Giant epithelial nonparasitic splenic cyst a pre-operative diagnosis dilemma: A case report.

Giant splenic cyst is rare disorder affecting the spleen. As the occurrence is so in-frequent that the diagnosis preoperatively remains a challenge. We report a 12-year-old boy who presented to Sarawak General Hospital, Malaysia with left upper abdominal pain initially mistaken as a complex left liver cyst. He underwent surgery which turned out to be a giant splenic cyst and underwent laparotomy and total splenectomy. He was discharged well and remains asymptomatic after 6 months postoperative follow up.

Relapsing retroperitoenal abscess secondary to juvenile dermatomyositis: Complexity in management.

Juvenile dermatomyositis (JDM) is a systemic autoimmune condition with myopathy. Gastrointestinal and pulmonary manifestations are rare presentation of JDM. Gastrointestinal perforation incidence in JDM is associated with vasculopathy and ischaemia. There are only few reported case of management of JDM with gastrointestinal complication. Management of such condition is challenging. We present a 21-year-old man with spontaneous descending colon perforation undergoing Hartmann's procedure. He subsequently presented with recurrent retroperitoneal abscess at five and 30 months following the initial presentation which was treated with percutaneous drainage. A high index of suspicion is necessary in JDM patients presenting with acute abdomen.

Delayed diagnosis of tuberculosis: risk factors and effect on mortality among older adults in Hong Kong.

OBJECTIVE: To assess the risk factors and effects of delayed diagnosis on tuberculosis (TB) mortality in Hong Kong. METHODS: All consecutive patients with TB notified in 2010 were tracked through their clinical records for treatment outcome until 2012. All TB cases notified or confirmed after death were identified for a mortality survey on the timing and causes of death. RESULTS: Of 5092 TB cases notified, 1061 (20.9%) died within 2 years of notification; 211 (4.1%) patients died before notification, 683 (13.4%) died within the first year, and 167 (3.3%) died within the second year after notification. Among the 211 cases with TB notified after death, only 30 were certified to have died from TB. However, 52 (24.6%) died from unspecified pneumonia/sepsis possibly related to pulmonary TB. If these cases are counted, the total TB-related deaths increases from 191 to 243. In 82 (33.7%) of these, TB was notified after death. Over 60% of cases in which TB diagnosed after death involved patients aged ≥80 years and a similar proportion had an advance care directive against resuscitation or investigation. Independent factors for TB notified after death included female sex, living in an old age home, drug abuse, malignancy other than lung cancer, sputum TB smear negative, sputum TB culture positive, and chest X-ray not done. CONCLUSIONS: High mortality was observed among patients with TB aged ≥80 years. Increased vigilance is warranted to avoid delayed diagnosis and reduce the transmission risk, especially among elderly patients with co-morbidities living in old age homes.

Association of CDX1 binding site of periostin gene with bone mineral density and vertebral fracture risk.

SUMMARY: Periostin (POSTN) as a regulator of osteoblast differentiation and bone formation may affect susceptibility to osteoporosis. This study suggests POSTN as a candidate gene for bone mineral density (BMD) variation and vertebral fracture risk, which could better our understanding about the genetic pathogenesis of osteoporosis and will be useful in clinic in the future. INTRODUCTION: The genetic determination of osteoporosis is complex and ill-defined. Periostin (POSTN), an extracellular matrix secreted by osteoblasts and a regulator of osteoblast differentiation and bone formation, may affect susceptibility to osteoporosis. METHODS: We adopted a tag-single nucleotide polymorphism (SNP) based association method followed by imputation-based verification and identification of a causal variant. The association was investigated in 1,572 subjects with extreme-BMD and replicated in an independent population of 2,509 subjects. BMD was measured by dual X-ray absorptiometry. Vertebral fractures were identified by assessing vertebral height from X-rays of the thoracolumbar spine. Association analyses were performed with PLINK toolset and imputation analyses with MACH software. The top imputation finding was subsequently validated by genotyping. Interactions between POSTN and another BMD-related candidate gene sclerostin (SOST) were analyzed using MDR program and validated by logistical regression analyses. The putative transcription factor binding with target sequence was confirmed by electrophoretic mobility shift assay (EMSA). RESULTS: Several SNPs of POSTN were associated with BMD or vertebral fractures. The most significant polymorphism was rs9547970, located at the -2,327 bp upstream (P = 6.8 × 10(-4)) of POSTN. Carriers of the minor allele G per copy of rs9547970 had 1.33 higher risk of vertebral fracture (P = 0.007). An interactive effect between POSTN and SOST upon BMD variation was suggested (P < 0.01). A specific binding of CDX1 to the sequence of POSTN with the major allele A of rs9547970 but not the variant G allele was confirmed by EMSA. CONCLUSIONS: Our results suggest POSTN as a candidate gene for BMD variation and vertebral fracture risk.

Role for alpha-dystrobrevin in the pathogenesis of dystrophin-dependent muscular dystrophies.

A dystrophin-containing glycoprotein complex (DGC) links the basal lamina surrounding each muscle fibre to the fibre's cytoskeleton, providing both structural support and a scaffold for signalling molecules. Mutations in genes encoding several DGC components disrupt the complex and lead to muscular dystrophy. Here we show that mice deficient in alpha-dystrobrevin, a cytoplasmic protein of the DGC, exhibit skeletal and cardiac myopathies. Analysis of double and triple mutants indicates that alpha-dystrobrevin acts largely through the DGC. Structural components of the DGC are retained in the absence of alpha-dystrobrevin, but a DGC-associated signalling protein, nitric oxide synthase, is displaced from the membrane and nitric-oxide-mediated signalling is impaired. These results indicate that both signalling and structural functions of the DGC are required for muscle stability, and implicate alpha-dystrobrevin in the former.

Differences Between the East and the West in Managing Advanced-Stage Non-small Cell Lung Cancer.

Lung cancer is a common cancer associated with high mortality rates worldwide. Unfortunately, it usually presents at a late stage, precluding the chance of curative therapy. The discovery of oncogenic driver mutations in patients with non-small cell lung cancer over the past 20 years has led to new molecular targeted therapies that have dramatically improved treatment efficacy and quality of life. New generations of therapy that target the drug-resistant mutations have also quickly evolved, benefiting patients who are refractory or intolerant to first-line targeted therapy. Eastern patients, from Southeast Asia, Japan and China, are known to have a higher incidence of epidermal growth factor receptor mutation. Therefore, compared with the West, more patients would benefit from these recent advances. In contrast, survival of patients without driver mutations has benefited from advances in novel therapeutics, including the immune checkpoint inhibitors. The current review aims to highlight the recent developments in the management of advanced-stage non-small cell lung cancer and to compare the differences in clinical practice between Eastern and Western countries.

Real-world treatment patterns and outcomes in refractory metastatic colorectal cancer.

AIM: To investigate treatment patterns and outcomes of metastatic colorectal cancer (mCRC) patients beyond second progression (PD2) since regorafenib and TAS-102 became available in Hong Kong. METHODS: The clinical records of consecutive mCRC patients who were treated beyond PD2 at Department of Clinical Oncology, Queen Mary Hospital between June 2013 and February 2018, were retrospectively reviewed. RESULTS: Of 176 PD2 patients (76.7% Eastern Cooperative Oncology Group performance status 0/1 and a median follow-up time of 6.6 [range, 0.4-37.2] months), 104 (59%) underwent palliative care only and 72 (41%) received active third-line (3L) treatment: regorafenib (n = 22), TAS-102 (n = 6), chemotherapy + antiepidermal growth factor receptor (n = 12), chemotherapy + antivascular endothelial growth factor (n = 28) or clinical trials (n = 4). Patients on active 3L treatment had significantly longer OS than those on palliative care only: 11.7 versus 5.5 months (adjusted hazard ratio = 0.41, 95% confidence interval: 0.28-0.61, P < 0.001). For those on active treatment, OS was significantly associated with the time from diagnosis of metastasis to PD2 (P < 0.001) and post-3L treatments (P = 0.009). When analyzing treatment eligibility according to trial criteria, half of the eligible patients (54/109) did not receive active treatment, but both eligible and ineligible patients achieved better OS when receiving active 3L treatment versus palliative care only (P < 0.001 and P = 0.002). No unexpected toxicity was reported. CONCLUSION: Active 3L and beyond treatment significantly prolonged OS versus palliative care, even in selected "trial ineligible" patients. Given a high rate of palliation only care in eligible patients, improved patient access to medicine and counseling may be needed to maximize outcomes.

Ethanolic extract of Actaea racemosa (black cohosh) potentiates bone nodule formation in MC3T3-E1 preosteoblast cells.

Aceaea racemosa (formerly Cimicifuga racemosa, black cohosh, AR) extracts have been widely used as an alternative to hormonal replacement therapy for menopausal symptoms. Recent evidences suggest AR extracts are also effective in protecting against postmenopausal bone loss. To determine whether AR has any direct anabolic effect on osteoblasts, we investigated the ethanolic extract of AR on bone nodule formation in mouse MC3T3-E1 preosteoblast cells. AR did not stimulate osteoblast proliferation. Rather, at high doses of 1000 ng/mL for 48 h, AR suppressed (7.2+/-0.9% vs. control) osteoblast proliferation. At 500 ng/mL, a significant increase in bone nodule formation was seen with Von Kossa staining. Using quantitative PCR analysis, AR was shown to enhance the gene expression of runx2 and osteocalcin. Co-treatment with ICI 182,780, the selective estrogen receptor antagonist, abolished the stimulatory effect of AR on runx2 and osteocalcin gene induction, as well as on bone nodule formation in MC3T3-E1 cells. This is a first report of the direct effect of AR on enhancement of bone nodule formation in osteoblasts, and this action was mediated via an estrogen receptor-dependent mechanism. The results provide a scientific rationale at the molecular level for the claim that AR can offer effective prevention of postmenopausal bone loss.

Endothelial nitric oxide synthase is expressed in cultured human bronchiolar epithelium.

Nitric oxide (NO) is an important mediator of physiologic and inflammatory processes in the lung. To better understand the role of NO in the airway, we examined constitutive NO synthase (NOS) gene expression and function in NCI-H441 human bronchiolar epithelial cells, which are believed to be of Clara cell lineage. NOS activity was detected by [3H]arginine to [3H]citrulline conversion (1,070 +/- 260 fmol/mg protein per minute); enzyme activity was inhibited 91% by EGTA, consistent with the expression of a calcium-dependent NOS isoform. Immunoblot analyses with antisera directed against neuronal, inducible, or endothelial NOS revealed expression solely of endothelial NOS protein. Immunocytochemistry for endothelial NOS revealed staining predominantly in the cell periphery, consistent with the association of this isoform with the cellular membrane. To definitively identify the NOS isoform expressed in H441 cells, NOS cDNA was obtained by degenerate PCR. Sequencing of the H441 NOS cDNA revealed 100% identity with human endothelial NOS at the amino acid level. Furthermore, the H441 NOS cDNA hybridized to a single 4.7-kb mRNA species in poly(A)+ RNA isolated from H441 cells, from rat, sheep, and pig lung, and from ovine endothelial cells, coinciding with the predicted size of 4.7 kb for endothelial NOS mRNA. Guanylyl cyclase activity in H441 cells, assessed by measuring cGMP accumulation, rose 6.6- and 5.4-fold with calcium-mediated activation of NOS by thapsigargin and A23187, respectively. These findings indicate that endothelial NOS is expressed in select bronchiolar epithelial cells, where it may have autocrine effects through activation of guanylyl cyclase. Based on these observations and the previous identification of endothelial NOS in a kidney epithelial cell line, it is postulated that endothelial NOS may be expressed in unique subsets of epithelial cells in a variety of organs, serving to modulate ion flux and/or secretory function.

An innovative web-based peer support system for medical students in Hong Kong.

BACKGROUND: Psychological morbidity is commonly found in medical students. AIMS: The Mental Health Support Group (MSG), a student-initiated and student-run web-based peer support service aims to provide mental health information, e mail counseling and an online forum for medical students. METHODS: The development process of MSG is described in the paper with presentation of preliminary evaluation results. RESULTS: Preliminary evaluation shows promising results. Student members of MSG acquired valuable skills in counseling, communication, webpage design and maintenance of an online forum. CONCLUSIONS: Future challenges include succession issues, strategies to keep up the momentum, enhancement of publicity and further diversification of service to meet the needs of our students.

Alterations in Gastric Microbiota After H. Pylori Eradication and in Different Histological Stages of Gastric Carcinogenesis.

The role of bacteria other than Helicobacter pylori (HP) in the stomach remains elusive. We characterized the gastric microbiota in individuals with different histological stages of gastric carcinogenesis and after receiving HP eradication therapy. Endoscopic gastric biopsies were obtained from subjects with HP gastritis, gastric intestinal metaplasia (IM), gastric cancer (GC) and HP negative controls. Gastric microbiota was characterized by Illumina MiSeq platform targeting the 16 S rDNA. Apart from dominant H. pylori, we observed other Proteobacteria including Haemophilus, Serratia, Neisseria and Stenotrophomonas as the major components of the human gastric microbiota. Although samples were largely converged according to the relative abundance of HP, a clear separation of GC and other samples was recovered. Whilst there was a strong inverse association between HP relative abundance and bacterial diversity, this association was weak in GC samples which tended to have lower bacterial diversity compared with other samples with similar HP levels. Eradication of HP resulted in an increase in bacterial diversity and restoration of the relative abundance of other bacteria to levels similar to individuals without HP. In conclusion, HP colonization results in alterations of gastric microbiota and reduction in bacterial diversity, which could be restored by antibiotic treatment.

Clustering of protein structures using hydrophobic free energy and solvent accessibility of proteins.

The hydrophobic free energy and solvent accessibility of amino acids are used to study the relationship between the primary structure and structural classification of large proteins. A measure representation and a Z curve representation of protein sequences are proposed. Fractal analysis of the measure and Z curve representations of proteins and multifractal analysis of their hydrophobic free energy and solvent accessibility sequences indicate that the protein sequences possess correlations and multifractal scaling. The parameters from the fractal and multifractal analyses on these sequences are used to construct some parameter spaces. Each protein is represented by a point in these spaces. A method is proposed to distinguish and cluster proteins from the alpha, beta, alpha + beta, and alpha/beta structural classes in these parameter spaces. Fisher's linear discriminant algorithm is used to give a quantitative assessment of our clustering on the selected proteins. Numerical results indicate that the discriminant accuracies are satisfactory. In particular, they reach 94.12% and 88.89% in separating proteins from {alpha, alpha + beta, alpha/beta} proteins in a three-dimensional space.

Inhibition of the bovine branched-chain 2-oxo acid dehydrogenase complex and its kinase by arylidenepyruvates.

A novel class of inhibitors for the branched-chain 2-oxo acid dehydrogenase (BCOAD) complex has been synthesized and studied. The sodium salts of arylidenepyruvates: e.g., furfurylidenepyruvate (compound I), 4-(3-thienyl)-2-oxo-3-butenoate (compound II), cinnamalpyruvate (compound III) and 4-(2-thienyl)-2-oxo-3-butenoate (compound IV) inhibit the overall and kinase reactions of the BCOAD complex from bovine liver. Inhibitions of the overall reaction occur at the decarboxylase (E1) step as determined by a spectrophotometric assay with 2,6-dichlorophenolindophenol as an electron acceptor. Inhibition of the E1 reaction by compound I (Ki = 0.5 microM) is competitive, whereas inhibitions by compounds II (Ki = 150 microM) and III (Ki = 500 microM) are non-competitive with respect to the substrate 2-oxoisovalerate. The Km value for 2-oxoisovalerate is 6.7 microM as measured by the E1 assay. Inhibition of the E1 step by compounds I, II and III are reversible at low inhibitor concentrations based on the Michaelis-Menten kinetics observed. By comparison, compound I does not significantly inhibit pyruvate and 2-oxoglutarate dehydrogenase complexes. The arylidenepyruvates (compounds I, II and IV) inhibit the BCOAD kinase reaction in a manner similar to the substrate 2-oxo acids. The inhibition of the kinase reaction by compound I is non-competitive with respect to ATP, with an apparent Ki value of 4.5 mM. The results suggest that arylidenepyruvates may be useful probes for elucidating the reaction mechanisms of the BCOAD complex and its kinase.

The complete cDNA sequence for dihydrolipoyl transacylase (E2) of human branched-chain alpha-keto acid dehydrogenase complex.

We have determined the complete nucleotide sequence for the cDNA encoding human dihydrolipoyl transacylase (E2) using the rapid amplification of cDNA ends (RACE) procedure. The full-length E2 cDNA is 3535 nucleotides in length. The coding region spans 1446 bp and the 3'-noncoding region spans 2074 bp. The latter contains three Alu repetitive sequences and two transcription termination sites.

nNOS and Ca2+ influx in rat pancreatic acinar and submandibular salivary gland cells.

Regulation of agonist-activated Ca2+ influx by the NOS pathway through generation of cGMP is being found in an increasing number of cell types. In the present work, we examined the role of the NOS pathway in agonist-evoked [Ca2+]i oscillations and attempted to identify the NOS isoform most likely to regulate Ca2+ influx. For this, we first show that two Ca(2+)-mobilizing agonists acting on pancreatic acinar cells, bombesin (BS) and the cholecystokinin analog CCK-JMV-180 (CCKJ), evokes different type of [Ca2+]i oscillations. The BS-evoked [Ca2+]i oscillations rapidly became acutely dependent on the presence of extracellular Ca2+, whereas the CCKJ-evoked oscillations continue for long periods of time in the absence of Ca2+ influx. This differential behavior allowed us to isolate Ca2+ influx and study its regulation while controlling for non specific effects on all other Ca2+ transporting events involved in generating [Ca2+]i oscillations. Inhibitors of selective steps in the NOS pathway inhibited agonist-induced cGMP production. The inhibitors were then used to show that scavenging NO with reduced hemoglobin, inhibition of guanylyl cyclase with 1H-[1,2,4] oxadiazolo[4,3-a] quinoxaline-1-one (ODQ) and inhibition of protein kinase G with Rp-8-pCPT-cGMPS inhibited [Ca2+]i oscillations evoked by BS but not those evoked by CCKJ. These findings were extended to duct and acinar cells of the SMG. In these cells, Ca(2+)-mobilizing agonists stimulate large Ca2+ influx, which was inhibited by all inhibitors of the NOS pathway. Western blot analysis and immunolocalization revealed that the cells did not express iNOS, eNOS was expressed only in blood vessels and capillaries whereas nNOS was expressed at high levels next to the plasma membrane of all cells. Accordingly, the nNOS inhibitor 7-nitroindazole (7-NI) inhibited BS- but not CCKJ-evoked [Ca2+]i oscillations and Ca2+ influx into SMG acinar and duct cells. Thus, together, our findings favor nNOS as the isoform activated by the Ca2+ released from internal stores to generate cGMP and regulate Ca2+ influx.

Nitric oxide contributes to vascular smooth muscle relaxation in contracting fast-twitch muscles.

During skeletal muscle contraction, NO derived from neuronal nitric oxide synthase (nNOS) in skeletal muscle fibers or from endothelial cells (eNOS) may relax vascular smooth muscle contributing to functional hyperemia. To examine the relative importance of these pathways, smooth muscle myosin regulatory light chain (smRLC) phosphorylation was assessed as an index of vascular tone in isolated extensor digitorum longus (EDL) muscles from C57, nNOS(-/-), and eNOS(-/-) mice. The smRLC phosphorylation (in mol phosphate per mol smRLC) in C57 resting muscles (0.12 +/- 0.04) was increased 3.7-fold (0.44 +/- 0.03) by phenylephrine (PE). Reversal of this increase with electrical stimulation (to 0.19 +/- 0.03; P < 0.05) was partially blocked by N(omega)-nitro-l-arginine (NLA). In nNOS(-/-) EDL, the PE-induced increase in smRLC phosphorylation (0.10 +/- 0.02 to 0.49 +/- 0.04) was partially decreased by stimulation (0.25 +/- 0.04). In eNOS(-/-) EDL, the control value for smRLC was increased (0.24 +/- 0.04), and PE-induced smRLC phosphorylation (0.36 +/- 0.06) was decreased by stimulation even in the presence of NLA (to 0.20 +/- 0.02; P < 0.05). These results suggest that in addition to NO-independent mechanisms, NO derived from both nNOS and eNOS plays a role in the integrative vascular response of contracting skeletal muscle.

nNOS and eNOS modulate cGMP formation and vascular response in contracting fast-twitch skeletal muscle.

Nitric oxide (NO) from Ca(2+)-dependent neuronal nitric oxide synthase (nNOS) in skeletal muscle fibers may modulate vascular tone by a cGMP-dependent pathway similar to NO derived from NOS in endothelial cells (eNOS). In isolated fast-twitch extensor digitorum longus (EDL) muscles from control mice, cGMP formation increased approximately 166% with electrical stimulation (30 Hz, 15 s). cGMP levels were not altered in slow-twitch soleus muscles. The NOS inhibitor N(omega)-nitro-l-arginine abolished the contraction-induced increase in cGMP content in EDL muscles, and the NO donor sodium nitroprusside (SNP) increased cGMP content approximately 167% in noncontracting EDL muscles. SNP treatment but not electrical stimulation increased cGMP formation in muscles from nNOS(-/-) mice. cGMP formation in control and stimulated EDL muscles from eNOS(-/-) mice was less than that obtained with similarly treated muscles from control mice. Arteriolar relaxation in contracting fast-twitch mouse cremaster muscle was attenuated in muscles from mice lacking either nNOS or eNOS. These findings suggest that increases in cGMP and NO-dependent vascular relaxation in contracting fast-twitch skeletal muscle may require both nNOS and eNOS.

Interleukin-1 beta modulates thyrotropin-induced thyroglobulin mRNA transcription through 3',5'-cyclic adenosine monophosphate.

It has been reported that interleukin-1 possesses not only immunoregulatory action, but also multiple hormone like effects. We studied the action of recombinant interleukin-1 beta (IL-1 beta) on the synthesis of thyroglobulin (TG), the precursor of thyroid hormone. Human thyrocytes dispersed from normal and Graves' thyroid tissues were incubated with TSH with or without IL-1 beta. TSH stimulated TG release from cultured human thyrocytes after 4 days. This effect was mimicked by dibutyryl cAMP (dBcAMP). IL-1 beta had no effect on basal TG release but modulates the TSH-stimulated TG secretion. At low dose (10(-5) to 10(-3) U/ml) IL-1 beta increased the TSH-stimulated TG secretion while higher doses (1-100 U/ml) of IL-1 beta had an inhibitory effect. Similar responses were observed with both normal and Graves' thyrocytes. The effect of IL-1 beta occurred at the gene transcription level as reflected by changes in TG mRNA level. At 100 U/ml, IL-1 beta suppressed TG mRNA level to near unmeasurable level. This biphasic effect of IL-1 beta on TG synthesis is paralleled by a similar change in TSH-stimulated cAMP secretion. We conclude that IL-1 beta possesses hormonal action on TG gene transcription and its effect is mediated via cAMP.

Interferon-gamma increases intracellular calcium and inositol phosphates in primary human thyroid cell culture.

Interferon-gamma (IFN gamma) is believed to play a role in the pathogenesis of autoimmune thyroid disease, as it is known to exert diverse effects on thyroid metabolism. These include induction of human leukocyte antigen class II expression, inhibition of gene expression of thyroglobulin and thyroid peroxidase, as well as inhibition of cellular proliferation. However, the mechanism of action of IFN gamma in thyrocytes has not been clearly defined. We studied the action of IFN gamma on the production of inositol phosphates and intracellular Ca2+ mobilization in primary cultures of human thyrocytes using the fluorescent Ca2+ indicator fura-2. IFN gamma increased the production of inositol mono-, bis-, and trisphosphates and caused a dose-dependent increase in intracellular Ca2+ ([Ca2+]i) at 37 C. Preincubation with 12-O-tetradecanoylphorbol-13-acetate, which activates protein kinase C, resulted in the abolition of the IFN gamma response, suggesting that protein kinase C was involved in a negative feedback loop resulting in inhibition of IFN gamma-induced [Ca2+]i rise. Prior release of intracellularly stored Ca2+ with thapsigargin, the microsomal Ca2+ pump inhibitor, also abolished the response of IFN gamma. Mobilization of [Ca2+]i resulted in Ca2+ entry across the plasma membrane, which could be blocked by La3+, the inorganic Ca2+ antagonist. The tyrosine protein kinase inhibitor, genistein, inhibited the production of inositol phosphates and the elevation of [Ca2+]i induced by IFN gamma, but had no effect on ATP, suggesting that tyrosine protein kinase is involved in the signaling transduction of IFN gamma. We conclude that the mobilization of intracellular Ca2+ and the production of inositol phosphates are two important signaling events for the action of IFN gamma in human thyrocytes.

Interferon-gamma inhibits thyrotropin-induced thyroglobulin gene transcription in cultured human thyrocytes.

It has been shown that interferon-gamma (IFN gamma) can induce HLA class II antigen expression by thyroid epithelial cells and may play a role in the pathogenesis of autoimmune thyroid disease. We have examined the metabolic effect of recombinant human IFN gamma (0.001-500 U/mL) on thyroglobulin (TG) synthesis and secretion in cultured human thyrocytes. Thyrocytes dispersed from human Graves' thyroid tissues were cultured in the presence of TSH with or without IFN gamma. IFN gamma alone had not effect on either basal TG secretion or de novo TG synthesis, as measured by immunoprecipitation. At 100 U/mL and above, IFN gamma inhibited TSH-induced TG secretion into the medium. At 500 U/mL, IFN gamma inhibited TSH- or dibutyryl cAMP-induced TG synthesis at the gene transcription level, as evidenced by the decrease in steady state TG mRNA. IFN gamma had no effect on either basal or TSH-induced cAMP release by the thyrocytes, suggesting that the inhibitory effect occurs at a site distal to cAMP formation. These data demonstrate that IFN gamma directly inhibits TSH-stimulated TG gene expression and TG secretion. This provides further evidence that IFN gamma has a metabolic effect on thyroid hormone synthesis.