Glucocorticoid-induced Immunosuppression Research Articles

Executive Summary: State-of-the-Art Review: Unintended Consequences: Risk of Opportunistic Infections Associated with Long-term Glucocorticoid Therapies in Adults.

Glucocorticoid-induced immunosuppression is linked to the dose, duration, and intensity, but the dose-dependent model may inaccurately predict the risk of opportunistic infections. We discuss details of glucocorticoid treatments to determine their effect on immune function and risk of opportunistic infections.

Transcriptomic profiling of TLR-7-mediated immune-challenge in zebrafish embryos in the presence and absence of glucocorticoid-induced immunosuppression

Although numerous studies imply a correlation between chemical contamination and an impaired immunocompetence of wildlife populations, the assessment of immunomodulatory modes of action is currently not covered in the regulatory requirements for the approval of new substances. This is not least due to the complexity of the immune system and a lack of standardised methods and validated biomarkers. To tackle this issue, in this study, the transcriptomic profiles of zebrafish embryos were analysed in response to the immunosuppressive compound clobetasol propionate, a synthetic glucocorticoid, and/or the immunostimulatory compound imiquimod (IMQ), a TLR-7 agonist. Using IMQ, known for its potential to induce psoriasis-like effects in mice and human, this study additionally aimed at evaluating the usability of the zebrafish embryo model as an alternative and 3R conform system for the IMQ-induced psoriasis mouse model. Our study substantiates the suitability of previously proposed genes as possible biomarkers for immunotoxicity, such as socs3, nfkbia, anxa1c, fkbp5 and irg1l. Likewise, however, our findings indicate that these genes may be less suitable to distinguish a suppressive from stimulating fashion of action. In contrast, based on a differential regulation in opposite direction in response to both compounds, krt17, rtn4a, and1, smhyc1 and gmpr were identified as potential novel biomarkers with said power to differentiate. Observed IMQ-induced alterations in the expression of genes previously associated with the pathogenesis of psoriasis such as krt17, nfkbia, parp1, pparg, nfil3–6, per2, stat4, klf2, rtn4a, anxa1c and nr1d2 indicate the inducibility of psoriatic effects in the zebrafish embryo.Our work contributes to the establishment of an approach for a 3R-compliant investigation of immunotoxic mechanisms of action in aquatic vertebrates. The validated and newly identified biomarker candidates of specific immunotoxic effects can be used in future studies in the context of environmental hazard assessment of substances or also for human-relevant immunotoxicological questions.

Phase II study of pembrolizumab plus mifepristone in patients with advanced HER2-negative breast cancer.

1095 Background: Metastatic breast cancer is incurable, and novel treatment (tx) strategies are needed. Single agent immune checkpoint inhibitor (ICI) tx has limited efficacy; combination approaches may yield better results. Multiple mechanisms of glucocorticoid-induced immunosuppression have been proposed, including the suppression of the cytotoxic Th1 cytokine response via glucocorticoid receptor (GR) activation. We hypothesize that pretreatment with a GR antagonist shifts the cytotoxic immune response toward Th1, thus enhancing response to ICIs. We present the safety and efficacy of the combination of pembrolizumab and mifepristone in advanced HER2-negative breast cancer. Methods: This (NCT03225547) was a phase II non-randomized study of pembrolizumab and mifepristone in patients (pts) with advanced HER2-negative breast cancer. Pts with prior ICI tx were excluded. Pts received mifepristone 300mg daily and pembrolizumab 200mg every 3 weeks; mifepristone was started 7 days prior to pembrolizumab. The primary endpoint was objective response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), disease control rate (DCR), and safety and tolerability. Results: 18 patients were enrolled from March 2018 – November 2020; 10 patients with TNBC (cohort 1) and 8 patients with HR+ BC (cohort 2). Mean age was 53 yrs (range 33-74) and 33% of patients were self-reported Black. In cohort 1, 50% of patients were tx naive in this advanced setting, and 90% of patients had < 2 prior lines of tx. In cohort 2, 25% of patients had not received prior chemo in the metastatic setting. The overall ORR was 6%. One pt with TNBC had a complete response (CR). She received 36 cycles of tx; tx was discontinued due to mucositis and rash, and she remains in CR at >48 mos from start of tx. No patients in cohort 2 had a partial or complete response. The most common treatment-related adverse events were rash (61%), thyroid abnormality (17%), and pruritis (17%). 45% of patients experienced a grade 3 or 4 adverse event; all except one (hypokalemia) were due to rash. Rash was described as maculopapular dermatitis. The DCR at 18 weeks was 33.3% in the overall population; it was 44.4% in cohort 1 and 16.7% in cohort 2. Overall median PFS was 1.9 months [95% CI 1.8 – 3.6]. Overall median OS was 12.9 months [95% CI 5.8 – 23.0]. Conclusions: While this regimen demonstrated efficacy in a small subset of patients, including one pt with long-term CR, given the non-randomized design, we cannot determine if mifepristone enhanced the efficacy of ICI. In addition, a higher than anticipated rate of skin toxicity, possibly related to mifepristone enhancing the activity of ICI, was observed in the study, leading to early closure. While the benefit/risk analysis of this combination does not support further evaluation, additional investigation of alternative chemotherapy-free, immunomodulatory strategies is warranted. Clinical trial information: NCT03225547 .

Secondary Cutaneous Mucormycosis Post-COVID-19: Case Series from a Tertiary Center.

Background:Mucormycosis is an angioinvasive mucorales fungal infection. Cutaneous type formed 10.5% of cases in India in precovid-19 era. Glucocorticoid-induced immunosuppression and hyperglycemia, reusable oxygen humidifiers in COVID-19 therapy, and preexisting uncontrolled diabetes mellitus contribute to post-COVID-19 mucormycosis. However, for post-COVID-19 cutaneous mucormycosis, sufficient data is not available.Aim:To study factors related to post-COVID-19 cutaneous mucormycosis.Methodology:Clinical and investigation details of six patients admitted in tertiary center with post-COVID-19 cutaneous mucormycosis.Results:Among six patients, three were males and three females; all in 45–60 years age group from districts under tertiary center. Site of eschar was face (four) and lips (two). All six were positive for COVID-19 10–12 days prior to admission for mucormycosis. All had intravenous steroids and supportive humidified oxygen therapy for minimum 1 week under COVID-19 treatment. They presented to emergency with ophthalmic/ENT complaints; subsequently, they developed cutaneous manifestations within 2–3 days. All six had diabetes mellitus, with above 400 mg/dL sugar levels at admission.Conclusion:This study's findings correlated with various studies across the country and elsewhere. Preexisting diabetes mellitus and steroid therapy for COVID-19 increase the risk of mucormycosis. Caution for early diagnosis, maintaining blood glucose levels, and judicious use of steroids for treatment of COVID-19 are indicated.

Protective Effects of Collagen Peptides on the Dexamethasone-Induced Immunosuppression in Mice

Collagen peptides are collagen derived products by enzymatic proteolysis, which is widely distributed in mammalian connective tissues. They have exhibited various bioactivities, including antioxidant activity, antihypertensive activity, improvement of joint pain, etc. However, the immunomodulatory effects of collagen peptides in the condition of immune suppression have not been elucidated. The objective of this study was to investigate the effects of collagen peptides on immune function in immunosuppressed mice. The immunosuppression was induced by intraperitoneal injection of dexamethasone for three days and at same time, collagen peptides (0, 300, 600, 900 mg/kg body weight) were given by gavage for seven days. On the day 8, the mice were sacrificed by decapitation. The body weight and the weights of thymus and spleen were recorded. Thymus and spleen indexes were calculated. The proliferation and interleukin-2 production of splenic T lymphocytes and ratio of CD4+/CD8+T lymphocytes in the peripheral blood were examined. Compared with the control mice, the body weight, thymus and spleen indexes, the proliferations and interleukin-2 production in T lymphocytes and the ratios of CD4+/CD8+T cells were significantly decreased in dexamethasone induced immunosuppressed mice. However, in collagen peptides treated mice, the thymus indexes, proliferation index, secretion of interleukin-2 and the ratio of CD4+/CD8+ were significantly increased compared with the mice in experimental model group. These results indicate that collagen peptides could play a protect role in glucocorticoid-induced immunosuppression.

High dietary vitamin C intake reduces glucocorticoid-induced immunosuppression and measures of oxidative stress in vitamin C-deficient senescence marker protein 30 knockout mice.

Vitamin C (VC) is a vital micronutrient for humans and some other mammals and also has antioxidant activity. Stress-induced elevation of glucocorticoid production is well known to cause immunosuppression. The present study evaluated the effect of high VC intake on glucocorticoid-induced immune changes in mice. Senescence marker protein 30 knockout mice with genetic VC deficiency were fed a diet containing the recommended VC content (20 mg/kg per d; 0·02 %VC group) or a high VC content (200 mg/kg per d; 0·2 %VC group) for 2 months, then dexamethasone was given by intraperitoneal injection. After administration of dexamethasone, the plasma ascorbic acid concentration decreased significantly in the 0·02 %VC group and was unchanged in wild-type C57BL/6 mice on a VC-deficient diet (wild-type group), while it was significantly higher in the 0·2 %VC group compared with the other two groups. In the 0·02 %VC and wild-type groups, dexamethasone caused a significant decrease in the cluster of differentiation (CD)4+ and CD8+ T cells among splenocytes as well as a significant decrease in IL-2, IL-12p40 and interferon-γ protein production by splenocytes and a significant decrease in T-cell proliferation among splenocytes. In the 0·2 %VC group, these dexamethasone-induced immunosuppression improved when compared with the other two groups. In addition, reduction in the intracellular levels of ascorbic acid, superoxide dismutase and glutathione in splenocytes by dexamethasone as well as elevation in thiobarbituric acid-reactive substances were significantly suppressed in the 0·2 %VC group. These findings suggest that high dietary VC intake reduces glucocorticoid-induced T-cell dysfunction by maintaining intracellular antioxidant activity.

KAPOSI SARCOMA RELATED TO AN ECTOPIC HYPOTHALAMIC ADRENOCORTICOTROPIC HORMONE-SECRETING ADENOMA

We aim to report a case of Kaposi sarcoma (KS) with Cushing's syndrome caused by endogenic glucocorticoid-induced immunosuppression. A 43-year-old woman presented with delirium, hirsutism, fatigue, and hypertension. At the time of presentation, physical findings showed a Cushingoid appearance, with moon-like facies, hirsutism, and hyperpigmentation. Laboratory findings showed the following: adrenocorticotropic hormone, 86.7 pg/mL (normal range, 0-46 pg/mL); baseline cortisol level, 50 microg/dL (normal range, 6.2-19 microg/dL); potassium, 2.2 mEq/L (normal range, 3.5-5 mEq/L); and midnight cortisol level, 33 microg/dL. Serum cortisol levels failed to suppress after low and high doses of dexamethasone; these findings confirmed the diagnosis of ectopic adrenocorticotropic hormone production. Magnetic resonance imaging revealed a 12 x 15-mm, round, hypothalamic mass lesion in the center of the median eminence. Endoscopic biopsy from the floor of the third ventricle was performed, and pathological examination of the lesion showed a diffuse adrenocorticotropic hormone-secreting adenoma. The patient developed diffuse skin lesions that were proven to be a KS by skin biopsy while she was prepared for transcranial surgery. After surgical removal of the adenoma, she became hypocortisolemic and required cortisol replacement. Within 1 month after surgery, all KS lesions disappeared spontaneously. Excessive cortisol may induce immunosuppression. KS is one of the most common malignant tumors of patients with immunosuppression. To the best of our knowledge, this is the first case of Cushing's syndrome with KS caused by endogenous glucocorticoid-induced immunosuppression.

Experimental systemic infection withCryptococcus neoformansvar.grubiiandCryptococcusgattiiin normal and immunodeficient mice

Cryptococcus neoformans (Cn) var. grubii or Cryptococcus neoformans var. neoformans infection is usually associated with immunocompromised hosts, whereas Cryptococcusgattii more frequently causes disease in immunocompetent hosts. We examined the effects of immunodeficiency and glucocorticoid-induced immunosuppression on systemic murine infection induced by i.v. inoculation with these pathogens. SCID and immunocompetent BALB/c and C57BL/6 mice were infected with <or=107 yeast of Cn var. grubii or C. gattii; immunosuppressed BALB/c mice were infected with <or=106 yeast. Mortality was inoculum size-dependent in each model system, for both organisms. Following infection with 106 CFU of either Cn var. grubii or C. gattii immunocompetent BALB/c mice survived longer than immunosuppressed mice (P<0.0001 in both cases); no differences were found using lower inocula. SCID mice infected with Cn var. grubii or C. gattii died sooner than BALB/c mice (P<0.0013, all comparisons). Unexpectedly, BALB/c mice infected with C. gattii developed external lesions. Immunocompetent mice developed rectal prolapse more frequently whereas immunosuppressed mice developed more frequent skin lesions, predominantly on the tail. The fungal burden was especially high in rectum, skin and lung tissues. Histologic examination showed extensive infection of the rectum and skin and pneumonitis. Determination of CFU from various organs of immunocompetent BALB/c mice infected i.v. with 105 CFU of C. gattii or Cn var. grubii showed significant temporal increase of burdens of Cn var. grubii in brain and liver (P<0.003); other organs showed decreasing fungal burden. C.gattii was recovered only from liver and lungs, no CFU were detected in the other organs. As opposed to epidemiologic observations, our results demonstrate no predilection by C. gattii for infection of immunocompetent over immunosuppressed hosts; immunosuppression increased the risk of severe cryptococcosis by both varieties, especially at high inocula. This is the first report of C. gattii inducing experimental cutaneous and intestinal mucosal infection; Cn var. grubii did not affect these tissues, indicating differences in tissue tropism of these pathogens.

Glucocorticoids and invasive fungal infections.

Since the 1990s, opportunistic fungal infections have emerged as a substantial cause of morbidity and mortality in profoundly immunocompromised patients. Hypercortisolaemic patients, both those with endogenous Cushing's syndrome and, much more frequently, those receiving exogenous glucocorticoid therapy, are especially at risk of such infections. This vulnerability is attributed to the complex dysregulation of immunity caused by glucocorticoids. We critically review the spectrum and presentation of invasive fungal infections that arise in the setting of hypercortisolism, and the ways in which glucocorticoids contribute to their pathogenesis. A better knowledge of the interplay between glucocorticoid-induced immunosuppression and invasive fungal infections should assist in earlier recognition and treatment of such infections. Efforts to decrease the intensity of glucocorticoid therapy should help to improve outcomes of opportunistic fungal infections.

Disruption of Poly(ADP-ribose) Polymerase (PARP) Protects Against Stress-Evoked Immunocompromise

Chronic stress, mediated by adrenal hormones, is a major risk factor in the progression and outcome of human disease. While the secretion of adrenal hormones is known to be the primary endocrine mediator of stress-induced immunocompromise, the molecular mechanisms underlying the immunocompromise remain unspecified. Overproduction of the nuclear enzyme, poly (ADP-ribose) polymerase (PARP) has been implicated in the molecular pathway that leads to cell death by energy depletion following stress. Wild-type (WT) mice and mice with targeted disruption of the gene encoding PARP-1 (PARP-1 -/-) were subjected to 2 wk daily cold-water swim; splenocyte proliferation, anti-KLH IgG, and serum corticosterone concentrations were assessed. Additional mice of each genotype received daily i.p. injections of dexamethasone (DEX) (0.75 mg/kg) for 2 wk, and splenocyte proliferation and anti-KLH IgG were assessed. Splenocyte proliferation and specific antibody concentrations of stressed WT mice were reduced by ~20% of their pre-stress levels. In contrast, PARP-1 -/- mice maintained normal cell-mediated and humoral immune function following enforced cold-water swim stress. PARP-1 -/- mice also failed to compromise immune function following DEX treatment, whereas WT mice displayed significant reductions of immune function following this treatment. These results provide support for the involvement of PARP activation in immunological damage following physical stress. These results suggest that glucocorticoid-induced immunosuppression may require the activation of PARP in order for apoptosis of immune cells to take place. Taken together, these results suggest that therapies designed to inhibit PARP may prove valuable in the treatment of stress-related diseases.

Inhibition of AP-1 by the Glucocorticoid-inducible Protein GILZ

The immunosuppressive effects of glucocorticoids arise largely by inhibition of cytokine gene expression, which has been ascribed to interference between the glucocorticoid receptor and transcription factors such as AP-1 and NF-kappa B as well as by competition for common coactivators. Here we show that glucocorticoid-induced inhibition of interleukin-2 mRNA expression in activated normal T cells required new protein synthesis, suggesting that this phenomenon is secondary to expression of glucocorticoid-regulated genes. One of the most prominent glucocorticoid-induced genes is glucocorticoid-induced leucine zipper (GILZ), which has been reported to inhibit activation-induced up-regulation of Fas ligand (FasL) mRNA. Indeed, transient expression of GILZ in Jurkat T cells blocked induction of a reporter construct driven by the FasL promoter. This could be accounted for by GILZ-mediated inhibition of Egr-2 and Egr-3, NFAT/AP-1-inducible transcription factors that bind a regulatory element in the FasL promoter and up-regulate FasL expression. GILZ also potently inhibited AP-1-driven and IL-2 promoter-driven reporter constructs, and recombinant GILZ specifically interacted with c-Fos and c-Jun in vitro and inhibited the binding of active AP-1 to its target DNA. Whereas homodimerization of GILZ required the presence of its leucine zipper, the interaction with c-Fos and c-Jun occurred through the N-terminal 60-amino acid region of GILZ. Thus, GILZ represents a glucocorticoid-induced gene product that can inhibit a variety of activation-induced events, at least in part by direct interference with AP-1, and is therefore a candidate for a mediator of glucocorticoid-induced immunosuppression.

Interleukin-6 treatment augments cutaneous wound healing in immunosuppressed mice.

It has been postulated that the inflammatory response that occurs after cutaneous wounding is a prerequisite for healing and that inflammatory cytokines, such as interleukin-6 (IL-6) are involved in this process. We showed previously that IL-6-deficient mice display delayed wound healing, which could be reversed by administration of a murine IL-6 expression plasmid or recombinant murine IL-6 (rMuIL-6). In the present study, we observed that delayed cutaneous wound healing, which occurs as a result of glucocorticoid-induced immunosuppression, can also be reversed by rMuIL-6, as evidenced by epithelialization, granulation tissue formation, and wound closure. In vehicle control mice, rMuIL-6 did not augment healing but rather delayed the process. Immunochemical studies indicated that the expression of matrix metalloproteinase-10 (MMP-10) was increased in dexamethasone-treated mice and that rMuIL-6 treatment reduced its expression, indicating that IL-6 may influence dermal matrix formation and, specifically, collagen synthesis. These results demonstrate that IL-6 can restore abnormal wound repair that occurs in immunodeficiency and suggest its use as a potential therapy.

Protection of Immunosuppressed Mice from Lethal Candida Infection by Oral Administration of a Kampo Medicine, Hochu-Ekki-To

The protective effect of a Kampo medicine, Hochu-ekki-to (TJ-41) on experimental candidiasis in immunosuppressed mice was investigated. ICR mice were immunosuppressed by injection of prednisolone or cyclophosphamide, given TJ-41 orally and challenged intravenously with Candida albicans (day 0). Treatments with a daily dose of 1g/kg/day of TJ-41 for 8 days from day-4 or for 4 days from day 0 significantly grolonged the life span of the Candida-infected mice pretreated with prednisolone. The latter treatment appeared to inhibit the colanization of Candida in kidneys of the infected mice. These results suggest that Hochu-ekki-to can be used as a therapeutic agent against candidiasis in patients with glucocorticoid-induced immunosuppression.

Glucocorticoid-Induced Alterations of Monocyte Defense Mechanisms against Candida albicans

The mechanisms of glucocorticoid-induced immunosuppression of human monocytes for the defense of Candida albicans were examined in this in vitro study. Dexamethasone at pharmacological concentrations (10-7-10-5M) dose-dependently attenuated growth inhibition of C. albicans by resident monocytes. In interferon-γ (IFN-γ)-primed monocytes, fungal growth inhibition was maximal and not altered by dexamethasone. Similarly, phagocytosis and killing of Candida by monocytes were not affected by steroids. To study the underlying mechanisms, we found that Candida-induced synthesis of tumor necrosis factor-α (TNF-α) by monocytes was completely abrogated by dexamethasone. Substitution of TNF-α to dexamethasone-treated monocytes fully reversed the alterations of growth inhibition of C. albicans induced by steroids. These findings suggest that glucocorticoids affect the growth control of Candida by monocytes indirectly via suppression of the formation of TNF-α, which is required as an autocrine cofactor for full monocyte activation.

Inhibition of interleukin 2-induced proliferation of cloned murine T cells by glucocorticoids. Possible involvement of an inhibitory protein.

The ability of glucocorticoids to inhibit interleukin 2 (IL 2)-induced T cell proliferation in two cytotoxic T cell (CTL) clones has been studied. A complete inhibition of DNA synthesis by dexamethasone (Dx) could be observed when IL 2-depleted cultures of CTL were either incubated for 6 h with the hormone prior to the addition of IL 2 or treated simultaneously with Dx and a low concentration of IL 2. No significant reduction in the number and affinity of IL 2 receptors was seen after 6 h incubation with Dx. The order of potency observed with the different steroids indicated that this inhibitory effect was mediated through binding to a specific glucocorticoid receptor. The action of these hormones possibly involves the synthesis of an inhibitory protein(s), since the presence of cycloheximide during the incubation with Dx prevented the inhibition of DNA synthesis. Furthermore, supernatant from Dx-treated CTL contained a nondialyzable factor which inhibited DNA synthesis and cell growth of CTL clones induced by IL 2. Blocking of IL 2 synthesis and IL 2 receptor formation have been proposed as one of the major mechanisms of glucocorticoid-induced immunosuppression. Our results indicate that these hormones may also affect T cell proliferation by inhibiting IL 2 activity.

Glucocorticoid effects on the production and actions of immune cytokines

The immunosuppressive actions of glucocorticoids form the basis for their use in treatment of autoimmune diseases and prevention of allograft rejection. However, the mechanisms responsible for glucocorticoid-induced immunosuppression are still poorly understood. It is now clear that glucocorticoids do not inhibit all aspects of the immune response and, in some cases, may enhance certain functions of immune effector cells. One example is that of the dramatic increase induced by IFN-γ in the number of IgG Fc receptors on human mononuclear phagocytes, which is enhanced rather than inhibited by glucocorticoids. An aspect of the immune response which appears to be consistently suppressed by glucocorticoids is the production of immune cytokines. Since these hormones appear to be essential mediators for a vigorous immune response, inhibition of their production may be an effective way for glucocorticoids to block the immune response.

Mechanisms of glucocorticoid-induced immunosuppression: Inhibitory effects on expression of fc receptors and production of T-cell growth factor

T-cell growth factor, produced by mitogen or antigen-stimulated spleen cells, is necessary for the proliferation of T-lymphocytes in culture, and may be responsible for clonal expansion of antigen-responsive T-cells. We have found that treatment of Con A-stimulated rat spleen cells or human peripheral mononuclear cells with 100 n M dexamethasone inhibited the production of the growth factor by 95%. This effect was specific for glucocorticoids at physiologic concentrations. Addition of T-cell growth factor completely reversed the inhibition by glucocorticoid of mitogen-induced blastogenesis. We propose that the inhibitory actions of glucocorticoids on antigen- or mitogen-induced T-cell blastogenesis are related to inhibition of production of T-cell growth factor. These inhibitory effects may be responsible for the delay in the primary immune response produced by glucocorticoids. Fc receptors play important roles in phagocytosis and other aspects of immune responses. We have studied the effects of glucocorticoids on Fc receptors on the human progranulocytic cell line HL-60. Treatment of HL-60 cells with dexamethasone for 72 h reduced by 35–50% the number of Fc receptors per cell (normally about 20.000) with no effect on cell viability or proliferation. Overall rates of leucine incorporation were stimulated by 10–20%. A half-maximal response was obtained with 10nM dexamethasone. The effect was specific for glucocorticoids. These findings suggest that an important component in glucocorticoid-induced immunosuppression may be a reduction in Fc receptors.

Glucocorticoids and immune responses

AbstractWe describe a series of investigations on mechanisms of antiinflammatory and immunosuppressive actions of glucocorticoids. Glucocorticoid receptors and primary mechanisms of action have been studied with isolated rat thymus cells. When added to these cells glucocorticoids immediately form cytoplasmic hormone‐receptor complexes which after activation bind to the nuclei where they apparently induce mRNA for specific proteins that rapidly inhibit glucose transport and acetate incorporation into lipids. Protein and RNA metabolism are inhibited more slowly and eventually the cells die. With normal peripheral human lymphocytes, similar but slower effects are produced. A dramatic increase in receptor sites per cell is seen in lymphocytes stimulated with concanavalin A or antigen. This increase is probably associated with preparation for mitosis. We do not find, contrary to widespread belief, that these stimulated cells are insensitive to glucocorticoids. Such insensitivity has been invoked to explain the insensitivity to glucocorticoid suppression of secondary compared to primary immune responses. An alternative explanation emerges from our experiments with T‐cell growth factor. T‐cell growth factor, produced by mitogen or antigen stimulated spleen cells, is necessary for the proliferation of T‐lymphocytes in culture and may be responsible for clonal expansion of antigen‐responsive T‐cells. Treatment of Con A‐stimulated rat spleen cells or human peripheral mononuclear cells with 100 nM dexamethasone inhibits the production of the growth factor by 95%. This effect is specific for glucocorticoids. Addition of T‐cell growth factor completely reverses the inhibition by glucocorticoid of mitogen‐induced blastogenesis. We propose that the inhibitory actions of glucocorticoids on antigen‐ or mitogen‐induced T‐cell blastogenesis are related to inhibition of production of T‐cell growth factor and that the reason the primary immune response is more sensitive to glucocorticoids is that by inhibiting production of T‐cell growth factor, glucocorticoids block the clonal expansion necessary to amplify the primary response. We have also studied effects of glucocorticoids on Fc receptors, which play important roles in phagocytosis and other aspects of immune responses. Treatment of the human progranulocytic cell line HL‐60 with dexamethasone for 72 hours reduces by 35‐50% the Fc receptors per cell with no effect on cell viability or proliferation and slight increase in leucine incorporation. The effect is specific for glucocorticoids. These findings indicate that an important component in glucocorticoid‐induced immunosuppression may be a reduction in Fc receptors, and with the results on T‐cell growth factor, suggest that glucocorticoids regulate immune processes via effects on lymphokines and other immunologically important proteins.