POS0256 CLINICAL PREDICTORS OF ATTENUATED ANTIBODY RESPONSE TO PRIMARY SARS-CoV-2 VACCINATION IN A LARGE PROSPECTIVE STUDY OF PATIENTS WITH RHEUMATIC AND MUSCULOSKELETAL DISEASES

Background

An attenuated humoral response to SARS-CoV-2 vaccination has been observed in some patients with rheumatic and musculoskeletal diseases (RMD) (1). We sought to identify clinical factors associated with poor humoral response following primary (two-dose mRNA or single adenoviral vector dose) SARS-COV-2 vaccination in patients with RMD on immunosuppression.

Objectives

To identify clinical predictors of an attenuated antibody response to primary SARS-CoV-2 vaccination in RMD patients on immunosuppression.

Methods

We included patients ≥18 years old with RMD on immunosuppression who received either two-dose mRNA or single dose Janssen/Johnson and Johnson (J&J) vaccination. Demographics, diagnoses, and therapeutic regimens were collected via participant report; those with prior COVID-19 infection were excluded. One month after vaccination, participants underwent SARS-CoV-2 antibody testing on the semi-quantitative Roche Elecsys anti-SARS-CoV-2 S enzyme immunoassay, which measures antibody to the SARS-CoV-2 S-receptor binding domain (RBD) protein (ceiling >250U/mL later expanded to >2500U/mL). Associations were evaluated using Fisher’s exact and Wilcoxon rank sum tests. Logistic regression analyses were performed to evaluate for clinical factors associated with antibody response. We adapted survival methods to address right-truncation of titers; this methodology was used to calculate medians. Participants provided informed consent electronically and the study was approved by the local Institutional Review Board.

Results

We studied 1138 RMD participants on immunosuppression; most were female (93%) and white (91%) (Table 1). One-hundred and fifteen (10%) had anti-RBD response in the negative range at a median (IQR) of 29 days (28-34) following completion of vaccine series. A greater proportion of participants with negative response were non-white, received J&J vaccine, reported use of mycophenolate, rituximab, or glucocorticoids. Antibody response differed by immunosuppressive regimen, with those receiving rituximab having poorest response (Figure 1). Use of mycophenolate (aOR 9.92, p=0.001), rituximab (aOR 56.99, p=0.001), glucocorticoids (aOR 2.99, p=0.001) or receipt of J&J (aOR 3.13, p=0.039) were associated with negative antibody response.

Table 1.

Clinical characteristics stratified by anti-SARS-CoV-2 RBD response

Negative (n=115)*Positive (n=1023)*p-value†Age,median(IQR)49(42, 58)47(37, 58)0.07Female sex,no.(%)108(94%)952(93%)0.78Non-white,no.(%)16(13.9%)83(8.1%)0.04Diagnosis,no.(%)Inflammatory arthritis22(19.1%)469(45.8%)<0.01SLE27(23.5%)193(18.9%)0.27Sjὅgren’s syndrome5(4.3%)46(4.5%)0.53Myositis13(11.3%)49(4.8%)<0.01Systemic sclerosis2(1.7%)9(0.9%)0.55Vasculitis12(10.4%)16(1.6%)<0.01Overlap connective tissue disease¶34(29.5%)24(23.6%)0.65  Vaccine,no.(%) Pfizer/BioNTech66(57.4%)548(53.6%)0.01Moderna38(33.0%)438(42.8%)J&J11(9.6%)37(3.6%)Non-biologic in regimen89(77.4%)725(70.9%)0.52Biologic in regimen84(73.0%)570(55.7%)0.01 Mycophenolate**56(48.7%)120(11.7%)<0.01 Rituximab54(47.0%)29(2.8%)<0.01 Glucocorticoid**61(53.0%)284(27.8%)<0.01Withheld immunosuppression18(21.2%)260(39.6%)<0.01

* Negative defined as anti-RBD titer <0.8 U/mL.

† Comparisons between negative and positive groups.

¶ Denotes a combination of two or more of the above conditions

** Mycophenolate: mycophenolic acid and mycophenolate mofetil. Corticosteroid: prednisone and prednisone equivalents

Figure 1.

Conclusion

Use of mycophenolate, glucocorticoids, rituximab and receipt of J&J vaccine were the strongest predictors of an attenuated antibody response to primary SARS-CoV-2 vaccination; these data support use of an additional primary dose in RMD patients.

References

[1]Deepak P, Kim W, Paley MA, et al. Effect of Immunosuppression on the Immunogenicity of mRNA Vaccines to SARS-CoV-2: A Prospective Cohort Study. Ann Intern Med. 2021.

Acknowledgements

We would like to acknowledge the contributions of: Brian J. Boyarsky MD, PhD, Jake A. Ruddy BS, and Jacqueline M. Garonzik-Wang MD PhD.

Disclosure of Interests

Caoilfhionn Connolly: None declared, Teresa Po-Yu Chiang: None declared, Mayan Teles: None declared, Sarah Frey: None declared, Jennifer Alejo: None declared, Allan Massie: None declared, Lisa Christopher Stine Consultant of: Janssen, Boehringer-Ingelheim, Mallinckrodt, EMD-Serono, Allogene, and ArgenX., William Werbel: None declared, Dorry Segev Speakers bureau: Sanofi, Novartis, CSL Behring, Jazz Pharmaceuticals, Veloxis, Mallincrodt, Thermo Fisher Scientific, Regeneron, and Astra-Zeneca, Consultant of: Sanofi, Novartis, CSL Behring, Jazz Pharmaceuticals, Veloxis, Mallincrodt, Thermo Fisher Scientific, Regeneron, and Astra-Zeneca, Julie Paik: None declared

Impaired insulin-receptor autophosphorylation is an early defect in fat-fed, insulin-resistant rats

High-fat feeding results in impaired insulin signaling in skeletal muscle, but the role of the insulin receptor (IR) remains controversial. In the present study, female Fischer 344 rats were fed diets either low in fat [low fat, complex carbohydrate (LFCC)] or high in fat and sucrose (HFS). Insulin-stimulated skeletal muscle glucose transport, measured in purified sarcolemmal vesicles, was lower in rats consuming the HFS diet for 2 and 8 wk compared with LFCC controls (72.9 +/- 3.5, 67.6 +/- 3.5, and 86.1 +/- 3.5 pmol x mg(-1) x 15 s(-1), respectively; P < 0.05). Muscle IR content was unchanged in 2-wk HFS animals but was 50% lower in the 8-wk HFS group (P < 0.001). However, compared with LFCC, insulin-stimulated IR autophosphorylation was 26% lower in 2-wk HFS and 40% lower in 8-wk HFS animals (P < 0.005). Total muscle content of the proposed IR inhibitors cytokine tumor necrosis factor-alpha and membrane glycoprotein PC-1 was not significantly changed in HFS animals at either 2 or 8 wk. These results demonstrate that high-fat feeding induces insulin resistance in muscle concomitant with a diminished IR signaling capacity, although the mechanism remains unknown.

Expression and characterization of a murine enzyme able to cleave beta-carotene. The formation of retinoids

Because animals are not able to synthesize retinoids de novo, ultimately they must derive them from dietary provitamin A carotenoids through a process known as carotene cleavage. The enzyme responsible for catalyzing carotene cleavage (beta-carotene 15,15'-dioxygenase) has been characterized primarily in rat intestinal scrapings. Using a recently reported cDNA sequence for a carotene cleavage enzyme from Drosophila, we identified a cDNA encoding a mouse homolog of this enzyme. When the cDNA was expressed in either Escherichia coli or Chinese hamster ovary cells, expression conferred upon bacterial and Chinese hamster ovary cell homogenates the ability to cleave beta-carotene to retinal. Several lines of evidence obtained upon kinetic analyses of the recombinant enzyme suggested that carotene cleavage enzyme interacts with other proteins present within cell or tissue homogenates. This was confirmed by pull-down experiments upon incubation of recombinant enzyme with tissue 12,000 x g supernatants. Matrix-assisted laser desorption ionization-mass spectrometry analysis of pulled-down proteins indicates that an atypical testis-specific isoform of lactate dehydrogenase associates with recombinant carotene cleavage enzyme. mRNA transcripts for the carotene cleavage enzyme were detected by reverse transcription-polymerase chain reaction in mouse testes, liver, kidney, and intestine. In situ hybridization studies demonstrated that carotene cleavage enzyme is expressed prominently in maternal tissue surrounding the embryo but not in embryonic tissues at 7.5 and 8.5 days postcoitus. This work offers new insights for understanding the biochemistry of carotene cleavage to retinoids.

9-cis-retinoids: biosynthesis of 9-cis-retinoic acid

Retinoids function through conformational alterations of ligand-dependent nuclear transcription factors, the retinoic acid receptors, and retinoid X receptors. 9-cis-Retinoic acid is a known biological ligand for retinoid X receptors, but its synthesis pathway in vivo is largely unknown. Recently, we identified a cis-retinol dehydrogenase (cRDH) that oxidizes 9-cis-retinol to 9-cis-retinal. Since both the expression of cRDH mRNA and its substrate are found in liver, we studied 9-cis-retinol metabolism and 9-cis-retinoic acid biosynthesis in two hepatic-derived cell types, Hep G2 hepatoma cells and HSC-T6 stellate cells. Both cell lines accumulate similar amounts of 9-cis-retinol provided in the medium. However, Hep G2 cells preferentially incorporate all-trans-retinol when equimolar concentrations of all-trans- and 9-cis-retinol were provided. In contrast, HSC-T6 cells did not exhibit a preference between all-trans- and 9-cis-retinol under the same conditions. Esterification of 9-cis-retinol occurred in both cell types, likely by acyl-CoA:retinol acyltransferase and lecithin:retinol acyltransferase. In vitro enzyme assays demonstrated that both cell types can hydrolyze 9-cis-retinyl esters via retinyl ester hydrolase(s). In Hep G2 cells, 9-cis-retinoic acid synthesis was strongly inhibited by high concentrations of 9-cis-retinol, which may explain the low levels of 9-cis-retinol in liver of mice. Cell homogenates of Hep G2 can convert all-trans-retinol to 9-cis-retinal, suggesting that the free form of all-trans-retinol may be used as a source for 9-cis-retinol and, thus, 9-cis-retinoic acid synthesis. Our studies provide the basis for identification of additional pathways for the generation of 9-cis-retinoic acid in specialized tissues.

Mutational analysis of the Streptococcus pneumoniae bimodular class A penicillin-binding proteins

One group of penicillin target enzymes, the class A high-molecular-weight penicillin-binding proteins (PBPs), are bimodular enzymes. In addition to a central penicillin-binding-transpeptidase domain, they contain an N-terminal putative glycosyltransferase domain. Mutations in the genes for each of the three Streptococcus pneumoniae class A PBPs, PBP1a, PBP1b, and PBP2a, were isolated by insertion duplication mutagenesis within the glycosyltransferase domain, documenting that their function is not essential for cellular growth in the laboratory. PBP1b PBP2a and PBP1a PBP1b double mutants could also be isolated, and both showed defects in positioning of the septum. Attempts to obtain a PBP2a PBP1a double mutant failed. All mutants with a disrupted pbp2a gene showed higher sensitivity to moenomycin, an antibiotic known to inhibit PBP-associated glycosyltransferase activity, indicating that PBP2a is the primary target for glycosyltransferase inhibitors in S. pneumoniae.

A putative monofunctional glycosyltransferase is expressed in Ralstonia eutropha

A gene, mgt, encoding a protein homologous to the N-terminal module of class A high-molecular-mass penicillin-binding proteins was identified in Ralstonia eutropha. By using specific antibodies, the corresponding Mgt protein was detected in association with the membrane, confirming that the N-terminal hydrophobic segment functioned as a membrane anchor. A derivative in which the hydrophobic sequence was deleted was overexpressed as a maltose-binding fusion protein in Escherichia coli. Cleavage of the product resulted in substantial amounts of soluble Mgt derivative, indicating that folding occurs independently on other proteins or on homologous domains of penicillin-binding proteins.

A novel resistance mechanism against beta-lactams in Streptococcus pneumoniae involves CpoA, a putative glycosyltransferase

Piperacillin resistance in Streptococcus pneumoniae was mediated by mutations in a novel gene, cpoA, that also confer transformation deficiency and a decrease in penicillin-binding protein la. cpoA is part of an operon located downstream of the primary sigma factor of S. pneumoniae. The deduced protein, CpoA, and the peptide encoded by the adjacent 3' open reading frame contained domains homologous to glycosyltransferases of procaryotes and eucaryotes that act on membrane-associated substrates, such as enzymes functioning in lipopolysaccharide core biosynthesis of gram-negative bacteria, RodD of Bacillus subtilis, which is involved in teichoic acid biosynthesis, and the human PIG-A protein, which is required for early steps of glycosylphosphatidylinositol anchor biosynthesis. This suggests that the cpo operon has a similar function related to cell surface components.

Factors influencing pulmonary venous flow velocity patterns in mitral regurgitation: an in vitro study

OBJECTIVES

The aim of this study was to investigate factors affecting pulmonary venous flow patterns in mitral regurgitation.

BACKGROUND

Although pulmonary venous flow velocity patterns have been reported to be helpful in assessing the severity of mitral regurgitation, the influence of regurgitant jet direction, pulmonary venous location and left atrial pressures on pulmonary venous flow patterns has yet to be clarified.

METHODS

The mitral regurgitant jet was produced by a pulsatile piston pump at 10, 30 and 40 ml/beat through a circular orifice, whereas the pulmonary venous flow was driven by gravity. Four different patterns of pulmonary venous flow and mitral regurgitation were examined. The V wave pressure was set at 10, 30 and 50 mm Hg and pulmonary venous flow velocity at 30 cm/s. Color and pulsed Doppler recordings were obtained with a VingMed 800 scanner interfaced with a computer facilitating digital analysis.

RESULTS

The decrease in the velocity time integral of pulmonary venous flow was more prominent for any given volume of mitral regurgitation at higher left atrial pressure. When the mitral regurgitant jet was directed toward the pulmonary vein, a more prominent decrease in the velocity time integral was seen, especially for severe mitral regurgitation (40 ml) with high left atrial pressure (95% vs. 55%, p < 0.001); and the time to peak deceleration of forward flow was significantly shorter (485 vs. 523 ms, respectively, p < 0.01). Also, two different types (laminar and turbulent) of reversed pulmonary venous flow were observed.

CONCLUSIONS

Multiple factors, including jet direction, mitral regurgitant volume and left atrial pressure, determine the effect of mitral regurgitation on pulmonary venous flow velocity patterns.

Effects of pulmonary venous flow direction on mitral regurgitation jet area as imaged by color Doppler flow mapping. An in vitro study

BACKGROUND

Although the effects of adjacent walls and left atrial pressure on mitral regurgitation (MR) jet area imaged by color Doppler have been examined, few data exist regarding the influence of pulmonary venous (PV) filling flow on regurgitant jets. Therefore, we designed a left atrial model to examine the relation between PV flow direction and MR jet area.

METHODS AND RESULTS

The left atrial chamber (7.6 cm in diameter) was built with a PV inflow (1.0 cm in diameter) and mitral valve regurgitant orifice in the same plane. The MR jet was simulated as fixed in volume and velocity (3.5 m/s) and directed with a pulsatile pump into the left atrial model. PV flow with a constant velocity (30 cm/s) was driven by gravity (83 cm H2O). With left atrial mean pressure at either 10, 30, or 50 mm Hg, four flow patterns were examined: (1) PV flow away from the mitral valve, MR jet toward the pulmonary vein; (2) PV flow toward the mitral valve, MR jet toward the pulmonary vein; (3) PV flow away from the mitral valve, MR jet away from the pulmonary vein; and (4) PV flow toward the mitral valve, MR jet away from the pulmonary vein. MR color Doppler images were recorded with a 3.5-mHz frequency transducer and at 7-kHz pulse repetition frequency. For each condition, we compared jet area, length, and width of the MR signal. MR jet areas for conditions 3 and 4 were larger at 10 mm Hg than at 30 or 50 mm Hg left atrial pressure. Especially at the lower pressures, PV flow diminished the MR jet area in condition 4 compared with that in condition 3, such that MR jets were smaller in condition 4. In conditions 1 and 2, the jets were imaged at an oblique angle and were smaller than in conditions 3 and 4 (P < .001), but they were not significantly different from each other as imaged.

CONCLUSIONS

In this model, factors including the direction of PV flow, the direction of MR as relates to the angle of interrogation, and the level of left atrial pressure influenced the size of MR jets. The effect of PV flow direction was diminished by increased left atrial pressure. PV flow directed away from the mitral valve was associated with larger MR jets than when PV flow was directed toward it (condition 4), probably because of jet distortion and flattening.

Inactivation of nitric oxide synthase after prolonged incubation of mouse macrophages with IFN-gamma and bacterial lipopolysaccharide

Large amounts of nitric oxide (NO) are produced by the inducible isoform of NO synthase (iNOS) in many cell types once the iNOS gene is transcriptionally activated. In primary mouse peritoneal macrophages elicited by thioglycolate broth, expression of iNOS follows treatment with IFN-gamma and is synergistically increased by the addition of bacterial LPS. Expression of iNOS is suppressible at transcriptional and translational levels by certain cytokines and microbial products. The present study describes a novel form of inactivation of iNOS that is post-translational and nondegradative. Mouse peritoneal macrophages cultured in the presence of IFN-gamma alone or IFN-gamma plus LPS rapidly depleted the medium of L-arginine, a substrate for iNOS, and stopped producing NO. Repletion of L-arginine permitted cells treated with IFN-gamma alone to resume NO production for at least 5 days, leading to the release of more NO than macrophages were previously believed capable of generating. L-Arginine repletion also boosted NO production by macrophages cultured for up to 2 to 3 days in the presence of IFN-gamma plus LPS, but thereafter, iNOS was inactive in these cells whether or not L-arginine was repleted. Activity of iNOS could be restored by adding both L-arginine and fresh IFN-gamma with or without LPS, likely reflecting the synthesis of new enzyme. However, the inactivation of iNOS seen late in culture with a single application of IFN-gamma plus LPS could be attributed neither to loss of iNOS protein nor to its autoinactivation by NO. Thus, LPS, a co-inducer of iNOS, causes macrophages to inactivate iNOS about 3 days after the onset of its induction. The mechanism, which remains to be identified, is novel for iNOS, in that it decreases neither its amount nor its apparent molecular mass.

Inactivation of nitric oxide synthase after prolonged incubation of mouse macrophages with IFN-gamma and bacterial lipopolysaccharide

Large amounts of nitric oxide (NO) are produced by the inducible isoform of NO synthase (iNOS) in many cell types once the iNOS gene is transcriptionally activated. In primary mouse peritoneal macrophages elicited by thioglycolate broth, expression of iNOS follows treatment with IFN-gamma and is synergistically increased by the addition of bacterial LPS. Expression of iNOS is suppressible at transcriptional and translational levels by certain cytokines and microbial products. The present study describes a novel form of inactivation of iNOS that is post-translational and nondegradative. Mouse peritoneal macrophages cultured in the presence of IFN-gamma alone or IFN-gamma plus LPS rapidly depleted the medium of L-arginine, a substrate for iNOS, and stopped producing NO. Repletion of L-arginine permitted cells treated with IFN-gamma alone to resume NO production for at least 5 days, leading to the release of more NO than macrophages were previously believed capable of generating. L-Arginine repletion also boosted NO production by macrophages cultured for up to 2 to 3 days in the presence of IFN-gamma plus LPS, but thereafter, iNOS was inactive in these cells whether or not L-arginine was repleted. Activity of iNOS could be restored by adding both L-arginine and fresh IFN-gamma with or without LPS, likely reflecting the synthesis of new enzyme. However, the inactivation of iNOS seen late in culture with a single application of IFN-gamma plus LPS could be attributed neither to loss of iNOS protein nor to its autoinactivation by NO. Thus, LPS, a co-inducer of iNOS, causes macrophages to inactivate iNOS about 3 days after the onset of its induction. The mechanism, which remains to be identified, is novel for iNOS, in that it decreases neither its amount nor its apparent molecular mass.

Mechanism of suppression of nitric oxide synthase expression by interleukin-4 in primary mouse macrophages

Nitric oxide (NO) contributes to the antitumor, antimicrobial, and immunosuppressive activity of macrophages. An inducible form of NO synthase (iNOS) is responsible for high output generation of nitric oxide by macrophages after stimulation with cytokines and/or lipopolysaccharide (LPS). In the present study, we demonstrate that interleukin 4 (IL-4) suppressed production of NO by primary mouse peritoneal macrophages exposed to IFN-gamma with or without LPS, even while synergizing with IFN-gamma to increase the secretion of TNF-alpha. Suppression of NO production was paralleled by decreases in iNOS enzyme activity and iNOS antigen. IL-4 did not inhibit induction of iNOS mRNA 4-6 h after exposure to IFN-gamma, but strongly reduced iNOS mRNA at later times of stimulation (24-72 h), without increasing its turnover. The conditions for maximal suppression of iNOS expression by IL-4 and the mechanisms of suppression differed from those determined in parallel for transforming growth-factor-beta as described elsewhere. These results illustrate the diversity of phenotypes of macrophages deactivated by different cytokines, and demonstrate that IL-4 has the potential to reduce one component of the anti-tumor, antimicrobial, and immunosuppressive activities of macrophages.

Effects of adjacent surfaces of different shapes on regurgitant jet sizes: an in vitro study using color Doppler imaging and laser-illuminated dye visualization

OBJECTIVES

The present study was designed to estimate the influence of different-shaped adjacent surfaces on regurgitant jets as assessed by color Doppler imaging and laser-illuminated dye optical visualization.

BACKGROUND

Because color Doppler techniques provide real-time two-dimensional imaging of flow, the evaluation of valvular regurgitation by analysis of variance-encoded regurgitant jets by this method has been widely used in clinical studies. However, recent studies have demonstrated that color Doppler jet sizes are affected not only by several hemodynamic factors and instrument settings but also by the interaction between jets and adjacent wall surfaces. In clinical conditions, jets may interact with adjacent walls of variable shapes that might have different effects on the jet size.

METHODS

An in vitro model was constructed consisting of a rigid, optically clear receiving chamber that had no outlet resistance and had a pulsatile pump ejecting through 1.5, 2.3 and 3.1 mm2 inflow orifices into the chamber. The surfaces were flat or smoothly and equally curved, convex and concave aluminum positioned at 0, 2 and 4 mm from and to the side of the inflow orifices. The pump was run with stroke volumes from 0.5 to 3.0 ml and with a pulse frequency of 70 beats/min. The echocardiographic and laser beams were aimed at the inflow orifice imaging jets perpendicular to the surfaces (vertical view) through the central plane of the jet flows. Maximal jet areas were measured by both color Doppler techniques and laser-illuminated dye visualization.

RESULTS

Color Doppler study showed fair correlation between the jet areas and the stroke volumes (r = 0.83 to 0.99), but the jet sizes under different surface conditions were variable. All the surface jet areas at a jet-surface distance of 0 and 2 mm were smaller than free jet areas at the same stroke volume for both flat and convex surfaces (p < 0.001). Flow constraint by the concave surface resulted in the smallest jet areas (p < 0.001). The color Doppler jet areas on the curved surfaces were significantly smaller than the laser-illuminated dye visualization jet areas (p < 0.01 to 0.0001). However, at intermediate jet-surface distances (4 mm and sometimes 2 mm with higher velocity flows), jet interaction with the flat and especially with the convex surface resulted in larger jets. This effect was most pronounced on dye fluorescence studies because flow around these jets consisted mainly of low velocity vortical events with only partial surface adherence and these low velocity swirling flows were not well imaged by color Doppler technique.

CONCLUSIONS

Our study suggests that the different-shaped adjacent surfaces with different degrees of flow alterations resulted in variable decreases in jet size and that color Doppler imaging could not encode and image the angled and low velocity swirling events well when jets flowed along the curved surfaces. These effects need to be taken into account when interpreting color Doppler images.

Mechanisms of suppression of macrophage nitric oxide release by transforming growth factor beta

Activated mouse peritoneal macrophages produce nitric oxide (NO) via a nitric oxide synthase that is inducible by interferon gamma (IFN-gamma): iNOS. We have studied the mechanisms by which transforming growth factor beta 1 (TGF-beta) suppresses IFN-gamma-stimulated NO production. TGF-beta treatment reduced iNOS specific activity and iNOS protein in both cytosolic and particulate fractions as assessed by Western blot with monospecific anti-iNOS immunoglobulin G. TGF-beta reduced iNOS mRNA without affecting the transcription of iNOS by decreasing iNOS mRNA stability. Even after iNOS was already expressed, TGF-beta reduced the amount of iNOS protein. This was due to reduction of iNOS mRNA translation and increased degradation of iNOS protein. The potency of TGF-beta as a deactivator of NO production (50% inhibitory concentration, 5.6 +/- 2 pM) may reflect its ability to suppress iNOS expression by three distinct mechanisms: decreased stability and translation of iNOS mRNA, and increased degradation of iNOS protein. This is the first evidence that iNOS is subject to other than transcriptional regulation.

Traces of bacterial lipopolysaccharide suppress IFN-gamma-induced nitric oxide synthase gene expression in primary mouse macrophages

A nitric oxide synthase (iNOS) inducible by cytokines and microbial products contributes to the cytotoxic and antimicrobial activity of mouse macrophages. Bacterial LPS interacts synergistically with IFN-gamma to induce iNOS when both stimuli are added together. In contrast, we show here that pre-exposure of peritoneal macrophages to low concentrations of LPS suppresses the induction of iNOS when IFN-gamma is added subsequently. Suppression required pretreatment with LPS for at least 8 h and was optimal with LPS concentrations in the range of 50 to 200 pg/ml. Suppression was exerted by smooth and rough forms of LPS from Escherichia coli and by lipid A from Salmonella minnesota, but not by a biologically inactive lipid A from Rhodobacter sphaeorides. Suppression of nitrite accumulation and iNOS enzyme activity by prior exposure of macrophages to LPS could be explained by their markedly decreased content of iNOS protein, as revealed by immunoblot with monospecific anti-iNOS IgG. Messenger RNA for iNOS was affected in a biphasic manner by pretreatment with LPS. Five hours after addition of IFN-gamma, iNOS mRNA levels were unaltered or even enhanced by pretreatment with LPS, but by 24 to 48 h, expression of iNOS mRNA was inhibited strongly enough to account for the reduced levels of iNOS protein. Suppression by LPS did not appear to be mediated by endogenous prostaglandins, transforming growth factor-beta, or TNF-alpha, even though pretreatment with exogenous TNF-alpha was also suppressive. These findings suggest that preactivation of pathways normally contributing to synergistic induction of iNOS may deplete macrophages of factors needed for its expression. Regulation of iNOS in vivo may depend on the relative tempo with which the inflammatory and immune responses evolve.

Traces of bacterial lipopolysaccharide suppress IFN-gamma-induced nitric oxide synthase gene expression in primary mouse macrophages

A nitric oxide synthase (iNOS) inducible by cytokines and microbial products contributes to the cytotoxic and antimicrobial activity of mouse macrophages. Bacterial LPS interacts synergistically with IFN-gamma to induce iNOS when both stimuli are added together. In contrast, we show here that pre-exposure of peritoneal macrophages to low concentrations of LPS suppresses the induction of iNOS when IFN-gamma is added subsequently. Suppression required pretreatment with LPS for at least 8 h and was optimal with LPS concentrations in the range of 50 to 200 pg/ml. Suppression was exerted by smooth and rough forms of LPS from Escherichia coli and by lipid A from Salmonella minnesota, but not by a biologically inactive lipid A from Rhodobacter sphaeorides. Suppression of nitrite accumulation and iNOS enzyme activity by prior exposure of macrophages to LPS could be explained by their markedly decreased content of iNOS protein, as revealed by immunoblot with monospecific anti-iNOS IgG. Messenger RNA for iNOS was affected in a biphasic manner by pretreatment with LPS. Five hours after addition of IFN-gamma, iNOS mRNA levels were unaltered or even enhanced by pretreatment with LPS, but by 24 to 48 h, expression of iNOS mRNA was inhibited strongly enough to account for the reduced levels of iNOS protein. Suppression by LPS did not appear to be mediated by endogenous prostaglandins, transforming growth factor-beta, or TNF-alpha, even though pretreatment with exogenous TNF-alpha was also suppressive. These findings suggest that preactivation of pathways normally contributing to synergistic induction of iNOS may deplete macrophages of factors needed for its expression. Regulation of iNOS in vivo may depend on the relative tempo with which the inflammatory and immune responses evolve.

Contrasting mechanisms for suppression of macrophage cytokine release by transforming growth factor-beta and interleukin-10

Transforming growth factor (TGF)-beta and interleukin (IL)-10 inhibited lipopolysaccharide (LPS)-induced macrophage production of the inflammatory cytokines tumor necrosis factor-alpha (TNF), IL-1 alpha, and IL-1 beta by contrasting post-transcriptional mechanisms. TGF-beta acted slowly and late, as it required 12-16 h to exert a suppressive effect, and inhibited TNF production even when added 6 h after LPS. TGF-beta affected neither the level of TNF mRNA, the release of preformed TNF nor the degradation of TNF. Thus, TGF-beta appeared to inhibit translation of TNF mRNA. IL-10 not only suppressed TNF release to a 25-fold greater extent than TGF-beta, but also inhibited release of IL-1. In contrast to TGF-beta, IL-10 acted on an early step in cytokine production, its effect being maximal 3 h after addition of LPS. Unlike TGF-beta, IL-10 markedly suppressed TNF, IL-1 alpha, and IL-1 beta mRNA levels. However, this was accomplished without suppressing transcription of the corresponding genes. Moreover, cycloheximide antagonized the IL-10-dependent reduction in cytokine mRNA levels. Thus, IL-10 may induce a ribonuclease active on cytokine transcripts or may induce a protein that enhances the susceptibility of TNF, IL-1 alpha, and IL-1 beta mRNAs to ribonucleolytic action. We conclude that IL-10 and TGF-beta induce different phenotypes of macrophage deactivation, and deactivate macrophages by different mechanisms: IL-10 promotes degradation of cytokine mRNA, while TGF-beta primarily suppresses translation.