H-2z homozygous New Zealand mice as a model for B-cell chronic lymphocytic leukemia: elevated bcl-2 expression in CD5 B cells at premalignant and malignant stages

In New Zealand mice, the major histocompatibility complex (MHC) controls the development of both autoimmune disease and B cell chronic lymphocytic leukemia (B-CLL). While H-2d/H-2z heterozygosity acts as one major predisposing genetic element for autoimmune disease, H-2z/H-2z homozygosity acts as an element for B-CLL. In the H-2z/H-2z homozygotes, there was an age-dependent increase in frequencies of CD5 B cells in the blood and spleen, and such CD5 B cells showed oligoclonal to monoclonal expansion, giving rise to B-CLL. B-CLL cells from these mice had surface phenotypes typical of CD5 B lineage cells, and expressed high levels of proto-oncogene bcl-2. Elevated bcl-2 expression was also observed in premalignant B cells in the aged mice, thereby suggesting that apoptosis-resistant, long-surviving CD5 B cells with a self-renewal capacity form the basis of malignant transformation. This model not only provides clues for analyzing multiple steps of genetic alterations involved in the generation of B-CLL, but also sheds light on the correlation between B-CLL and autoimmune disease.

Concentrations of lomefloxacin in radicular cyst and oral tissues following single or multiple oral administration

Concentrations of lomefloxacin in serum, the wall and fluid of radicular cyst, gingiva, and jawbone following single or multiple oral administration were measured. The highest concentrations of lomefloxacin in serum, cyst wall, cyst fluid, gingiva, and jawbone occurred at 3 h after multiple administration, and were 2.31 micrograms/ml, 4.06 micrograms/g, 1.54 micrograms/ml, 4.72 micrograms/g and 2.79 micrograms/g, respectively. The mean concentration ratios of wall/serum, fluid/serum, fluid/wall, gingiva/serum, and jawbone/serum at the highest concentrations were 1.74, 0.73, 0.47, 2.52 and 1.20, respectively. Although most lomefloxacin concentrations in cyst and oral tissues following single oral administration did not exceed the MICs for 80% of clinically isolated strains of alpha-hemolytic streptococci, Staphylococcus aureus and Niesseria spp., most of those obtained after multiple oral administration exceeded the MICs except in the case of fluid.

Factor IX Fukuoka. Substitution of ASN92 by His in the second epidermal growth factor-like domain results in defective interaction with factors VIIa/X

Hemophilia B Fukuoka, a moderately severe bleeding disorder, is a naturally occurring mutant of factor IX. Plasma from our patient had 3% clotting activity even though 64% of factor IX antigen was present. The purified mutant protein was cleaved normally by factor Xla, factor VIIa-tissue factor complex, or RVV-X (factor X-activating enzyme from Russell's viper venom), yielding a two-chain factor IXa. Amino acid composition and sequence analyses of one of the lysyl endopeptidase peptides derived from factor IX Fukuoka revealed that Asn92 in the second epidermal growth factor (EGF)-like domain had been replaced by His. The active site of the factor IXa Fukuoka was normally competent for the incorporation of p-aminobenzamidine and for the hydrolysis of a synthetic substrate, N alpha-benzyloxycarbonyl-L-arginine p-nitrobenzyl ester. Factor Xa formation by factor IXa Fukuoka was only 8% of the normal factor IXa, even in the presence of polylysine, and only 0.2% of the normal in the system containing phospholipids, Ca2+, and factor VIIIa, thereby indicating a functional defect in interaction of the mutant with factors VIIIa/X. Furthermore, catalytic efficiency (kcat/Km) of factor IXa Fukuoka toward factor X in the presence of Ca2+, phospholipids, and factor VIIIa was only 2.3% of the normal factor IXa. These results suggest that an Asn-to-His substitution at position 92 in the second EGF-like domain of factor IX Fukuoka would have an untoward effect on the specific conformational state of factor IX for binding with factors VIIIa/X.

Atypical anxiolytic profile of buspirone and a related drug, SM-3997, in a modified forced swim test employing straw suspension

Previous reports have shown that immobility time increases in the presence of suspended straws in association with an inhibition of straw-climbing behavior after acute administration of a prototypical anxiolytic benzodiazepine (BZD) such as diazepam. In this modified forced swim (MFS) test employing straw suspension, the effects of two new non-BZD compounds were tested and compared with those of diazepam (0.5, 1, and 5 mg/kg, IP) used in a previous MFS test. After a 5-min test of forced swimming, four straws were suspended just above the surface of the water and subsequently the straw-climbing trials were counted for 5 min as an index of escape behaviors induced by negative emotionality (stress and/or anxiety). Rats were injected IP with either saline, buspirone HCl (0.5, 1, and 5 mg/kg), or a related compound, SM-3997 (5, 10, and 20 mg/kg), 30 min before testing. At lower doses, both buspirone (0.5, 1 mg/kg) and SM-3997 (5, 10 mg/kg) reduced the duration of immobility, as opposed to that of diazepam. Conversely, buspirone at the highest dose of 5 mg/kg significantly prolonged the duration of immobility, and SM-3997 at 20 mg/kg also prolonged its duration, indicating a biphasic effects. All doses of buspirone and SM-3997 inhibited straw-climbing counts, in the same manner as diazepam. These results suggest that buspirone may possess relatively weak and/or atypical anxiolytic effects at lower doses, whereas at 5 mg/kg this compound may have an anxiolytic effect. In addition, SM-3997 may be a less potent anxiolytic drug than buspirone in the MFS test following a single-injection protocol.

Effects of renal denervation on pressure-natriuresis in spontaneously hypertensive rats

To investigate the role of renal sympathetic nerve activity (RSNA) under developing and established hypertension, renal function was studied in chronically renal-denervated and sham-operated male spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY) at 8 (early hypertensive) and 22 (established hypertensive) weeks of age. To further characterize the renal pressure-natriuresis-diuresis relationship in SHR, renal perfusion pressure (RPP) was reduced by aortic constriction to the level seen in age-matched WKY and the same studies were repeated. After denervation, urinary sodium excretion (UNaV), fractional excretion of sodium (FENa) and urine flow (UF) were increased in 8-week-old SHR (p < 0.01). With the exceptions of UNaV and FENa in denervated 8-week-old SHR, renal cortical blood flow, glomerular filtration rate, UF, UNaV and FENa decreased with the reduction of RPP in all of the SHR groups. These results suggest that RSNA significantly influences renal sodium and fluid handling, thus contributing to the shifting of the arterial pressure-renal sodium excretion curve to the right along the pressure axis and/or to an increase in the steepness of the relationship in 8-week-old SHR. There appeared to be a marked difference in renal sodium handling between 8- and 22-week-old SHR.

Induction of metallothionein and its localization in the nucleus of rat hepatocytes after partial hepatectomy

Metallothioneins, a group of cysteine-rich heavy-metal binding proteins, are induced in the regenerating rat liver in response to the stimuli evoked by partial hepatectomy. We have investigated the expression of metallothionein genes and proto-oncogenes (c-fos, c-jun and c-myc), as well as specific localization of metallothionein in the liver cells after partial hepatectomy. Metallothionein mRNA was detected as early as 3 hr and reached a maximal level by 6 hr. Expression of the proto-oncogenes apparently preceded the elevation of metallothionein protein because the latter was maximal 18 hr after partial hepatectomy, followed by a decrease until 70 hr. Hepatocytes of the intact rat liver have metallothionein in the cytoplasm only. Interestingly, metallothionein was localized predominantly in the nucleus as early as 6 hr after partial hepatectomy, and the staining intensity of metallothionein became maximal at 15 hr, followed by detection in both the cytoplasm and nucleus at 24 hr or longer. The use of a confocal laser scanning microscope with both tissue sections and isolated nuclei has clearly shown that metallothionein immunofluorescence exists inside hepatocyte nuclei after partial hepatectomy. Expression of the proto-oncogenes c-fos and c-jun is elevated after partial hepatectomy, and the resultant heterodimer of gene products may contribute to the observed metallothionein gene induction. However, the observation that metallothionein protein levels were elevated until 18 hr after partial hepatectomy suggests that an alternative pathway for the induction of metallothionein gene expression may also be present.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatic diversification and affinity maturation of IgM and IgG anti-DNA antibodies in murine lupus

Molecular events occurring during the process of generation of pathogenic immunoglobulin (Ig)G anti-DNA antibodies in systemic lupus erythematosus (SLE) were studied using a newly established method. We analyzed the Ig variable (V) region gene sequence and DNA-binding activity of IgM and IgG anti-DNA monoclonal antibodies (mAb) from individual SLE-prone (NZB x NZW) F1 mice. The first event appeared to be clonal selection and expansion of IgM anti-DNA clones, in which several clones had intraclonal V gene mutations. Although the number of mutations was small, the mutated IgM clones were associated with an increase in DNA-binding activity. The somatic mutations located in complementarity-determining regions (CDR) and in framework regions (FR) of V genes were apparently related to changes in DNA-binding activity. IgG anti-DNA clones that progressively increased in number with aging had numerous somatic mutations in the V region genes and there was a pair of clones which showed an intraclonal accumulation of mutations, in association with increase in the DNA-binding activity. All these findings show that somatic mutations associated with affinity maturation of the V region begin immediately before isotype-switching from IgM to IgG of the clones that have been selected and expanded, in an antigen-driven manner and/or by other forces. We propose that further accumulations of intraclonal somatic hypermutation, in association with selection and expansion of high affinity IgG clones, may lead to formation of highly pathogenic anti-DNA antibodies.

[Rest and stress myocardial perfusion imaging on the same day with two injections of 99mTc-tetrofosmin]

99mTc-tetrofosmin myocardial perfusion imagings under different protocols were performed at rest and stress on the same day. In the stress/rest protocol, the exercise study was carried out first, and then the rest one followed. Eight patients were involved in the stress/rest protocol. Seven patients were examined in the reverse, rest/stress protocol. In any protocols, the injection interval was 3 hours, and injection doses in the first and second studies were 370 MBq and 740 MBq, respectively. Myocardial counts were obtained by placing region of interest over the myocardial walls in short axial SPECT images. Based on myocardial counts from the first injection and the wash-out rate of tetrofosmin, we calculated, at the second imaging, counts caused from the first injection. Approximately 20-25% of counts in the second study were found to be caused from the residual radiotracer. The residual radiotracers affected the interpretation of imagings of two patients we examined: one with marked reversible ischemia examined in the stress/rest protocol and the other with mild ischemic change examined in the rest/stress one. Our results suggested that some modifications of studies, such as the increase in the injection intervals or the reduce of the first-to-second dose ratio, might be necessary to conduct the same day protocols.

Glucose transporter recycling in rat adipose cells. Effects of potassium depletion

Depletion of intracellular potassium (K+) induced a 4-fold increase in basal and 1 microM phorbol-12-myristate-13-acetate (PMA)-stimulated 3-O-methylglucose transport in rat adipose cells. K+ depletion had no effect on the maximum insulin (0.7 microM)-stimulated transport rate but enhanced the sensitivity to insulin 3-fold (EC50 = 0.05 versus 0.15 nM) by a mechanism that did not result from changes in the insulin receptor binding, autophosphorylation, or tyrosine kinase activity. Western blotting analysis revealed that K+ depletion induced a 2.2-fold increase in GLUT4 in plasma membranes from basal cells, enhanced the PMA-stimulated GLUT4 translocation by 4-fold, and increased the 5-fold insulin-stimulated GLUT4 translocation by 15%, indicating the presence of an inactive GLUT4 intermediate. The time course for insulin's stimulation of transport activity was accelerated by K+ depletion (t1/2 = 3 versus 1.5 min). Conversely, the reversal of transport activity, on removal of insulin, was delayed (t1/2 = 11 versus 22 min). The corresponding t1/2 values for the loss of GLUT4 were 22 min in control cells and 40 min in K(+)-depleted cells, again indicating the existence of an inactive intermediate. Photolabeling intact cells with the impermeant, exofacial photolabel 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 - yloxy)-2-propylamine in the continuous presence of insulin revealed that K+ depletion had no effect on the GLUT4 externalization rate but halved the rate of internalization. K+ depletion elicited entirely analogous effects on the recycling of insulin-like growth factor II/mannose 6-phosphate receptor, strongly supporting the involvement of a coated pit mechanism in the recycling of GLUT4 transporters. An inactive conformation of GLUT4 has been detected in plasma membranes from insulin-stimulated cells, which is enhanced by K+ depletion, suggesting a limitation in the adipose cells' capacity to express active GLUT4 transporters.

Disseminated pancreatic polypeptidioma

Pancreatic polypeptidioma, a pancreatic endocrine tumor, is an extremely uncommon disease and its clinical features and responses to therapy are not well known. We present a 33-year-old woman with disseminated pancreatic polypeptidioma, who subsequently showed various signs and symptoms of metastases, including bone pain, cranial nerve palsy, spinal block, and hematuria, and died 22 months after the presentation. Responses to various therapeutic regimens including hepatic arterial embolization, radiation therapy, systemic chemotherapy, and administration of interferon-alpha or somatostatin analogue, are discussed. Particular note in this case is a prompt response of bone metastases to the radiotherapy.

Long-term alpha 1 blockade does not reverse cardiac hypertrophy in spontaneously hypertensive rats

Not all antihypertensive drugs induce regression of left ventricular (LV) hypertrophy in hypertension, although they may equally lower blood pressure. The effects of alpha 1-blockers on regression have been inconsistent. In this study, bunazosin, a selective alpha 1-blocker, (15 mg/kg/day in food) was given to male spontaneously hypertensive rats (SHR) from 15 to 35 weeks of age to evaluate its effects on cardiac hypertrophy, hemodynamics, and neurohumoral factors. Age- and sex-matched SHR served as controls. LV function and cardiac output were determined by a micromanometer and thermodilution, respectively. Bunazosin significantly decreased blood pressure in conscious rats (from 209 to 192 mmHg, p < 0.01) but did not reduce LV mass. Heart rate, LV end-diastolic pressure, dp/dtmax, and cardiac output were similar in the 2 groups. Plasma renin activity was unaltered but plasma norepinephrine levels were higher in the treated rats (p < 0.05). Thus, bunazosin produced a significant relative reduction of blood pressure but did not reverse LV hypertrophy in SHR. Inadequate afterload reduction (8%) due to severe hypertension (> 200 mmHg) may explain the absence of regression. The rise of plasma norepinephrine levels may also offset the beneficial effects of bunazosin.

Use of bismannose photolabel to elucidate insulin-regulated GLUT4 subcellular trafficking kinetics in rat adipose cells. Evidence that exocytosis is a critical site of hormone action

The subcellular trafficking of tracer-tagged GLUT4 between the plasma membranes and low-density microsomes of rat adipose cells has been studied. Cell-surface GLUT4 have been initially tracer-tagged in the insulin-stimulated state with the [3H]bismanose photolabel 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2- propylamine. The half-time for internalization of tracer-tagged GLUT4 when insulin is removed by collagenase treatment is similar to that observed for the decrease in immunodetectable GLUT4 in the plasma membranes and the decrease in glucose transport activity in the intact cells. In contrast, internalization of tracer-tagged GLUT4 also occurs when cells are maintained in the continuous presence of insulin even though the plasma membrane level of immunodetectable GLUT4 and glucose transport activity in the intact cells are unaltered. These data show, for the first time, that insulin has little, if any, effect on the rate constant for GLUT4 endocytosis, but instead, primarily increases the rate constant for exocytosis. Tracer-tagged GLUT4 that is returned to the low-density microsomes can be restimulated with fresh insulin to recycle to the plasma membranes and to a steady-state distribution level that is the same as that observed in cells that are maintained in the continuous presence of insulin. These data suggest that the cells' entire complement of GLUT4 is involved in the recycling process. Following insulin stimulation of adipose cells initially in the basal state, the increase in immunodetectable GLUT4 in the plasma membranes precedes the increase in accessibility of GLUT4 to exofacial 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 -yloxy)-2- propylamine photolabeling, and this in turn precedes the increase in cellular glucose transport activity. Such time course data suggest that there may be plasma membrane intermediate states in the GLUT4 trafficking pathway. The kinetic properties of GLUT4 translocation and its recycling have been interpreted in terms of a subcellular trafficking model that identifies exocytosis, possibly involving-hypothetical "docking" and "fusion" steps, as the critical site of hormone action.

Isolation and characterization of a thiamin pyrophosphokinase gene, THI80, from Saccharomyces cerevisiae

The thi80 mutant of Saccharomyces cerevisiae (Nishimura, H., Kawasaki, Y., Nosaka, K., Kaneko, Y., and Iwashima, A. (1991) J. Bacteriol. 173, 2716-2719) shows markedly reduced activity of thiamin pyrophosphokinase (TPK; EC 2.7.6.2). We have isolated a DNA fragment carrying the THI80 gene from a yeast genomic library by its ability to complement constitutive synthesis of the thiamin-repressible acid phosphatase, encoded by the PHO3 gene, of thi80 mutant cells. On the other hand, the thi80 locus was found to be located 3.3 centimorgans proximal to the smp3 locus on the right arm of chromosome XV by genetic mapping analysis, and one more fragment bearing the THI80 gene trailing SMP3 gene was obtained by the plasmid eviction method. The nucleotide sequence of the overlapped region between the two isolated DNAs contained an open reading frame of 957 base pairs, encoding a 319-amino acid polypeptide with a calculated molecular weight of 36,616. When the intact THI80 open reading frame was expressed as a fusion protein carrying three vector-encoded amino acids at its N terminus in Escherichia coli lacking TPK, marked TPK activity was detected in the procaryotic cells, proving that the THI80 gene of S. cerevisiae encodes a structural gene of TPK. A gene disruption experiment demonstrated that the THI80 gene was essential for growth, and therefore, revealed that TPK is the only enzyme capable of synthesizing thiamin pyrophosphate in yeast. Studies of Northern blot analysis and the enzyme assay demonstrated that the THI80 gene expression is regulated mainly at the mRNA level by the intracellular thiamin pyrophosphate and requires the positive regulatory factors encoded by THI2 and THI3 genes. However, unlike thiamin-repressible acid phosphatase and the enzymes involved in thiamin synthesis of S. cerevisiae, TPK was found to be expressed constitutively at a low level and incompletely repressed by exogenous thiamin.

Construction of an antigenic map of the haemagglutinin-esterase protein of influenza C virus

Four different antigenic sites (A-1, A-2, B-1, B-2) have been identified previously on the haemagglutinin-esterase (HE) glycoprotein of influenza C/Ann Arbor/1/50 virus with seven monoclonal antibodies (MAbs). In this study we produced 30 additional anti-HE MAbs, nine of which demonstrated at least one of the following activities: haemagglutination inhibition, receptor-destroying enzyme inhibition, haemolysis inhibition, and neutralization (group A). The remaining had none of these activities (group B). These antibodies, and those previously isolated, were used to construct a more complete antigenic map of the HE molecule. Operational and topological analyses showed that a minimum of nine non-overlapping or partially overlapping antigenic sites were present on the HE protein, five recognized by group A MAbs (A-1 to A-5) and four by group B (B-1 to B-4). Among these antigenic sites, site A-5 was unique in that MAbs to this site inhibited the receptor-destroying activity without influencing the receptor-binding activity, which supports the idea that the sites responsible for these two functions are separate. It was also found that several group B MAbs were cross-reactive with host cell antigens.

Rescue of neuronal function by cross-regeneration of cutaneous afferents into muscle in cats

1. This study investigates the relation between the peripheral innervation of low-threshold cutaneous afferents and the postsynaptic potentials elicited by electrical stimulation of those afferents. 2. In cats deeply anesthetized with pentobarbital sodium, cord dorsum potentials (CDPs) and postsynaptic potentials (PSPs) in spinal motoneurons were elicited by stimulation of the caudal cutaneous sural nerve (CCS), the lateral cutaneous sural nerve (LCS), and the medial gastrocnemius (MG) muscle nerve. We tested 1) unoperated cats, and cats in which CCS has been 2) chronically axotomized and ligated, 3) cut and self-reunited, 4) cut and cross-united with LCS, or 5) cut and cross-united with the MG. Terminal experiments were performed 3-36 mo after initial surgery. 3. In cats in which the CCS had been self-reunited or cross-united distally with LCS, tactile stimulation of the hairy skin normally innervated by the distal nerve activated afferents in the CCS central to the coaptation, indicating that former CCS afferents had regenerated into native or foreign skin, respectively. 4. In cats in which the CCS had been cross-united distally with the MG, both stretch and contraction of the MG muscle activated the former CCS afferents. 5. In unoperated cats, CDPs elicited by stimulation of CCS and of LCS exhibited a low-threshold N1 wave and a higher-threshold N2 wave. These waves were greatly delayed and appeared to merge after chronic axotomy of CCS. Regeneration of CCS into itself, into LCS, or into MG restored the normal latencies and configurations of these potentials. 6. In unoperated cats, stimulation of CCS, of LCS, and of MG each produced PSPs of characteristic configurations in the various subpopulations of motoneurons of the triceps surae. CDPs and PSPs elicited by the CCS cross-regenerated into LCS or MG were typical of those generated by the normal CCS, i.e., there was no evidence of respecification of central synaptic connections to bring accord between center and periphery after cross-regeneration. 7. Chronic axotomy of CCS increased the latencies of PSPs from CCS; regeneration of CCS into the CCS, LCS, or MG restored normal latencies. 8. In summary, CDPs and PSPs in motoneurons from the cutaneous sensory nerve CCS are altered by chronic axotomy of CCS, thus indicating their target dependency. These alterations are restored by regeneration of CCS into not only a native or foreign cutaneous target, but also into skeletal muscle. We conclude that muscle as well as skin is capable of providing trophic support for cutaneous afferents.

[A case of bronchial artery aneurysm communicating with pulmonary artery]

A 48-year-old man was admitted to our hospital because of an abnormal shadow on the chest rentogenogram detected by the regular health screening. A tumorous shadow about 10 mm in diameter existed in the right lower lobe on chest X-ray film. It was suggested that the tumor was receiving blood flow from the aortic system by IVDSA and dynamic CT, right bronchial angiogram demonstrated a dilatation and aneurysm formation associated with anastomosis of the pulmonary artery. Aneurysmectomy and right bronchial arterial ligation were performed, and no other complication was observed. Bronchial artery aneurysm is a rare disease, and 25 cases have been previously reported in the literature in Japan.

Ampicillin concentrations in radicular cysts following a single oral administration of bacampicillin

1. Ampicillin concentrations in cyst wall (wall) and cyst fluid (fluid) of radicular cyst and serum following a single oral administration of bacampicillin (equivalent to 500 mg of ampicillin) were measured by a paper disk method. 2. The mean peak concentrations of ampicillin in wall, fluid, and serum occurred at identical times, 1.5 hr, and were 2.39 micrograms/g, 0.77, and 10.24 micrograms/ml, respectively. 3. Mean ampicillin concentration ratios of wall/serum, fluid/serum, and fluid/wall at the peak time were 0.23, 0.07, and 0.40, respectively. 4. Mean ampicillin concentrations in wall and fluid at the peak time exceeded MIC (minimum inhibitory concentration) for 90% (0.5 microgram/ml) for clinically isolated strains of alpha-hemolytic Streptococci.

Myelo-monocytoid immunophenotypes of B-cell chronic lymphocytic leukemia cells

Leukemia cells from ten patients with B-cell chronic lymphocytic leukemia (B-CLL) and one with B-CLL of mixed cell type (B-CLL/PL) were analyzed to delineate the cellular characteristics, especially the myelomonocytic nature. Most of the surface phenotypes were consistent with the previous reports. However, the frequency of positivity for CD22 and CD25 was much higher in the examined cases of B-CLL than in Western reports. B-CLL cells frequently possessed antigens which are mainly expressed in myelomonocytic cells: 8/10 for CD11b and 4/10 for CD11c, although the presence of CD14 was not apparent (0/10). In addition, colony stimulating factor-1 receptors (CSF-1R) were expressed in 6 of the 10 B-CLL cases. The reactivity with antigens such as CD14, CD11c, and CSF-R was markedly enhanced by in vitro incubation. Alterations in antigen expression and in in vitro survival by growth factors for myelomonocytic lineage were observed in certain cases. These data imply that not only are B-CLL cells phenotypically closely related to myelomonocytic lineage but that they may also be influenced by growth factors for that lineage.

Mixed haplotype A beta Z/A alpha d class II molecule in (NZB x NZW)F1 mice detected by T cell clones

We have tried to demonstrate the existence of a mixed haplotype MHC class II molecule in (NZB x NZW)F1 (B/WF1) mice. When a large panel of keyhole limpet hemocyanin-specific T cell clones derived from B/WF1 mice was analyzed, several clones were shown to be restricted by a F1-specific A beta Z/A alpha d class II molecule. Autoreactive A beta Z/A alpha d-specific T cell clones were also obtained. The ability of the association and expression of A beta Z with A alpha d was confirmed by hybridoma and transfection experiments. Hybridoma cell lines created by fusion of NZW (H-2z) spleen cells with M12.C3 (a A beta d- variant cell line derived from M12.4.1 (H-2d) B lymphoma) cells expressed A beta Z determinants. Transfection of A beta Z genomic DNA to M12.C3 cells resulted in the expression of A beta Z determinants. These hybridoma cell lines and transfectants were able to stimulate A beta Z/A alpha d-specific T cell clones, suggesting the expression of A beta Z/A alpha d molecules on the cell surface. However, attempts to demonstrate the existence of mixed haplotype MHC class II molecules in B/WF1 mice by two-dimensional (nonequilibrium pH gradient gel electrophoresis/SDS-PAGE) gel electrophoresis analysis with the use of anti-class II mAb failed to demonstrate the existence of mixed haplotype A beta Z/A alpha d or A beta d/A alpha z class II molecules in B/WF1 mice. Analysis of mixture of TA beta Z cell and B/WF1 spleen cell lysates immunoprecipitated by anti-A beta Z mAb suggested that the amount of haplotype mixed A beta Z/A alpha d molecules in B/WF1 spleen cells is less than 1/10 that of haplotype matched A beta/A alpha pairs. Our results suggest that, although undetectable by biochemical analysis, small amounts of mixed haplotype A beta Z/A alpha d molecules exist in B/WF1 spleen cells. Also, T cell clones which recognize them exists in B/WF1 mice. Because autoimmune symptoms of B/WF1 mice are shown to be related to heterozygosity at the H-2 region, autoreactive T cell clones which recognize the mixed haplotype A beta Z/A alpha d class II molecule might be involved for the induction of autoimmunity in B/WF1 mice.