Prostaglandin E2 control of T cell cytokine production is functionally related to the reduced lymphocyte proliferation in atopic dermatitis

Past studies of peripheral blood mononuclear cells (PBMC) from patients with atopic dermatitis (AD) have demonstrated reduced proliferation. We have studied phytohemagglutinin-induced lymphocyte proliferation in the context of interleukin-4 (IL-4), interferon-gamma (IFN-gamma), and prostaglandin E2 (PGE2) production in cultures of PBMC from patients without and with AD. The proliferation index was found to correlate proportionally to IFN-gamma production and inversely to T-cell IL-4 and monocyte PGE2 production. Assays in parallel cultures showed significantly increased PGE2 production by purified AD monocytes. The proliferation index in PBMC from persons with AD was significantly reduced compared with normal PBMC. This difference was normalized in the presence of extrinsic IFN-gamma but exaggerated when IL-4 was added. Increased AD monocyte production of inflammatory factors (e.g., PGE2) and cytokines appears to increase IL-4 production by Th2 while suppressing IFN-gamma production by Th1. Restoration of the normal proliferation of PBMC by the addition of IFN-gamma may represent one mechanism for the clinical efficacy of IFN-gamma treatment of AD.

Monocyte phosphodiesterase abnormalities and dysregulation of lymphocyte function in atopic dermatitis

The immunologic aberrations associated with atopic dermatitis include the paradox of reduced cell-mediated immune responses in the setting of increased cell-mediated immunity features that resemble allergic contact dermatitis. In this review, we present evidence that abnormalities in monocytes and Langerhans cells alter the function of T-helper-cell subpopulations to cause the immunologic defects associated with atopic dermatitis. Increased monocyte prostaglandin E2 production inhibits Th1 responses, accentuating interleukin (IL)-4 secretion by Th2 cells. Elevated prostaglandin E2 secretion correlates with abnormally increased cyclic adenosine monophosphate-phosphodiesterase activity in monocytes and this, along with other defective inflammatory cell responses, can be normalized in vitro by phosphodiesterase inhibitors. It appears that in addition to prostaglandin E2, IL-10 acts to regulate the balance between Th1 and Th2 functional responses accounting for many atopic features, including increased IL-4, IL-5, and IL-6 production by T cells; increased IgE synthesis; decreased interferon-gamma production; and impaired cell-mediated immune responses. All of these abnormalities can be related to increased phosphodiesterase activity in atopic monocytes, and inhibition of this key enzyme appears to reverse atopic dermatitis inflammatory abnormalities in vitro and in vivo.

Primary penile lymphoma presenting as a penile ulcer

Primary penile lymphoma is rare. The clinical manifestations can be quite subtle, which may lead to misdiagnosis. Treatments have included radical surgery, chemotherapy and radiation. We report on an 18-year-old man with primary penile lymphoma whose lesion caused prolonged diagnostic uncertainty. He was treated with chemotherapy alone, and he has had no tumor recurrence for 27 months.

Overexpression of IL-10 in atopic dermatitis. Contrasting cytokine patterns with delayed-type hypersensitivity reactions

The skin lesions of patients with atopic dermatitis provide a model to study immunoregulation in human allergy. To determine the local cytokine pattern of cells present (both endogenous and recruited) at the site of disease, we extracted RNA from skin biopsy specimens from patients with atopic dermatitis, allergic contract dermatitis, and positive tuberculin reactions and used PCR to assay for cytokine mRNA. cDNAs were normalized to the intensity of the CD3 delta PCR product as a marker of T cell mRNA. We found overexpression of IL-10 mRNA in atopic dermatitis lesions, in comparison with allergic contact dermatitis lesions and tuberculin reactions. In contrast, IL-4 mRNA was most strongly expressed in allergic contact dermatitis lesions and IFN-gamma mRNA was the predominant cytokine in tuberculin reactions. Using an anti-IL-10 mAb with immunoperoxidase, we localized IL-10 protein to large mononuclear cells in the dermal infiltrate of atopic lesions. After immunomagnetic sorting of mononuclear cell populations from PBMC of atopic dermatitis subjects, IL-10 mRNA as measured by PCR was found to be strongly expressed in CD14+ cells. Spontaneous release of IL-10 from PBMC-derived adherent cells was greater in atopic dermatitis donors than normal controls. We therefore renormalized skin biopsy cDNA according to the level of beta-actin PCR product, as a marker of total cellular mRNA, and found by PCR that IL-10 was nevertheless greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis may contribute to the up-regulation of humoral responses and the down-regulation of Th1 responses.

Overexpression of IL-10 in atopic dermatitis. Contrasting cytokine patterns with delayed-type hypersensitivity reactions

The skin lesions of patients with atopic dermatitis provide a model to study immunoregulation in human allergy. To determine the local cytokine pattern of cells present (both endogenous and recruited) at the site of disease, we extracted RNA from skin biopsy specimens from patients with atopic dermatitis, allergic contract dermatitis, and positive tuberculin reactions and used PCR to assay for cytokine mRNA. cDNAs were normalized to the intensity of the CD3 delta PCR product as a marker of T cell mRNA. We found overexpression of IL-10 mRNA in atopic dermatitis lesions, in comparison with allergic contact dermatitis lesions and tuberculin reactions. In contrast, IL-4 mRNA was most strongly expressed in allergic contact dermatitis lesions and IFN-gamma mRNA was the predominant cytokine in tuberculin reactions. Using an anti-IL-10 mAb with immunoperoxidase, we localized IL-10 protein to large mononuclear cells in the dermal infiltrate of atopic lesions. After immunomagnetic sorting of mononuclear cell populations from PBMC of atopic dermatitis subjects, IL-10 mRNA as measured by PCR was found to be strongly expressed in CD14+ cells. Spontaneous release of IL-10 from PBMC-derived adherent cells was greater in atopic dermatitis donors than normal controls. We therefore renormalized skin biopsy cDNA according to the level of beta-actin PCR product, as a marker of total cellular mRNA, and found by PCR that IL-10 was nevertheless greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis may contribute to the up-regulation of humoral responses and the down-regulation of Th1 responses.

Abnormal skin irritancy in atopic dermatitis and in atopy without dermatitis

BACKGROUND AND DESIGN

Past observations have shown increased irritancy in patients with "conditioned hyperirritability" due to active dermatitis, including atopic dermatitis (AD). In less active atopic conditions, irritancy levels are less certain. We have utilized 48-hour Finn Chamber testing with graded dilutions of sodium lauryl sulfate to detect irritancy thresholds in well-defined groups of patients with AD, inactive AD, and allergic respiratory disease with no dermatitis and in normal nonatopic subjects.

RESULTS

Significantly greater frequency of response to sodium lauryl sulfate in both AD groups and also in patients with allergic rhinitis with no dermatitis was seen. Effective concentrations of sodium lauryl sulfate causing irritation in 50% or more of subjects (ED50) ranged from 0.0625% to 0.31% in all atopic groups, percentages that were significantly lower than the normal ED50 of 0.60%. Response intensity was also significantly greater in each atopic group.

CONCLUSIONS

Our results showed significantly greater irritant responses in atopic subjects with no skin disease or in subjects with inactive AD and confirmed past findings that showed greatly increased irritancy in patients with active AD. We hypothesize that abnormal intrinsic hyperreactivity in inflammatory cells, rather than in skin cells, in atopic individuals predisposes to a lowered threshold of irritant responsiveness.

Neonatal leukocyte cAMP-phosphodiesterase determination is not suitable for allergy prediction

The atopy-predictive value of cord blood (CB) cyclic adenosine monophosphate-phosphodiesterase (cAMP-PDE) in mononuclear leukocytes (MN) was studied prospectively in 57 neonates. Reliable determination of cAMP-PDE was achieved in only 20 CB samples. The levels tended to be higher in infants developing signs of atopy up to 18 months of age. The combination of CB cAMP-PDE and family history (FH) of allergy showed a higher predictive value (P = 0.040) than each of them separately (P = 0.370 and P = 0.102, respectively). The cAMP-PDE levels in CB also correlated to FH of allergy/atopy in accordance with earlier studies (P = 0.027). In conclusion, determination of cAMP-PDE in neonates may have some predictive value, but it is not suitable for general screening.

Olecranon and pretibial bursitis in atopic dermatitis: coincidence or association?

BACKGROUND

Bursal fluid accumulations are not usually associated with skin disease; however, several cases have been observed in a large atopic dermatitis (AD) clinic.

OBJECTIVE

We sought to characterize the clinical features of bursitis in AD and to assess the evidence for a mechanistic association between these conditions.

METHODS

We retrospectively evaluated the clinical presentation of bursitis in six adults with lifelong severe AD. The course of the bursitis and possible causative factors were assessed for each patient.

RESULTS

Ten episodes of bursitis were documented in six patients with chronic active AD. Two cases initially appeared as pretibial bursal fluid accumulations, a type of bursitis that is previously undescribed. Onset of bursitis in all cases coincided with flaring of dermatitis. The frequency of these 10 episodes in six patients among an AD population of 792 appears to be greater than the three cases per 1000 in the local Veterans Administration outpatient center.

CONCLUSION

The unusual pretibial bursal fluid accumulations in AD, along with multiple recurrences of olecranon bursitis during flares of dermatitis, suggest that the association may not be coincidental.

Altered prostaglandin E2 regulation of cytokine production in atopic dermatitis

The monocyte-derived inflammatory mediator, prostaglandin E2 (PGE2), can reduce IFN-gamma production, and this in turn may relate to IL-4 up-regulation of IgE synthesis and impaired delayed hypersensitivity in atopy. These abnormalities may relate to the cyclic nucleotide dysregulation in atopic dermatitis (AD), where monocyte cyclic AMP-phosphodiesterase (PDE) activity is increased and the consequent reduction in cAMP levels allows increased inflammatory responsiveness. In this study, we assessed the relationship between PGE2 and IFN-gamma production along with abnormal PDE activity in AD monocytes. Blood mononuclear leukocytes (MNL) from normal and AD donors were cultured for 24 hours, and supernatants were assayed for PGE2 and IFN-gamma by RIA. Spontaneous PGE2, but not leukotriene C4 release, was significantly increased in AD MNL (p < 0.05), although IFN-gamma levels were reduced (p < 0.05). In contrast, purified AD T cells, after removal of PGE2-producing monocytes, produced levels of IFN-gamma significantly higher than in normal T cell cultures. Inhibition of PGE2 synthesis by indomethacin caused increased IFN-gamma production by MNL cultures. We noted a strong negative correlation (r = 0.77) between PDE activity and IFN-gamma production in MNL cultures. We speculate that abnormal cyclic nucleotide metabolism caused by increased PDE activity may allow elevated levels of PGE2 production by AD monocytes. This study demonstrates a regulatory interaction between monocytes and T cells in AD and suggests that PGE2 may be an extracellular messenger between these cells to modulate IFN-gamma production.

Altered prostaglandin E2 regulation of cytokine production in atopic dermatitis

The monocyte-derived inflammatory mediator, prostaglandin E2 (PGE2), can reduce IFN-gamma production, and this in turn may relate to IL-4 up-regulation of IgE synthesis and impaired delayed hypersensitivity in atopy. These abnormalities may relate to the cyclic nucleotide dysregulation in atopic dermatitis (AD), where monocyte cyclic AMP-phosphodiesterase (PDE) activity is increased and the consequent reduction in cAMP levels allows increased inflammatory responsiveness. In this study, we assessed the relationship between PGE2 and IFN-gamma production along with abnormal PDE activity in AD monocytes. Blood mononuclear leukocytes (MNL) from normal and AD donors were cultured for 24 hours, and supernatants were assayed for PGE2 and IFN-gamma by RIA. Spontaneous PGE2, but not leukotriene C4 release, was significantly increased in AD MNL (p < 0.05), although IFN-gamma levels were reduced (p < 0.05). In contrast, purified AD T cells, after removal of PGE2-producing monocytes, produced levels of IFN-gamma significantly higher than in normal T cell cultures. Inhibition of PGE2 synthesis by indomethacin caused increased IFN-gamma production by MNL cultures. We noted a strong negative correlation (r = 0.77) between PDE activity and IFN-gamma production in MNL cultures. We speculate that abnormal cyclic nucleotide metabolism caused by increased PDE activity may allow elevated levels of PGE2 production by AD monocytes. This study demonstrates a regulatory interaction between monocytes and T cells in AD and suggests that PGE2 may be an extracellular messenger between these cells to modulate IFN-gamma production.

Presence of IgE antibodies to staphylococcal exotoxins on the skin of patients with atopic dermatitis. Evidence for a new group of allergens

In the current study, we investigated whether Staphylococcus aureus grown from affected skin of atopic dermatitis (AD) patients secreted identifiable toxins that could act as allergens to induce IgE-mediated basophil histamine release. The secreted toxins of S. aureus grown from AD patients were identified by ELISA using antibodies specific for staphylococcal enterotoxin (SE) exfoliative toxin (ET), or toxic shock syndrome toxin (TSST-1). S. aureus isolates from 24 of 42 AD patients secreted identifiable toxins with SEA, SEB, and TSST accounting for 92% of the isolates. 32 of 56 AD sera (57%) tested contained significant levels of IgE primarily to SEA, SEB, and/or TSST. In contrast, although SEA, SEB, or TSST secreting S. aureus could be recovered from the skin of psoriasis patients, their sera did not contain IgE antitoxins. Freshly isolated basophils from 10 AD patients released 5-59% of total histamine in response to SEA, SEB, or TSST-1 but only with toxins to which patients had specific IgE. Basophils from eight other AD patients and six normal controls who had no IgE antitoxin failed to demonstrate toxin-induced basophil histamine release. Stripped basophils sensitized with three AD sera containing IgE to toxin released 15-41% of total basophil histamine only when exposed to the relevant toxin, but not to other toxins. Sensitization of basophils with AD sera lacking IgE antitoxin did not result in release of histamine to any of the toxins tested. These data indicate that a subset of patients with AD mount an IgE response to SEs that can be grown from their skin. These toxins may exacerbate AD by activating mast cells, basophils, and/or other Fc epsilon-receptor bearing cells armed with the relevant IgE antitoxin.

Modulation of leukocyte cyclic AMP phosphodiesterase activity by recombinant interferon-gamma: evidence for a differential effect on atopic monocytes

Mechanisms of interferon-gamma (IFN-gamma) effects on monocytes are poorly defined. Evidence for altered IFN-gamma responses and increased monocyte cyclic AMP phosphodiesterase (PDE) activity in atopic dermatitis (AD) suggested a possible relationship. PDE activity in response to IFN-gamma was assessed in normal and atopic monocytes to evaluate the IFN-gamma regulatory role in cell function. Adherence-isolated peripheral blood monocytes were exposed to recombinant human IFN-gamma at 0.1-300 U/ml in Gey's balanced salt solution for varying time periods. Anti-IFN-gamma was used as control. PDE activity was measured by radioenzyme assay using 1 microM cyclic AMP as final substrate concentration. IFN-gamma caused a dose-dependent increase in PDE activity of normal monocytes and the effect was neutralized by anti-IFN-gamma. By contrast, in atopic monocytes, PDE activity was not affected by IFN-gamma at low dose, while at concentrations greater than 200 U/ml, it significantly reduced phosphodiesterase activity. IFN-gamma of PDE activity may alter normal monocyte functions by decreasing cyclic AMP levels. Paradoxical PDE unresponsiveness probably reflects maximal PDE activation in atopic monocytes. This elevated PDE activity is inhibited by high IFN-gamma levels. Reduction of atopic monocyte PDE activity may help to normalize immune function and could account for recent reports of therapeutic efficacy of IFN-gamma in AD.

Immunochemical characterization of the distinct monocyte cyclic AMP-phosphodiesterase from patients with atopic dermatitis

BACKGROUND

Previous findings have suggested that the immunopathology of patients with atopic dermatitis (AD) results from altered cellular responses caused by cyclic nucleotide regulatory abnormalities. One such defect is the increased degradation of the second messenger, cyclic adenosine monophosphate (cAMP), by elevated cAMP-phosphodiesterase (PDE) activity in patients with AD.

METHODS

We used two monoclonal antibodies to identify the major PDE isoform in AD blood monocytes. We have also characterized the abnormal PDE activity by means of chromatofocusing and sucrose gradient centrifugation.

RESULTS

The chromatofocusing technique allowed the separation of a PDE-containing fraction (isoelectric point = 6.1) from AD monocytes but not from normal cells. This monocyte fraction accounted for most of the elevated leukocyte-PDE activity and was a cytosolic, cAMP-specific, low Michaelis constant, calcium-calmodulin-dependent enzyme, inhibited by the cAMP-PDE inhibitor, Ro 20-1724. The majority of the PDE activity in this chromatofocused fraction was immunoadsorbed by the solid-phase immobilized antibodies against calcium-calmodulin-dependent PDE.

CONCLUSIONS

The increased degradation of cAMP by a unique form of PDE may cause defective regulation of intracellular functions of AD monocytes, leading to the characteristic hyperreactive immune and inflammatory events. Characterization of PDE isoenzymes from different leukocyte subpopulations may allow further expansion of cell-directed therapy for inflammatory disease.

Increased interleukin-4 production by atopic mononuclear leukocytes correlates with increased cyclic adenosine monophosphate-phosphodiesterase activity and is reversible by phosphodiesterase inhibition

Previous studies have shown that leukocytes from patients with atopic dermatitis have increased levels of cyclic adenosine monophosphate (cAMP)-phosphodiesterase activity. This increased activity accounts for subnormal cAMP responses and correlates with increased in vitro immunoglobulin E production. To better understand the mechanism of this effect, we studied the relationship between phosphodiesterase activity and interleukin-4, a T-cell-derived cytokine that is a major regulator of immunoglobulin E production. Cultures stimulated with anti-CD3 or with phorbol myristate acetate plus ionophore significantly increased interleukin-4 production, and levels were consistently highest in cells from atopic subjects. Interleukin-4 production was higher, on a per T-cell basis, in mononuclear leukocyte cultures than in cultures of pure T cells, suggesting the possibility of a monocyte factor acting to increase interleukin-4 production. We next examined the effect of the phosphodiesterase inhibitor Ro 20-1724 on interleukin-4 production and found a significant reduction in cultures of atopic mononuclear leukocytes. This phosphodiesterase inhibitor effect appeared to act primarily on monocytes and correlated with increased intracellular cAMP levels. These studies demonstrate increased interleukin-4 production by atopic T cells. This abnormality can be reversed by inhibition of cAMP-phosphodiesterase, suggesting a possible therapeutic target for control of atopic disease.

Increased interleukin 6 production by T cells derived from patients with atopic dermatitis

Many immunologic aspects of atopic dermatitis have been studied, but basic pathobiologic mechanisms of this disease remain unknown. In this study, we measured the production of interleukin-6 (IL-6) by peripheral blood T cells and monocytes from patients with atopic dermatitis in comparison to normal control subjects and patients with chronic psoriasis. We found that peripheral blood T cells isolated from patients with atopic dermatitis produced significantly higher levels of IL-6 (36.1 +/- 5.1 units/ml, n = 22) than T cells derived from either normal subjects (12.6 +/- 1.9 units/ml, n = 22) or patients with chronic psoriasis (26.7 +/- 4.1 units/ml, n = 7). T-cell activation was also measured in the patients with atopic dermatitis by soluble serum IL-2 receptor levels and were found to be significantly higher (623.7 +/- 8.1 units/ml, n = 8) than normal subjects (357.2 +/- 26.0 units/ml, n = 8). In contrast to the increased production of IL-6 by T cells in atopic dermatitis, there was no significant difference in the IL-6 production by peripheral blood monocytes derived from patients with atopic dermatitis compared to normal subjects. Thus, peripheral blood T cells derived from patients with AD spontaneously produce increased amounts of IL-6 compared to T cells from normal subjects, which may reflect the increased activation state of T cells in atopic dermatitis. These data support the concept that activated T cells or subsets of T cells may be important effector cells in mediating inflammatory activity in atopic disease.

Recombinant interferon gamma therapy for atopic dermatitis

BACKGROUND

Atopic dermatitis is characterized by immunologic abnormalities including evidence for reduced interferon gamma production. Therapeutic options for treatment of atopic dermatitis are limited and unsatisfactory. Previous open trials have suggested efficacy for recombinant interferon-gamma (rIFN-gamma) in treatment of severe atopic dermatitis. We describe the results of treatment with rIFN-gamma, assessing clinical, immunologic, and laboratory safety parameters in 83 patients with moderate to severe atopic dermatitis.

OBJECTIVE

Our purpose was to determine in a randomized, placebo-controlled, double-blind multicenter study the effects of recombinant human interferon gamma therapy in patients with atopic dermatitis.

METHODS

Patients received 50 micrograms/m2 rIFN-gamma (n = 40) or placebo (n = 43) by daily subcutaneous injection for 12 weeks. Seventy-eight patients completed the treatment course; two patients receiving rIFN-gamma (one because of constitutional side effects) and three receiving placebo discontinued treatment before completion. Physician and patient overall response evaluations, clinical severity scores, body surface area involvement, and laboratory parameters were monitored throughout the trial.

RESULTS

Patients in both treatment groups were similar except that the rIFN-gamma group was older and had a longer disease duration. Forty-five percent of rIFN-gamma-treated patients and 21% of placebo-treated patients achieved greater than 50% improvement in physicians' overall response evaluations (p = 0.016). As estimated by patients, responses also showed significant improvement in the rIFN-gamma group compared with the placebo group (53% vs 21%, p = 0.002). Significant reductions in erythema (p = 0.035) and in excoriations or erosions (p = 0.045) occurred in rIFN-gamma-treated patients. Other atopic symptoms such as conjunctivitis (p < 0.002) were also reduced in the rIFN-gamma group. Occasional headaches, myalgias, or chills occurred in 30% to 60% of rIFN-gamma-treated patients but were effectively prevented by pretreatment acetaminophen and by dosing at bedtime. Grade II granulocytopenia occurred in five rIFN-gamma patients but normalized with continued treatment. Reduction to alternate-day dosing was necessary for six patients in the rIFN-gamma group and two in the placebo group. Seven had mild elevations of hepatic transaminase levels that did not affect therapy. The mean eosinophil count was significantly reduced (p = 0.003), whereas a nonsignificant increase in serum IgE levels occurred in the active treatment group.

CONCLUSION

This study demonstrated that rIFN-gamma given by daily subcutaneous injection over a 12-week period was safe, well accepted, and effective in reducing inflammation, clinical symptoms, and eosinophilia in severe atopic dermatitis.

Differential inhibitor effects on cyclic adenosine monophosphate-phosphodiesterase isoforms in atopic and normal leukocytes

Increased cyclic adenosine monophosphate-phosphodiesterase activity in atopic leukocytes correlates with abnormal inflammatory and immune cell function in atopic dermatitis. The increased phosphodiesterase activity may affect many pathways of cell regulation and thus could be an important therapeutic target for management of cutaneous and respiratory inflammation. The increased PDE activities in atopic monocytes and lymphocytes reflect isoforms with increased maximum rate of metabolism but first order rate constant similar to that of the enzyme in normal cells. Both isoforms can be classed into the phosphodiesterase IV group with sensitivity to the inhibitor Ro 20-1724. In this study we used an in vitro assay to assess the effects of various phosphodiesterase inhibitors on enzyme isoforms in mononuclear leukocytes and purified leukocyte subpopulations from patients with atopic dermatitis and normal subjects. The atopic isoenzyme was found to be consistently more sensitive to a number of phosphodiesterase inhibitors. The descending order of potency for mononuclear leukocytes was rolipram, Ro 20-1724, nitraquazone, isobutyl methyl xanthine, and theophylline. Nitraquazone showed greater inhibitory effect on atopic T cells than did Ro 20-1724. Cyclic adenosine monophosphate levels increased in atopic mononuclear leukocytes incubated with Ro 20-1724 but not in normal cells. We also measured inhibitor effects on intact cells and cell homogenates, allowing discrimination of inhibitor capacity to enter intact cells. The differential inhibitor effect on various leukocyte subpopulations was demonstrated by a greater sensitivity of atopic lymphocytes and T cells for nitraquazone than for Ro 20-1724. In contrast, the latter inhibitor was a more potent inhibitor of mononuclear leukocyte and monocyte phosphodiesterase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Synergistic effects of interleukin 4 and interferon-gamma on monocyte phosphodiesterase activity

Patients with atopic dermatitis (AD) have elevated leukocyte cyclic AMP-phosphodiesterase (PDE) activity and increased in vitro IgE synthesis compared to normal (NL) subjects. Interleukin 4 (IL-4), interferon-gamma (IFN-gamma), and PDE inhibitor have been shown to regulate in vitro IgE synthesis. This study investigated whether soluble T-cell factors such as IL-4 and IFN-gamma could account for elevated PDE activity in patients with AD. Both rhIL-4 and IFN-gamma significantly increased normal monocyte PDE activity to a maximum of 188% (n = 6, p less than 0.05) and 315% above control (n = 3, p less than 0.05), respectively. At concentrations below 0.1 units/ml IL-4 and IFN-gamma had synergistic effects on activation of monocyte PDE. AD and NL T-cell culture supernatants also significantly stimulated normal monocyte PDE activity, but the stimulatory activity was not significantly greater in the AD T-cell supernatants. The effect of both cytokines and T-cell supernatants on normal monocytes was inhibited by antibodies against IL-4 and IFN-gamma, respectively. This study demonstrates that IL-4 and IFN-gamma can increase PDE activity in normal monocytes. Though the levels of IL-4 and IFN-gamma in T-cell supernatants are undetectable with an enzyme-linked immunosorbent assay (ELISA) assay, the concentration of these cytokines below the detectable level can significantly increase PDE activity of monocytes in a synergistic and dose-dependent manner. These results suggest that cytokine-mediated activation of monocytes can increase PDE activity. Furthermore, lymphokines may play an important role in modulating the cyclic nucleotide regulatory pathway.