Calcium mediates one of the signals required for interleukin 1 and 2 production by murine cell lines

A bovine whey protein extract stimulates human neutrophils to generate bioactive IL-1Ra through a NF-kappaB- and MAPK-dependent mechanism

Innate immunity depends on the efficiency of neutrophils to be activated rapidly to restore homeostasis. It can benefit from priming agents that enhance neutrophil capacity to respond more efficiently to a subsequent stimulation. Among natural products, a bovine whey protein extract (WPE) has been shown to prime normal human blood neutrophils by enhancing their chemotaxis, phagocytosis, oxidative burst, and degranulation. These leukocytes are also an important source of cytokines, some of which have antiinflammatory functions. We investigated the role of WPE, as well as its mechanisms of action, on the production of interleukin (IL)-1 receptor antagonist (IL-1Ra) by neutrophils in vitro. WPE dose-dependently stimulated de novo synthesis and release of IL-1Ra by normal human blood neutrophils. Among the major proteins present in WPE, beta-lactoglobulin (beta-LG) and alpha-lactalbumin (alpha-LA) were the only active components. They had additive effects that exactly reproduced those of WPE. Similarly to WPE, they also stimulated the accumulation of IL-1beta, IL-8, IL-6, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and tumor necrosis factor-alpha. However, neutrophils incubated with WPE, beta-LG, and alpha-LA produced IL-1Ra in excess of IL-1beta and the ratio IL-1Ra:IL-1beta increased linearly. The amounts of IL-1Ra stimulated by WPE or beta-LG + alpha-LA significantly reduced the IL-1 activity in EL4 cells. Inhibitors of p38 and extracellular signal-regulated kinases (ERK)1/2 mitogen-activated protein kinase, and nuclear factor-kappaB cascades reduced neutrophil production of IL-1Ra. Our data suggest that WPE, through beta-LG + alpha-LA, has immunomodulatory properties and the potential to increase host defenses.

Disordered calcium homeostasis of sepsis: association with calcitonin precursors

BACKGROUND

Hypocalcemia and increased serum levels of calcitonin precursors are common in critically ill patients, especially in those with sepsis. We investigated calcium homeostasis in such patients.

PATIENTS AND METHODS

Serum concentrations of total and ionized calcium and known factors influencing or reflecting calcium homeostasis were measured in 101 consecutive patients of a medical intensive care unit. Calcitonin precursor levels were determined using a highly sensitive radioimmunoassay.

RESULTS

Critical illness per se was associated with decreased serum total and ionized calcium levels, which correlated with the severity of the underlying disease as measured by the APACHE II score. In addition, total and ionized hypocalcemia was more pronounced with increasing severity of infection (P < 0.02), and occurred in parallel with a marked increase of calcitonin precursors (P < 0.001). Mature calcitonin levels, however, remained normal. Changes of serum ionized calcium concentrations from admission to discharge correlated significantly with changes in the serum calcitonin precursor concentration (r2 = - 0.14, P < 0.001). Circulating vitamin D levels, parathyroid hormone levels and other markers reflecting calcium homeostasis did not correlate with the severity of infection.

CONCLUSIONS

In critically ill patients with sepsis, markedly elevated circulating calcitonin precursors might play a role in the development of the pronounced hypocalcemia. The specific calcitonin precursor(s) responsible for this effect and the pathophysiological mechanism remain to be elucidated.

Calcium dependency of interleukin-1 secretion by a chicken macrophage cell line

The role of calcium in transducing the signal for interleukin-1 (IL-1) secretion was examined in the MQ-NCSU chicken macrophage cell line. Cells were maintained in RPMI 1640 medium supplemented with 5% chicken serum and antibiotic-antimycotic solution at 40 C and 5% CO2. The effects of stimulation with lipopolysaccharide (LPS), calcium ionophore A23187, or a combination of both on IL-1 secretion were examined. Calcium ionophore A23187 did not replace LPS in MQ-NCSU stimulation but the LPS + A23187 combination stimulated more IL-1 than ionophore alone in these cells. The combination of LPS and ionophore did not increase IL-1 secretion above the levels observed with LPS alone. No synergistic effects between LPS and A23187 were evident. In order to demonstrate that IL-1 secretion by the MQ-NCSU cells is a calcium-dependent process, ethylene glycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA) was used to chelate free calcium in the cultures. Incorporation of 5 mM EGTA in the cultures lowered IL-1 stimulated by LPS + A23187 to control levels. Addition of 5 mM CaC12 to EGTA-suppressed cultures restored IL-1 secretion. These results indicate that the calcium ionophore, A23187, augments IL-1 secretion by LPS-stimulated MQ-NCSU macrophages and that IL-1 secretion by these cells is a calcium-dependent process.

p21ras contributes to HIV-1 activation in T-cells

Activation of T-cells infected by HIV-1 results in activation of long terminal repeat (LTR)-dependent viral transcription and ultimately the production of infectious virus. Although full T-cell activation requires a complex series of intracellular signals, including protein kinase C activation, calcium mobilisation, and less-well defined lymphokine-induced signals, the HIV-1 LTR can be activated by subsets of these signals. We have studied the interaction of these signals in the human lymphoma line, Jurkat, in activation of the HIV-1 LTR. The HIV promoter was induced by IL-1 and phorbol ester activation of PKC but not by a calcium ionophore. The constitutively active form of Ha-ras could replace phorbol ester stimulation of the HIV promoter and of a synthetic promoter containing NF kappa B binding sites.

Interleukin-1 synergy with phosphoinositide pathway agonists for induction of interleukin-2 gene expression: molecular basis of costimulation

The macrophage-derived cytokine interleukin-1 (IL-1) can provide a second signal with antigen to elicit production of interleukin-2 (IL-2) by helper T cells. The pathway(s) involved remains controversial, with protein kinase C and cyclic AMP (cAMP) invoked as possible second messengers. In the murine thymoma EL4.E1, IL-1 could synergize with the phosphoinositide pathway, because the cells made higher levels of IL-2 in the presence of IL-1 than could be induced by phorbol ester plus calcium ionophore alone. IL-1 is unlikely to act through a sustained increase in cAMP in these cells because it did not raise cAMP levels detectably and because IL-1 and forskolin had opposite effects on IL-2 gene expression. Inducible expression of a transfected reporter gene linked to a cloned fragment of the murine IL-2 gene promoter was initially increased by IL-1 costimulation, implying that IL-1 can increase the rate of transcription of IL-2. The minimal promoter elements required for iL-1 responsiveness were located within 321 bp of the IL-2 RNA cap site, and further upstream sequences to -2800 did not modify this response. IL-1 costimulation resulted in enhanced activity of both an inducible NF-kappa B-like factor and one of two distinct AP-1-like factors that bind to IL-2 regulatory sequences. Neither was induced, however, by IL-1 alone. Another AP-1-like factor and NFAT-1, while inducible in other cell types, were expressed constitutively in the EL4.E1 cells and were unaffected by IL-1. These results are discussed in terms of the combinatorial logic of IL-2 gene expression.

Interleukin-1 synergy with phosphoinositide pathway agonists for induction of interleukin-2 gene expression: molecular basis of costimulation

The macrophage-derived cytokine interleukin-1 (IL-1) can provide a second signal with antigen to elicit production of interleukin-2 (IL-2) by helper T cells. The pathway(s) involved remains controversial, with protein kinase C and cyclic AMP (cAMP) invoked as possible second messengers. In the murine thymoma EL4.E1, IL-1 could synergize with the phosphoinositide pathway, because the cells made higher levels of IL-2 in the presence of IL-1 than could be induced by phorbol ester plus calcium ionophore alone. IL-1 is unlikely to act through a sustained increase in cAMP in these cells because it did not raise cAMP levels detectably and because IL-1 and forskolin had opposite effects on IL-2 gene expression. Inducible expression of a transfected reporter gene linked to a cloned fragment of the murine IL-2 gene promoter was initially increased by IL-1 costimulation, implying that IL-1 can increase the rate of transcription of IL-2. The minimal promoter elements required for iL-1 responsiveness were located within 321 bp of the IL-2 RNA cap site, and further upstream sequences to -2800 did not modify this response. IL-1 costimulation resulted in enhanced activity of both an inducible NF-kappa B-like factor and one of two distinct AP-1-like factors that bind to IL-2 regulatory sequences. Neither was induced, however, by IL-1 alone. Another AP-1-like factor and NFAT-1, while inducible in other cell types, were expressed constitutively in the EL4.E1 cells and were unaffected by IL-1. These results are discussed in terms of the combinatorial logic of IL-2 gene expression.

Fever induced by Escherichia coli or intrahypothalamic prostaglandin E2 enhances interferon-gamma synthesis

We previously showed that hyperthermia induced in rhesus monkeys (Macaca mulatta) by forced passive heating "primes" the peripheral lymphocyte population for increased synthesis of interferon-gamma (IFN-gamma). It was not clear whether these data could be extrapolated to the physiological response in naturally occurring fever. Therefore, in the current experiments, the temperature of rhesus monkeys was raised either by systemic injection of killed Escherichia coli or by intrahypothalamic administration of prostaglandin E2. Mononuclear cells collected subsequently from such monkeys produced more IFN-gamma in response to stimulation with mitogens than cells from control monkeys. Direct administration of IFN-alpha, -beta, or -gamma to the hypothalamus did not affect the body temperature of rhesus monkeys.

A role for protein kinase C activity in interleukin-1 (IL-1) induction of IL-2 gene expression but not in IL-1 signal transduction

Interleukin-1 (IL-1) is known to synergize with phorbol esters in the induction of interleukin-2 (IL-2) expression in T-lymphoid leukemia cells and proliferation of mouse thymocytes. We used a plasmid construct containing the bacterial gene for chloramphenicol acetyltransferase under the control of the human IL-2 promoter to study the nature of this synergism in the murine thymoma cell line EL4. Although IL-1 induction of the IL-2 promoter in these cells required costimulus with phorbol myristate acetate, the signal induced by IL-1 was qualitatively different. We provide evidence to support the hypothesis that the phorbol ester signal is mediated by protein kinase C, and we show that the IL-1 signal is not. That IL-1 and phorbol myristate acetate represent different stimuli was shown by their response to protein kinase C inhibitors, capacity to synergize with increased intracellular free calcium, and requirement for protein synthesis. In addition we show that pretreatment with IL-1 can prime EL4 cells to subsequent activation by concentrations of phorbol esters not normally sufficient to induce IL-2 expression. Pretreated cells remained primed for at least 40 h after removal of the IL-1. Neither phorbol myristate acetate nor a calcium ionophore was capable of preactivating EL4 cells.

A role for protein kinase C activity in interleukin-1 (IL-1) induction of IL-2 gene expression but not in IL-1 signal transduction

Interleukin-1 (IL-1) is known to synergize with phorbol esters in the induction of interleukin-2 (IL-2) expression in T-lymphoid leukemia cells and proliferation of mouse thymocytes. We used a plasmid construct containing the bacterial gene for chloramphenicol acetyltransferase under the control of the human IL-2 promoter to study the nature of this synergism in the murine thymoma cell line EL4. Although IL-1 induction of the IL-2 promoter in these cells required costimulus with phorbol myristate acetate, the signal induced by IL-1 was qualitatively different. We provide evidence to support the hypothesis that the phorbol ester signal is mediated by protein kinase C, and we show that the IL-1 signal is not. That IL-1 and phorbol myristate acetate represent different stimuli was shown by their response to protein kinase C inhibitors, capacity to synergize with increased intracellular free calcium, and requirement for protein synthesis. In addition we show that pretreatment with IL-1 can prime EL4 cells to subsequent activation by concentrations of phorbol esters not normally sufficient to induce IL-2 expression. Pretreated cells remained primed for at least 40 h after removal of the IL-1. Neither phorbol myristate acetate nor a calcium ionophore was capable of preactivating EL4 cells.

Beta-endorphin modulation of IL-1-induced IL-2 production

We have studied the effects of natural opioids on interleukin-1 (IL-1) -induced interleukin 2 (IL-2) production by the lymphoid cell line EL-4. beta-Endorphin (beta-end) significantly enhanced IL-2 production by IL-1-stimulated EL-4 cells. Similar results were obtained using the LBRM33-1A5 cell line. beta-End induced significant enhancement (35-100%) of IL-1-induced IL-2 production at all concentrations of IL-1 tested (2-0.25 U/ml) and the effects were seen with both IL-1 alpha and IL-1 beta. The dose response of beta-end augmentation of IL-1-induced IL-2 production was bimodal, with peak activities seen at high (10(-8)-10(-10) M) and low (10(-16) M) beta-end concentrations. The specificity of beta-end effect was studied using the opioid antagonist naloxone. Naloxone completely abolished the enhancing effects of beta-end, indicating that the effects might be mediated through binding to opioid receptors. In addition, other opioid peptides, including gamma-endorphin and enkephalins, elicited similar effects. Northern blotting analysis revealed higher levels of IL-2 mRNA in beta-end-treated IL-1-induced EL-4 cells than in IL-1-induced control cells. Thus, beta-end might enhance IL-2 production by either augmenting the transcription rate or increasing IL-2 mRNA stability. These results suggest that beta-end might play an important role in the regulation of lymphokine production in the periphery in addition to its known interactions with IL-1 in the central nervous system.

Characterization of a subclone (D10S) of the D10.G4.1 helper T-cell line which proliferates to attomolar concentrations of interleukin-1 in the absence of mitogens

Most studies have shown that interleukin-1 (IL-1) acts as a helper or co-stimulator in T-lymphocyte activation and proliferation by mitogens or antigens. We describe here a stable subclone (D10S) of the murine D10.G4.1 helper T-cell which proliferates to subfemtomolar (attomolar) concentrations of IL-1 beta or alpha in the absence of mitogens. D10S cells have been maintained in culture for over two years without splenic cell feeder layers nor antigen stimulation. Detection of proliferation can be made by either uptake of tritiated thymidine at 72 h or in 48 h by a colorimetric assay which measures mitochondrial dehydrogenases; the latter assay is rapid and inexpensive. D10S cells are distinct from the parent clone D10.G4., which requires mitogens for IL-1 activity. IL-1-induced proliferation is independent of the elaboration of IL-2, IL-4, or IL-6, although these cells proliferate to these lymphokines at considerably higher concentrations when compared to IL-1. The D10S cells proliferate in direct correlation to the duration of IL-1 presence in the culture. We found no evidence that IL-1 induced more IL-1 in these cells. The subclone is highly specific for IL-1: proliferation was not observed to endotoxin, human or murine interferon-gamma (IFN gamma), tumor necrosis factor (TNF), lymphotoxin, or granulocyte-macrophage colony stimulating factor (GM-CSF). There was no suppressive effect of transforming growth factor (TGF beta). Only at high concentrations (100 ng/ml) did IL-6 induce proliferation. We conclude that this stable, feeder layer-free cell line is highly sensitive to IL-1 which acts as a direct stimulant for these cells; they are also useful for bioassays as well as the study of IL-1 receptors as described in the accompanying paper.

Inhibition of macrophage-induced antigen-specific T-cell proliferation by interferon-gamma

The effects of IFN-gamma on macrophage (M phi)-mediated antigen-specific T-cell proliferation was investigated. A well-defined assay system using purified resident populations of antigen-pulsed peritoneal M phi and immune T cells was used to measure M phi-induced antigen-specific T-cell proliferation. Antibody affinity purified or recombinant IFN-gamma inhibited M phi-induced T-cell proliferation when KLH-pulsed M phi from mice given IFN-gamma prior to KLH were cultured with KLH immune T cells from normal mice. Monoclonal rat anti-IFN-gamma antibody neutralized the inhibitory effect of IFN-gamma. This inhibition of T-cell proliferation occurred despite the fact that these M phi appeared to be activated by IFN-gamma treatment as measured by increased tumoricidal activity. The mechanism for the inhibition was unrelated to class II (Ia) expression, IL-1 secretion, and prostaglandin secretion. These results demonstrate the complex and sensitive role IFN-gamma has in regulating the immune response.

Lack of a central role for calcium in the induction and release of human interleukin-1

This study examines the potential role of calcium in the activation of human monocytes by bacterial lipopolysaccharide (LPS) to produce interleukin-1 (IL-1). Monocytes cannot be triggered to produce IL-1 through addition of calcium ionophores. Triggering of IL-1 production by LPS cannot be blocked by depletion of extracellular calcium, blockade of calcium channels, or addition of agents which antagonize the effects of intracellular calcium. Finally, the addition of LPS does not induce the mobilization of intracellular free calcium as measured by quin-2 fluorescence.

Suppression of human lymphocyte responsiveness by forskolin: reversal by 12-O-tetradecanoyl phorbol 13-acetate, diacylglycerol and ionomycin

Forskolin, a potent activator of adenylate cyclase, was examined for its ability to alter human peripheral blood lymphocyte (HPBL) activation by both mitogens and antigens. We found that forskolin, at concentrations ranging from 0.04 to 25 micrograms/ml, caused a dose-dependent inhibition of HPBL responses to mitogens (concanavalin A, phytohemagglutinin, pokeweed mitogen and Staphylococcus aureus) and to recall antigens (tetanus toxoid and streptokinase/streptodornase). Inhibition was reflected in altered DNA, RNA and protein synthesis, including immunoglobulin production, and was not due to altered cell viability. Forskolin also induced a 19-fold increase in HPBL cyclic AMP levels at the same concentrations that suppressed HPBL function. To further define the mechanism(s) by which these elevations in cyclic AMP suppressed HPBL function, we tried to reverse these inhibitory effects with several agents; ascorbic acid, carbachol and levamisole had no effect. However, the phorbol ester, 12-O-tetradecanoyl phorbol 13-acetate, as well as L-alpha-1,2-dioleoyl diacylglycerol were able to completely reverse the inhibition. Furthermore, the Ca2+ ionophore, ionomycin, was also able to act synergistically with lower and less effective concentrations of 12-O-tetradecanoyl phorbol 13-acetate to reverse the inhibitory effects of forskolin. The data suggest that forskolin-induced elevations in cyclic AMP may lead to inhibition (or, more correctly, prevents the activation) of protein kinase C, presumably by inhibiting phospholipid turnover. Our studies suggest a linkage between these two opposing membrane-signal transduction systems with protein kinase C representing a pivotal point for various regulatory signals that ultimately control lymphocyte activation and function.

Interleukin 1 and protein kinase C activator are dissimilar in their effects on Il-2 receptor expression and Il-2 secretion by T lymphocytes

T lymphocytes respond to mitogenic stimulation by expressing the receptor for interleukin 2 (Il-2) and secreting Il-2; once the receptor is expressed, Il-2 induces these cells to proliferation. In the present report using mouse T lymphocytes, thymocytes, and the lymphoma cell line EL4, we studied receptor expression and Il-2 secretion as early parameters for T-lymphocyte activation in response to ionomycin, concanavalin A (Con A), 12-O-tetradecanoyl-phorbol 13-acetate (TPA), and interleukin 1 (Il-1). Il-1 is required for mitogenic response of lymphocyte preparations that are rigorously depleted of macrophages. On its own, Il-1 had very little effect on Il-2 secretion and Il-2 receptor expression by T lymphocytes. TPA strongly synergized with ionomycin both for Il-2 secretion and for Il-2 receptor expression whereas Il-1 did not. Il-1 required the simultaneous presence of ionomycin and TPA to have any demonstrable effect on T lymphocytes from spleen and on thymocytes. However, on EL4 cells which were also partially responsive to TPA alone, Il-1 showed strong synergy with TPA to induce Il-2 secretion and Il-2 receptor expression. The effect of Il-1 on EL4 cells was dose dependent where increasingly higher concentrations of Il-1 in the presence of a fixed concentration of TPA caused higher percentage of EL4 cells to become Il-2 receptor positive. The present results suggest that Il-1 does not cause its effect on T lymphocytes via the same mechanism of protein kinase C activation that has been proposed for TPA.

Taenia taeniaeformis: inhibition of mitogen induced proliferation and interleukin-2 production in rat splenocytes by larval in vitro product

Splenocytes from rats infected with Taenia taeniaeformis showed an early decreased proliferative response to the mitogen concanavalin A with larval growth. When larvae culture supernatant (in vitro product) was added to normal rat splenocytes, there was a decrease in the proliferative response to concanavalin A and phytohemagglutinin. The ability of infected rat splenocytes to produce interleukin-2 was decreased with larval growth. Addition of in vitro product to culture medium significantly depressed interleukin-2 production by normal as well as infected rat spleen cells. Culturing normal rat splenocytes with in vitro product for 3 days induced a suppressor cell population. When these cultured cells were admixed with fresh normal rat splenocytes plus concanavalin A, the proliferative response of the fresh cells was significantly reduced. The present results suggest that in vitro product secreted by larvae in hepatic cysts causes subversion of the cellular immune response in the host. Induction of a suppressor cell population could suppress interleukin-2 production which may lead to the inhibition of differentiation and proliferation of specific cytotoxic T lymphocytes.

Inhibition of T3 mediated T-cell proliferation by Ca2+-channel blockers and inhibitors of Ca2+/phospholipid-dependent kinase

The potential roles of Ca2+ ions in the response of T lymphocytes to stimulation with monoclonal antisera to the T3 antigen were investigated by means of pharmacological agents that predominantly inhibit the flux of Ca2+ ions into cells (verapamil, nifedipine) or the activity of Ca2+-dependent kinases (trifluoperazine, polymyxin B). As assessed by uptake of [3H]thymidine, proliferation induced with anti-T3 +/- recombinant IL-2 at 72 h was inhibited by greater than 80% in the presence of nifedipine at 50 microM, and almost completely arrested (greater than 95% inhibition) with the other agents at the same concentration. Further quantitative assays of the effects of polymyxin B and trifluoperazine on C-kinase labelling of exogenous substrate showed a major reduction with both agents, but inhibition was substantially greater with polymyxin B that with trifluoperazine (IC50 = 14 and 70 microM respectively). These results were confirmed by qualitative assessment of Ca2+/phospholipid-dependent phosphorylation of endogenous substrates, which demonstrated major phosphoproteins of MW 56,000, 52,000, 43,000, and 20,000, and dose-dependent reduction in labelling in the presence of polymyxin B. Similar results were obtained under more physiological conditions in intact cells labelled with 32P orthophosphate. These findings indicate several possible roles for Ca2+ in T-cell activation, and several possible levels of activity, including modulation of calmodulin-dependent kinases and effects on Ca2+/phospholipid-dependent kinases and Ca2+ channels.

Phylogenetic studies on lymphokines. Fish lymphocytes respond to human IL-1 and epithelial cells produce an IL-1 like factor

The results obtained indicate, that catfish peripheral blood lymphocytes recognize and respond to human IL-1. The second part of this report is dealing with a substance produced by carp epidermal cells with functional similarities to mammalian IL-1.

Isoprinosine effects on interleukin-1 production in acquired immune deficiency syndrome (AIDS)

The in vitro effects of isoprinosine (ISO) on the production of IL-1 in AIDS patients and normal controls were investigated in this study. IL-1 production from adherent cells was measured by an indirect method using EL-4 cells. Five of eleven AIDS patients had depressed IL-1 production. Various concentrations of ISO were used to treat the adherent cells in vitro and the optimal concentration for stimulating IL-1 production was determined to be 100 micrograms/ml/10(6) cells. IL-1 production was augmented to normal or to near normal levels in four of five AIDS patients. Our results indicate that depressed immunity seen in some AIDS patients may be partly due to the depressed in IL-1 production and also that ISO can act as an immune potentiation in enhancing the production of this lymphokine in vitro.

A modified assay for interleukin-1 (IL-1)

A simple and reliable biological assay for interleukin-1 (IL-1) was developed, based on the production of interleukin-2 (IL-2) from the EL-4 murine T-cell lymphoma cell line, in the presence of 2-5 X 10(-7) M calcium ionophore A23187. The assay was generally performed in 2 stages ((a) IL-1-dependent IL-2 production, and (b) IL-2 assay) and took 36-48 h to complete. This assay was found to be 10-25 times more sensitive than the mouse thymus cell assay, was not sensitive to the presence of bacterial endotoxin, and had the advantage of not requiring the use of animal tissue as a source of cells. The assay was used in our laboratory to detect human, mouse, rat, and rabbit IL-1 of all isoelectric-point types.

Partial restoration of impaired interleukin-2 production and Tac antigen (putative interleukin-2 receptor) expression in patients with acquired immune deficiency syndrome by isoprinosine treatment in vitro

The in vitro effects of isoprinosine (ISO) on interleukin-2 (IL-2) production, the expression of Tac antigen (IL-2 receptor) on lymphocytes, and the ability of Leu 3(+) cells to absorb interleukin-1 (IL-1) were investigated in 10 patients with acquired immune deficiency syndrome (AIDS). In 9 of the 10 patients, production of IL-2 from mononuclear cells and Leu 3(+) cells was depressed; expression of Tac antigen on mononuclear cells and Leu 2(+) cells was found to be depressed in 9 of 10 patients. The ability of the Leu 3(+) lymphocytes to absorb IL-1 was depressed in all (four of four) patients studied. After ISO treatment, IL-2 production, Tac antigen expression and IL-1 absorption were restored to normal or near normal levels in most of the patients. These results suggest that ISO has an immunostimulating capacity in AIDS patients and that the potential of ISO in immune response restoration in AIDS patients deserves critical consideration.