The fatal case of "Pigmentibacter" bacteremia following aspiration pneumonia in elderly patient

"Pigmentibacter ruber" was first reported in 2021, a novel bacterium of the family Silvanigrellaceae, isolated from human blood of the patient with aspiration pneumonia after the drowning accident in Republic of China. However, until now, there is only one report describing "P. ruber" infection, and no case of isolation from natural environment has been reported so far. Thus, the infectivity and pathogenicity of "Pigmentibacter" spp. has not been clearly understood. In this report, we described the fatal case of "Pigmentibacter" bacteremia subsequently occurred after aspiration pneumonia probably due to accidental ingestion of irrigation water in the elderly patient. Despite administration of broad-spectrum antibiotic, the patient dramatically deteriorated and eventually deceased. Whole-genome sequencing showed the strain isolated from the patient was identified as "Pigmentibacter" sp. (designated as strain Takaoka) and antimicrobial sensitivity testing showed it displayed high minimum inhibitory concentrations against various antibiotics including β-lactam. Further studies are needed to clarify the clinical characteristics of "Pigmentibacter" and its relative's infections and their antimicrobial sensitivity; however, the present case supported the clinical characteristics of "Pigmentibacter" infection, which can lead to bacteremia following aspiration pneumonia caused by mis-swallowing contaminated water, and poor outcome potentially due to multidrug resistances.

High Incidence of Metastatic Infections in Panton-Valentine Leucocidin-Negative, Community-Acquired Methicillin-Resistant Staphylococcus aureus Bacteremia: An 11-Year Retrospective Study in Japan

Panton-Valentine leucocidin (PVL)-negative community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) was originally disseminated in Japan and has since replaced healthcare-associated MRSA (HA-MRSA). However, the clinical characteristics of CA-MRSA bacteremia (CA-MRSAB) compared with those of HA-MRSA bacteremia (HA-MRSAB) are unknown. We aim to clarify differences and investigate associations between the clinical manifestations and virulence genes associated with plasma-biofilm formation in PVL-negative CA-MRSA. From 2011 to 2021, when CA-MRSA dramatically replaced HA-MRSA, 79 MRSA strains were collected from blood cultures and analyzed via SCCmec typing and targeted virulence gene (lukSF-PV, cna, and fnbB) detection. The incidence of metastatic infection was significantly higher in CA-MRSAB than in HA-MRSAB. PVL genes were all negative, although cna and fnbB were positive in 55.6% (20/36) and 50% (18/36) of CA-MRSA strains and 3.7% (1/27) and 7.4% (2/27) of HA-MRSA strains, respectively. cna and fnbB carriage were not associated with the development of metastatic infections in MRSAB; however, the bacteremia duration was significantly longer in CA-MRSAB harboring cna. CA-MRSAB may be more likely to cause metastatic infections than HA-MRSAB. Since CA-MRSA is dominant in Japan, suspected metastatic infection foci should be identified by computed tomography, magnetic resonance imaging, and echocardiography when treating MRSAB.

Myositis with sarcoplasmic inclusions in Nakajo-Nishimura syndrome: a genetic inflammatory myopathy

AIMS

Nakajo-Nishimura syndrome (NNS) is an autosomal recessive disease caused by biallelic mutations in the PSMB8 gene that encodes the immunoproteasome subunit β5i. There have been only a limited number of reports on the clinicopathological features of the disease in genetically confirmed cases.

METHODS

We studied clinical and pathological features of three NNS patients who all carry the homozygous p.G201V mutations in PSMB8. Patients' muscle specimens were analysed with histology and immunohistochemistry.

RESULTS

All patients had episodes of typical periodic fever and skin rash, and later developed progressive muscle weakness and atrophy, similar to previous reports. Oral corticosteroid was used for treatment but showed no obvious efficacy. On muscle pathology, lymphocytes were present in the endomysium surrounding non-necrotic fibres, as well as in the perimysium perivascular area. Nearly all fibres strongly expressed MHC-I in the sarcolemma. In the eldest patient, there were abnormal protein aggregates in the sarcoplasm, immunoreactive to p62, TDP-43 and ubiquitin antibodies.

CONCLUSIONS

These results suggest that inflammation, inclusion pathology and aggregation of abnormal proteins underlie the progressive clinical course of the NNS pathomechanism.

Primary collagen VI deficiency is the second most common congenital muscular dystrophy in Japan

OBJECTIVES

To determine the frequency of primary collagen VI deficiency in congenital muscular dystrophy (CMD) in Japan and to establish the genotype-phenotype correlation.

METHODS

We performed immunohistochemistry for collagen VI in muscles from 362 Japanese patients with CMD, and directly sequenced the three collagen VI genes, COL6A1, COL6A2, and COL6A3, in patients found to have collagen VI deficiency.

RESULTS

In Japan, primary collagen VI deficiency accounts for 7.2% of congenital muscular deficiency. Among these patients, five had complete deficiency (CD) and 29 had sarcolemma-specific collagen VI deficiency (SSCD). We found two homozygous and three compound heterozygous mutations in COL6A2 and COL6A3 in all five patients with CD, and identified heterozygous missense mutations or in-frame small deletions in 21 patients with SSCD in the triple helical domain (THD) of COL6A1, COL6A2, and COL6A3. All mutations in SSCD were sporadic dominant. No genotype-phenotype correlation was seen.

CONCLUSION

Primary collagen VI deficiency is the second most common CMD after Fukuyama type CMD in Japan. Dominant mutations located in the N-terminal side from the cysteine residue in the THD of COL6A1, COL6A2, and COL6A3 are closely associated with SSCD.

A new congenital form of X-linked autophagic vacuolar myopathy

In a new family with X-linked congenital autophagic vacuolar myopathy (AVM), seven affected boys presented with congenital hypotonia, dyspnea, and dysphagia with delayed motor milestones. Muscle pathology revealed autophagic vacuoles with sarcolemmal features, multilayered basal lamina with marked sarcolemmal deposition of C5-9 membrane attack complex and calcium, histologically indistinguishable from childhood-onset X-linked myopathy with excessive autophagy (XMEA). Haplotype analysis suggests that this new AVM and XMEA may be allelic despite different clinical presentations.

Ullrich disease due to deficiency of collagen VI in the sarcolemma

The authors identified eight patients with Ullrich disease in whom collagen VI was present in the interstitium but was absent from the sarcolemma. By electron microscopy, collagen VI in the interstitium was never linked to the basal lamina. These findings suggest that in these patients it is not the total absence of collagen VI from the muscle but the failure of collagen VI to anchor the basal lamina to the interstitium that is the cause of Ullrich disease. Only one of the patients had a mutation in the collagen VI gene, suggesting that the primary abnormality in most of the patients involved some other molecules.

A novel form of autophagic vacuolar myopathy with late-onset and multiorgan involvement

The authors report a 41-year-old man with a novel form of adult-onset autophagic vacuolar myopathy (AVM) with multiple organ involvement including eyes, heart, liver, lung, kidney, and skeletal muscle. The vacuolar membranes had sarcolemmal features similar to vacuoles in Danon disease, X-linked myopathy with excessive autophagy, and infantile AVM. Lysosome associated membrane protein-2, absent in Danon disease, was present. Defined by distinct clinical features, this disease constitutes the fourth entity in the group of autophagic vacuolar myopathy in which the vacuolar membranes have features of sarcolemma.

Fukutin-related protein gene mutated in the original kindred limb-girdle MD 2I

The authors mapped an autosomal recessive form of limb-girdle MD on chromosome 19q13.3 (LGMD2I), further narrowed down the candidate region to 1.1 Mb, and identified one new homozygous mutation in the fukutin-related protein (FKRP) gene on patients of the original Tunisian family. Immunohistochemical and immunoblot analysis showed abnormal expression of alpha-dystroglycan and laminin-alpha2 supporting the hypothesis that FKRP has a role in the interaction between the extracellular matrix components.

Eosinophilic major basic protein and interleukin-5 in eosinophilic myositis

To determine whether eosinophils play a critical role in muscle fiber damage in patients with eosinophilic myositis (EM). We investigated expression of eosinophilic major basic protein (MBP) and interleukin (IL)-5 at the protein and mRNA levels in muscle biopsies from three patients with idiopathic EM. MBP deposits were found on the surface of eosinophils and muscle fibers surrounded by the eosinophils. Reverse transcriptase-polymerase chain reaction analysis showed increased IL-5 expression in EM muscle but not in control muscle. These results suggest that IL-5 induces local accumulation of eosinophils and their release of MBP. The secreted proteins adhere to the muscle fiber membrane, resulting in muscle damage.

Distal myopathy with rimmed vacuoles is allelic to hereditary inclusion body myopathy

BACKGROUND

Distal myopathy with rimmed vacuoles (DMRV) is an autosomal-recessive disorder with preferential involvement of the tibialis anterior muscle that starts in young adulthood and spares quadriceps muscles. The disease locus has been mapped to chromosome 9p1-q1, the same region as the hereditary inclusion body myopathy (HIBM) locus. HIBM was originally described as rimmed vacuole myopathy sparing the quadriceps; therefore, the two diseases have been suspected to be allelic. Recently, HIBM was shown to be associated with the mutations in the gene encoding the bifunctional enzyme, UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE).

OBJECTIVE

To determine whether DMRV and HIBM are allelic.

METHODS

The GNE gene was sequenced in 34 patients with DMRV. The epimerase activity in lymphocytes from eight DMRV patients was also measured.

RESULTS

The authors identified 27 unrelated DMRV patients with homozygous or compound-heterozygous mutations in the GNE gene. DMRV patients had markedly decreased epimerase activity.

CONCLUSIONS

DMRV is allelic to HIBM. Various mutations are associated with DMRV in Japan. The loss-of-function mutations in the GNE gene appear to cause DMRV/HIBM.

Ullrich disease: collagen VI deficiency: EM suggests a new basis for muscular weakness

Ullrich disease is a form of congenital muscular dystrophy characterized clinically by generalized muscle weakness, contractures of the proximal joints, and hyperflexibility of the distal joints from birth or early infancy. Recently, mutations of the collagen VI gene have been associated with Ullrich disease. The authors report on a boy with Ullrich disease who has complete deficiency of collagen VI and harbors compound heterozygous mutations in the collagen VI alpha 2 gene. Absence of microfibrils on EM, together with normal collagen fibrils and basal lamina, suggests that loss of a link between interstitium and basal lamina may be a new molecular pathomechanism of muscular dystrophy.

Clinicopathological features of genetically confirmed Danon disease

BACKGROUND

Danon disease is due to primary deficiency of lysosome-associated membrane protein-2.

OBJECTIVE

To define the clinicopathologic features of Danon disease.

METHODS

The features of 20 affected men and 18 affected women in 13 families with genetically confirmed Danon disease were reviewed.

RESULTS

All patients had cardiomyopathy, 18 of 20 male patients (90%) and 6 of 18 female patients (33%) had skeletal myopathy, and 14 of 20 male patients (70%) and one of 18 female patients (6%) had mental retardation. Men were affected before age 20 years whereas most affected women developed cardiomyopathy in adulthood. Muscle histology revealed basophilic vacuoles that contain acid phosphatase-positive material within membranes that lack lysosome-associated membrane protein-2. Heart transplantation is the most effective treatment for the otherwise lethal cardiomyopathy.

CONCLUSIONS

Danon disease is an X-linked dominant multisystem disorder affecting predominantly cardiac and skeletal muscles.

Antitumor effects of Marginisporum crassissimum (Rhodophyceae), a marine red alga

Marginisporum crassissimum (Yendo) Ganesan, a marine red alga found in the ordinal coastal sea around Japan, revealed antitumor (antimetastatic) effects in vitro and in vivo. In in vitro experiments, extracts of this alga inhibited not only the growth of several tumor cell lines, such as B16-BL6 (a mouse melanoma cell line), JYG-B (a mouse mammary carcinoma cell line) and KPL-1 (a human mammary carcinoma cell line), but also invasion of B16-BL6 cells in a culture system. In in vivo experiments, the lung metastasis of B16-BL6 cells inoculated to the tail vein of B57BL/6J mice was inhibited by intraperitoneal administration of an extract from the alga. In addition, life prolongation of B57BL/6J mice inoculated with B16-BL6 cells was also observed by the intraperitoneal administration of the extract. An effective substance showing B16-BL6 growth inhibition in vitro was partially purified by filtration and hydrophobic column chromatography, and was revealed to be sensitive to trypsin-digestion and heat-treatment. The molecular weight of the substance was greater than 100 kDa. This is the first study demonstrating antitumor (antimetastatic) effects of M. crassissimum.

Antigen-induced translocation of PKC-theta to membrane rafts is required for T cell activation

Protein kinase C-theta (PKC-theta) is essential for mature T cell activation; however, the mechanism by which it is recruited to the TCR signaling machinery is unknown. Here we show that T cell stimulation by antibodies or peptide-major histocompatibility complex (MHC) induces translocation of PKC-theta to membrane lipid rafts, which localize to the immunological synapse. Raft translocation was mediated by the PKC-theta regulatory domain and required Lck but not ZAP-70. In addition, PKC-theta was associated with Lck in the rafts. An isolated PKC-straight theta catalytic fragment did not partition into rafts or activate the transcription factor NF-kappa B, although addition of a Lck-derived raft-localization sequence restored these functions. Thus, physiological T cell activation translocates PKC-theta to rafts, which localize to the T cell synapse; this PKC-theta translocation is important for its function.

Induction of plant gp91 phox homolog by fungal cell wall, arachidonic acid, and salicylic acid in potato

The oxidative burst has been suggested to be a primary event responsible for triggering the cascade of defense responses in various plant species against infection with avirulent pathogens or pathogen-derived elicitors. The molecular mechanisms of rapid production of active oxygen species (AOS), however, are not well known. We isolated homologs of gp91 phox, a plasma membrane protein of the neutrophil NADPH oxidase, from a potato cDNA library. Molecular cloning of the cDNA showed that there are two isogenes, designated StrbohA and StrbohB, respectively. The RNA gel blot analyses showed that StrbohA was constitutively expressed at a low level, whereas StrbohB was induced by hyphal wall components (HWC elicitor) from Phytophthora infestans in potato tubers. Treatment of potato tubers with HWC elicitor caused a rapid but weak transient accumulation of H2O2 (phase I), followed by a massive oxidative burst 6 to 9 h after treatment (phase II). Diphenylene iodonium (DPI), an inhibitor of the neutrophil NADPH oxidase, blocked both bursts, whereas pretreatment of the protein synthesis inhibitor cycloheximide with the tuber abolished only the second burst. These results suggest that the expression of StrbohA and StrbohB contributes to phase I and II bursts, respectively. The same is true for arachidonic acid, a lipid component of P. infestans-stimulated biphasic oxidative burst, whereas an endogenous signaling molecule, salicylic acid, only induced a weak phase II burst. Both molecules induced the StrbohB expression, which is in agreement with the second burst. To characterize the signal transduction pathway leading to the oxidative burst, we examined the role of protein phosphorylation in HWC-stimulated StrbohB gene expression. K252a and staurosporine, two protein kinase inhibitors, blocked the transcript accumulation. Two inhibitors of extracellular Ca2+ movement, however, did not abolish the transcript accumulation of StrbohB, suggesting that certain calcium-independent protein kinases are involved in the process of StrbohB gene expression. Additionally, we examined a causal relationship between the oxidative burst and expression of defense genes induced by the HWC elicitor. The transcript accumulation of genes related to sesquiterpenoid phytoalexin synthesis (lubimin and rishitin) and phenylpropanoid pathway was inhibited slightly by the DPI treatment, suggesting that the oxidative burst is not essential to activate these genes. Interestingly, the concomitant presence of DPI with the elicitor resulted in an increase in lubimin accumulation and a decrease in rishitin accumulation. Because it is known that lubimin is metabolized into rishitin via oxylubimin, we propose that AOS mediates the synthesis of rishitin from lubimin.

GIF inhibits Th effector generation by acting on antigen-presenting B cells

Glycosylation-inhibiting factor (GIF) is a 13-kDa cytokine secreted from T cells. Administration of bioactive recombinant GIF inhibits IgG1 and IgE Ab responses in vivo. Treatment of B cells with the cytokine reduces the secretion of IgG1 and IgE induced by LPS and IL-4. To examine the effect on cognate T-B interaction, GIF was added to low-density B cells from MD4 transgenic (Tg) mice, which express B cell receptor specific for hen egg lysozyme (HEL). The B cells were subsequently pulsed with HEL-OVA conjugate and cultured with OVA-specific naive CD4 T cells from DO11.10 Tg mice. Treatment of Ag-presenting B cells with GIF reduced expansion and IL-2 secretion of naive T cells and rendered them hyporesponsive to antigenic restimulation, resulting in 50--95% reduction of IL-4 and IFN-gamma secretion upon restimulation with Ag. GIF dramatically inhibited Th effector generation when it was added to B cells before pulsing with HEL-OVA, whereas it showed little to no effect when added after B cells were pulsed with Ag. GIF was more effective when B cells from MD4 Tg mice were pulsed with HEL-OVA than when they were pulsed with OVA. This cytokine did not affect Th effector generation when B cells or irradiated splenocytes pulsed with OVA(323--339) peptide stimulated naive DO11.10 T cells. Confocal microscopy revealed that GIF inhibited internalization of HEL by B cells from MD4 Tg mice. Therefore, the cytokine may regulate early steps of Ag presentation involving B cell receptors to diminish Th effector generation from naive CD4 T cells.

[A case of antiphospholipid antibody syndrome with cerebral infarction showing slowly progressive pure motor monoparesis in unilateral upper extremity]

We reported a 68-year-old man with anti-phospholipid antibody syndrome who presented slowly progressive pure motor monoparesis(PMM) in left upper extremity as a sign of cerebral infarction. He had history of hypertension and hyperlipidemia. He first noticed clumsiness in left fingers, then weakness of left fingers with drop hand developing gradually in 2 to 6 weeks. He began to feel difficulty in raising left upper arm in 8 weeks and was admitted to our hospital. On admission, he exhibited severe weakness in distal portion and moderate weakness in proximal portion of left upper extremity. Deep tendon reflexes were slightly hyperactive in left side. Muscle strength of right upper extremity and bilateral lower extremities were normal. There was no sensory and autonomic abnormality. Laboratory examination revealed high titer of anti-cardiolipin IgM antibody. Brain MRI demonstrated a small cortical infarction in the right precentral gyrus. Cerebral angiography revealed severe stenosis in right common carotid artery. Other examinations including EMG were unremarkable. PMM in left upper extremity was considered to be caused by the ischemic lesion in the precentral motor cortex. Slowly progressive course might be explained by the hypovolemic factor due to the marked stenosis in right common carotid artery, poor collateral circulation, and abnormal coagulation caused by anti-phospholipid antibody syndrome.

T-cell receptor antagonists induce Vav phosphorylation by selective activation of Fyn kinase

T cell receptor (TCR) antagonists inhibit antigen-induced T cell activation and by themselves fail to induce phenotypic changes associated with T cell activation. However, we have recently shown that TCR antagonists are inducers of antigen-presenting cell (APC)-T cell conjugates. The signaling pathway associated with this cytoskeleton-dependent event appears to involve tyrosine phosphorylation and activation of Vav. In this study, we investigated the role played by the protein tyrosine kinases Fyn, Lck, and ZAP-70 in antagonist-induced signaling pathway. Antagonist stimulation increased tyrosine phosphorylation and kinase activity of Fyn severalfold, whereas little or no increase in Lck and ZAP-70 activity was observed. Second, TCR stimulation of Lck(-), Fyn(hi) Jurkat cells induced strong tyrosine phosphorylation of Vav. In contrast, minimal increase in tyrosine phosphorylation of Vav was observed in Lck(hi), Fyn(lo) Jurkat cells. Finally, study of T cells from a Fyn-deficient TCR transgenic mouse also showed that Fyn was required for tyrosine phosphorylation and activation of Vav induced by both antagonist and agonist peptides. The deficiency in Vav phosphorylation in Fyn-deficient T cells was associated with a defect in the formation of APC-T cell conjugates when T cells were stimulated with either agonist or antagonist peptide. We conclude from these results that Vav is a selective substrate for Fyn, especially under conditions of low-affinity TCR-mediated signaling, and that this signaling pathway involving Fyn, Vav, and Rac-1 is required for the cytoskeletal reorganization that leads to T cell-APC conjugates and the formation of the immunologic synapse.

[A patient of Charcot-Marie-tooth disease with rigid spine and respiratory failure]

This report describes a case of a 17-year-old girl with Charcot-Marie-Tooth disease (CMT) representing rigid spine and respiratory failure. At age 11, she tended to walk on her toes and had difficulty in getting up from the floor without support. She became aware of flexion limitation of the neck at the age of 12. At 15 years of age, She began to have dyspnea on effort. When she was 17 years old, neurological examination revealed mild weakness of the upper extremities and severe weakness of the distal lower extremities, generalized wasting and areflexia. Superficial sensation was mildly impaired distally, and vibration sensation was severely impaired in the lower extremities. Motor and sensory nerve conduction velocities were mildly reduced, and compound muscle action potential of the tibial and peroneal nerves and sensory nerve action potential on ulnar and sural nerves were absent. Electromyography showed neurogenic changes with denervation potentials. Sural nerve biopsy revealed severe loss of myelinated fibers without any onion-bulb formation. As for family history, her elder sister showed moderate loss of vibration sensation in the lower extremities. On the basis of these findings, she was diagnosed as having CMT type 2, though a mode of inheritance was uncertain. She also had peculiar findings of flexion limitation of the spine (rigid spine), contracture of the hip joint, and fatty degeneration of paraspinal muscles on CT. Percent vital capacity (VC) was 22.5%, and arterial blood gas analysis showed PaO2 of 60.5 mmHg and PaCO2 65.0 mmHg. To our knowledge, this is the first case of CMT accompanied by rigid spine and respiratory failure. Motor and sensory neuropathy combined with rigid spine also have not been reported previously. The relationship between rigid spine syndrome with neurogenic muscular atrophy and CMT type 2C with the clinical characteristics of diaphragm and vocal cord paresis is discussed.

TCR antagonist peptides induce formation of APC-T cell conjugates and activate a Rac signaling pathway

T cell receptor antagonists inhibit T cell activation by antigen, and by themselves fail to induce phenotypic changes associated with T cell activation. However, they can induce limited tyrosine phosphorylation of TCRzeta chain. Here we show that TCR antagonists are potent inducers of APC-T cell conjugates, cytoskeletal reorganization, and capping of certain T cell proteins. These events are associated with a signaling pathway involving tyrosine phosphorylation of Vav and SLP-76, activation and capping of Rac-1, a protein previously linked with cytoskeletal reorganization, and activation of JNK. The finding that antagonist peptides stimulate this pathway, while failing to stimulate other TCR-mediated signaling pathways, indicates the presence in T cells of a hierarchy of signaling that is sensitive to the avidity of Ag / MHC-TCR interaction.

[A case of acute transverse myelopathy and bilateral optic neuritis associated with anticardiolipin antibodies, lupus anticoagulant and perinuclear antineutrophil cytoplasmic antibodies]

A 69-year-old woman developed paraplegia and hypesthesia on upper extremities and below T4 level. Examination of cerebrospinal fluid showed increased protein levels and pleocytosis. MRI of the cervical spinal cord revealed syrinx formation from C3 to upper thoracic cord. A diagnosis of acute transverse myelitis was made. A high dose of corticosteroid including pulse therapy did not improve her symptoms and signs of myelopathy, but the syrinx could not be found thereafter. One year later, she developed severe visual loss due to bilateral optic neuritis which was improved spontaneously. The clinical course and MRI findings were similar to those of the optic-spinal form of multiple sclerosis (MS). The presence of anticardiolipin antibodies, lupus anticoagulant and perinuclear anti-neutrophil cytoplasmic antibodies, however, strongly suggested that vasculitic and/or ischemic mechanisms induced by these autoantibodies might play a role on the development of the disease. We conclude that our case should be distinguished from MS.

Target cells for an immunosuppressive cytokine, glycosylation-inhibiting factor

Receptors for bioactive glycosylation-inhibiting factor (GIF) were demonstrated using a bioactive mutant of recombinant human (rh) GIF, which is comparable to the suppressor T (Ts) cell-derived bioactive GIF in its affinity for the receptors on helper T (Th) hybridoma cells. Both naive T and B cells in normal mouse spleen lacked GIF receptors. However, presentation of specific antigen to naive T cells resulted in the expression of the receptors on activated T cells. Furthermore, activation of small resting B cells with F(ab')2 fragments of anti-mouse IgM plus IL-4, lipopolysaccharide (LPS) plus IL-4 or LPS plus dextran sulfate induced the expression of the receptors within 48 h of B cell stimulation. It was also found that NK T cells freshly isolated from mouse spleen, but not conventional NK cells, expressed receptors for GIF. CD4(+) and CD4(-) subpopulations of NK T cells showed a similar binding capability. Mature dendritic cells derived from bone marrow did not bear the receptors. The dissociation constant (Kd) of the interaction between the bioactive rhGIF mutant and the high-affinity receptors was 10-100 pM, whereas inactive wild-type rhGIF failed to bind to the receptors. A bioactive derivative of rhGIF suppressed both IgG1 and IgE synthesis by purified B cells activated by LPS and IL-4, indicating that the binding of bioactive GIF to its receptors on activated B cells results in suppression of their differentiation.