Glucocorticoid-mediated generation of suppressor macrophages with high density Fc gamma RII during acute cold stress

Neuroendocrine Control of Macrophage Development and Function

Macrophages carry out numerous physiological activities that are essential for both systemic and local homeostasis, as well as innate and adaptive immune responses. Their biology is intricately regulated by hormones, neuropeptides, and neurotransmitters, establishing distinct neuroendocrine axes. The control is pleiotropic, including maturation of bone marrow-derived myeloid precursors, cell differentiation into functional subpopulations, cytotoxic activity, phagocytosis, production of inflammatory mediators, antigen presentation, and activation of effector lymphocytes. Additionally, neuroendocrine components modulate macrophage ability to influence tumor growth and to prevent the spreading of infective agents. Interestingly, macrophage-derived factors enhance glucocorticoid production through the stimulation of the hypothalamic–pituitary–adrenal axis. These bidirectional effects highlight a tightly controlled balance between neuroendocrine stimuli and macrophage function in the development of innate and adaptive immune responses. Herein, we discuss how components of neuroendocrine axes impact on macrophage development and function and may ultimately influence inflammation, tissue repair, infection, or cancer progression. The knowledge of the crosstalk between macrophages and endocrine or brain-derived components may contribute to improve and create new approaches with clinical relevance in homeostatic or pathological conditions.

Specific Features of the Hypothalamic Leptin Signaling Response to Cold Exposure Are Reflected in Peripheral Blood Mononuclear Cells in Rats and Ferrets

Objectives: Cold exposure induces hyperphagia to counteract fat loss related to lipid mobilization and thermogenic activation. The aim of this study was investigate on the molecular mechanisms involved in cold-induced compensatory hyperphagia.

Methods: We analyzed the effect of cold exposure on gene expression of orexigenic and anorexigenic peptides, and of leptin signaling-related genes in the hypothalamus of rats at different ages (1, 2, 4, and 6 months), as well as in ferrets. We also evaluated the potential of peripheral blood mononuclear cells to reflect hypothalamic molecular responses.

Results: As expected, cold exposure induced hypoleptinemia in rats, which could be responsible for the increased ratio of orexigenic/anorexigenic peptides gene expression in the hypothalamus, mainly due to decreased anorexigenic gene expression, especially in young animals. In ferrets, which resemble humans more closely, cold exposure induced greater changes in hypothalamic mRNA levels of orexigenic genes. Despite the key role of leptin in food intake control, the effect of cold exposure on the expression of key hypothalamic leptin signaling cascade genes is not clear. In our study, cold exposure seemed to affect leptin signaling in 4-month-old rats (increased Socs3 and Lepr expression), likely associated with the smaller-increase in food intake and decreased body weight observed at this particular age. Similarly, cold exposed ferrets showed greater hypothalamic Socs3 and Stat3 gene expression. Interestingly, peripheral blood mononuclear cells (PBMC) mimicked the hypothalamic increase in Lepr and Socs3 observed in 4-month-old rats, and the increased Socs3 mRNA expression observed in ferrets in response to cold exposure.

Conclusions: The most outstanding result of our study is that PBMC reflected the specific modulation of leptin signaling observed in both animal models, rats and ferrets, which points forwards PBMC as easily obtainable biological material to be considered as a potential surrogate tissue to perform further studies on the regulation of hypothalamic leptin signaling in response to cold exposure.

Protection against renal ischemia-reperfusion injury through hormesis? Dietary intervention versus cold exposure

AIM

Dietary restriction (DR) and fasting (FA) induce robust protection against the detrimental effects of renal ischemia-reperfusion injury (I/RI). Several mechanisms of protection have been proposed, such as hormesis. Hormesis is defined as a life-supporting beneficial effect resulting from the cellular responses to single or multiple rounds of (mild) stress. The cold exposure (CE) model is a stress model similar to DR, and has been shown to have hormetic effects and has proved to increase longevity. CE is considered to be the most robust method to increase metabolism through activation of brown adipocytes. BAT has been considered important in etiology of obesity and its metabolic consequences.

MATERIALS AND METHODS

Since DR, FA, and CE models are proposed to work through hormesis, we investigated physiology of adipose tissue and effect on BAT in these models and compared them to ad libitum (AL) fed mice. We also studied the differential effect of these stress models on immunological changes, and effect of CE on renal I/RI.

KEY FINDINGS

We show similar physiological changes in adiposity in male C57Bl/6 mice due to DR, FA and CE, but the CE mice were not protected against renal I/RI. The immunophenotypic changes observed in the CE mice were similar to the AL animals, in contrast to FA mice, that showed major immunophenotypic changes in the B and T cell development stages in primary and secondary lymphoid organs.

SIGNIFICANCE

Our findings thus demonstrate that DR, FA and CE are hormetic stress models. DR and FA protect against renal I/IR, whereas CE could not.

Direct and indirect suppression of interleukin-6 gene expression in murine macrophages by nuclear orphan receptor REV-ERBα

It is now evident that many nuclear hormone receptors can modulate target gene expression. REV-ERBα, one of the nuclear hormone receptors with the capacity to alter clock function, is critically involved in lipid metabolism, adipogenesis, and the inflammatory response. Recent studies suggest that REV-ERBα plays a key role in the mediation between clockwork and inflammation. The purpose of the current study was to investigate the role of REV-ERBα in the regulation of interleukin-6 (il6) gene expression in murine macrophages. REV-ERBα agonists, or overexpression of rev-erbα in the murine macrophage cell line RAW264 cells, suppressed the induction of il6 mRNA following a lipopolysaccharide (LPS) endotoxin challenge. Also, rev-erbα overexpression decreased LPS-stimulated nuclear factor κB (NFκB) activation in RAW264 cells. We showed that REV-ERBα represses il6 expression not only indirectly through an NFκB binding motif but also directly through a REV-ERBα binding motif in the murine il6 promoter region. Furthermore, peritoneal macrophages from mice lacking rev-erbα increased il6 mRNA expression. These data suggest that REV-ERBα regulates the inflammatory response of macrophages through the suppression of il6 expression. REV-ERBα may therefore be identified as a potent anti-inflammatory receptor and be a therapeutic target receptor of inflammatory diseases.

Stress- and aging-associated modulation of macrophage functions

Effects of environmental (cold) stress and aging on cells in monocyte/macrophage lineage were investigated. We demonstrated that immune suppressive states seen in acute cold-stressed mice (8-10 weeks of age) is attributable to FcγRII(bright) suppressor macrophages. Serum corticosterone levels were markedly increased in acute cold-stressed mice. In addition, expression of glucocorticoids (GC) receptor mRNA was observed in FcγRII(bright) cells from these mice. The increase of FcγRII(bright) cells in peritoneal exudate cells caused by acute cold stress was inhibited by adrenalectomy or administration of a saturating amount of the GC antagonist RU 38486 (mifepristone). On the contrary, administration of the GC agonist, dexamethasone, markedly increased the proportion of FcγRII(bright) cells in peritoneal exudate cells of control mice. These results suggest that the generation of FcγRII(bright) suppressor cells of monocyte/macrophage lineage by acute cold stress was mediated by action of GC through the GC receptor. We likewise found that the proportion of FcγRII(bright) suppressor macrophages is increased in aged mice (22-24 months of age). Meanwhile, activated macrophages which function as antigen presenting cells were decreased in aged rats. Both the basal corticosterone concentrations in serum and the expression of mRNA for GC receptor in peritoneal macrophages increased significantly in aged animals, suggesting that these populational and functional changes of macrophages in aged animals were mediated, in part, by the increased basal levels of GC. This is probably being responsible for immunosenescence.

Enhancing versus suppressive effects of stress on immune function: implications for immunoprotection and immunopathology

Stress is known to suppress immune function and increase susceptibility to infections and cancer. Paradoxically, stress is also known to exacerbate asthma, and allergic, autoimmune and inflammatory diseases, although such diseases should be ameliorated by immunosuppression. Moreover, the short-term fight-or-flight stress response is one of nature's fundamental defense mechanisms that enables the cardiovascular and musculoskeletal systems to promote survival, and it is unlikely that this response would suppress immune function at a time when it is most required for survival (e.g. in response to wounding and infection by a predator or aggressor). These observations suggest that stress may suppress immune function under some conditions while enhancing it under others. The effects of stress are likely to be beneficial or harmful depending on the type (immunoprotective, immunoregulatory/inhibitory, or immunopathological) of immune response that is affected. Studies have shown that several critical factors influence the direction (enhancing vs. suppressive) of the effects of stress or stress hormones on immune function: (1) Duration (acute vs. chronic) of stress: Acute or short-term stress experienced at the time of immune activation can enhance innate and adaptive immune responses. Chronic or long-term stress can suppress immunity by decreasing immune cell numbers and function and/or increasing active immunosuppressive mechanisms (e.g. regulatory T cells). Chronic stress can also dysregulate immune function by promoting proinflammatory and type-2 cytokine-driven responses. (2) Effects of stress on leukocyte distribution: Compartments that are enriched with immune cells during acute stress show immunoenhancement, while those that are depleted of leukocytes, show immunosuppression. (3) The differential effects of physiologic versus pharmacologic concentrations of glucocorticoids, and the differential effects of endogenous versus synthetic glucocorticoids: Endogenous hormones in physiological concentrations can have immunoenhancing effects. Endogenous hormones at pharmacologic concentrations, and synthetic hormones, are immunosuppressive. (4) The timing of stressor or stress hormone exposure relative to the time of activation and time course of the immune response: Immunoenhancement is observed when acute stress is experienced at early stages of immune activation, while immunosuppression may be observed at late stages of the immune response. We propose that it is important to study and, if possible, to clinically harness the immunoenhancing effects of the acute stress response, that evolution has finely sculpted as a survival mechanism, just as we study its maladaptive ramifications (chronic stress) that evolution has yet to resolve. In view of the ubiquitous nature of stress and its significant effects on immunoprotection as well as immunopathology, it is important to further elucidate the mechanisms mediating stress-immune interactions and to meaningfully translate findings from bench to bedside.

Neuroimmune regulation in immunocompetence, acute illness, and healing

Adaptive immunocompetence is maintained by growth hormone (GH), prolactin (PRL), and vasopressin (VP). Innate or natural immunocompetence depends on cytokines, hormones (especially of the hypothalamus-pituitary-adrenal axis), and catecholamines. The acute phase response (APR, or acute febrile illness) is an emergency defense reaction whereby the adaptive, T cell-dependent, immune reactions are suppressed and the innate immune function is dramatically amplified. Infection and various forms of injury induce APR. Cytokines [interleukin (IL)-1beta, tumor necrosis factor-alpha, and IL-6] stimulate corticotropin-releasing hormone (CRH) and VP secretion and cause a "sympathetic outflow." Colony-stimulating factors activate leukocytes. CRH is a powerful activator of the pituitary adrenocortical axis and elevates glucocorticoid (GC) levels. Cytokines, GCs, and catecholamines play fundamental roles in the amplification of natural immune defense mechanisms. VP supports the APR at this stage. However, VP remains active and is elevated for a longer period than is CRH. VP, but not CRH, is elevated during chronic inflammatory diseases. VP controls adaptive immune function and stimulates adrenocorticotropic hormone (ACTH) and PRL secretion. PRL maintains the function of the thymus and of the T cell-dependent adaptive immune system. The ACTH-adrenal axis stimulates natural immunity and of suppressor/regulatory T cells, which suppress the adaptive immune system. VP also has a direct effect on lymphoid cells, the significance of which remains to be elucidated. It is suggested that VP regulates the process of recovery from acute illness.

Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice

Indigenous microbiota have several beneficial effects on host physiological functions; however, little is known about whether or not postnatal microbial colonization can affect the development of brain plasticity and a subsequent physiological system response. To test the idea that such microbes may affect the development of neural systems that govern the endocrine response to stress, we investigated hypothalamic-pituitary-adrenal (HPA) reaction to stress by comparing germfree (GF), specific pathogen free (SPF) and gnotobiotic mice. Plasma ACTH and corticosterone elevation in response to restraint stress was substantially higher in GF mice than in SPF mice, but not in response to stimulation with ether. Moreover, GF mice also exhibited reduced brain-derived neurotrophic factor expression levels in the cortex and hippocampus relative to SPF mice. The exaggerated HPA stress response by GF mice was reversed by reconstitution with Bifidobacterium infantis. In contrast, monoassociation with enteropathogenic Escherichia coli, but not with its mutant strain devoid of the translocated intimin receptor gene, enhanced the response to stress. Importantly, the enhanced HPA response of GF mice was partly corrected by reconstitution with SPF faeces at an early stage, but not by any reconstitution exerted at a later stage, which therefore indicates that exposure to microbes at an early developmental stage is required for the HPA system to become fully susceptible to inhibitory neural regulation. These results suggest that commensal microbiota can affect the postnatal development of the HPA stress response in mice.

Elevated IL-1beta contributes to antibody suppression produced by stress

Acute stressor exposure can facilitate innate immunity and suppress acquired immunity. The present study further characterized the potentiating effect of stress on innate immunity, interleukin-1beta (IL-1beta), and demonstrated that stress-induced potentiation of innate immunity may contribute to the stress-induced suppression of acquired immunity. The long-term effect of stress on IL-1beta was measured by using an ex vivo approach. Sprague-Dawley rats were challenged with lipopolysaccharide (LPS) in vivo, and the IL-1beta response was measured in vitro. Splenocytes, mesenteric lymphocytes, and peritoneal cavity cells had a dose- and time-dependent ex vivo IL-1beta response to LPS. Rats that were exposed to inescapable shock (IS, 100 1.6 mA, 5-s tail shocks, 60-s intertrial interval) and challenged with a submaximal dose of LPS 4 days later had elevated IL-1beta measured ex vivo. To test whether the acute stress-induced elevation in IL-1beta contributes to the long-term suppression in acquired immunity, IL-1beta receptors were blocked for 24 h after stress. Serum anti-keyhole limpet hemocyanin (KLH) immunoglobulin (Ig) was measured. In addition, the acute elevation (2 h post-IS) of splenic IL-1beta in the absence of antigen was verified. Interleukin-1 receptor antagonist prevented IS-induced suppression in anti-KLH Ig. These data support the hypothesis that stress-induced increases in innate immunity (i.e., IL-1beta) may contribute to stress-induced suppression in acquired immunity (i.e., anti-KLH Ig).

Activation and apoptosis of murine peritoneal macrophages by acute cold stress

Effects of acute cold stress (5 degrees C for 24 h) on the functions of peritoneal macrophages and the mechanisms for controlling host homeostasis were investigated in mice. Phagocytic activity and expression of the cell surface adhesion molecule CD11b/CD18 were markedly increased in peritoneal exudate cells by acute cold stress. These alterations were attributable to an increased number and phenotypical changes of adherent cells from acute cold-stressed mice. On the other hand, a lipopolysaccharide-induced activity of src-family tyrosine kinase Fgr, an expression of interleukin-1beta (IL-1 beta) mRNA, and a bioactivity of IL-1 in the culture supernatants of adherent cells from acute cold-stressed mice were markedly lower than those from control mice. A time course study revealed that the number of adherent cells in peritoneal exudate cells was markedly increased in mice exposed to cold for 24 h but returned to normal numbers when mice were exposed to cold for 72 h. DNA fragmentation and Annexin-V(+) cells were observed in peritoneal exudate cells from acute-cold stressed mice. Thus, cold stress activated macrophages but these macrophages were destined to be eliminated by apoptosis.

The effect of vitamin D3 on resistance to stress-related infection in an experimental model of turkey osteomyelitis complex

Male turkeys immunosuppressed by injection with dexamethasone (DEX) were given supplemental vitamin D3 in their drinking water in two experiments. In Experiment 1, vitamin D3 was supplemented at a dosage of either 2,064 IU/kg (low level) or 4,128 IU/kg (high level) in drinking water provided ad libitum only from Days 1 through 5 after hatch. In Experiment 2, vitamin D3 was provided at the low dosage for the first 5 d after hatch, followed by treatment with the high dosage for 12 h before and 12 h after each stressful event, which included weekly weighings and two DEX treatments. In both experiments, at 5 wk of age half of the birds were given intramuscular injections of 2 mg/kg DEX on 3 alternating d. In Experiment 1, 100 cfu of Escherichia coli was inoculated into the left thoracic airsac at the time of the third DEX injection. All mortalities were examined, and 10 birds per pen were necropsied 2 wk after treatment and examined for lesions of airsacculitis and turkey osteomyelitis complex (TOC). Four birds per pen were bled before necropsy, and white blood cell total counts, differential white blood cell counts, and clinical chemistry values were determined. In Experiment 2, healthy surviving birds were grown for an additional 5-wk period, after which the DEX-treated birds were given a second series of DEX injections and were bled and necropsied 2 wk later. There were no significant effects of vitamin D3 treatment in combined general linear models analysis of Experiment 1; however, when birds not treated with DEX or E. coli were compared with those treated with both DEX and E. coli, supplementation with the low level of vitamin D3 significantly decreased TOC incidence. There were no significant effects of vitamin D3 treatment in birds treated with DEX at 5 wk of age in Experiment 2. However, when surviving birds were given a second DEX treatment at 12 wk, vitamin D3 treatment resulted in significantly lower incidence of mortality, TOC, green liver, isolation of bacteria from tissues, and lower airsacculitis scores and heterophil-to-lymphocyte ratios than controls. Vitamin D3 also improved BW, relative weights of the liver and heart, and serum levels of glucose and alanine aminotransferase (ALT) of birds receiving two treatments with DEX. The ability of vitamin D3 supplementation to protect turkeys from the immunosuppressive effects of multiple DEX treatments emphasizes the role of vitamin D3 as a prohormone that affects health and disease resistance in turkeys.

Stress-induced enhancement of skin immune function: A role for gamma interferon

Contrary to the widespread belief that stress is necessarily immunosuppressive, recent studies have shown that, under certain conditions, stress can induce a significant enhancement of a skin cell-mediated immune response [delayed-type hypersensitivity (DTH) or contact hypersensitivity]. Adrenal stress hormones and a stress-induced trafficking of leukocytes from the blood to the skin have been identified as systemic mediators of this immunoenhancement. Because gamma interferon (IFNgamma) is an important cytokine mediator of DTH, the studies described here were designed to examine its role as a local mediator of the stress-induced enhancement of skin DTH. The effect of acute stress on skin DTH was examined in wild-type and IFNgamma receptor-deficient (IFNgammaR-/-) mice that had previously been sensitized with 2,4-dinitro-1-fluorobenzene. Acutely stressed wild-type mice showed a significantly larger DTH response than nonstressed mice. In contrast, IFNgammaR-/- mice failed to show a stress-induced enhancement of skin DTH. Immunoneutralization of IFNgamma in wild-type mice significantly reduced the stress-induced enhancement of skin DTH. In addition, an inflammatory response induced by direct IFNgamma administration to the skin was significantly enhanced by acute stress. Our results suggest that IFNgamma is an important local mediator of a stress-induced enhancement of skin DTH. These studies are clinically relevant because, depending on the nature of the antigen, DTH reactions mediate numerous protective (e.g., resistance to viral, bacterial, parasitic, and fungal infections) or pathological (e.g., autoimmune reactions and contact sensitivity reactions such as that to poison ivy) immune responses.

Influence of psychosocial, psychogenic and neurogenic stressors on several aspects of immune functioning in mice

Analysis of stressor effects on immune functioning is complicated by the fact that the nature of the changes observed may be influenced by organismic factors (e.g., species, strain, age), the nature, severity and chronicity of the stressor, as well as the specific immune parameters being examined. It is demonstrated in the present investigation that in the highly reactive inbred BALB/cByJ mouse, the relatively hardy C57BL/6ByJ strain, as well as in the noninbred CD-1 strain, acute psychogenic (predator exposure) and neurogenic (footshock) stressors reduced splenic macrophage activity, and this effect was less marked after a chronic stressor. With protracted, but not transient, psychosocial disturbances (isolated housing) similar effects were seen, suggesting that the effect was not simply due to a change of the social mileau. The psychogenic and neurogenic stressors also enhanced LPS-stimulated lymphocyte proliferation in CD-1, but not in the inbred strains. However, isolated housing reduced both B and T cell proliferation, indicating that social isolation likely affects processes distinct from those of other stressors. Interestingly, when the aversiveness of the psychogenic stressor was increased (by decreasing the distance between the rat and the mouse) LPS-stimulated lymphocyte proliferation was reduced in the reactive BALB/cByJ strain, but increased in the hardy C57BL/6ByJ mice. This stressor, however, enhanced T cell proliferation in both strains of mice. It is suggested that analysis of stressor effects need to consider in greater detail the characteristics of the organism being stressed, as well as the characteristics of the stressor itself.

Glucocorticoids modulate the development of dendritic cells from blood precursors

Dendritic cells (DC) are professional antigen-presenting cells, capable of priming naive T cell responses. Glucocorticoids (GC) are frequently used in asthmatic patients. In this study we describe the effects of GC on the development and function of monocyte-derived DC (MoDC) in vitro and in vivo. Monocytes from healthy individuals were isolated and incubated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 for 6 days, to induce maturation into MoDC. To study the role of GC on DC differentiation in vitro cells were incubated with dexamethasone at different stages of MoDC development. At day 6 cells were characterized phenotypically by flow cytometry and functionally in an allogeneic mixed leucocyte reaction. To study the effect of GC in vivo patients with mild/moderate atopic asthma were selected. In one group no GC were used, whereas the other group used inhalation GC. MoDC from these patients were generated as described above and tested functionally. Incubation of MoDC or its peripheral blood precursors with dexamethasone decreased the accessory potency dose-dependently. The functional differences could not be explained by the changes in the expression of MHC II and the costimulatory molecules CD40 and CD86. The relevance of this mechanism was confirmed for the in vivo situation as well. MoDC from patients using inhalation GC showed a decreased accessory potency. These data suggest a modulatory effect of GC therapy at the level of the peripheral blood monocyte. The results indicate that GC influence DC development and function in vitro as well as in vivo.

Influence of a psychogenic and a neurogenic stressor on several indices of immune functioning in different strains of mice

It is demonstrated that cell proliferation in response to mitogens, natural killer cell (NK) activity, and macrophage functioning of mice may be influenced by either a neurogenic stressor (footshock) or a psychogenic stressor (exposing the mouse to a predator, namely a rat). The nature and magnitude of the immune changes, however, varied across three strains of mice (BALB/cByJ, C57BL/6ByJ, and CD-1), differing in reactivity to stressors and also as a function of the type of stressor employed. While footshock reduced mitogen-stimulated B-cell proliferation in BALB/cByJ mice, it had the opposite effect in the CD-1 strain. Exposure to the predator, however, had little effect in any of the strains. Macrophage activity and NK cytotoxicity were reduced in response to both stressors in a strain-dependent fashion. Plasma corticosterone in response to footshock was greater in BALB/cByJ than in C57BL/6ByJ mice; however, the strain difference was not evident in response to the psychogenic stressor. It is suggested that analyses of stressor effects on immune functioning need to consider the specific strain/species employed, the particular immune parameters being examined, and the nature of the stressor employed.

An increase in basal glucocorticoid concentration with age induces suppressor macrophages with high-density Fc gamma RII/III

Ageing is usually accompanied by a decline in immune and neuroendocrine functions. To elucidate the mechanisms underlying age-related immunosuppression, the functions and surface phenotypes of peritoneal cells in the monocyte/macrophage lineage from old mice were investigated. The role of glucocorticoids (GC) in the immunomodulation was also examined. Proliferative responses of spleen cells from control mice stimulated with concanavalin A (Con A) were significantly suppressed by adding peritoneal exudate cells from old mice. Flow cytometry analysis revealed that the proportion of MAC-1+ cells with a high density of type II or type III receptor for the Fc portion of IgG (Fc gamma RII/IIIbright cells) was increased markedly in the periotoneal exudate cells from old mice. The prominent suppressor activity for Con A responses of control spleen cells was found in the Fc gamma RII/IIIbright cells, whereas MAC-1+ cells with a low density of Fc gamma RII/III (Fc gamma RII/IIIdull cells) did not suppress the Con A responses. On the other hand, both the basal corticosterone concentrations in serum and the mRNA expression for GC receptor in peritoneal exudate cells increased significantly in old mice. Furthermore, the proportion of Fc gamma RII/IIIbright cells in peritoneal exudate cells from old mice was normalized on administration of the GC antagonist RU 38,486 (mifepristone). These results suggest that the increase in basal corticosterone concentrations in old mice induces the generation of Fc gamma RII/IIIbright suppressor cells, possibly leading to the immune-suppressive state.

Relationship between cold tolerance and generation of suppressor macrophages during acute cold stress

Acute cold stress induces suppressor macrophages expressing large numbers of receptors to the crystallizable fragment (Fc) portion of immunoglobulin G (MAC-1+ FcgammaRII/IIIbright cells), resulting in the immunosuppression of splenocyte mitogenesis. The generation of MAC-1+ FcgammaRII/IIIbright cells is mediated by the action of glucocorticoids (GCs) through the GC-receptor. In the present study, the generation of MAC-1+ FcgammaRII/IIIbright cells in peritoneal exudate cells was closely related to the decrease of rectal temperature during 3-day exposure to 5 degrees C. We next investigated the effects of improved cold tolerance on the generation of MAC-1+ FcgammaRII/IIIbright cells during acute cold stress. Mice were adapted to cold by exposure to 5 degrees C for 3 wk (cold-acclimated mice) and then reexposed to 5 degrees C for 3 h (acute cold stress) after living at 25 degrees C for 24 h. The rectal temperature of cold-acclimated mice was not decreased by the acute cold stress. In addition, the proportion of MAC-1+ FcgammaRII/IIIbright cells in peritoneal exudate cell population from cold-acclimated mice was unaffected by the acute cold stress. The cold acclimation significantly attenuated the increases in serum corticosterone levels and the expression of the GC-receptor mRNA on peritoneal exudate cells in response to acute cold stress. These results suggest that the altered GC response to acute cold stress by the improvement of cold tolerance inhibits the generation of suppressor macrophages during acute cold stress.