest a role for IL-1β in the pathophysiology of upper extremity soft tissue disorders (UESTDs). We studied the levels of interleukin-1 family members in patients with incipient UESTDs and compared them with healthy controls. In this case control study, we included 163 patients with UESTDs and symptom duration shorter than 1 month and 42 healthy controls matched for age and gender at the group level. Serum levels of cytokines IL-1α, IL-1β, IL-1Ra, IL-6, IL-8, IL-18, IL-33, TNFα and sensitized C-reactive protein as well as IL-1 family soluble receptors sIL-1RII and sST2 were assessed. We used unconditional logistic regression models to study the associations between cytokines and UESTDs. After adjustment for potential confounders, the serum levels of sIL-1RII (p<0.001) and sST2 (p=0.014) were higher in the patients than the controls. The level of IL-18 was lower in the patients than the controls (p=0.005). There were no significant differences between the patients and controls regarding the levels of IL-1α, IL-1β, IL-1Ra, IL-33, IL-6, IL-8, TNFα, or sensitized C-reactive protein. The levels of circulating sIL-1RII and IL-18 are associated with incipient UESTDs, suggesting an important role for these IL-1 family members in the early course of UESTDs.     

Role of interleukin-15 and interleukin-18 in the secretion of sIL-6R and sgp130 by human neutrophils

BACKGROUND: Available data indicate that neutrophils (PMN) produce a wide range of cytokines with the potential to modulate immune response. Recent investigation have shown that interleukin (IL)-15 and IL-18 potentiated several functions of normal neutrophils. It has been reported that IL-18-induced cytokine production may be significantly enhanced by coincident addition of IL-15. AIMS: In the present study we compared the effect of recombinant human (rh)IL-15 and rhIL-18 as well as effect of a rhIL-15 and rhIL-18 combination on the induction secretion of sIL-6Ralpha and sgp130 by human neutrophils. METHODS: PMN were isolated from heparinized whole blood of healthy persons. The PMN were cultured for 18 h at 37 degrees C in a humidified incubator with 5% CO(2). rhIL-15 and/or rhIL-18 and lipopolysaccharide were tested to PMN stimulation. The culture supernatants of PMN were removed and examined for the presence of sIL-6R and sgp130 by human enzyme-linked immunosorbent assay kits. Cytoplasmic protein fractions of PMN were analysed for the presence of sIL-6R and sgp130 by western blotting using monoclonal antibodies capable of detecting these proteins. Cells were lysed and cytoplasmic proteins were electrophoresed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The resolved proteins were transferred onto nitrocellulose and incubated with the primary monoclonal antibodies anti-sIL-6R and anti-sgp130. The membranes were incubated at room temperature with alkaline phosphatase anti-mouse immunoglobulin G. Immunoreactive protein bans were visualized by an AP Conjugate Substrate Kit. RESULTS AND CONCLUSIONS: The results of our investigation revealed that IL-15 alone, similarly to IL-18, has no significant ability for the regulation of both soluble IL-6 receptors, sIL-6R and sgp130, released by human neutrophils. It is interesting to note that the secretion of sgp130 was changed after PMN stimulation with rhIL-15 in the presence of rhIL-18. The combination of rhIL-15 and rhIL-18 was shown to induce PMN to secretion relatively higher amounts of sgp130 compared with the stimulation of PMN with rhIL-15 alone and rhIL-18 alone. The results obtained suggest that IL-15 and IL-18, belonging to the inflammatory cytokines, through the regulation of sgp130 secretion must be also considered as anti-inflammatory mediators that may influence the balance reactions mediated by the IL-6 cytokine family.     

Production of intracellular IL-1alpha, IL-1beta, and IL-1Ra isoforms by activated human dermal and synovial fibroblasts: phenotypic differences between human dermal and synovial fibroblasts

We compared the production of IL-1alpha, IL-1beta, and of IL-1Ra isoforms by cultured human dermal (HDF) and synovial fibroblasts (HSF) in response to IL-1alpha, TNF-alpha, or direct T cell membrane contact. IL-1Ra was constitutively present in the cell lysates of cultured HDF and its synthesis increased in stimulated cells, whereas IL-1Ra was present in low amounts in the supernatants. Secreted IL-1Ra (sIL-1Ra) and intracellular IL-1Ra type 1 (icIL-1Ra1) mRNA levels followed the same pattern. In stimulated HDF, IL-1alpha and IL-1beta were increased intracellularly but remained undetectable in the supernatants. In HSF, IL-1Ra levels increased in both cell lysates and supernatants upon stimulation. IL-1beta was only present in HSF cell lysates after stimulation, whereas IL-1alpha was undetectable. Both sIL-1Ra and icIL-1Ra1 mRNAs were detected in stimulated HSF. icIL-1Ra1 was the predominant intracellular isoform in both cell types. In conclusion, stimulated HDF produce high amounts of intracellular IL-1Ra, IL-1alpha, and IL-1beta. In contrast, HSF synthesized both intracellular and secreted IL-1Ra, whereas IL-1beta was present only in cell lysates. The presence of high amounts of icIL-1Ra1 and intracellular IL-1alpha in HDF suggests that these cytokines may carry out important function inside cells.     

VEGF, IL-18 and NO production by neutrophils and their serum levels in patients with oral cavity cancer

It is known that the relationship between pro-angiogenic and anti-angiogenic factors is responsible for the presence and intensity of neoangiogenesis. The angiogenic factors are produced by tumour cells and/or by tumour-infiltrating inflammatory cells such as macrophages or polymorphonuclear leukocytes (PMN). In the present study we compared VEGF secretion with IL-18 and NO release by PMN derived from oral cavity cancer patients. Knowledge of the relationship between mediators above could help in better understanding the role of PMN in angiogenesis in this patient group. The results from culture supernatants of PMN were confronted with the serum levels of parameters examined. We found an interesting relationship between VEGF and IL-18 concentrations in the culture supernatants of PMN derived from patients with oral cavity cancer. High production of VEGF was associated with low production of IL-18 by PMN derived from patients before treatment. During examinations after treatment we found lower concentrations of VEGF and higher concentrations of IL-18 than those in the study before treatment. In contrast to VEGF and IL-18, the NO production by PMN of cancer patients, before and after treatment, was unchanged. We also demonstrated markedly elevated serum levels of VEGF as well as IL-18 according to the progression of the disease. Results obtained indicate that relations between VEGF and IL-18 released by PMN may promote neoangiogenesis and may be important for benign tumour cells to acquire metastatic phenotype in the early stage of oral cavity cancer. Furthermore, our results suggest that the concentrations of VEGF and IL-18 in the serum are sensitive tumour markers in this patient group before and after treatment.     

Reversal of autocrine and paracrine effects of interleukin 1 (IL-1) in human arthritis by type II IL-1 decoy receptor. Potential for pharmacological intervention

Interleukin 1 (IL-1), produced by both synovial cells and chondrocytes, plays a pivotal role in the pathogenesis of cartilage destruction in osteoarthritis (OA). We examined the specific expression and function of IL-1 receptor family-related genes in human joint tissues. Gene array analysis of human normal and OA-affected cartilage showed mRNA expression of IL-1 receptor accessory protein (IL-1RAcp) and IL-1 type I receptor (IL-1RI), but not IL-1 antagonist (IL-1ra) and IL-1 type II decoy receptor (IL-1RII). Similarly, human synovial and epithelial cells showed an absence of IL-1RII mRNA. Functional genomic analyses showed that soluble (s) IL-1RII, at picomolar concentrations, but not soluble TNF receptor:Fc, significantly inhibited IL-1beta-induced nitric oxide (NO) and/or prostaglandin E(2) production in chondrocytes, synovial and epithelial cells. In OA-affected cartilage, the IC(50) for inhibition of NO production by sIL-1RII was 2 log orders lower than that for sIL-1RI. Human chondrocytes that overexpressed IL-1RII were resistant to IL-1-induced IL-1beta mRNA accumulation and inhibition of proteoglycan synthesis. In osteoarthritis, deficient expression by chondrocytes of innate regulators or antagonists of IL-1 such as IL-1ra and IL-1RII (soluble or membrane form) may allow the catabolic effects of IL-1 to proceed unopposed. The sensitivity of IL-1 action to inhibition by sIL-1RII has therapeutic implications that could be directed toward correcting this unfavorable tissue(s) dependent imbalance.     

Soluble interleukin-1 receptor type II, IL-18 and caspase-1 in mild cognitive impairment and severe Alzheimer's disease

In the present study, we have determined levels of soluble interleukin-1 (IL-1) receptor type II (sIL-1RII), interleukin-18 (IL-18) and caspase-1 in cerebrospinal fluid and serum from mild cognitive impairment patients that later progressed to Alzheimer's disease (AD) and severe AD patients. Previous studies have shown that a chronic local inflammatory process is a part of AD neuropathology. In this process, activated microglial production of IL-1 seems to play an important role. In a previous study, we have shown increased levels of sIL-1RII in CSF from AD patients in a mild-moderate disease stage. In the present study, we found no significant differences in CSF or serum levels of sIL-1RII in either mild cognitive impairment or advanced AD patients as compared to control subjects. Likewise, there was no significant difference between mild cognitive impairment and severe AD patients. The same was true for caspase-1 and IL-18 serum levels, whereas CSF levels of caspase-1 and IL-18 were below detection limits. Our data indicate that the IL-1 system is relatively intact in the early and late stages of AD.     

Stimulation of human polymorphonuclear leukocytes by recombinant human interleukin-1 beta.

Leukocyte activation is a property of systemic infection. Animal experiments indicate interleukin-1 (IL-1) as a possible modulator, while contradictory results have been reported from in-vitro stimulation of isolated leukocytes. The purpose of the present study was to investigate the activation of isolated polymorphonuclear (PMN) leukocytes in vitro by preparations of recombinant human IL-1 beta and IL-1 receptor antagonist, which in earlier studies could elicit and abrogate, respectively, a sepsis-like syndrome in rabbits. They have also been shown to influence acute phase protein synthesis in mice and rats, and release of leukocyte cathepsin G in vivo. It was found that recombinant human IL-1 beta elicited a dose-dependent luminol-enhanced chemiluminescence response in isolated human PMN leukocytes in the dose range 8.8 x 10(-11)-8.8 x 10(-8) M. The effect could be blocked by prior treatment with the IL-1 receptor antagonist, indicating a direct effect on the specific IL-1 receptor. Preincubation by IL-1 beta enhanced the effect of a secondary challenge with phorbol 12-myristate 13-acetate or formyl-Met-Leu-Phe by 30-40%. The priming effect of rhIL-1 beta could also be blocked by the specific receptor antagonist. In this study, incubation of PMN leukocytes with rhIL-1 beta failed to induce degranulation of both azurophil (neutrophil proteinase 4/proteinase 3) and specific (lactoferrin) granules. rhIL-1 beta has been shown to induce degranulation in vivo, which is thus indicated as an indirect effect. We conclude that IL-1 beta is a direct and specific, but probably weak stimulator of the PMN leukocyte.(ABSTRACT TRUNCATED AT 250 WORDS)     

IL-1 beta scavenging by the type II IL-1 decoy receptor in human neutrophils

IL-1 elicits its cellular effects by binding a heterodimeric receptor consisting of IL-1RI and the accessory protein, IL-1RAcPr. In addition, it binds to IL-1RII, which lacking signaling function has been ascribed a decoy role. The fate of the ligand following interaction with the decoy receptor was examined in human polymorphonuclear cells (PMN), which express predominantly (>90%) IL-1RII. Incubation of PMN with IL-1beta results in a rapid decrease in cell surface-associated ligand accompanied by a concomitant increase in internalized IL-1 with 50-60% of IL-1beta located intracellularly within 1 h at 37 degrees C. The use of blocking Abs revealed that IL-1 internalization is mediated exclusively by the decoy receptor. The results of inhibitor analysis demonstrate that internalization requires ATP synthesis and involves clathrin-mediated endocytosis. Following removal of the ligand, the receptor was rapidly re-expressed on the cell surface. Cyclohexamide, a protein synthesis inhibitor, had no effect upon the process, suggesting that the re-expressed receptor was recycled. In addition, human keratinocytes stably transfected with IL-1RII (HaCAT 811) also internalized the IL-1RII with 43% cell surface receptor internalized after 90 min. Immunofluorescence microscopy revealed colocalization of the internalized receptor with wheat germ agglutinin-labeled internalized glycoproteins and early endosome Ag-1, a protein associated with the early endosome compartments, indicative of cellular uptake of IL-1RII by endocytosis. In contrast, little or no internalization was observed in other cells of immune origin. These results suggest that the decoy receptor IL-1RII can act as a scavenger of IL-1, representing a novel autoregulatory mechanism of the IL-1 system.     

Human milk anti-inflammatory component contents during acute mastitis

Mastitis is a common complication of human lactation. We examined milk specimens from eight women with clinical mastitis to determine their content of anti-inflammatory components. Antioxidant activity (spontaneous cytochrome c reducing activity), selected pro-inflammatory cytokines (IL-6, IL-1beta), selected endogenous cytokine control molecules (sIL-6R, sIL-1RII, and sTNFRI), lactoferrin, Na(+):K(+) ratios, and milk bioactivities that cause shedding of sIL-1RII from human polymorphonuclear leukocytes (PMN), suppress PMN aggregation, and suppress PMN adherence responses were not increased compared to normal milks. Neither the bioactivities that deplete PMN intracellular Ca(2+) stores nor those that block Ca(2+) influx into fMLP-stimulated PMN were significantly increased in mastitis milks. In contrast, levels of TNFalpha, sTNFRII, and IL-1RA and bioactivities that cause shedding of sTNFRI from human PMN were significantly increased compared to normal milks. Mastitis milk has the same anti-inflammatory components and characteristics of normal milk, with elevations in selected components/activities that may help protect the nursing infant from developing clinical illness due to feeding on mastitis milk.     

Elevated circulating levels of soluble interleukin-1 receptor type II during interleukin-2 immunotherapy

Interleukin-1 (IL-1) is a critical mediator of inflammation. Two naturally occurring IL-1 antagonists have been described, namely the IL-1 receptor antagonist (IL-1Ra) and the IL-1 receptor type II (IL-1RII). IL-1RII does not transmit a signal upon binding of IL-1, but competes with the signaling of IL-1RI for binding of IL-1. Shedding of IL-1RII yields the soluble IL-1 receptor type II (IL-1sRII) which retains the ability of membrane-bound IL-1RII to bind IL-1beta avidly, but binds IL-1Ra and IL-1alpha with low affinity. In contrast, IL-1sRI retains the ability of membrane-bound IL-1RI to bind IL-1Ra and IL-1alpha with high affinity, but binds IL-1beta poorly. We have previously shown that immunotherapy with IL-2 or IL-6 in cancer patients is associated with a dramatic increase in IL-1Ra plasma levels. In the present study, plasma levels of soluble IL-1 receptors were monitored in healthy individuals and cancer patients. In healthy controls, the mean IL-1sRII level was 4.76 0.16 ng/ml. IL-1sRII levels in cancer patients were comparable to those measured in healthy controls. IL-1sRII levels did not vary during the first 52 hours after initiation of IL-2 therapy, but increased significantly thereafter to reach 9.56 1.16 ng/ml on day 5. In contrast, IL-6 immunotherapy with a 5-day continuous infusion did not trigger an increase in IL-1sRII levels. IL-1sRI levels did not increase during immunotherapy with IL-2 or IL-6. Our results indicate that IL-1sRII, unlike IL-1Ra, remains a modest, natural, anti-inflammatory mechanism triggered by immunotherapy with IL-2, but not with IL-6.     

The balance between IL-1 and IL-1Ra in disease

IL-1 is an important mediator of inflammation and tissue damage in multiple organs, both in experimental animal models of disease and in human diseases. The IL-1 family consists of two agonists, IL-1alpha and IL-1beta, two receptors, biologically active IL-1RI and inert IL-1RII, and a specific receptor antagonist, IL-1Ra. The balance between IL-1 and IL-1Ra in local tissues plays an important role in the susceptibility to and severity of many diseases. An allelic polymorphism in the IL-1Ra gene has been associated with a variety of human diseases primarily of epithelial and endothelial cell origin. This association may be secondary to an imbalance in the IL-1 system with enhanced production of IL-1beta and reduced production of the major intracellular isoform of IL-1Ra. Treatment of RA with daily subcutaneous injections of recombinant IL-1Ra protein has been shown to be efficacious. Gene therapy approaches with IL-1Ra are being evaluated for the treatment of RA and other human diseases.     

Soluble murine IL-1 receptor type I induces release of constitutive IL-1 alpha

IL-1 alpha and IL-1 beta are proinflammatory cytokines involved in the pathogenesis of many infectious and noninfectious inflammatory diseases. To reduce IL-1 toxicity, extracellular domains of the soluble (s) IL-1R are shed from cell membranes and prevent triggering of cell-bound receptors. We investigated to what extent murine sIL-1RI can neutralize the IL-1 produced by LPS-stimulated macrophages. When mouse peritoneal macrophages were incubated with LPS, addition of sIL-1RI significantly inhibited the bioactivity of IL-1. Stimulation of cells with sIL-1RI alone induced no bioactive IL-1. When immunoreactive cytokine concentrations were measured with specific radioimmunoassays, sIL-1RI alone appeared to induce a significant release of IL-1 alpha in a concentration-dependent manner. This effect was independent of new protein synthesis. The production of IL-1 beta or TNF-alpha was not influenced by sIL-1RI. There was no interference of sIL-1RI with the IL-1 alpha radioimmunoassay. In mice, an i.v. injection of sIL-RI alone induced a rapid release of IL-1 alpha, but not of TNF-alpha or IL-1 beta. Treatment of mice with sIL-1RI improved the survival during a lethal infection with Candida albicans. In conclusion, sIL-1RI induces a rapid release of IL-1 alpha from cells, as well as into the systemic circulation. Although this IL-1 alpha may be inactivated in circulation by the same sIL-1RI, this phenomenon probably has immunostimulatory effects at local levels where the sIL-1RI-induced IL-1 alpha acts in a paracrine or autocrine manner.     

Endogenous IL-1 and type II IL-1 receptor expression modulate anoikis in intestinal epithelial cells

We previously reported that IL-1beta and the decoy receptor for IL-1 (IL-1RII) are expressed by intestinal epithelial cells (IEC) during detachment-induced cell death, or "anoikis." We now investigated whether IL-1 regulates anoikis. Skewing the balance in favor of IL-1, by blocking IL-1RII or by adding IL-1beta to detached rat IEC-18 cells, reduced cell death. The protective effect of anti-IL-1RII was reversed by blocking IL-1beta, confirming the anti-apoptotic effect was due to endogenous IL-1beta. Added IL-1beta also rescued cells from anoikis and was associated with considerable aggregation of the detached cells. Aggregate formation and the anti-apoptotic effect of added IL-1beta were prevented by blocking E-cadherin, indicating that IL-1 promoted aggregation and indirectly, survival. On the other hand, treating detached cells with IL-1beta and an anti-beta(1) integrin antibody abolished the protective effect of IL-1beta but not the aggregates. We conclude that the anti-apoptotic effect of IL-1 is mediated through a beta(1) integrin-dependent event secondary to cell-cell adhesion. This illustrates a previously uncharacterized role for IL-1 in the intestine wherein this cytokine may facilitate the preservation of the epithelial monolayer integrity.     

Intracellular IL-1 receptor antagonist is elevated in human dermal fibroblasts that overexpress intracellular precursor IL-1 alpha.

Cultured dermal fibroblasts from systemic sclerosis patients express higher levels of intracellular IL-1 alpha than fibroblasts from healthy controls. In this study, we found that systemic sclerosis dermal fibroblasts also express higher levels of the intracellular isoform of IL-1 receptor antagonist (icIL-1Ra) than normal fibroblasts after stimulation with IL-1 beta or TNF-alpha. A possible relationship between elevated precursor IL-1 alpha (preIL-1 alpha) and elevated icIL-1Ra was investigated by transducing normal dermal fibroblasts to overexpress preIL-1 alpha, preIL-1 beta, or icIL-1Ra. Fibroblasts that overexpressed icIL-1Ra did not have elevated levels of IL-1 alpha. On the other hand, fibroblasts that overexpressed preIL-1 alpha had at least 4-fold higher basal levels of icIL-1Ra than control fibroblasts and 4-fold higher levels of icIL-1Ra after induction with IL-1 beta or TNF-alpha. Fibroblasts overexpressing preIL-1 beta did not exhibit elevated icIL-1Ra. The differences in icIL-1Ra protein levels were reflected in differences in mRNA. In contrast, IL-1-stimulated levels of MCP-1 and IL-6 were not different in control and preIL-1 alpha-transduced fibroblasts. Addition of neutralizing anti-IL-1 alpha Abs to fibroblast cultures did not diminish basal or stimulated levels of icIL-1Ra in the preIL-1 alpha-transduced cells, supporting an intracellular site of action of preIL-1 alpha. This is the first report of an association between intracellular levels of these IL-1 family members. We hypothesize that intracellular preIL-1 alpha participates in the regulation of icIL-1Ra.     

Presence of IL-1 receptors on human and murine neutrophils. Relevance to IL-1-mediated effects in inflammation

Inflammatory responses are characterized by the infiltration of polymorphonuclear neutrophils (PMN) at the involved site. IL-1 may have an important role in mediating this response, but whether IL-1 acts directly on PMN is controversial. In this study, we examined PMN for the presence of IL-1R and determined the effect of IL-1 on PMN migration in vivo. Thioglycollate, proteose-peptone, or IL-1 elicited peritoneal exudate cells were found to bind 125I-IL-1 alpha in a specific and saturable manner. This binding was localized to the PMN in the exudate. Scatchard plot analysis indicates the presence of approximately 1700 receptors per PMN and an apparent dissociation constant of 3.0 x 10(-10) M. Binding sites for 125I-IL-1 alpha were also found on human PMN prepared from peripheral blood. There are approximately 900 receptors per cell on human PMN with a dissociation constant similar to that observed for elicited murine PMN. Binding of 125I-IL-1 alpha to the mouse and human PMN is inhibited by both recombinant human IL-1 alpha and IL-1 beta, indicating that both IL-1 proteins bind to the same receptor on these cells. Human PMN were able to internalize radioiodinated IL-1. We conclude that PMN possess receptors for IL-1 and that these binding sites may be important in mediating IL-1 effects on granulocytes that are involved in the inflammatory response.     

The effects of IL-1, IL-2, and tumor necrosis factor on polymorphonuclear leukocyte Fc gamma receptor-mediated phagocytosis. IL-2 down-regulates the effect of tumor necrosis factor

It has been reported that the Fc gamma R-mediated phagocytic activity of polymorphonuclear leukocytes (PMN) from patients with acute bacterial infections is markedly enhanced when compared with healthy controls. Inasmuch as several potent cytokines are known to be involved in inflammatory and infectious processes, we studied the effects of three such cytokines (IL-1 beta, IL-2, and TNF-alpha) on normal PMN Fc gamma R-mediated phagocytosis. IL-1 beta and TNF alpha both caused a significant increase in the ingestion of EIgG by adherent PMN. In combination, IL-1 beta and TNF-alpha had an additive effect, even when each was used at its optimal concentration. In contrast to the enhancing effects mediated by IL-1 beta and TNF-alpha, IL-2 alone had no significant effect on PMN phagocytosis. Notably, however, IL-2 at a concentration of 10(4) U/ml partially inhibited TNF-alpha-mediated enhancement of phagocytosis by decreasing TNF binding to the PMN cell surface. This inhibitory effect of IL-2 on TNF was reversed by anti-IL-2 antibody and mAb directed against the low affinity IL-2R (anti-Tac), whereas mAb directed against the intermediate affinity receptor (mik-beta 1) had no such effect. These findings may have important physiologic implications, because patients receiving IL-2 therapy have been shown to have increased susceptibility to infection.