Characterization of macrophage subsets regulating murine natural killer cell activity

Arachidonic acid metabolism in TNS-induced chronic and immunologic enteritis in rats, and the effect of 5-ASA

Inflammation of the rat distal intestine was induced by intradermal sensitization and subsequent multiple intrajejunal challenge with the hapten 2,4,6-trinitrobenzenesulphonic acid (TNBS) via an implanted catheter. The time course of the inflammatory reaction was followed by determination of the enteritis score and measurement of in vitro eicosanoid formation of homogenates of the gut after 0, 1, 2, 4, 7, 14 and 21 days of local daily challenge with 0.08% TNBS. There was a small initial increase of eicosanoid formation, reached at days 1 and 2, followed by a significant increase in metabolism of arachidonic acid on day 21. Although at day 1 a four-fold increase in inflammation score was reached, no further significant changes were observed during the following 3 weeks. The greatest increase in metabolite formation was observed in prostanoids TxB₂, PGE₂. and PGD₂ and the 5-lipoxygenase product LTC₄, whereas minor changes were found for LTB₄ and other lipoxygenase products such as 12- and 15-HETE. The formation of these metabolites was already inhibited by low-dose 5-aminosalicylic acid (5-ASA), given orally twice daily during the 3 weeks challenge period, while the enteritis score was affected dosedependently.

Mechanism of pentoxifylline mediated down-regulation of killer lineage cell functions

The authors reported recently that endotoxaemia mediated elevated levels of tumour necrosis factor (TNF-α) and interleukin-1α (IL-1α) were involved in the pathophysiology of acute heat stroke patients. Pentoxifylline (PTX) is known to modulate neutrophil functions. In the present study the effects of PTX on lipopolysaccharide (LPS) and cytokine induced T-cell and macrophage (ΦM) activation, and on natural killer (NK) cell and lymphokine activated killer (LAK) cell mediated cytotoxicity were examined. Finally, the effect of PTX on the expression of adhesion molecules (LFA-1, Mac-1 and ICAM-1), and cytokine (IL-1α, IL-2, TNF-α, IL-6 and IFN-γ) production and their surface receptor expression in response to LPS activation was investigated. PTX free cultures served as a control. Results revealed that PTX can down-regulate all the above-mentioned immunological parameters in a dosedependent manner. These findings might have far reaching clinical implications.

Oral Administration of Aqueous Extract ofCarthami FlosInduces Macrophage Activation and Preferentially Potentiates Type 1 Helper T-Cell ResponseIn Vivo

In vivo immunomodulatory activity of aqueous extract of Carthami Flos (AECF) was investigated using a mouse model immunized with keyhole limpet hemocyanin. Serum level of Ag-specific IgG2a was significantly elevated by oral administration of AECF but not IgG1. However, no selective B-cell proliferation by AECF was observed in vivo. Ag-specific proliferation and IFN-gamma and IL-5 production of draining lymph node T cells also was higher in AECF-treated mice when compared with water-treated control mice. However, AECF failed to enhance nonspecific T-cell response under CD3 stimulation. These results led us to hypothesize that AECF potentiates Ag-specific T-cell response, possibly through activation of antigen presenting cells (APC) other than B cells. Functional assessment of splenic macrophages showed that AECF administration significantly enhances IL-12 production as well as APC activity for IFN-gamma production and STAT-4 activation by T cells. Collectively, these data strongly support that AECF preferentially potentiates immune response polarized toward TH1 and for which increased activation of macrophages is most likely to be responsible. The present data implicate a possible application of AECF to potentiate cellular immunity and, we hope, prevent intracellular infections.

Increased IL-12 P40 homodimer secretion by spleen cells during in vivo growth of the BW-19 T cell hybridoma accompanies suppression of natural immunity

The high capacity of the T cell hybridoma BW-19 to metastasize to the spleen, despite its high and moderate sensitivity to lysis by macrophages and natural killer (NK) cells, respectively, appears to be linked to its capacity to suppress local resident NK cell and macrophage activity. Such suppression of splenic NK cell and macrophage activity is accompanied by an increased production of the p40 subunit of interleukin-12 (IL-12) by spleen cells. Closer examination revealed that most of the p40 subunit is present under the form of the homodimer (p40)2, whereas the heterodimeric form of IL-12 is present only in small amounts. Since (p40)2 is known to be a strong antagonist of IL-12-mediated effects, i.e., NK cell activation and interferon-gamma (IFN-gamma) secretion, the increased production of (p40)2 after BW-19 cell inoculation may contribute to the suppression of NK cell and macrophage activity. In addition, we found that the high production of (p40)2 in our tumor model was accompanied by a drastic decrease in IL-2 and IFN-gamma production by spleen cells, further favoring the possibility that (p40)2 plays a role in the suppression of NK cell and macrophage cytotoxicity. Our results show that normal spleen cells can produce (p40)2 in response to cancer cell growth in vivo and are highly suggestive of a role for (p40)2 in the suppression of natural immunity.

In vitro effects of prostaglandin E2 or indomethacin on the proliferation of lymphokine-activated killer cells and their cytotoxicity against bladder tumor cells in patients with bladder cancer

PURPOSE

To investigate the combined effects of interleukin-2 (IL-2) with either prostaglandin E2 (PGE2) or indomethacin (IM) on the proliferation and cytolysis of bladder tumor cells by lymphokine-activated killer (LAK) cells in patients with bladder cancer.

METHODS

LAK cell proliferation was assayed in the presence of various concentrations of either PGE2 or IM by cell counting. Bladder cancer cell lines BIU-87, EJ and bladder tumor cells (BTC) from the patients were cultured as target cells, and the cytotoxicity of LAK cells was determined by 3-(4.5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In addition, PGE2 in samples of conditioned medium from bladder cancer cells or peripheral blood mononuclear cells (PBMC) as well as plasma from 21 patients with bladder cancer and 20 healthy donors were determined by radioimmunoassay (RIA).

RESULTS

The proliferation of LAK cells induced by IL-2 was inhibited by PGE2 (0.05 to 5 ng/mL) in concentration-dependent manner. The enhanced growth of LAK cells was observed at certain concentrations of IM (100-400 ng/mL) from 48 to 96 h. Pretreatment of LAK cells with IM (200 ng/mL) significantly enhanced cytotoxicity against BIU-87, EJ cells, or BTC. More PGE2 was present in conditioned medium from BIU-87 cells than in the conditioned medium from PBMC.

CONCLUSIONS

These studies indicate that LAK cell proliferation induced by IL-2 in patients with bladder cancer is inhibited by PGE2 produced by PBMC and bladder cancer cells. This inhibition can be overcome by IM, which may be of use in immunotherapy of bladder cancer.

Modulation of NK cell cytolytic activity by macrophages in chronically exercise-stressed mice

This study was designed to investigate the effects of moderate-intensity endurance training on basal natural killer (NK) cell cytolytic activity in murine splenocytes that were enriched for 1) NK1.1+ cells or 2) macrophages and NK1.1+ cells. Mice were assigned to sedentary (Sed), treadmill control (TM), or treadmill-trained (Trn) groups. Splenocyte number, the percentages of NK1.1+, large granular lymphocytes (NK1.1+, LGL-1+), and other subpopulations did not change in Trn mice. Approximately 70% of cells enriched for NK1.1+ expressed this surface antigen. Lytic units (LU) expressed per LGL-1+ cell were significantly lower in Trn [83.9 +/- 3.2 (SE)] compared with Sed (109.5 +/- 7.5) and TM (101.3 +/- 6.4) groups. When macrophages remained in the in vitro assay, LU per LGL-1(+) cell did not differ across groups. The results indicate that highly enriched NK1.1+ cells from Trn mice had lower NK cell activity compared with Sed mice. No differences in NK cell activity were observed when cells were enriched for NK1.1+ cells and macrophages. These findings support the hypothesis that macrophage modulation of NK cells may be one mechanism contributing to augmented basal NK cell activity in endurance-trained individuals.

Enhanced Kupffer cell activity after repeated hepatic arterial ischaemia in an experimental model

Kupffer cells are important for host defence against both foreign invaders and neoplasia. Several studies have demonstrated that ischaemia and reperfusion activates Kupffer cells. The effect of hepatic arterial ischaemia on Kupffer cell function was assessed using blood clearance and organ uptake of radiolabelled Escherichia coli. Transient ischaemia for 1 h did not alter Kupffer cell function in comparison with sham operation. However, prolonging arterial ischaemia for 2 h stimulated Kupffer cell function; both the phagocytic index and liver uptake of radiolabelled E. coli increased significantly (P < 0.01). Furthermore, this enhanced Kupffer cell activity was achieved each time the ischaemia was induced over a period of 5 days compared with repeated sham procedures (P < 0.05). Serum tumour necrosis factor (TNF) was significantly released after both single and repeated arterial occlusion for 2 h (P < 0.01). These observations show that transient arterial ischaemia enhances Kupffer cell function and induces TNF production.

Immunophenotyping of murine peritoneal macrophages and lymphocytes by flow cytometry

Peritoneal cells include mainly macrophages and both T and B lymphocytes. We describe a simple procedure to analyze by flow cytometry the antigens expressed on macrophage and/or lymphocyte membranes. F4/80 and CR3 macrophage antigens were detected with anti-F4/80 and anti-Mac-1 monoclonal antibodies (mAb) respectively, CD4 and THY1.2 T lymphocyte antigens with GK1.5 and J1j mAbs respectively, B CD5 lymphocytes were identified with LY1.2 mAb and Fc gamma RII/Fc gamma RIII were detected with 2.4G2 mAb.

Alveolar macrophage inhibition of lung-associated NK activity: involvement of prostaglandins and transforming growth factor-beta 1

Natural killer (NK) activity plays an important role in host defense. It is likely that this defensive role is shaped by compartmental and local environmental factors. The present study investigated the regulatory effects of alveolar macrophages (AM) on lung-associated NK activity. AM and lung lymphocytes (LL) were permitted to interact in a two-chamber system which prohibited cell contact but supported diffusion of soluble factors. AM were found to inhibit NK activity from LL in a time-dependent and reversible manner. The inhibitory event was shown to be mediated by soluble factors acting upon a post-binding event(s) in the lytic pathway of LL. AM inhibition was sensitive to indomethacin treatment (10(-5) M), which caused a decrease in prostaglandin E2 (PGE2) concentrations. Quantitation of PGE2 levels and treatment of LL with exogenous PGE2 indicated that the inhibitory effect could not be exclusively due to PGE2. It was subsequently found that exogenous transforming growth factor-beta 1 (TGF-beta 1) also inhibited LL NK activity and that treatment of inhibitory AM supernatant with a neutralizing antibody to TGF-beta 1 adsorbs up to 55% of its inhibitory activity. Moreover, the amount of TGF-beta 1 found in AM-LL co-culture media (25 pg/mL) correlated well with the level of NK inhibition observed. By contrast, platelet-derived growth factor and nitric oxide did not play a significant role in mediating AM suppression. Taken together, the data suggest that AM inhibit lung NK activity by interfering with post-binding lytic event(s) through the production of PGE2 and TGF-beta 1.

Inhibition of spontaneous and mitogen-induced lymphocyte proliferation by murine bone marrow-derived macrophages: role of prostaglandins, nitric oxides and cell-to-cell contact

Spontaneous and mitogen-stimulated proliferation of spleen lymphocytes was inhibited by coculturing the cells with murine bone marrow derived macrophages (BM-M phi). The inhibitory effect was found to be dependent on the maturation stage of BM-M phi reflected by the appearance of the phenotype BM 8 and on the number of BM-M phi added to the lymphocytes. The spontaneous proliferation was only inhibited by the addition of high numbers of BM-M phi of late maturation stage. The lipopolysaccharide (Lps) induced response was strongly suppressed by increasing proportions of BM-M phi of either cultivation stage. The suppressive effect on the concanavalin A (Con A)-induced proliferative activity increased with the maturation of the macrophages. Inhibition of prostanoid release with indomethacin had no effect. Blocking of nitric oxide synthesis partially reversed the inhibitory effect of macrophages mainly on the Con-A response. Addition of culture supernatant of BM-M phi to the lymphocytes did not mimic the effect of the macrophages themselves. BM-M phi only slightly inhibited the proliferation when lymphocyte-BM-M phi cell-to-cell contact was prevented. These results show that BM-M phi differently influence the spontaneous and mitogen-induced lymphoproliferation and that the inhibitory effect of BM-M phi on the lymphocyte proliferation is only partially mediated by secretory products of macrophages but apparently requires cell-to-cell contact between both cell types.

Interferon-gamma-activated immature macrophages exhibit a high Trypanosoma cruzi infection rate associated with a low production of both nitric oxide and tumor necrosis factor-alpha

Murine peritoneal macrophages (MPM) can be subdivided into two subpopulations of mature and immature macrophages. In contrast to mature macrophages, immature ones were highly susceptible to Trypanosoma cruzi infection. This highly susceptibility was associated with a low production of alpha 2-macroglobulin. Interferon-gamma (IFN-gamma)-activated immature macrophages also exhibited a higher infection rate than did IFN-gamma-activated mature ones. This higher rate of infection was associated with a low production of both nitric oxide (N = O) and tumor necrosis factor-alpha (TNF-alpha). In contrast, mature MPM showed a lower rate of infection and produced higher levels of N = O and TFN-alpha. Taken together, these results show a clear-cut difference in the course of T. cruzi infection in relation to the macrophage maturation state.

Elevated prostaglandin E2 production by monocytes is responsible for the depressed levels of natural killer and lymphokine-activated killer cell function in patients with breast cancer

BACKGROUND

Human natural killer (NK) cells mediate spontaneous cytotoxicity against tumor cells and represent the main precursors of lymphokine-activated killer (LAK) cell activity. A comparison of some aspects of NK and LAK cell activity was undertaken in 85 preoperative patients with breast cancer and 75 healthy donors.

METHODS

NK cell activity (tested in 18-hour cultures of effector peripheral blood mononuclear cells [PBMC] with K562 or MOLT-4 tumor target cells) was significantly diminished in these patients as it was the fully mature LAK cell activity (i.e., interleukin-2 (IL-2)-induced cytotoxicity in PBMC) against NK resistant target cells. Using immunoenzymatic methods we showed that the reduced NK cell activity was due to abnormally high levels of prostaglandin E2 (PGE2) produced by monocytes in culture.

RESULTS

PGE2 was found to suppress the production of IL-2 in these cultures. Removal of monocytes from PBMC restored to almost normal levels the deficient NK and LAK cell activity in patients with breast cancer and was also associated with a normalization in the levels of PGE2 and IL-2. Indomethacin and gamma-interferon (IFN-gamma) increased the NK and LAK cell activity in these patients up to the levels of healthy donors. When highly purified CD56+ cells (obtained by an immunomagnetic isolation technique) were used as effector cells, no differences in LAK cell activity could be noticed between healthy donors and patients with cancer. FACS and northern blot analyses demonstrated a PGE2-mediated down-regulation of IL-2 receptor (IL-2R) expression on CD56+ cells that correlated with reduced LAK cell activity. This inhibitory effect of PGE2 was noticeable in long-term LAK cultures and was abrogated in the presence of IFN-gamma or indomethacin.

CONCLUSION

This study may have important implications in the potentiation of NK and LAK cell activity for immunotherapeutic protocols in patients with breast cancer.

Tumor-induced modulation of macrophage class II MHC molecule mRNA expression

Class II MHC protein expression in macrophages (M phi) is reduced during tumor growth. Because regulation of class II MHC proteins occurs during transcription, tumor growth may suppress class II MHC protein expression by suppressing mRNA. The decrease in class II mRNA may result from (i) a decrease in M phi responsiveness to an inducing agent, such as interferon-gamma (IFN-gamma), or (ii) an increase in M phi sensitivity to suppressing agents, such as prostaglandin E2 (PGE2). To determine how tumors induce suppression of class II mRNA, M phi were cultured in the presence of IFN-gamma with or without other factors, and Northern blot analyses were performed. Unstimulated normal host (NH) or tumor-bearing host (TBH) M phi do not express detectable class II mRNA. The addition of IFN-gamma induces class II mRNA expression in NH and TBH M phi, but class II mRNA expression is significantly lower in TBH M phi. Kinetic studies suggested that NH M phi class II mRNA is induced faster and in greater amounts than TBH M phi class II mRNA. There is a decrease in M phi class II mRNA stability during tumor growth that may account for the decreased induction by IFN-gamma. Lipopolysaccharide (LPS) suppresses class II mRNA induction in both NH and TBH IFN-gamma-treated M phi, but TBH M phi are more sensitive to its suppression. PGE2 and tumor-necrosis factor-alpha (TNF-alpha), two factors produced by LPS-stimulated M phi, were tested for their ability to modulate class II mRNA expression in NH and TBH IFN-gamma-treated M phi. PGE2 suppressed class II mRNA expression in both NH and TBH M phi. The addition of TNF-alpha to IFN-gamma-treated M phi suppressed class II mRNA in NH M phi but, surprisingly, had an additive effect on IFN-gamma-induced class II mRNA expression. TNF-alpha did not induce class II mRNA expression in TBH M phi in the absence of IFN-gamma. The cause of the reduced class II mRNA expression during tumor growth is a decreased response to IFN-gamma and an increased sensitivity to PGE2. This change may cause the observed suppression mediated by TBH M phi.

Effects of histamine type-2 receptor antagonists on indomethacin and IL-2 immunotherapy of metastasis

Histamine type-2 receptor antagonists (H-2RA) have been used chronically to prevent dyspepsia in cancer patients subjected to immunotherapy with chronic indomethacin (Indo) and intermittent IL-2 in our cancer centre. We tested the effects of these agents during immunotherapy of C3H/HeJ mice transplanted s.c. with 5 x 10(5) C3L5 mammary adenocarcinoma cells. Tumor-transplanted mice were divided into groups receiving: (1) Indo (14 micrograms/ml); (2) H-2RA, i.e. (a) ranitidine at 28.6 micrograms/ml (Ran-lo) or 143 micrograms/ml (Ran-hi), or (b) famotidine (Fam) at 4.3 micrograms/ml, or (c) cimetidine (Cim) at 107 micrograms/ml, all in the drinking water on days 5-24; (3) IL-2 (1.5 x 10(3) Cetus U i.p. every 8 h on days 10-14 and 20-24); (4) combinations of H-2RA + Indo; or (5) combinations of H-2RA + Indo + IL-2. Animals were killed on day 24 for examination of primary s.c. tumor growth, secondary lung metastasis and splenocyte cytotoxicity against YAC-1 lymphoma cells (51Cr release assay). Results revealed: (1) primary tumor growth was reduced in mice treated with Fam + Indo, Indo + IL-2 and any of the H-2RA + Indo + IL-2 (no difference observed within the last two groups); (2) lung metastases decreased in mice treated with IL-2 alone, Indo + IL-2, and Indo + IL-2 + Ran-hi; (3) splenic cytotoxicity was suppressed in tumor-bearing controls, with partial restoration seen in Ran (both doses), Ran-lo + Indo, Ran-lo + Indo + IL-2, and Cim + Indo + IL-2 treated groups. Nearly complete restoration was seen in Cim, Cim + Indo, Indo + IL-2, Ran-hi + Indo + IL-2, and Fam + Indo + IL-2 groups. Thus, addition of H-2RA did not alter the overall therapeutic efficacy of the standard Indo + IL-2 tumor immunotherapy.

Interferon-gamma reduces tumor-induced Ia- macrophage-mediated suppression: role of prostaglandin E2, Ia, and tumor necrosis factor-alpha

Tumor growth enhances macrophage (M phi) suppressor activity by causing M phi to increase synthesis of inhibitory molecules such as prostaglandin E2 (PGE2) or decreasing their expression of up-regulatory molecules such as the class II MHC protein Ia. Although these tumor-induced changes are correlated, it is unknown whether tumor-bearing host (TBH) Ia- M phi become more suppressive by increasing their PGE2 synthesis. To assess the role of PGE2 in tumor-induced Ia- M phi-mediated suppression of CD4+ T-cell alloreactivity, unseparated (Ia(+)-enriched) or Ia(+)-depleted (Ia-) populations of murine normal host (NH) or TBH splenic M phi were added to mixed lymphocyte reaction (MLR) cultures. NH or TBH Ia- M phi were significantly more suppressive than their respective unseparated populations, and TBH Ia- M phi were more suppressive than their NH counterparts. When PGE2 production was blocked with indomethacin, TBH Ia- M phi-mediated suppression was reduced more than suppression mediated by all other M phi populations. A PGE2-specific ELISA showed more PGE2 in Ia- M phi-containing cultures than in those with whole M phi and more in cultures containing TBH Ia- M phi than in their NH counterparts. Because interferon-gamma (IFN-gamma) is a potent M phi activation molecule that regulates both Ia expression and PGE2 production, the effects of IFN-gamma on tumor-induced Ia- M phi-mediated suppression were investigated. Exogenous IFN-gamma reduced suppression mediated by all M phi populations except NH unseparated M phi. IFN-gamma suppressed alloreactivity without M phi or with NH unseparated M phi. Suppression mediated by NH or TBH Ia-, and TBH unseparated M phi was also reduced when M phi were pre-incubated with IFN-gamma before their addition to MLR cultures. IFN-gamma addition did not block Ia- M phi-mediated suppression by decreasing M phi PGE2 production. In fact, IFN-gamma addition increased PGE2 production two-fold in MLR cultures. However, IFN-gamma partly reduced suppression mediated by exogenous PGE2 added to M phi-depleted cultures. Cytofluorometric analysis showed that IFN-gamma increased the percentage of Ia+ M phi in NH and TBH Ia- M phi populations. Blocking TNF-alpha activity with anti-TNF-alpha antibodies caused IFN-gamma to suppress alloreactivity in all M phi-added cultures. Collectively, these data show that tumor-induced suppression mediated by Ia- M phi is caused by increased PGE2 synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Pancreas-specific venular labeling by monastral blue B in the BB rat: modulation by prostaglandins and their inhibitors

Leaky blood vessels in the microcirculation can be detected in vivo by injecting an animal with colloidal pigments like Monastral blue B (MbB). We have previously used this labeling method in the BB rat, an animal model of spontaneous autoimmune diabetes, and detected increased vascular permeability restricted to the venules of the pancreas. The earlier data suggested that pancreata of animals susceptible to labeling contain trapped intravascular monocytes that are activated to release vasoactive mediators after phagocytosis of MbB. To explore these observations further, we investigated the effects of prostaglandins on this system. Prostaglandins are known to be important mediators of inflammatory responses and to modulate the expression of disease in other animal models of autoimmunity. We now report that MbB-induced pancreatic labeling is modulated by misoprostol (an analogue of prostaglandin E1), prostaglandins of the E series, and inhibitors of prostaglandin synthesis. The nonsteroidal anti-inflammatory drugs ibuprofen and ketorolac both reduced the intensity of labeling in susceptible BB rats in a dose dependent manner. In contrast, both misoprostol and prostaglandin E2 given at low doses induced pancreatic permeability in the labeling-resistant Wistar Furth rat. To extend this finding, we also tested much higher drug doses, since at high concentrations, E series prostanoids exert anti-inflammatory effects. We observed that large doses of prostaglandin E1, prostaglandin E2, and misoprostol all suppressed labeling in the BB rat. We conclude that presence of MbB in the pancreatic circulation of the rat induces organ specific venular leakage by an inflammatory process involving prostaglandins.

Ia- macrophages and cytokine networks contribute to tumor-induced suppression of CD4+ autoreactive T cells

Tumor growth changes the functions and phenotypes of macrophages (M phi) and T cells. Suppression of CD4+ T cell autoresponses during tumor growth was contributed primarily by M phi. Tumor-induced alterations in the abilities of these cells to mediate autorecognition were assessed through syngeneic mixed lymphocyte reaction (SMLR) assays. Tumor-bearing host (TBH) M phi were significantly more suppressive (60-90%) than normal host (NH) M phi, and this suppression was caused partly by reduced Ia expression. TBH Ia- M phi were significantly more suppressive (50-80%) than their NH counterparts. The suppression mechanism was controlled partly by prostaglandin E2 (PGE2), because treating cultures with indomethacin and titrated NH and TBH Ia- M phi led to increased T-cell responsiveness, although responsiveness never reached levels of assays containing unseparated M phi. Blocking studies using anti-interferon-gamma (anti-IFN-gamma) monoclonal antibodies (mAb), anti-interleukin 4 (anti-IL-4) mAb, and indomethacin suggested that IFN-gamma, IL-4, and PGE2 contributed to tumor-induced M phi-mediated suppression. Our results suggested that a quantitative shift in M phi phenotype and a qualitative shift in M phi function in addition to differences in cytokine-directed accessory activities are partly responsible for tumor-induced suppression CD4+ T cell autoresponses.

Glucocorticoid effects on natural and humoral immunity in mallards

Two studies were conducted to determine the effects of dexamethasone (DEX) on immune function in mallard ducks. Each day ducks were injected intramuscularly with DEX at doses ranging from 0.2-4.0 mg/kg for 28-30 days. Physiologic effects consistent with high dose glucocorticoid (GC) treatment were observed at the 4 mg/kg dose, and included significant body weight loss, lowered hematocrit, and elevated alanine aminotransferase (ALT) activity. At all doses, effects of DEX on the immune system were observed. When DEX was given at 0.2 mg/kg/day, significant suppression of primary IgG antibody titers to sheep erythrocytes (SRBC) was observed. At 1 mg/kg/day, primary IgM and secondary IgM and IgG titers were suppressed as well. These doses of DEX also produced significant elevation in natural killer cell (NKC) activity of peripheral blood mononuclear cells (PBMNC). Removal of adherent cells from the PBMNC prior to NKC assay eliminated the enhancement in NKC activity. Based on these results, it was postulated that the elevation in NKC activity may be due to suppression by DEX of monocyte production of prostaglandin-E2 (PGE-2) resulting in the release of NKC activity from the inhibitory effects of PGE-2. This hypothesis was supported by a measured decrease in PGE-2 production during the NKC assay by cells from DEX-treated birds. Furthermore, an enhanced NKC activity could be reproduced in vitro with the addition of indomethacin or DEX to NKC cultures containing adherent cells from PBMNC. Direct effects of DEX on nonadherent cell NKC activity and lymphocyte viability were only observed at high concentrations (10(-4) M) of DEX, while the phagocytic activity of adhered blood monocytes was inhibited at 10(-6) M DEX. The suppressed phagocytic activity may contribute to the suppressed antibody responses observed in DEX-treated birds. Together, these results support an indirect immunomodulatory effect of DEX on NKC activity and perhaps antibody responses in vivo via altered monocyte function in mallard ducks.