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Glycated hemoglobin (HbA1c) is an important indicator of glycemic control in patients with diabetes. High-performance liquid chromatography (HPLC) is the most commonly used method for measuring HbA1c levels; as HPLC measures all hemoglobin types, the values can be influenced by hemoglobin variants. Moreover, as HPLC-HbA1c levels are low in some diseases, including hemolytic anemia, it may be difficult to differentiate hemoglobin variants from these diseases based on HPLC-HbA1c levels alone. Similar HbA1c values using both HPLC and immunoassays (IAs) are noted for these diseases, while discrepancies are noted in the case of hemoglobin variants. Herein, we describe our process of differential diagnosis for hereditary spherocytosis, the most common inherited hemolytic anemia, in a 56-year-old man presenting with a low HPLC-HbA1c level compared to the glucose concentration, concomitant with anemia, jaundice, hyperbilirubinemia, cholelithiasis, and splenomegaly. There was a discrepancy between HbA1c levels measured with HPLC and IAs and glycated albumin levels. The possibility of hemoglobin variants was unlikely, based on the chromatography and isoelectric focusing results. The haptoglobin levels and reticulocyte counts were low and high, respectively. The direct and indirect Coomb’s tests were negative. The presence of spherocytes on blood smears and flow cytometric analysis of the eosin-5-maleimide binding test supported a diagnosis of hereditary spherocytosis. We recommend that when a discrepancy between HPLC-HbA1c levels and glucose concentrations is noted, clinicians should consider hemolysis or hemoglobin variants as the diagnosis. It should be considered that a discrepancy between HbA1c levels measured with HPLC and IAs does not specifically exclude hemolysis.

A failure in the compensate proliferation of pancreaticβ-cells, as the primary pathogenic event, has been reported in OLETF rat, a model of NIDDM. The aim of the present study is to define whether theβ-cell defect is attributed to the fetal stage islet development, if so, whether the defect involves down regulation of PDX-1 protein expression. Morphological changes,β-cell function, and the expression of PDX-1 protein were examined in the cultured fetal islet-like cell clusters (ICCs) from OLETF rats along with their diabetes-resistant control counterpart LETO rats in the presence of 5.5 or 11.1mM glucose for 48, 72, 96, and 120-hr, respectively. We have observed four abnormalities in the ICCs of OLETF rats. First, a defective morphogenesis was noted during the 72 to 120-hr ICC culture, a period characterized by a dramatic increase in bothβ-cell and non-β-cell (α,σ, and PP) populations in control rats. This defective morphogenesis was demonstrated by a growth retardation of epithelial stratification and poor development of bothβ-cell and non-β-cell masses along with a parallel decline in relevant islet hormone contents. Second, a functional defect was characterized by failure to response to glucose during the 96 to 120- hr-cultured ICCs. Third, the ultrastructural analysis revealed a significant reduction in the number of secretory granules. Four, Western blot analysis showed a significant decrease of PDX-1 protein expression in the OLETF ICCs cultured in 11.1mM glucose for 48 to 72-hr and in 5.5mM glucose for 120-hr. Therefore, we concluded that during the fetal stage of islet development, OLETF rats exhibit both morphological and functional defects.

The Otsuka-Long-Evans-Tokushima fatty (OLETF) rat is a genetic model of spontaneous development of non-insulin-dependent diabetes mellitus (NIDDM) established as an inbred strain after 20 generations of selective breeding. Although they are thought to be genetically homogeneous, they show a dimorphism regarding the diabetic phenotype at an advanced age, with one remaining obese and modestly diabetic while the other becomes lean and overtly diabetic. To clarify the causes for this divergence, we examined the physical, biochemical, and histopathological features in rats at 50 weeks of age, including an analysis of islet angioarchitecture. Sixty-one of 85 male OLETF rats lost weight, while the remainder remained obese. Mean nonfasting plasma glucose in the lean group was 21.8+/-4.6 mmol/L, significantly higher versus the obese group (10.5+/-1.4 mmol/L) and the age-matched control Long-Evans-Tokushima-Otsuka (LETO) group (7.1+/-0.6 mmol/L). Morphological studies of the pancreas from the lean group showed enlarged multilobulated fibrotic islets with a paucity of B cells, whereas islets from the obese group appeared slightly enlarged and showed a relative abundance of B cells. The fine capillaries that form a network in the islets were extremely sparse in the lean group, resulting in a defective glomerular-like configuration, whereas those from the obese group were dense, forming a nearly typical glomerular-like configuration. Increased plasma insulin responses to oral and intravenous (i.v.) glucose and i.v. glucagon loads were nearly absent in the lean group, while they were evident in the obese group, although to a lesser extent compared with the LETO group. Mean insulin secretory output from the perfused pancreas in response to 11.1 mmol/L glucose in the lean group (3.5+/-2.2 pmol/20 min) was significantly lower versus the obese group (8.8+/-6.5 pmol/20 min) and LETO group (22.0+/-10.8 pmol/20 min). Similarly, pancreatic insulin content was significantly lower in the lean group (9.3+/-6.1 microg) versus the others (26.1+/-17.3 microg for obese and 41.1+/-24.8 microg for LETO). In vivo insulin-stimulated glucose uptake measured by a euglycemic clamp technique was significantly higher in the lean group compared with the obese group. These results demonstrate that the dimorphism regarding the diabetic phenotype in male OLETF rats at 50 weeks of age was due to differences in the number of islet B cells, which could be the result of a variation in the capacity for B-cell proliferation among male OLETF rats.

Otsuka Long–Evans Tokushima Fatty (OLETF) rats are a new strain of spontaneous non-insulin-dependent diabetes mellitus (NIDDM) models. To evaluate the role of glucose transporters (GLUT) in the development of diabetes in this model, we examined the action of insulin on the translocation of GLUT4 and GLUT1 in isolated adipocytes, and the GLUT4 protein levels in muscles. Long–Evans Tokushima Otsuka (LETO) rats were used as a control strain. In adipocytes, the GLUT4 protein levels in OLETF rats at 30 weeks of age (diabetic stage) were considerably lower than those in LETO rats at the same age. At a pre-diabetic stage (7 weeks), there were no significant differences in GLUT4 protein levels in adipocytes between LETO and OLETF rats. However, the degree of GLUT4 translocation in OLETF rats was lower than that in LETO rats at 7 weeks of age. There were no differences in GLUT1 levels in adipocytes between the two strains. In muscles, the decrease in GLUT4 protein was observed in OLETF rats at 30 weeks of age. Whether such a difference is under the influence of hyperglycemia was also examined using rats rendered diabetic by 70% pancreatectomy. OLETF rats aged 7 weeks were subjected to partial pancreatectomy (Px) and sham pancreatectomy (sham). At 4 weeks after surgery, GLUT4 protein levels in adipose tissues and skeletal muscles were determined. GLUT4 decrease was observed for both tissues of hyperglycemic Px rats compared with euglycemic sham. Moreover, we examined the direct effect of glucose on GLUT4 protein using primary cultured adipocytes of OLETF rats at 5 weeks of age. After 7-day culture with normal (5.6 mmol/l) or high (25 mmol/l) concentrations of glucose, the GLUT4 protein levels in adipocytes decreased at 25 mmol/l glucose compared with 5.6 mmol/l glucose. These findings suggest an early defect in the insulin resistance of OLETF rats probably reflects impaired GLUT4 translocation. The GLUT4 decrease, which occurs later in the process appears to be a consequence, rather than a cause of diabetes in OLETF rats.

Glucokinase (GK) plays a key role in the regulation of glucose-induced insulin secretion, and questions have been raised about its relationship to the glucose transporter GLUT2 and its function in diabetes. This study examined the location of immunostained GK and GLUT2 in beta-cells using confocal microscopy. On double stained sections from pancreases of normal fed rats, GLUT2 Texas Red staining was restricted to the plasma membrane, and GK fluorescein isothiocyanate staining was found in a limited area of cytoplasm that was perinuclear with slight extension toward the apical pole. The GK staining occupied 8.6 +/- 1.7% of total cytoplasmic area and was almost never adjacent to the GLUT2 staining of the plasma membrane. To determine whether the GK staining pattern is altered by metabolic perturbation, normal rats were made acutely hyperglycemic with iv glucose injections; after 20 min the GK staining changed from being localized to become diffusely distributed throughout the cytoplasm. To examine the influence of chronic hyperglycemia, rats were subjected to 90% partial pancreatectomy (Px), which produced glucose levels of 10.9-20.8 mM. When studied 6 or 14 days after Px, those rats with glucose levels greater than 17.7 mM had an altered GK staining pattern that was variable; in some beta-cells GK staining was diffuse and in others the localized staining pattern was preserved. GLUT2 staining was reduced overall, but variability between cells was observed, unlike the more uniform reductions seen with hyperglycemia of longer duration. Other rats received islet transplants to prevent hyperglycemia after Px; their GK and GLUT2 staining patterns were normal. These findings indicate that GK is translocated in association with acute and chronic hyperglycemia. The translocation of this key enzyme for glucose recognition by beta-cells may lead to altered rates of insulin secretion during acute perturbations of fuel provision and in the diabetic state.

Either 200 or 400 syngeneic islets were transplanted under the kidney capsule of normal or streptozocin-induced diabetic B6/AF1 mice. The diabetic mice with 400 islets became normoglycemic, but those with 200 islets, an insufficient number, were still diabetic after the transplantation (Tx). Two weeks after Tx, GLUT2 expression in the islet grafts was evaluated by immunofluorescence and Western blots, and graft function was examined by perfusion of the graft-bearing kidney. Immunofluorescence for GLUT2 was dramatically reduced in the β-cells of grafts with 200 islets exposed to hyperglycemia. However, it was plentiful in grafts with 400 islets in a normoglycemic environment. Densitometric analysis of Western blots on graft homogenates demonstrated that GLUT2 protein levels in the islets, when exposed to chronic hyperglycemia for 2 weeks, were decreased to 16% of those of normal recipients. Moreover, these grafts had defective glucose-induced insulin secretion, while the effects of arginine were preserved. We conclude that GLUT2 expression in normal β-cells is promptly down-regulated during exposure to hyperglycemia and may contribute to the loss of glucose-induced secretion of diabetes.

We studied the effect of treatment with cyclophosphamide (CY) on the incidence of diabetes in Long-Evans Tokushima Lean (LETL) rats, a newly established strain of spontaneously type I diabetic rats. The overall incidence of diabetes among 356 LETL rats treated with CY was 25.6%, which was significantly higher than the 10.5% among 857 untreated LETL rats at 27 weeks of age, and there was no significant sex difference. The incidence of CY-induced diabetes in adult (>16 weeks of age) female LETL rats was 7.7% ( 10 130 ), which was significantly lower than that in other CY-treated groups of LETL rats. No diabetes mellitus was induced by administration of CY to 23 diabetes-resistant LETO rats. There were no significant differences in the degrees of hyperglycemia or hyperketonemia in spontaneously and CY-induced diabetic LETL rats, but the plasma glycated albumin level of CY-induced diabetic rats (10.3% ± 2.1%) was significantly higher than that of spontaneously diabetic rats (8.2% ± 1.3%), suggesting that plasma glucose levels increased more rapidly in the latter. More than half of the diabetic rats showed type C or D morphological changes of the islets, ie, atrophic change with little mononuclear cell infiltration or almost complete loss of the islets. However, distributions of various types of morphological changes in the islets were not significantly different in the two groups. Ovariectomy (OVX) significantly increased the incidence of CY-induced diabetes in adult female rats from 7.7% to 20.8%. The number of CD8 + cells was significantly increased in noncastrated adult female LETL rats and decreased to the level of other groups after OVX. These results indicate that CY is diabetogenic in our colony, and that its effect is related to the gonadal hormone environment.

To determine whether starvation affects the metabolism of glucagon-like peptide-1 (GLP-1), we measured the plasma levels of proglucagon-derived peptides and the biosynthesis and posttranslational processing of proglucagon in groups of six rats starved for 1, 3 and 5 days. The plasma levels of GLP-1 immunoreactivity (GLP-1 IR) and glucagon-like immunoreactivity (GLI) decreased during starvation reaching 79 and 56% of the respective control values by day 5 (P less than 0.05 and less than 0.01 vs control). The same is true of the plasma IRI level. The ileal contents of GLP-1 IR and GLI were 50.8 +/- 3.8 pmol/g wet weight and 161.8 +/- 13.2 pmol/g wet weight, respectively, on day 5 of starvation, which were significantly lower (P less than 0.01) than the respective values of 94.8 +/- 16.6 pmol/g wet weight and 262.7 +/- 28.1 pmol/g wet weight in control rats. However, the pancreatic contents of proglucagon-derived peptides tended to increase during starvation, although their increases were not statistically significant. No significant change in the posttranslational processing of proglucagon was detected during starvation. The decrease in the ileal proglucagon-derived peptides content was not associated with a decrease in intestinal proglucagon mRNA transcripts. These results suggested that decreased synthesis of proglucagon-derived peptides by the intestine was largely responsible for the reductions in their circulating levels in starved rats.

A sexual dimorphism regarding the incidence of diabetes mellitus in OLETF rat, a model of Type II diabetes, has been reported. As a result, the effects of ovarian hormones on beta cells per se was examined by comparing the capacity of beta-cell proliferation and changes in blood glucose and plasma insulin concentrations after a 70 % pancreatectomy. All female animals were randomly assigned to two protocols. The rats involved in protocol I received either a 70 % pancreatectomy (Px) or a sham pancreatectomy (sham) at 6 weeks of age, along with their diabetes-resistant counterparts, female LETO rats, which served as normal controls. The rats belonging to protocol II were given an ovariectomy (Ox) at 5 weeks of age, and one week later, they were subjected to either Px or the sham operation, with/without hormone (estradiol, 50 μg/kg; testosterone, 1 mg/kg) replacement. The findings indicate that the capacity for compensatory growth of beta cells after Px was affected by both sex hormonal and genetic components, since a 70 % Px resulted in sustained hyperglycaemia within the first week after surgery, but was ameliorated by an increase in beta-cell mass thereafter in the non-Ox Px OLETF rats. The Ox also caused a decline in beta-cell mass which could be improved by replacement with ovarian hormones. Not only endogenous but also replacement ovarian hormones, led to a beneficial effect on beta cells per se in OLETF female rats. This was reflected by an increased beta-cell mass accompanied by a parallel increase in plasma immunoreactive insulin concentration. The effects of ovarian hormones, however, contributed to the beta-cell hypertrophy rather than expansion of the beta-cell population to achieve glucose homeostasis, as evidenced by an increased area of individual beta-cell after Px rather than an increased BrdU-labelling index for the beta cells. The present study suggests that ovarian hormone-induced beta-cell hypertrophy may typically occur, to compensate for changes in functional demand as the results of a 70 % Px in female OLETF rats. [Diabetologia (1998) 41: 799–805]

Hypertriglyceridemia is known to be a feature of obesity-related NIDDM, but the patho-etiological significance of this association is obscure. The effects of triglycerides (TGs) on β-cell function and morphological changes in pancreas were examined using in vivo and in vitro approaches in male OLETF rats at ages 6, 12, and 30 weeks, with their diabetes-resistant counterpart, LETO rats, as normal controls. The results showed that, in the fasting state, plasma TGs in OLETF rats were increased 2.5-fold at age 6 weeks, 3.3-fold at age 12 weeks, and 6.2-fold at age 30 weeks, compared with age-matched LETO rats. The TG content in islets from 12-week-old OLETF rats was significantly increased when compared with those from their age-matched counterparts, but this was not the case with the 6-week-old OLETF rats. Therefore, the islets from 6-week-old rats were cultured with either free fatty acids (FFAs; 1.0 mmol/1 sodium oleate) or TG (5.0 mmoM Intralipide) for 72 h. Several abnormalities in OLETF rats were evident, in contrast to the results from control LETO rats: 1) glucose-induced insulin secretion was more inhibited by either FFAs or TGs in the presence of 27.7 mmol/l glucose, a result associated, at least in part, with reduced glucokinase activity in the islets; 2) a marked elevation in TG content was found in the islets; and 3) the deposition of fat droplets in the enlarged islets, even in the β-cells, was found by Oil Red O-insulin double staining at age 30 weeks. In conclusion, hypertriglyceridemia resulted in significant TG stores in the islets, which subsequently inhibited glucose-induced insulin secretion, at least in part, via reduced glucokinase activity in the islets. Fat droplets in islets, therefore, may play an important role in hastening the development of NIDDM in this rat model.

We studied whether obesity or inheritance was the more important factor in the development of non-insulin-dependent diabetes mellitus (NIDDM) using female Otsuka-Long-Evans-Tokushima Fatty rats (OLETF) possessing one of the diabetic genes, ODB-1 , and male Long-Evans-Tokushima-Otsuka rats (LETO) possessing no ODB-1 , neither of which were diabetic when bred normally. Diabetes-resistant male LETO rats and female OLETF rats (4 weeks old) were assigned to three groups of 6 rats each, respectively; two groups in which obesity was induced by high calorie ‘cafeteria’ diet (D), or ventromedial hypothalamus lesions (V) with normal chow diet and a control group fed on normal chow (C). Six male OLETF rats were used as NIDDM positive controls. The mean daily energy intakes of obese male LETO and female OLETF rats were higher than those of the respective C groups. At 27 weeks of age, the average body weights of the obese LETO and female OLETF rats were significantly higher than those of the respective C groups and similar to that of the male OLETF group. Abdominal fat deposits of the obese groups were significantly higher than those of the respective C groups. At 28 weeks of age, the cumulative incidence of diabetes mellitus in obese LETO rats was 0% in group D and 17% in group V, while that of obese female OLETF rats in groups D and V were 100%. At 29 weeks of age, the plasma immunoreactive insulin (IRI) responses to glucose in obese female OLETF rats, groups D and V, were higher than that in group C. In obese LETO rats, insulin-stimulated glucose disposal in vivo was similar to that in group C, but in obese female OLETF rats, it was reduced to 41% in group D and 37% in group V of that in group C. Sections of islets of the pancreas of obese LETO rats appeared histologically normal, whereas those of obese female OLETF rats showed enlarged multilobulated fibrotic islets. These results demonstrate that obesity is necessary, but not sufficient alone for the development of NIDDM in these rat models.

Long-term glyburide therapy has been reported to improve glucose-induced insulin secretion in patients with NIDDM. We examined the effects of glyburide on the synthesis release of insulin and insulin gene expression in isolated islets in vitro. Incubation with glyburide (500 ng/ml) significantly increased insulin release without affecting the insulin content. The PPI mRNA level was not increased after incubation for 1 h but was increased after incubation for 20 h. Incubation with 5 ng/ml of glyburide for 1 h or 20 h had no effect on the content or release of insulin, but incubation with 5 ng/ml of glyburide for 20 h significantly increased the PPI mRNA level and enhanced insulin release induced by 11 mM glucose. These results suggest that a high concentration of glyburide stimulates insulin release directly, while a low concentration of glyburide increases the PPI mRNA level and may thereby enhance glucose-induced insulin release.

DNA sequence analysis of class II HLA from Caucasian and black patients with type 1 (insulin-dependent) diabetes mellitus has suggested that aspartic acid at position 57 (Asp 57) of the DQ beta chain provides protection against insulin-dependent diabetes mellitus (IDDM). In contrast, most Japanese patients with IDDM have Asp 57-positive alleles. To determine the reason for the differences and to localize the HLA-linked diabetogenic gene in Japanese, we studied the DQA1 and DQB1 genes of Japanese patients with IDDM and control subjects by the polymerase chain reaction in combination with restriction fragment length polymorphism analysis. Associations of DQA1*0301 and DQB1*0303 with IDDM were observed. DQA1*01 was associated negatively with IDDM. The HLA-DR9 haplotype, which is associated positively with IDDM in Japanese, was associated with DQA1*0301 and DQB1*0303, indicating that the Japanese DR9 haplotype is the same as that in caucasians but different from that in blacks. Of the loci on Japanese DR9 haplotypes, the DQA1*0301 allele showed the highest association with IDDM. DQB1*0303 was also positively associated with IDDM. Since DQB1*0303 is identical to DQB1*0302 except that it contains Asp 57, the data suggests that an Asp 57-positive allele confers susceptibility to IDDM when the whole molecule of the DQ beta chain is similar to other susceptible DQ beta chains. DQA1*0301 appears to be a marker of IDDM in all these populations: Japanese, caucasian, and black.

The cellular mechanism of glucagon gene expression in intact rat islets and their synthesis and release of glucagon were investigated. Arginine significantly increased the amounts of preproglucagon mRNA and glucagon in the islets and glucagon release. H-7, a specific inhibitor of protein kinase C (PKC), significantly inhibited these effects of arginine. However, H-8, a potent inhibitor of cyclic nucleotide-dependent protein kinases, did not affect the arginine-induced biosynthesis of glucagon or glucagon release. These results suggest that the regulation of glucagon gene expression by arginine is mediated by PKC, not by cyclic nucleotide-dependent protein kinases.

Glucagon-like peptide-1 (GLP-1) has been reported to inhibit glucagon release. To investigate the mechanism involved, we examined the effects of GLP-1 on the preproglucagon mRNA level and the content and release of glucagon in the isolated rat islets. Arginine significantly increased the content and release of glucagon after incubation for 1 h or 18 h. The preproglucagon mRNA level was not increased after incubation for 1 h but was increased after incubation for 18 h. GLP-1(7–36 amide) significantly decreased the content and release of glucagon after incubation for 1 h or 18 h, but did not affect arginine-induced increase in the preproglucagon mRNA level after incubation for 18 h. These data suggest that GLP-1 suppresses post-transcriptional processes in the content and release of glucagon.

We have cloned cDNAs for IgG, induction factor and T cell replacing factor. The recombinant factors were shown to have multiple activities on B cells, which could explain most, if not all, of B cell growth and differentiation factor activities so far claimed. Since the recombinant factors were also shown to affect bone marrow-derived cells other than B cells, the names of interleukins 4 and 5 were proposed for IgG1 induction factor and T cell replacing factor, respectively.

Complementary DNA encoding the IgG1 induction factor, the first lymphokine directed to B lymphocytes, from a murine T-cell line has been cloned using a new strategy. The putative primary amino-acid sequence was deduced from the nucleotide sequence determined. The lymphokine synthesized by the direction of this cloned cDNA has many other functions, such as production of B-cell growth factor-1 and induction of Ia on B cells.

著明な低栄養状態にて血中CEAが異常高値を示し,栄養状態の改善とともにCEAが低下した症例を3例経験した. 3症例とも悪性腫瘍の術後で消化吸収不良症候群から極度の低栄養状態に陥ったが,臨床的には悪性腫瘍の再発は否定された.低栄養状態にてCEA高値が認められたが,栄養改善とともにCEAは低下,低栄養による代謝低下がCEA上昇に関連している可能性が示唆された.

We have determined the complete organization of the mouse CH gene family, which is comprised of the 8 CH genes in the order 5’-JH-6.5kb-Cμ-4.5kb-Cδ-55kb-Cγ3-34kb-Cγ1-21kb-Cγ2b-15kb-Cγ2a-14kb-Ce-12kb-Cα-3’. The S regions, which contain characteristic tandemly repeated unit sequences, are located 5’ to each CH gene except for the Cδ gene. There are at least two types of repetitive sequences dispersed in this 200 kb region. No pseudogenes are present. The arrangements of the CH genes in BALB/c and C57BL mice are similar, but the lengths of the S regions vary. The basic structures of all the CH genes are similar in that coding sequences are interrupted at the junctions of the domains and the hinge regions. Comparison of the nucleotide sequences of the CH genes revealed that sequence segments have been exchanged among members of the CH gene family. Cloning and characterization of human Cγ genes, i.e. Cγ1, Cγ2, Cγ3, Cγ4 and φCγ, indicate that the human Cγ gene family evolved by dynamic DNA rearrangements, including gene duplication, exon duplication, and exon reassortment by unequal crossing-over. A human pseudo-epsilon gene (Ce3) is a processed gene that has completely spliced out introns. The presence of movable genetic elements surrounding the Ce3 gene suggests that the Ce gene evolved by a translocation mechanism. Although S-S recombination has been shown to take place in myelomas and hybridomas secreting a large amount of immunoglobulin, analyses of the CH gene organization in normal spleen B cells bearing immunoglobulin on their surface suggest that RNA splicing may be responsible for the first step in class switching, followed by S-S recombination. The nucleotide sequences of S regions contain short common sequences, TGGG(G) and (G)AGCT. Comparison of nucleotide sequences surrounding recombination sites revealed common sequences TGAG and TGGG. A sister chromatid exchange model was proposed to explain deletion of CH genes accompanying S-S recombination. We have found that the S region serves as a preferred recombination site in E.coli extracts.

Flow cytometric analyses of surface immunoglobulins of human neoplastic B cells from four patients indicated that more than two isotypes were expressed on the surface of each patient's neoplastic B cells. Southern blot analysis of DNAs of these cells showed that each patient's neoplastic cells had the monoclonal rearrangement profile of the J segment of the immunoglobulin heavy-chain gene. Heavy-chain constant-region genes of these cells had no deletion associated with S-S recombination. Northern blot analysis of RNA from two neoplastic cells revealed that each RNA contained comparable amounts of mRNAs for two different isotypes which were identified by surface staining. These results support the hypothesis that the simultaneous expression of two different isotypes in a certain stage of B-cell differentiation is mediated by alternative RNA splicing without DNA deletion.

The involvement of soluble factors in the regulation of mammalian cell proliferation and differentiation has received considerable attention within the past decade. Extensive investigations have established the importance of soluble factor mediated control, during the ontogeny of many cellular populations, including normal epithelial, fibroblastic, hematopoetic and lymphoid (1).