Tumor lysis syndrome followed by tumor regression after COVID-19 in a patient with chronic lymphocytic leukemia

Coronavirus disease 2019 (COVID-19) can become lethal in patients with hematological malignancies; however, several cases of tumor regression after COVID-19 have been described, and the precise mechanism behind this paradoxical effect is unknown. Herein, we describe a case of Tumor lysis syndrome (TLS) followed by tumor regression after COVID-19. A 72-year-old woman with untreated chronic lymphocytic leukemia was admitted to our hospital with SARS-CoV-2 antigen-positive pneumonia. On admission, her anti-SARS-CoV-2 spike antibody was negative despite receiving two prior vaccinations. Immediately after admission, she developed confusion and ventricular tachycardia. Laboratory data showed acidosis, hyperkalemia, and a rapid decrease of tumor cells in peripheral blood, and she was diagnosed with clinical TLS. She was transferred to the intensive care unit and received continuous hemodialysis therapy. Although hyperferritinemia and bicytopenia, which suggest a cytokine storm followed, she recovered without steroids and additional COVID-19 treatment in 8 days. 2 months later, CT revealed a marked shrinking of lymphadenopathy, which was compatible with tumor regression after COVID-19. Considering the impaired humoral immunity and abrupt response, direct oncolysis caused by SARS-CoV-2 and cytokine storm-induced cell-mediated immune reaction may have been responsible for this paradoxical effect.

[Multiple microthromboses with autoimmune hemolytic anemia after BNT162b2 mRNA vaccination]

A 68-year-old man was referred to our hospital with dizziness and mild fever one week after receiving the second dose of the COVID-19 mRNA vaccine (BNT162b2). Laboratory tests showed hemolytic anemia and a positive direct Coombs test, and he was diagnosed with autoimmune hemolytic anemia (AIHA). On admission, the patient had impaired consciousness with auditory hallucinations, and a head MRI scan showed multiple high-signal areas on diffusion-weighted imaging, suggesting multiple recent infarctions. Echocardiography also showed decreased wall motion in the inferior and posterior walls. A skin biopsy to investigate the cause revealed many platelets and fibrin thrombi in the capillaries and small veins, which was considered the cause of the organ damage. After starting prednisolone (1 mg/kg) for AIHA, hemolytic anemia as well as impaired consciousness, and decreased wall motion rapidly improved. Microthrombosis after BNT162b2 mRNA vaccination is rare, and autoimmune abnormalities appeared to contribute to onset in this case.

[An elderly patient with lymphoplasmacytic lymphoma successfully treated with low-dose tirabrutinib]

A 93-year-old woman was diagnosed with lymphoplasmacytic lymphoma (LPL) with circulating tumor cells in her peripheral blood after presenting with anemia. LPL progressed eight months later, with anemia worsening and tumor cells increasing to 66% of leukocytes. She began tirabrutinib at a low dose (80 mg daily: 17% of the standard dose) because she preferred to maintain her quality of life (QOL). Within three weeks, she was free of transfusion dependency and had a partial response with the disappearance of peripheral tumor cells. The dosage of tirabrutinib was increased to 240 mg daily because it was well tolerated. She has been on the treatment for 13 months with no adverse effects. Tirabrutinib, a highly selective Bruton's tyrosine kinase inhibitor, has been reported to have promising efficacy for LPL, but it also has a high incidence of dermatological toxicity, which may impair QOL. Low-dose tirabrutinib initiation may be effective and assist elderly patients with LPL in maintaining their QOL.

Pretreatment levels of serum soluble interleukin-2 receptor are useful in selecting the treatment regimen for newly diagnosed advanced-stage follicular lymphoma with low tumor burden

High pre-treatment serum soluble interleukin-2 receptor (sIL-2R) levels are associated with poor overall survival (OS) of patients with newly diagnosed follicular lymphoma (FL). We evaluated the usefulness of pre-treatment sIL-2R levels in selecting a treatment regimen for advanced-stage FL with low tumor burden (FL-LTB). This retrospective, multicenter observational study enrolled consecutive patients who received a rituximab-containing regimen for newly diagnosed advanced stage FL-LTB (grade 1-3a) between 2008 and 2018. We applied a previously reported cut-off value of 1800 IU/mL for sIL-2R. A total of 211 patients were eligible for the analysis. Among patients with high sIL-2R (47 patients, 22.3%), the OS rates for patients treated by rituximab monotherapy (R-mono) (11 patients) were significantly lower than those treated by rituximab-combination chemotherapy (R-chemo) (36 patients): 5-year OS rates were 66.7% and 94.4%, respectively (P = 0.007). Among patients with low sIL-2R (164 patients, 77.7%), OS rates were comparably good between the R-mono group (34 patients) and the R-chemo group (130 patients): 5-year OS rates were 100% and 98.3%, respectively (P = 0.38). Our results suggest that R-chemo may yield better OS than R-mono for patients with newly diagnosed advanced-stage FL-LTB and high pre-treatment serum sIL-2R levels.

Publisher Correction: Shedding new light on the Crab with polarized X-rays

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data

The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42 GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10^{-3}. We take into account systematic effects that could mimic true anisotropies at this level. We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. The present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.

New variant of acute promyelocytic leukemia with IRF2BP2-RARA fusion

We present an acute promyelocytic leukemia (APL) patient with two subtypes of IRF2BP2–RARA, in which the IRF2BP2 gene showed completely new breakpoints. Bone marrow examination revealed morphologic features indicative of APL. However, promyelocytic leukemia–RARA fusion was not detected. A paired‐end mRNA sequencing followed by RT‐PCR and direct sequencing revealed two types of fusion transcripts between exon 1B of IRF2BP2 and exon 3 of RARA. The patient received all‐trans retinoic acid and conventional chemotherapy, but showed resistance. This is the second report of IRF2BP2 involvement in APL, and we describe various breakpoints for the IRF2BP2–RARA fusion gene.

Measurement of the high-energy gamma-ray emission from the Moon with the Fermi Large Area Telescope

We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first seven years of operation, in the energy range from 30 MeV up to a few GeV. We have also studied the time evolution of the flux, finding a correlation with the solar activity. We have developed a full Monte Carlo simulation describing the interactions of cosmic rays with the lunar surface. The results of the present analysis can be explained in the framework of this model, where the production of gamma rays is due to the interactions of cosmic-ray proton and helium nuclei with the surface of the Moon. Finally, we have used our simulation to derive the cosmic-ray proton and helium spectra near Earth from the Moon gamma-ray data.

Inferred cosmic-ray spectrum from Fermi large area telescope γ-ray observations of Earth's limb

Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly discovered features may offer a clue to the origin of high-energy CRs. We use the Fermi Large Area Telescope observations of the γ-ray emission from Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range ∼90  GeV-6  TeV (derived from a photon energy range 15 GeV-1 TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index 2.68±0.04 and 2.61±0.08 above ∼200  GeV, respectively.

Agonist stimulation, talin-1, and kindlin-3 are crucial for α(IIb)β(3) activation in a human megakaryoblastic cell line, CMK

Platelet integrin α(IIb)β(3) activation is regulated by inside-out signaling via agonist stimulation. However, when α(IIb)β(3) was exogenously expressed in cell lines such as Chinese hamster ovarian cells, physiological agonists hardly induced α(IIb)β(3) activation. To overcome this disadvantage, we characterized the functional regulation of endogenously expressed α(IIb)β(3) in a megakaryoblastic cell line, CMK, employing an initial velocity assay for PAC-1 binding. We firstly demonstrated that protease-activated receptor 1-activating peptide induced robust, but transient α(IIb)β(3) activation in CMK cells with high glycoprotein-Ib expression. Stable talin-1 or kindlin-3 knockdown cells confirmed that the protease-activated receptor 1-activating peptide-induced α(IIb)β(3) activation was dependent on talin-1 and kindlin-3 expression. In sharp contrast to exogenously expressed α(IIb)β(3) in Chinese hamster ovarian cells, transient overexpression of full-length talin (FL-talin) or talin-head domain (THD) alone did not activate α(IIb)β(3) in CMK cells, but required agonist stimulation. Similarly, kindlin-3 overexpression alone did not induce α(IIb)β(3) activation, but it significantly augmented agonist-induced α(IIb)β(3) activation. Several mutants of FL-talin and THD suggested that the head-rod interaction was critical for autoinhibition of talin-1, and the interaction between the THD and the membrane-proximal region of the β(3) cytoplasmic tail was essential for talin-mediated α(IIb)β(3) activation. In addition, THD and kindlin-3 cooperatively augmented protease-activated receptor 1-induced α(IIb)β(3) activation. We proposed that the CMK cell line is an attractive platform for investigating agonist-, talin-1-, and kindlin-3- dependent α(IIb)β(3) activation.

Measurement of separate cosmic-ray electron and positron spectra with the fermi large area telescope

We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 GeV. We confirm that the fraction rises with energy in the 20-100 GeV range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.

Constraining dark matter models from a combined analysis of Milky Way satellites with the Fermi Large Area Telescope

Satellite galaxies of the Milky Way are among the most promising targets for dark matter searches in gamma rays. We present a search for dark matter consisting of weakly interacting massive particles, applying a joint likelihood analysis to 10 satellite galaxies with 24 months of data of the Fermi Large Area Telescope. No dark matter signal is detected. Including the uncertainty in the dark matter distribution, robust upper limits are placed on dark matter annihilation cross sections. The 95% confidence level upper limits range from about 10(-26)  cm3  s(-1) at 5 GeV to about 5×10(-23)   cm3  s(-1) at 1 TeV, depending on the dark matter annihilation final state. For the first time, using gamma rays, we are able to rule out models with the most generic cross section (∼3×10(-26)  cm3  s(-1) for a purely s-wave cross section), without assuming additional boost factors.

Bleeding tendency and impaired platelet function in a patient carrying a heterozygous mutation in the thromboxane A2 receptor

BACKGROUND

Thromboxane A(2) receptor (TXA(2)R) abnormality appears to dominantly disturb platelet function.

OBJECTIVES

To reveal a molecular genetic defect in a patient with TXA(2)R abnormality and investigate the mechanism for the impaired response to TXA(2).

PATIENT

The proband (OSP-2, PT) was a 7-year-old Japanese girl, suffering from repeated mucocutaneous bleeding.

METHODS AND RESULTS

U46619 (2.5 and 10 μm)-induced platelet aggregation was remarkably impaired in the proband and her father. Immunoblots showed that TXA(2)R expression levels in their platelets were approximately 50% of controls, and nucleotide sequence analysis revealed that they were heterozygous for a novel mutation, c.167dupG in the TXA(2)R cDNA. Expression studies using Chinese hamster ovary (CHO) cells indicated that the mutation is responsible for the expression defect in TXA(2)R. We then examined α(IIb)β(3) activation by employing an initial velocity analysis and revealed that U46619 failed to induce a sustained α(IIb)β(3) and Rap1B activation in the proband. In addition, platelet secretion as monitored by P-selectin expression was markedly impaired in response to U46619 but not to ADP. The interaction between secreted ADP and P2Y(12) has been shown to play a critical role in the sustained α(IIb)β(3) activation (Kamae et al. J Thromb Haemost 2006; 4: 1379). As expected, small amounts of exogenous ADP (0.5 μm) partially restored the sustained α(IIb)β(3) activation induced by U46619.

CONCLUSION

Our present data strongly suggest that the impaired platelet activation in response to U46619 in the heterozygous subject for the TXA(2)R mutation is, at least in part, as a result of the decrease in ADP secretion.

Gamma-ray emission concurrent with the nova in the symbiotic binary V407 Cygni

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.

Spectrum of the isotropic diffuse gamma-ray emission derived from first-year Fermi Large Area Telescope data

We report on the first Fermi Large Area Telescope (LAT) measurements of the so-called "extragalactic" diffuse gamma-ray emission (EGB). This component of the diffuse gamma-ray emission is generally considered to have an isotropic or nearly isotropic distribution on the sky with diverse contributions discussed in the literature. The derivation of the EGB is based on detailed modeling of the bright foreground diffuse Galactic gamma-ray emission, the detected LAT sources, and the solar gamma-ray emission. We find the spectrum of the EGB is consistent with a power law with a differential spectral index gamma = 2.41 +/- 0.05 and intensity I(>100 MeV) = (1.03 +/- 0.17) x 10(-5) cm(-2) s(-1) sr(-1), where the error is systematics dominated. Our EGB spectrum is featureless, less intense, and softer than that derived from EGRET data.

Fermi large area telescope search for photon lines from 30 to 200 GeV and dark matter implications

Dark matter (DM) particle annihilation or decay can produce monochromatic gamma rays readily distinguishable from astrophysical sources. gamma-ray line limits from 30 to 200 GeV obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a gamma-ray line analysis, and integrated over most of the sky. We obtain gamma-ray line flux upper limits in the range 0.6-4.5x10{-9} cm{-2} s{-1}, and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.

Fermi large area telescope measurements of the diffuse gamma-ray emission at intermediate galactic latitudes

The diffuse galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission greater, > or approximately equal to 1 GeV relative to diffuse galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called "EGRET GeV excess"). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10 degrees < or = |b| < or = 20 degrees. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.

Detection of high-energy gamma-ray emission from the globular cluster 47 Tucanae with Fermi

We report the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17sigma from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. Globular clusters are expected to emit gamma rays because of the large populations of millisecond pulsars that they contain. The spectral shape of 47 Tucanae is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.

Detection of 16 gamma-ray pulsars through blind frequency searches using the Fermi LAT

Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.

Measurement of the cosmic ray e+ +e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m;{2} sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

The Fermi Gamma-Ray Space Telescope discovers the pulsar in the young galactic supernova remnant CTA 1

Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614 x 10(-13) seconds per second. Its characteristic age of 10(4) years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars.

Critical role of ADP interaction with P2Y12 receptor in the maintenance of alpha(IIb)beta3 activation: association with Rap1B activation

OBJECTIVE

Platelet integrin alpha(IIb)beta3 plays a crucial role in platelet aggregation, and the affinity of alpha(IIb)beta3 for fibrinogen is dynamically regulated. Employing modified ligand-binding assays, we analyzed the mechanism by which alpha(IIb)beta3 maintains its high-affinity state.

METHODS AND RESULTS

Washed platelets adjusted to 50 x 10(3) microL(-1) were stimulated with 0.2 U mL(-1) thrombin or 5 microm U46619 under static conditions. After the completion of alpha(IIb)beta3 activation and granule secretion, different kinds of antagonists were added to the activated platelets. The activated alpha(IIb)beta3 was then detected by fluorescein isothiocyanate (FITC)-labeled PAC1. The addition of 1 mum AR-C69931MX (a P2Y12 antagonist) or 1 mm A3P5P (a P2Y1 antagonist) disrupted the sustained alpha(IIb)beta3 activation by approximately 92% and approximately 38%, respectively, without inhibiting CD62P or CD63 expression. Dilution of the platelet preparation to 500 microL(-1) also disrupted the sustained alpha(IIb)beta3 activation, and the disruption by such dilution was abrogated by the addition of exogenous adenosine 5'-diphosphate (ADP) in a dose-dependent fashion. The amounts of ADP released from activated platelets determined by high-performance liquid chromatography were compatible with the amounts of exogenous ADP required for the restoration. We next examined the effects of antagonists on protein kinase C (PKC) and Rap1B activation induced by 0.2 U mL(-1) thrombin. Thrombin induced long-lasting PKC and Rap1B activation. AR-C69931MX markedly inhibited Rap1B activation without inhibiting PKC activation.

CONCLUSIONS

Our data indicate that the continuous interaction between released ADP and P2Y12 is critical for the maintenance of alpha(IIb)beta3 activation.

Adiponectin acts as an endogenous antithrombotic factor

OBJECTIVE

Obesity is a common risk factor in insulin resistance and cardiovascular diseases. Although hypoadiponectinemia is associated with obesity-related metabolic and vascular diseases, the role of adiponectin in thrombosis remains elusive.

METHODS AND RESULTS

We investigated platelet thrombus formation in adiponectin knockout (APN-KO) male mice (8 to 12 weeks old) fed on a normal diet. There was no significant difference in platelet counts or coagulation parameters between wild-type (WT) and APN-KO mice. However, APN-KO mice showed an accelerated thrombus formation on carotid arterial injury with a He-Ne laser (total thrombus volume: 13.36+/-4.25 x 10(7) arbitrary units for APN-KO and 6.74+/-2.87x10(7) arbitrary units for WT; n=10; P<0.01). Adenovirus-mediated supplementation of adiponectin attenuated the enhanced thrombus formation. In vitro thrombus formation on a type I collagen at a shear rate of 250 s(-1), as well as platelet aggregation induced by low concentrations of agonists, was enhanced in APN-KO mice, and recombinant adiponectin inhibited the enhanced platelet aggregation. In WT mice, adenovirus-mediated overexpression of adiponectin additionally attenuated thrombus formation.

CONCLUSIONS

Adiponectin deficiency leads to enhanced thrombus formation and platelet aggregation. The present study reveals a new role of adiponectin as an endogenous antithrombotic factor.

Negative regulation of platelet function by a secreted cell repulsive protein, semaphorin 3A

Semaphorin 3A (Sema3A) is a secreted disulfide-bound homodimeric molecule that induces growth cone collapse and repulsion of axon growth in the nervous system. Recently, it has been demonstrated that Sema3A is produced by endothelial cells and inhibits integrin function in an autocrine fashion. In this study, we investigated the effects of Sema3A on platelet function by using 2 distinct human Sema3A chimera proteins. We detected expression of functional Sema3A receptors in platelets and dose-dependent and saturable binding of Sema3A to platelets. Sema3A dose-dependently inhibited activation of integrin alphaIIbbeta3 by all agonists examined including adenosine diphosphate (ADP), thrombin, convulxin, phorbol 12-myristate 13-acetate, and A23187. Sema3A inhibited not only platelet aggregation induced by thrombin or collagen but also platelet adhesion and spreading on immobilized fibrinogen. Moreover, Sema3A impaired alphaIIbbeta3-independent spreading on glass coverslips and aggregation-independent granular secretion. Sema3A inhibited agonist-induced elevation of filamentous action (F-actin) contents, phosphorylation of cofilin, and Rac1 activation. In contrast, Sema3A did not affect the levels of cyclic nucleotides or agonist-induced increase of intracellular Ca2+ concentrations. Thus, the extensive inhibition of platelet function by Sema3A appears to be mediated, at least in part, through impairment of agonist-induced Rac1-dependent actin rearrangement.

Activation of integrin alpha IIb beta 3 in the glycoprotein Ib-high population of a megakaryocytic cell line, CMK, by inside-out signaling

Affinity/avidity state of integrin alpha IIb beta 3 is regulated by intracellular inside-out signaling. Although several megakaryocytic cell lines have been established, soluble ligand binding to alpha IIb beta 3 expressed in these cells by cellular agonists has not been demonstrated. We have re-examined agonist-induced alpha IIb beta 3 activation on megakaryocytic cell lines with a marker of the late stage of megakaryocytic differentiation, glycoprotein Ib (GPIb). Activation of alpha IIb beta 3 was assessed by PAC1 and soluble fibrinogen binding to the cells. We found that alpha IIb beta 3 expressed in CMK cells with high GPIb expression was activated by a phorbor ester, phorbol myristate acetate (PMA). Although the population of the GPIbhigh cells was <0.5% of the total cells, incubation with a nucleoside analog, ribavirin, efficiently increased the PMA-reactive GPIbhigh cells. Not only PMA but also a calcium ionophore, A23187, induced alpha IIb beta 3 activation, and PMA and A23187 had an additive effect on alpha IIb beta 3 activation. Ligand binding to the activated alpha IIb beta 3 in the GPIbhigh CMK cells is totally abolished by an alpha IIb beta 3-specific antagonist, and inhibited by wortmannin, cytochalasin-D and prostaglandin E1, and the effects of these inhibitors on alpha IIb beta 3 activation in the GPIbhigh CMK cells were compatible with those in platelets. We have also demonstrated that the ribavirin-treated CMK cells express PKC-alpha, -beta, -delta and -theta, and suggested that PKC-alpha and/or -beta appear to be responsible for PMA-induced activation of alpha IIb beta 3 in CMK cells.