Insulin down-regulates resistin mRNA through the synthesis of protein(s) that could accelerate the degradation of resistin mRNA in 3T3-L1 adipocytes.

AIMS/HYPOTHESIS: Resistin is a peptide secreted by adipocytes and recognized as a hormone that could link obesity to insulin resistance. This study was designed to examine the effect and mechanism(s) of insulin on resistin expression in 3T3-L1 adipocytes. METHODS: Differentiated 3T3-L1 adipocytes were stimulated with insulin and resistin mRNA expression was examined by Northern blot analysis. In some experiments, the insulin signal was blocked by several chemical inhibitors or overexpression of a dominant negative form (Deltap85) of the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase). RESULTS: Insulin treatment caused a reduction of resistin mRNA in time-dependent and dose-dependent manners in 3T3-L1 adipocytes. Pre-treatment with PD98059, an inhibitor of extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, or SB203580, an inhibitor of p38 mitogen-activated protein-kinase (p38 MAP-kinase) pathway, did not influence insulin-induced reduction of resistin mRNA. Inhibition of PI 3-kinase by LY294002 or Deltap85 also failed to block insulin-induced reduction of resistin mRNA. Cycloheximide, a protein synthesis inhibitor, completely blocked insulin-induced reduction of resistin mRNA. Actinomycin D, a RNA synthesis inhibitor, also blocked insulin-induced reduction of resistin mRNA, and the decreasing rate of resistin mRNA in cells treated with insulin alone was faster than that with actinomycin D. CONCLUSION/INTERPRETATION: Insulin downregulates resistin mRNA via PI 3-kinase, ERK or p38 MAP-kinase independent pathways in 3T3-L1 adipocytes. The downregulation mechanism of resistin mRNA by insulin would be an indirect event through the synthesis of novel protein(s) that could accelerate the degradation of resistin mRNA.

Heterozygous knockout of the IRS-1 gene in mice enhances obesity-linked insulin resistance: a possible model for the development of type 2 diabetes.

Insulin receptor substrate 1 (IRS-1) gene polymorphisms have been identified in type 2 diabetic patients; however, it is unclear how such polymorphisms contribute to the development of diabetes. Here we introduced obesity in heterozygous IRS-1 knockout (IRS-1(+/-)) mice by gold-thioglucose (GTG) injection and studied the impact of reduced IRS-1 expression on obesity-linked insulin resistance. GTG injection resulted in approximately 30% weight gain in IRS-1(+/-) and wild type (WT) mice, compared with saline-injected controls. There was no difference in insulin sensitivity between lean IRS-1(+/-) and lean WT. Elevated fasting insulin levels but no change in fasting glucose were noted in obese IRS-1(+/-) and WT compared with the respective lean controls. Importantly, fasting insulin in obese IRS-1(+/-) was 1.5-fold higher (P<0.05) than in obese WT, and an insulin tolerance test showed a profound insulin resistance in obese IRS-1(+/-) compared with obese WT. The islets of obese IRS-1(+/-) were 1.4-fold larger than those of obese WT. The expression of insulin receptor and IRS-1 and IRS-2 was decreased in obese IRS-1(+/-), which could in part explain the profound insulin resistance in these mice. Our results suggest that IRS-1 is the suspected gene for type 2 diabetes and its polymorphisms could worsen insulin resistance in the presence of other additional factors, such as obesity.

Second national external quality assessment scheme in hematology: the Philippine experience.

The Philippine Council for Quality Assurance In Clinical Laboratories has conducted two National External Quality Assessment Schemes (NEQAS) in Hematology. The first survey was conducted in December 1999 and the second in August 2000, with 95 and 187 laboratories, using mostly automated analyzers, participating respectively. Control materials were distributed during a two-week period by human network, and analyzed over a six to eight week period. For the first survey, only 36 laboratories (38.0%) submitted results. Data was divided into 4 peer groups based on the manufacturer. Since most of the samples were hemolysed upon analysis, only WBC and HGB parameters were evaluated. No outliers were detected in each peer group after analysis by the 'Peer Group Mean and SDI' method. Using the clinical laboratory improvement act of 1988 proficiency testing criteria (CLIA'88), only 5 results (13.9%) were unsatisfactory for WBC, and all results were satisfactory for HGB. For the second survey, 87 laboratories (47%) responded. Data was divided into 5 peer groups. There were few incidents of sample deterioration. Although majority of the coefficient of variations were acceptable, about 23 (12.6%) participants showed abnormality in at least one parameter after analysis by the 'Peer Group Mean and SDI'. Using CLIA'88, 5 WBC (6.5%), 6 RBC (7.6%), 8 HGB (9.7%), 15 HCT (19.0%), and 7 PLT (8.0%) results were unsatisfactory. In summary, the first NEQAS study served as a pilot study. Valuable lessons were learned for the improvement of the second NEQAS. The second NEQAS study was marked by a much larger sample size and better results.

Involvement of bradykinin in acute exercise-induced increase of glucose uptake and GLUT-4 translocation in skeletal muscle: studies in normal and diabetic humans and rats.

Acute exercise induces glucose uptake in skeletal muscle in vivo, but the molecular mechanism of this phenomenon remains to be identified. In this study, we evaluated the involvement of bradykinin in exercise-induced glucose uptake in humans and rats. In human studies, plasma bradykinin concentrations increased significantly during an ergometer exercise (20 minutes) in 8 healthy normoglycemic subjects and 6 well-controlled type 2 diabetic patients (mean hemoglobin A1c [HbA1c], 6.4% +/- 0.6%), but not in 6 poorly controlled type 2 diabetics (mean HbA1c, 11.6% +/- 2.6%). In rat studies, plasma bradykinin concentrations also significantly increased after 1 hour of swimming in nondiabetic and mildly diabetic (streptozotocin [STZ] 45 mg/kg intravenously [IV]) rats, but not in rats with severe diabetes (STZ 65 mg/kg IV). Glucose influx (maximum velocity [Vmax]) and GLUT-4 translocation in skeletal muscle of nondiabetic rats significantly increased after 1 hour of swimming, but these increases were abrogated by subcutaneous infusion of bradykinin B2 receptor antagonist HOE-140 (400 microg x kg(-1) x d(-1)). Insulin-stimulated tyrosine phosphorylation and phosphatidylinositol (PI) 3-kinase activity in response to insulin injection (20 U/kg IV) in the portal vein were significantly attenuated in exercised rats pretreated with HOE-140 compared with saline-treated exercised rats. Our results suggest that plasma bradykinin concentrations increase in response to acute exercise and this increase is affected by blood glucose status in diabetic patients. Moreover, the exercise-induced increase in bradykinin may be involved in modulating exercise-induced glucose transport through an increase of GLUT-4 translocation, as well as enhancement of the insulin signal pathway, during the postexercise period in skeletal muscle, resulting in a decrease of blood glucose.

Bradykinin enhances insulin receptor tyrosine kinase in 32D cells reconstituted with bradykinin and insulin signaling pathways.

We have previously shown that bradykinin potentiated insulin-induced glucose uptake through GLUT4 translocation in canine adipocytes and skeletal muscles. The aim of this study was to determine the molecular mechanism of bradykinin enhancement of the insulin signal. For this purpose, 32D cells, which express a limited number of insulin receptors and lack endogenous bradykinin B2 receptor (BK2R) or insulin receptor substrate (IRS)-1 were transfected with BK2R cDNA and/or insulin receptor cDNA and/or IRS-1 cDNA, and analyzed. In 32D cells that expressed BK2R and insulin receptor (32D-BKR/IR), bradykinin alone had no effect on the phosphorylation of the insulin receptor, but it enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor. In 32D cells that expressed BK2R, insulin receptor and IRS-1 (32D-BKR/IR/IRS1), bradykinin also enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1. An increase in insulin-stimulated phosphorylation of IRS-1 by treatment with bradykinin in 32D-BKR/IR/IRS1 cell was associated with increased binding of 85 kD subunit of phosphatidylinositol 3 (PI 3)-kinase and increased IRS-1 associated PI 3-kinase activity. These effects of bradykinin were not observed in 32D cells which lack the expression of BK2R (32D-IR/IRS1) or insulin receptor (32D-BKR/IRS1). Furthermore, tyrosine phosphatase activity against insulin receptor beta-subunit in plasma membrane fraction of 32D-BKR/IR cells was significantly reduced by bradykinin, suggesting that the effect of bradykinin was in part mediated by inhibition of protein tyrosine phosphatase(s). Our results clearly demonstrated that bradykinin enhanced insulin-stimulated tyrosine kinase activity of the insulin receptor and downstream insulin signal cascade through the BK2R mediated signal pathway.

Cellular characterization of pituitary adenoma cell line (AtT20 cell) transfected with insulin, glucose transporter type 2 (GLUT2) and glucokinase genes: insulin secretion in response to physiological concentrations of glucose.

We investigated the mechanisms of insulin secretion by transfecting into a pituitary adenoma cell line (AtT20) a combination of genes encoding human insulin (HI), glucose transporter type 2 (GLUT2) and glucokinase (GK), followed by studying the characteristics of these cells. In static incubation, a cell line transfected with insulin gene alone (AtT20HI) secreted mature human insulin but this was not in a glucose-dependent manner. Other cell lines transfected with insulin and GLUT2 genes (AtT20HI-GLUT2-3) or with insulin and GK genes (AtT20HI-GK-1) secreted insulin in response to glucose concentrations of only less than 1 mmol/l. In contrast, cell lines transfected with insulin, GLUT2 and GK genes (AtT20HI-GLUT2-GK-6, AtT20HI-GLUT2-GK-7 and AtT20HI-GLUT2-GK-10) showed a glucose-dependent insulin secretion up to 25 mmol/l glucose. Glucose utilization and oxidation were increased in AtT20HI-GLUT2-GK cell lines but not in AtT20HI, AtT20HI-GLUT2-3 and AtT20HI-GK-1 cells at physiological glucose concentrations, compared with AtT20 cells. Diazoxide, nifedipine and 2-deoxy glucose suppressed (p < 0.05) glucose stimulated insulin secretion in AtT20HI-GLUT2-GK-6 cells. Glibenclamide, KCl or corticotropin releasing factor (CRF) stimulated (p < 0.05) insulin secretion both in AtT20HI and AtT20HI-GLUT2-GK-6 cells. Insulin secretion stimulated by glibenclamide, KCl or CRF was further enhanced by the addition of 25 mmol/l glucose in AtT20HI-GLUT2-GK-6 cells but not in AtT20HI cells. In perifusion experiments, a stepwise increase in glucose concentration from 5 to 25 mmol/l stimulated insulin secretion in AtT20HI-GLUT2-GK cell lines but the response lacked a clear first phase of insulin secretion. Our results suggest that both GLUT2 and glucokinase are necessary for the glucose stimulated insulin secretion in at least rodent cell lines, and that other element(s) are necessary for a biphasic insulin secretion typically observed in beta cells.

Creation and characterization of a mitochondrial DNA-depleted pancreatic beta-cell line: impaired insulin secretion induced by glucose, leucine, and sulfonylureas.

It has been proposed that mitochondrial oxidative phosphorylation in pancreatic beta-cells plays an important role in insulin secretion. To examine the impact of mitochondrial dysfunction on insulin secretion, we created a MIN6 cell line that depleted mitochondrial DNA (mtDNA) by treatment with ethidium bromide (EtBr), and studied the response of the cell line to various secretagogues. MIN6 cells cultured with 0.5 microg/ml EtBr for over 2 months (termed MIN6 deltamt cells) revealed a marked (>90%) decrease in mtDNA content and a lack of mRNAs encoded by mtDNA. MIN6 deltamt cells showed the defects of cytochrome c oxidase activity, glucose- and leucine-induced increase in cellular ATP content, and respiratory chain-driven ATP synthesis, suggesting that MIN6 deltamt cells lost oxidative phosphorylation activity due to the selective disruption of the subunits of respiratory chain enzymes encoded by mtDNA. MIN6 deltamt cells also showed a decrease in glucose utilization, suggesting the impairment of the glycolytic pathway as well. After stimulation with glucose and leucine, MIN6 deltamt cells showed no response in insulin secretion or intracellular free Ca2+ concentration ([Ca2+]i). On the other hand, arginine stimulated insulin secretion and an increase in [Ca2+]i in MIN6 deltamt cells as in MIN6 cells. Glibenclamide also stimulated insulin secretion and an increase in [Ca2+]i in both types of cells, but the responses of MIN6 deltamt cells were significantly lower than those of MIN6 cells. These results suggest the importance of ATP production in insulin secretion and an increase in [Ca2+]i, both induced by glucose and leucine. Moreover, mitochondrial function turns out to be not essential but important for the activation of sulfonylurea-induced insulin secretion.

Molecular and genetic analysis of a compound heterozygote for dysprothrombinemia of prothrombin Tokushima and hypoprothrombinemia.

The molecular and genetic basis of a compound heterozygote for dys- and hypoprothrombinemia was analyzed. Abnormal nucleotide sequences of the human prothrombin gene were screened by PCR-single-strand conformation polymorphism (PCR-SSCP) with endonuclease digestion and mutated primer-mediated PCR-RFLP. A single nucleotide substitution responsible for dysprothrombinemia of prothrombin Tokushima was detected, as were three polymorphisms. The mutation for hypoprothrombinemia was detected by PCR-single-strand conformation polymorphism (PCR-SSCP) with endonuclease digestion in exon 6, near MboII-RFLP and NcoI-RFLP. Sequencing of PCR-amplified genomic DNA revealed a single base insertion of thymine (T) at position 4177. The resulting frameshift mutation caused both an altered amino acid sequence from codon 114 and a premature termination codon (i.e., TGA) at codon 174 in exon 7. Because exon 7 encodes the kringle 2 domain preceding the thrombin sequence, this frameshift leads to the null prothrombin phenotype. The inheritance of the hypoprothrombinemia gene from the father to the proband was proved by PCR-SSCP with endonuclease digestion and mutated primer-mediated PCR-RFLP.

Detection of a single base substitution of the gene for prothrombin Tokushima. The application of PCR-SSCP for the genetic and molecular analysis of dysprothrombinemia.

The genetic and molecular basis of a mutant prothrombin of 'prothrombin Tokushima' was studied by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and PCR-restriction fragment length polymorphism (PCR-RFLP) analyses. The abnormal gene was detected by altered migration by PCR-SSCP and by the loss of an MspI site by PCR-RFLP. The gene for prothrombin Tokushima was shown to be inherited from the mother of the proband. Sequencing analysis using PCR-amplified genomic DNA clarified a substitution of thymine (T) for cytosine (C) at position 9,490, changing arginine (Arg) to tryptophan (Trp) at position 418 of the polypeptide chain. This point mutation is assumed to be the molecular basis of prothrombin Tokushima, firstly, because of the absence of distinct changes in Southern blot analysis of the proband's DNA (using a full-length human prothrombin cDNA as a probe), secondly, because it has the same molecular weight as the abnormal gene product, and, thirdly, because of the absence of other amino acid abnormalities in the proteolytic peptide-fragments. It is concluded that PCR-SSCP and PCR-RFLP were useful for detecting the abnormal gene and for directly diagnosing the carrier status of dysprothrombinemia. This is the first report of gene analysis of dysprothrombinemia.

[IBL-type lymphadenopathy after infection of rubella virus].

A 52-year-old woman presented slight fever, diffuse papular skin rash and painful cervical lymph node swelling. Her lymph node swelling generally up to 3 cm in diameter, with petechiae on the lower legs and hepato-splenomegaly within a few weeks. ESR was 45 mm/h, Hb 10.0 g/dl, RBC 345 x 10(4)/microliter, WBC 22,600/microliter (atypical lymphocyte 47%), PLT 1.0 x 10(4)/microliter, GPT 91 U/L, gamma-globulin 34.3%, EBV-VCA x 2,560, EBNA x 20, and anti-rubella antibody x 512. The biopsied cervical lymph node showed histologic features of effacement of nodal architecture by an exuberant vascular proliferation accompanied with infiltration of the immunoblasts, and was diagnosed as immunoblastic lymphadenopathy (IBL)-type lymphadenopathy. The pulse therapy of methylprednisolone and high dose of gamma-globulin improved lymphadenopathy, thrombocytopenia and anemia. IBL-type lymphadenopathy after infection of rubella virus may be different from true IBL, but is important to discuss the pathogenesis of IBL.

Activation of blood coagulation and fibrinolysis in vibration syndrome.

The pathophysiology of peripheral circulatory disturbance in patients presenting with vibration syndrome was studied from the viewpoint of blood coagulation. Plasma levels of fibronectin (FN), vitronectin (VN), thrombin-antithrombin III complex (TAT), and alpha 2-plasmin inhibitor-plasmin complex (PIC) were measured in 23 subjects who showed no evidence of vibration-induced white finger [VWF(-) group] and in 24 patients who presented with VWF [VWF(+) group]. In the VWF(-) group, plasma FN concentrations were elevated but plasma TAT and PIC levels were within the normal ranges. In the VWF(+) group, plasma FN concentrations were normal but plasma TAT and PIC levels were significantly elevated. In both groups, plasma VN concentrations were similar to those in normal controls. For purposes of comparison, 32 patients presenting with diabetes mellitus were also studied. They were divided into 2 groups, 13 subjects who showed no evidence of angiopathy [complication(-) group] and 19 patients who presented with angiopathy [complication(+) group]. In the complication(+) group, plasma TAT and PIC concentrations were significantly elevated, as in the VWF(+) group. These results suggest that in vibration syndrome, vibration, cold stimulus, or other factors first injure the vascular endothelium, resulting in a rise in plasma FN, and that in the VWF(+) group, augmentation of coagulation and fibrinolysis induces a state of compensated disseminated intravascular coagulation (DIC).

Fibronectin receptor on polymorphonuclear leukocytes in families of Ehlers-Danlos syndrome and other hereditary connective tissue diseases.

Studies were made on the fibronectin receptor on polymorphonuclear leukocytes of patients with hereditary connective tissue diseases and of healthy members of their families. In four patients with Ehlers-Danlos syndrome type II (family E) and type VI (family M), the maximum number of binding sites (Bmax) of fibronectin receptor was significantly decreased to 2.2 to 2.9 x 10(3) sites/cell (normal range 6.3 +/- 1.5 x 10(3) sites/cell). The Bmax values of healthy members of their families were normal or moderately decreased to 3.8 to 5.1 x 10(3) sites/cell. In a patient with osteogenesis imperfecta type III (family K) the Bmax was significantly decreased to 1.1 x 10(3) sites/cell, but healthy members of his family had normal Bmax values. In a patient with Marfan syndrome (family A) the Bmax was decreased to 4.3 x 10(3) sites/cell. The dissociation constant of the fibronectin receptor was normal in all subjects examined. Some healthy members of the families of the patients with Ehlers-Danlos syndrome had moderately decreased Bmax values, suggesting that they are carriers of an abnormal gene causing this disorder. These data suggest that fibronectin receptor is closely related to the pathogenesis of hereditary connective tissue diseases.

HTLV-I-associated myelopathy with adult T-cell leukemia.

We report a 42-year-old Japanese woman with HTLV-I-associated myelopathy (HAM) combined with adult T-cell leukemia (ATL). Combination of the 2 diseases has been extremely rare. The infrequency is explained by HLA types unique to each disease. Our patient suggests that the HAM-associated HLA haplotype does not prevent the development of ATL.

Binding of plasma fibronectin to human polymorphonuclear leukocytes in normal subjects and patients with aplastic anemia and thyroid dysfunction.

The binding of iodine 125-labeled fibronectin to polymorphonuclear leukocytes (PMNs) from human peripheral blood was examined. The optimum temperature and time for the binding were 37 degrees C and 30 minutes, respectively. On increase in the amount of 125I-labeled fibronectin, its binding to PMNs became saturated. Scatchard analysis of data on binding indicated the presence of a single class of binding sites. PMNs from 15 normal subjects had approximately 6.3 +/- 1.6 x 10(3) sites per cell and a dissociation constant of 10.2 +/- 2.4 x 10(-9) mol/L, indicating that they had high affinity for soluble fibronectin. Arg-Gly-Asp-Ser inhibited the binding of fibronectin to PMNs, strongly suggesting that the fibronectin receptor is one of the Arg-Gly-Asp receptor family. The plasma level of fibronectin was higher in patients with hyperthyroidism and lower in patients with hypothyroidism than in normal subjects, without any significant change in the number of fibronectin binding sites of the PMNs. However, the number of binding sites of fibronectin on PMNs of patients with aplastic anemia was increased, probably because of sensitization of the PMNs with immune complex and other factors.

X-linked dominant control of F-cells in normal adult life: characterization of the Swiss type as hereditary persistence of fetal hemoglobin regulated dominantly by gene(s) on X chromosome.

Fetal hemoglobin (HbF) levels determined in healthy Japanese adults ranged from 0.3% to 16.0% as F cells and 0.17% to 2.28% as HbF content, which were the same as those obtained in other countries. The frequency distribution of 300 healthy adults with various numbers of F cells consisted statistically of two different groups, low and high F-cell groups. Individuals with greater than or equal to 4.4% of F cells (HbF about 0.7%) were defined as the high F-cell trait, which accounted for 11.3% of males and 20.7% of females. Family studies of 21 probands with this trait and sex-different frequency analyses in the population and probands revealed X-linked dominant inheritance. Two other families of the trait associated with color blindness were described, although no definitive evidence for linkage was obtained between the two. A review of population and family studies reported in the literature indicated that persons with Swiss-type hereditary persistence of fetal hemoglobin (HPFH) are of the same kind as this trait in their incidence and inheritance form, but represent a portion of the trait with higher levels of HbF or F cells. The existence of X chromosome-localized regulatory gene(s) for the developmental switch of human Hb production is discussed.

Metabolism of plasma fibronectin in rabbits with experimental hyperthyroidism and hypothyroidism.

We previously reported that the concentration of plasma fibronectin (pFN) is increased in patients with hyperthyroidism and decreased in those with hypothyroidism. In this work, labeled pFN was given intravenously to euthyroid, hyperthyroid, and hypothyroid rabbits to examine its metabolism in states of thyroid dysfunction. In euthyroid rabbits, the serum concentration of thyroxine (T4) was 2.94 +/- 0.59 micrograms/dL, and that of pFN was 24.2 +/- 1.2 mg/dL. With 125I-FN as tracer, the half life was estimated as 72.8 +/- 2.6 hours, the fractional catabolic rate (FCR) as 2.08 +/- 0.07%/h, the rate of synthesis (SR) as 3.84 +/- 0.20 mg/kg/day and j1/j2 (the ratio of the exchange coefficients between intravascular and extravascular compartments) of pFN as 0.295 +/- 0.051. With 3H-FN as tracer, these values were not significantly different. In hyperthyroid rabbits, obtained by treatment with I-thyroxine, the serum T4 concentration was increased to 5.73 +/- 1.58 micrograms/dL and the pFN concentration to 29.6 +/- 2.2 mg/dL. In these animals, the half life of pFN was shortened to 59.8 +/- 1.0 hour, the FCR was slightly increased to 3.07 +/- 0.52%/h and the SR was greatly increased to 7.13 +/- 1.17 mg/kg/d. In hypothyroid rabbits, obtained by treatment with methylthiouracil, the serum T4 and pFN levels were reduced to 1.50 +/- 0.36 micrograms/dL and to 20.7 +/- 1.7 mg/dL, respectively, the FCR and SR were also decreased to 1.39 +/- 0.04%/h and 2.26 +/- 0.14 mg/kg/d, respectively. The values of j1/j2 did not significantly change during this work.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in lymphocyte subsets and serum immunoglobulin levels in patients with silicosis.

The numbers of total lymphocyte and lymphocyte subsets in peripheral blood of patients with silicosis and their serum immunoglobulin (Ig) levels were studied to evaluate their immune status. The numbers of total lymphocytes and OKT4+ and OKT8+ cells tended to be decreased and the numbers of OKT3+ cells was significantly decreased (p less than 0.001), but that of OKIa-1+ cells was increased (p less than 0.001) in the patients. In the lymph nodes of the lung hilus, the ratio of OKT4+ cells to total lymphocytes was increased but that of OKT8+ cells to total lymphocytes was decreased. The serum levels of IgG and IgA were elevated in the patients with reduction in the numbers of total lymphocytes and OKT4+ cells in peripheral blood. The serum IgE levels in 17 of 82 patients were above 400 IU/ml. In 8 patients with serum IgE 82 patients were above 400 IU/ml. In 8 patients with serum IgE levels of more than 1,000 IU/ml, the numbers of total lymphocytes and OKT3+ and OKT4+ cells were decreased compared with those in controls. The following suggestions are proposed from the results: Increase and activation of helper T cells may be caused by the presentation of silica dust to macrophages in the lymph nodes, and these cells may then stimulate B cell proliferation and Ig production by B cells, resulting in increase in the serum Ig (IgG, IgA and IgE) level. Reduction in the number of OKT4+ cells helper/inducer T cells) in peripheral blood may be due to migration of helper T cells into the lymph nodes. These immunological events in patients with silicosis are probably due to the adjuvant effect of silica dust.