Immature Platelet Fraction: A Useful Marker for Identifying the Cause of Thrombocytopenia and Predicting Platelet Recovery

Abstract Introduction: The assessment of thrombopoietic activity in bone marrow is necessary for patients with thrombocytopenia to achieve correct diagnoses and effective treatments. We evaluated the discriminatory power of the immature platelet fraction (IPF%) in differentiating hyperdestructive/consumptive thrombocytopenia from hypoproductive thrombocytopenia, and its potential use as a predictive marker for platelet recovery. Methods: Platelet indices including IPF% were measured in 105 healthy individuals (the control group), 31 patients with hyperdestructive/consumptive thrombocytopenia (14 with immune thrombocytopenic purpura [ITP] and 17 with liver cirrhosis), and 34 patients with hypoproductive thrombocytopenia (4 with aplastic anemia and 30 with cancer who were undergoing chemotherapy) by using a Sysmex XN-3000 hematology analyzer. Results: The platelet number in the hyperdestructive/consumptive thrombocytopenia group was significantly lower than that in the hypoproductive thrombocytopenia group (P <0.001). The difference of plateletcrit (PCT) between the 2 thrombocytopenia groups was not statistically significant (P= 0.363). The IPF% was significantly higher in the hyperdestructive/consumptive thrombocytopenia group (median: 6.2% [IQR 4.3-10.3%]) than in both the control group (1.8% [1.3-2.4%]) and the hypoproductive thrombocytopenia group (1.8% [0.9-2.3%]) (all P-values < 0.001). However, the difference between the hypoproductive thrombocytopenia and control groups was not statistically significant (P= 0.331). Compared to the control group, the hyperdestructive/consumptive thrombocytopenia group showed a 190.5% increase in the median IPF% value, while the hypoproductive thrombocytopenia group showed a 9.5% decrease. The IPF# was significantly different between the 3groups; it was highest in the control group (median: 4.3 ×109/L [IQR 3.5-5.8×109/L]), followed by the hyperdestructive/consumptive thrombocytopenia group (3.2×109/L [1.7-4.5×109/L]), and lowest in the hypoproductive thrombocytopenia group (1.3 ×109/L [0.7-2.0×109/L]) (all P-values <0.001). Compared to the control group, the hyperdestructive/consumptive thrombocytopenia group showed a 25.6% decrease and the hypoproductive thrombocytopenia group a 69.8% decrease. PDW, MPV, and P-LCR were higher in the hyperdestructive/consumptive thrombocytopenia group (14.5 ± 3.0 fL, 12.0 fL [IQR: 11.0-12.0 fL], and 38.9 ± 6.8%, respectively) than in the other 2 groups, but there was no statistical difference between the other 2 groups. The IPF% in the hyperdestructive/consumptive group increased significantly as the number of platelets decreased, especially in patients with severe thrombocytopenia with platelet counts under 40.0 ×109/L. The IPF% was 4.7% (3.1-4.7%), 6.2% (3.2-7.6%), and 11.4% (7.1-16.6%) in patients with platelet counts>90.0 ×109/L, 40.0-90.0 ×109/L and<40.0 ×109/L, respectively (P = 0.010). However, this phenomenon was not observed in the hypoproductive thrombocytopenia group. The area under the curve (AUC) was highest for IPF% (0.938), indicating that this parameter showed the best discriminatory ability between the 2 groups, followed by PDW (0.885), P-LCR (0.859), IPF# (0.827), and MPV (0.824) (all P-values <0.001). The best IPF% cut-off value indicative of the highest sensitivity and specificity was 2.3%. The AUC of PCT was under 0.5 (0.445, P = 0.477), showing no discriminatory power. The IPF% decreased 3-4 days in advance of platelet count elevation in patients with ITP, while the IPF# ratio (compared to baseline) increased 3 days in advance of the same. Furthermore, the IPF% and IPF# ratio increased 5.5 days and 8.5 days, respectively, before platelet counts increased up to 130.0 × 109/L in cancer patients receiving chemotherapy. Conclusion: IPF% showed the most % value difference between the 3 groups and the largest AUC, showing it has the best discriminatory power in distinguishing the cause of thrombocytopenia. Also, IPF% showed an inverse correlation with platelet count in the hyperdestructive/consumptive thrombocytopenia group, but not in the hypoproductive thrombocytopenia group. The IPF% and IPF# were useful markers to predict the elevation of platelet count in advance in ITP and in cancer patients receiving chemotherapy. Disclosures No relevant conflicts of interest to declare.

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Enhancement of ADP-induced Platelet Aggregation by Adrenaline in Vivo and Its Prevention

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647788 ◽

1973 ◽

Vol 29 (02) ◽

pp. 490-498 ◽

Cited By ~ 6

Author(s):

Hiroh Yamazaki ◽

Itsuro Kobayashi ◽

Tadahiro Sano ◽

Takio Shimamoto

Keyword(s):

Platelet Count ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

The Other ◽

Endothelial Surface ◽

Important Interaction ◽

Blood Coagulability ◽

The Difference

SummaryThe authors previously reported a transient decrease in adhesive platelet count and an enhancement of blood coagulability after administration of a small amount of adrenaline (0.1-1 µg per Kg, i. v.) in man and rabbit. In such circumstances, the sensitivity of platelets to aggregation induced by ADP was studied by an optical density method. Five minutes after i. v. injection of 1 µg per Kg of adrenaline in 10 rabbits, intensity of platelet aggregation increased to 115.1 ± 4.9% (mean ± S. E.) by 10∼5 molar, 121.8 ± 7.8% by 3 × 10-6 molar and 129.4 ± 12.8% of the value before the injection by 10”6 molar ADP. The difference was statistically significant (P<0.01-0.05). The above change was not observed in each group of rabbits injected with saline, 1 µg per Kg of 1-noradrenaline or 0.1 and 10 µg per Kg of adrenaline. Also, it was prevented by oral administration of 10 mg per Kg of phenoxybenzamine or propranolol or aspirin or pyridinolcarbamate 3 hours before the challenge. On the other hand, the enhancement of ADP-induced platelet aggregation was not observed in vitro, when 10-5 or 3 × 10-6 molar and 129.4 ± 12.8% of the value before 10∼6 molar ADP was added to citrated platelet rich plasma (CPRP) of rabbit after incubation at 37°C for 30 second with 0.01, 0.1, 1, 10 or 100 µg per ml of adrenaline or noradrenaline. These results suggest an important interaction between endothelial surface and platelets in connection with the enhancement of ADP-induced platelet aggregation by adrenaline in vivo.

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Changes in Platelet Aggregability after Ovariectomy

Thrombosis and Haemostasis ◽

10.1055/s-0038-1657029 ◽

1979 ◽

Vol 42 (04) ◽

pp. 1332-1339 ◽

Cited By ~ 7

Author(s):

Hiroh Yamazaki ◽

Takeshi Motomiya ◽

Minoru Sonoda ◽

Noboru Miyagawa

Keyword(s):

Platelet Count ◽

Platelet Activation ◽

Ovarian Hormones ◽

Control Group ◽

Platelet Aggregability ◽

Appearance Rate ◽

Before And After ◽

The Difference ◽

Induced Aggregation ◽

Observation Period

SummaryChanges in platelets in 48 patients with uterine myoma before and after hysterectomy with and without ovariectomy were examined. Bilateral ovariectomy in 25 cases (ovariec-tomized group) and unilateral or non-ovariectomy in 23 cases (control group) were performed at the hysterectomy. Platelet count and an appearance rate of secondary aggregation decreased at one day after and increased at one week after the operation, similarly in both the ovariectomized and the control group. The appearance rate of secondary aggregation was reflected in an intensity of aggregation at 5 min after the addition of reagent to PRP. At one month after the operation, the appearance rate of secondary aggregation induced by 3 μM ADP showed a statistically significant decrease in comparison with the preoperation value (P <0.05) and the enhancement of 5-min aggregation was still observed in the control group, while ceased in the ovariectomized group. The difference between the two groups was significant (P < 0.05). There was almost no change in the speed and intensity of primary and secondary aggregation during the observation period. No significant differences in collagen-induced aggregation were noted between the two groups. The results suggest that ovarian hormones, mainly estrogen, facilitate platelet activation which is mediated by the so-called secondary aggregation.

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Involvement of the Inconstant Bursa of the Fifth Metatarsophalangeal Joint in Psoriatic Arthritis: A Clinical and Ultrasonographic Study

BioMed Research International ◽

10.1155/2014/174841 ◽

2014 ◽

Vol 2014 ◽

pp. 1-5 ◽

Cited By ~ 1

Author(s):

Giovanni Ciancio ◽

Stefania Volpinari ◽

Maria Fotinidi ◽

Federica Furini ◽

Ilaria Farina ◽

...

Keyword(s):

Psoriatic Arthritis ◽

Healthy Subjects ◽

Statistical Significance ◽

Metatarsophalangeal Joint ◽

Metatarsal Bone ◽

The Other ◽

Control Group ◽

Asymptomatic Patients ◽

Seronegative Spondyloarthritis ◽

The Difference

Objective. To evaluate the involvement of the bursa located next to the head of the 5th metatarsal bone in patients with psoriatic arthritis (PsA) in comparison with the other seronegative spondyloarthritis (SpA).Methods. All patients with PsA seen during a period of 24 months were enrolled. The control group included healthy subjects and patients with the other SpA. All subjects underwent clinical and ultrasound (US) examination of the lateral surface of the 5th metatarsal.Results. 150 PsA patients (88 M; 62 F), 172 SpA (107 M; 65 F), and 95 healthy controls (58 M; 37 F) were evaluated. Based on clinical and US evaluation, bursitis was diagnosed in 17/150 (11.3%) PsA patients but in none of the SpA (P<0.0001) and healthy (P=0.0002) controls. In detecting bursitis, US was more sensitive than clinical examination, although the difference did not reach statistical significance (P=0.09).Conclusion. The bursa of the 5th metatarsophalangeal joint appears to be involved in PsA more frequently than by chance. If confirmed by other studies, this finding could be considered as a distinctive clinical sign of PsA, useful for differential diagnosis with the other SpA. In asymptomatic patients, US proved to be more sensitive in the detection of bursitis.

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Analysis of the Impact of Personalized Nursing Service and Hospice Care on the Quality of Life of Elderly Cancer Patients

Tobacco Regulatory Science ◽

10.18001/trs.7.4.24 ◽

2021 ◽

Vol 7 (4) ◽

pp. 469-473

Author(s):

Ting Fang ◽

Nian Wang ◽

Meng Chen ◽

Hongmei Ma

Keyword(s):

Quality Of Life ◽

Cancer Patients ◽

Advanced Cancer ◽

Hospice Care ◽

Pain Treatment ◽

Control Group ◽

Study Group ◽

The Difference ◽

The Impact

Objective Explore the impact of personalized nursing services and hospice care on the quality of life of elderly patients with advanced cancer. Method We selected 80 elderly cancer patients admitted to our hospital from September 2020 to May 2021, and divided these patients into a study group and a control group using a random number table method. The patients in the control group used conventional nursing methods to treat and care for the patients, and the patients in the study group used hospice care measures and combined personalized nursing measures. The quality of life and pain treatment effects of the two groups of patients before and after treatment were compared. Result Before treatment, the quality-of-life scores of the two groups of patients were low, and there was no statistical difference (P>0.05); After treatment, the quality of life of the two groups of patients improved, but compared with the control group, the improvement was more obvious in the study group, and the difference was statistically significant (P<0.05). In terms of pain treatment effect, the total effective rate of pain treatment in the study group was 87.5%, which was significantly better than the 62.5% in the control group. The difference was statistically significant (P<0.05). Conclusion Personalized nursing services and hospice care are conducive to improving the survival and treatment of elderly patients with advanced cancer, and can be used as a clinical application program for the care of advanced cancer patients.

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Platelet Decrease and Efficacy of Platelet-Rich Plasma Return for Peripheral Blood Stem Cell Apheresis

Blood ◽

10.1182/blood-2020-142316 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 29-30

Author(s):

Takahiro Shima ◽

Teppei Sakoda ◽

Tomoko Henzan ◽

Yuya Kunisaki ◽

Takahiro Maeda ◽

...

Keyword(s):

Multivariate Analysis ◽

Stem Cell ◽

Platelet Count ◽

Peripheral Blood ◽

Peripheral Blood Stem Cell ◽

Platelet Rich Plasma ◽

Blood Stem Cell ◽

Platelet Recovery ◽

Platelet Counts ◽

Cd34 Cells

Peripheral blood stem cell (PBSC) transplantation is a key treatment option for hematological diseases and widely performed in clinical practice. Platelet loss is the major complication of PBSC apheresis, and platelet-rich plasma (PRP) return is recommended in case of severe platelet decrease following apheresis; however, little is known about the frequency and severity of platelet loss nor the efficacy of PRP return post-apheresis. To address these questions, we assessed changes in platelet counts following PBSC-related apheresis in 270 allogeneic (allo)- and 105 autologous (auto)-PBSC settings. We also evaluated efficacy of PRP transfusion on platelet recovery post-apheresis. Platelet counts reduced up to 70% post-apheresis in both allo- and auto-PBSC settings, while severe platelet count decrease (< 50 x 109/L) was only observed in auto-PBSC patients (Figure 1). We next analyzed the relationship between severe platelet (< 50 x 109/L) after apheresis and several clinical factors by using univariate and multivariate analysis for auto-PBSC patients. As shown in Table 1, in univariate analysis, severe platelet counts following auto-PBSC apheresis was found more frequently in patients with lower platelet count, lower percentage of CD34+ cells in PB at pre-apheresis, repeated round of apheresis, and smaller number of collected CD34+ cells. On the other hand, in multivariate analysis, the white blood cell (WBC) counts pre-apheresis was the only significant risk factor of severe platelet count following apheresis (p = 0.038). We finally analyzed the transitions of platelet counts in the setting of apheresis. The median platelet counts at pre-apheresis, post-apheresis, and post-PRP return were 187.0 x 109/L, 132.0 x 109/L, and 154.0 x 109/L for allo-PBSC apheresis, and 147.0 x 109/L, 111.0 x 109/L, and 127.0 x 109/L for auto-PBSC apheresis (p < 0.0001 for all, allo-PBSC donors and auto-PBSC patients, respectively) (Figure 2), indicating that PRP return post-apheresis facilitated a rapid platelet recovery in both allo- and auto-settings. Collectively, our data suggest that WBC counts pre-apheresis is a useful predictor for severe platelet decrease following auto-PBSC apheresis and that PRP return is an effective mean to facilitate platelet recovery post-apheresis. Disclosures No relevant conflicts of interest to declare.

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Effect of Nursing Measures Based on Self-Efficacy Theory on State Self-Esteem of Breast Cancer Patients

Tobacco Regulatory Science ◽

10.18001/trs.7.6.122 ◽

2021 ◽

Vol 7 (6) ◽

pp. 6469-6476

Author(s):

Li Qiu ◽

Hongli Wang ◽

Yuan Yuan ◽

Ying Wang ◽

Ping Yu

Keyword(s):

Breast Cancer ◽

Cancer Patients ◽

Self Efficacy ◽

Self Esteem ◽

The Self ◽

Control Group ◽

Observation Group ◽

Breast Cancer Patients ◽

Functional Exercise ◽

The Difference

To analyze the effect of nursing measures based on self-efficacy theory on the state self-esteem of breast cancer patients. 110 breast cancer patients who were treated in our hospital from October 2018 to October 2019 were randomly divided into control group and observation group. The control group was given routine nursing measures, and the observation group was given nursing measures under the guidance of self-efficacy theory. Before operation, 1 week after operation and 3 months after operation, the general data of the two groups before and after treatment were recorded. The self-efficacy level and self-esteem level of the patients before and after treatment were assessed by the self-efficacy scale (GSEs) and state self-esteem scale (SSEs). The compliance of functional exercise and shoulder joint activity (ROM) of the two groups were compared, and the physical status of the two groups were analyzed. To analyze the effect of nursing measures based on self-efficacy theory on the state self-esteem of breast cancer patients. The GSEs score of the two groups increased with the time, and there was no significant difference between the two groups before operation (P > 0.05). After 1 week and 3 months, the GSEs score of the observation group was significantly higher than that of the control group (P < 0.05). The compliance evaluation table of functional exercise in the two groups increased with the time, and the compliance evaluation table of functional exercise in the observation group was significantly higher than that in the control group, the difference was statistically significant (P < 0.05). ROM of the two groups increased with time, and ROM of the observation group was significantly better than that of the control group, the difference was statistically significant (P < 0.05). The self-esteem level of the two groups increased with time, and the self-esteem level of the observation group was significantly higherthan that of the control group, the difference was statistically significant (P <0.05). The nursing measures under tne guidance of self-efficacy theory can help patients to complete functionalexercise, improve theirquality of life, improve their self-esteem level, a nd can be widely used in clinical practice.

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Immature Platelet Fraction in Patients with Chronic Liver Disease, A Marker for Evaluating Cirrhotic Changes.

Annals of PIMS-Shaheed Zulfiqar Ali Bhutto Medical University ◽

10.48036/apims.v17i2.531 ◽

2021 ◽

Vol 17 (2) ◽

pp. 174-179

Author(s):

Muhammad Javaid Iqbal ◽

Muhammad Usman ◽

Mubarak Ali Anjum ◽

Yasir Yaqoob ◽

Ghulam Mujtaba Nasir ◽

...

Keyword(s):

Platelet Count ◽

Liver Disease ◽

Chronic Liver Disease ◽

White Blood Cells ◽

Chronic Liver ◽

Control Group ◽

P Value ◽

Master Program ◽

Immature Platelet Fraction ◽

The Mean

Objective: To evaluate the role of Immature platelet fraction in patients with chronic liver disease, a marker for evaluating cirrhotic changes. Methodology: This case control study was conducted at department of Pathology, Aziz Fatima Medical and Dental College, Faisalabad, over a period of Seven months from June 2020 to January 2021. A total of 126 participants were included in the study consisting of 63 patients with chronic liver disease in group A and 63 participants without any known disease in group B as control. The IPF master program in combination with XE-2100 multiparameter automatic hematology analyzer was used to measure the immature platelet fraction. Ethylene diamine tetraacetic acid was used to collect the blood sample for IPF measurement and was maintained till analysis on room temperature. Ten repeated analyses, immediately and after 24 hours were done for reproducibility of IPF%. Results: The mean age of liver disease patients was 52.35 ± 13.64 years and in control group the mean age was 51.62 ± 11.27 years. There was no significant (p-value > 0.05) difference between both groups based on age and gender. The hemoglobin level and red cell count was found to be significantly (p-value < 0.05) reduced in cases group. While white blood cells count was comparable in both groups. The mean platelet count was significantly (p-value < 0.05) less in cases group (163.5 ± 90.4 vs 233.4 ± 54.5 (x10*3/µl). The mean value of immature platelet fraction (IPF%) was significantly (p-value < 0.05) raised in cases group (5.62 ± 2.92 vs 3.06 ± 1.87). The multivariate discriminant analysis (MDA) score showed a significant (p-value < 0.05) association with chronic hepatis as compared to other liver related diseases. Conclusions: In chronic liver disease patients, there is an inverse relationship between platelet count and IPF% with decreased platelet count and increased IPF%. The proposed MDA function can be used to identify the cirrhotic changes in liver disease patients.

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Mature and immature platelets during the first week after birth and incidence of patent ductus arteriosus

Cardiology in the Young ◽

10.1017/s1047951120000943 ◽

2020 ◽

Vol 30 (6) ◽

pp. 769-773 ◽

Cited By ~ 1

Author(s):

Hannes Sallmon ◽

Boris Metze ◽

Petra Koehne ◽

Bernd Opgen-Rhein ◽

Katja Weiss ◽

...

Keyword(s):

Platelet Count ◽

Birth Weight ◽

Patent Ductus Arteriosus ◽

Very Low Birth Weight ◽

Ductus Arteriosus ◽

Postnatal Life ◽

Platelet Counts ◽

Immature Platelet Fraction ◽

Immature Platelets ◽

Patent Ductus

AbstractBackground:Thrombocytopenia is a risk factor for patent ductus arteriosus. Immature and mature platelets exhibit distinct haemostatic properties; however, whether platelet maturity plays a role in postnatal, ductus arteriosus closure is unknown.Methods:In this observational study, counts of immature and mature platelets (=total platelet count − immature platelet count) were assessed on days 1, 3, and 7 of life in very low birth weight infants (<1500 g birth weight). We performed echocardiographic screening for haemodynamically significant patent ductus arteriosus on day 7.Results:Counts of mature platelets did not differ on day 1 in infants with (n = 24) and without (n = 45) haemodynamically significant patent ductus arteriosus, while infants with significant patent ductus arteriosus exhibited lower counts of mature platelet on postnatal days 3 and 7. Relative counts of immature platelets (fraction, in %) were higher in infants with patent ductus arteriosus on day 7 but not on days 1 and 3. Receiver operating characteristic curve analysis unraveled associations between both lower mature platelet counts and higher immature platelet fraction (percentage) values on days 3 and 7, with haemodynamically significant ductus arteriosus. Logistic regression analysis revealed that mature platelet counts, but not immature platelet fraction values, were independent predictors of haemodynamically significant patent ductus arteriosus.Conclusion:During the first week of postnatal life, lower counts of mature platelets and higher immature platelet fraction values are associated with haemodynamically significant patent ductus arteriosus. Lower counts of mature platelet were found to be independent predictors of haemodynamically significant patent ductus arteriosus.

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Clinical Features and Effects of Eradication on Helicobacter Pylori Positive 207 ITP Cases in Japan.

Blood ◽

10.1182/blood.v104.11.2071.2071 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2071-2071

Author(s):

Kingo Fujimura ◽

Masataka Kuwana ◽

Yoshiyuki Kurata ◽

Masahiro Imamura ◽

Hiroshi Harada ◽

...

Keyword(s):

Helicobacter Pylori ◽

Platelet Count ◽

Eradication Therapy ◽

The Other ◽

First Line ◽

Platelet Counts ◽

Count Response ◽

Successful Group ◽

H Pylori ◽

Over 40 Years

Abstract In 1998, Gasbarrini et al reported that in ITP cases with Helicobacter pylori (H.pylori) infection, elevation of platelet counts was observed by eradication of this bacterium. Since then, several reports from Italy and Japan confirmed the elevation of platelet counts after eradication. However, the characteristic background in the H.pylori positive ITP and eradication effects on platelet counts is unclear. On the other hand, reports from Spain, North Europe and USA could not show the evidence that eradication is effective on elevating platelet counts in H.pylori positive ITP. Therefore, we designed a nationwide retrospective study in Japan to evaluate the incidence of H.pylori positive ITP cases and the effects of eradication on platelet counts and to clear above problems. Four hundred and thirty-five ITP cases were enrolled over a period of one and half years (2002. 7~2003.12) from 12 hospitals. H. pylori infection was found in 300 cases(65%), who were significantly (P<0.005) older and showed hyperplastic megakaryocyte in bone marrow (P=0.011) comparison with negative cases. Eradication to H. pylori was performed in 207 H. pylori positive ITP cases and as a whole, the platelet count response was observed in 63% of eradication succeeded group. In the successful group, CR and PR rate were 23% and 42% respectively at 12 months after eradication. The platelet count response was significant in the successfully eradicated group (P<0.005) and the increased platelet count was maintained without ITP treatment for over 12 months. In conclusion, H. pylori infection was involved in most ITP patients over 40 years old in Japan and eradication therapy proved effective for increasing platelet counts even in splenectomy non-responsive cases and the platelet count response appeared one month after eradication. This evidence suggests that eradication therapy is the first line of treatment in H. pylori positive ITP patients.

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Platelet Factor 4 Regulates Platelet Count In Vivo: Implications for Platelet Recovery after Cytotoxic Therapy.

Blood ◽

10.1182/blood.v106.11.3144.3144 ◽

2005 ◽

Vol 106 (11) ◽

pp. 3144-3144

Author(s):

Michele P. Lambert ◽

M. Anna Kowalska ◽

Mortimer Poncz

Keyword(s):

Bone Marrow ◽

Platelet Count ◽

Mononuclear Cells ◽

Physiological Role ◽

Platelet Factor 4 ◽

Cytotoxic Therapy ◽

Platelet Factor ◽

Platelet Recovery ◽

Platelet Counts

Abstract Platelet factor 4 (PF4), a platelet-specific CXC chemokine, was the first reported negative autocrine regulator of megakaryopoiesis in vitro. To define the physiological role(s) of PF4, we established mice that either were deficient in murine (m) PF4 (mPF4−/−) or that over-expressed human (h) PF4 (hPF4+/+). These mice had a level of PF4 ~6-fold greater than that present in human platelet controls. All lines studied had been backcrossed onto a C57Bl/6J background for >10 generations. Platelet counts in these animals correlated inversely with PF4 determined expression, beginning with a low platelet count of 702 ± 57 x 103/μL in the hPF4+/+ mice < hPF4+ < wildtype (WT) < mPF4+/− < mPF4−/− mice in which the platelet count was 1,404 ± 117 x 103/μL. The half-life of the platelets from the hPF4+/+ was identical to that of WT mice. Cultured bone marrow mononuclear cells (BMMNC) in serum-free media showed that each line had identical efficiency in growing megakaryocyte colonies, suggesting that megakaryocyte progenitor cells in these different genetic lines were intrinsically normal. Megakaryocyte colony numbers derived from WT BMMNC were reduced by the addition of recombinant PF4 or supernatant from irradiated bone marrow of hPF4+ mice, but not from mPF4−/− mice, suggesting that megakaryocyte lysis in vivo during cytoreductive therapy may contribute to the subsequent thrombocytopenia by releasing PF4. Additionally, a rabbit polyclonal anti-mPF4 antibody (Ab) was able in culture to significantly reverse this inhibitory effect of PF4 on megakaryopoiesis. Preliminary cytoreductive studies using either 600 cGy or 150 mg/kg of 5-fluorouracil (5-FU) intraperitoneally (IP) were performed. In irradiation studies, mPF4−/− mice began to recover on the same day as WT littermates, but they clearly had higher platelet counts at their nadir, with a drop to only 42 ± 7% of baseline vs. 32 ± 6% in the WT mice (n =12 in each arm, p = 0.06). By Day 13, 9 of 12 mPF4−/− mice had recovered to >75% of baseline, while only 3 of 12 WT mice had recovered (p <0.001). hPF4+ mice (n = 7) were studied after 5-FU treatment. Compared to WT littermates (n = 9), the hPF4+ recovered later (15.6 ± 2.2 vs. 11.2 ± 1.5 days, p < 0.0003), and clearly had significantly greater drop to 30 ± 6% vs. 56 ± 9% of baseline (p < 0.00001). By day 15, all of the WT mice had recovered, but only 43% of hPF4+ mice had returned to >75% of baseline platelet count (p = 0.009). To examine if anti-mPF4 Ab was protective of cytotoxic therapy-induced thrombocytopenia, WT mice were treated with 180 mg/kg of 5-FU and were given either anti-mPF4 Ab (25 mg/kg, IV, x 2) or an equal volume of vehicle. By day 5, the Ab-treated group had a platelet count of 45 ± 6% vs. 32 ± 4% in the untreated (n > 13 per arm, p = 0.015). Platelet counts remained higher in the Ab-treated arm throughout the study. By day 10 after intervention, 9 of 16 mice of the Ab-treated arm had platelet counts over 75% of the baseline, while only 3 of 13 control mice did (p < 0.001). Thus, it appears that PF4 is an important negative autocrine regulator of platelet count in vivo. Excessive release of PF4 following cytotoxic therapy may be a mediator of treatment-related thrombocytopenia. Strategies directed to alleviate the consequence of released PF4 may have clinical benefit in ameliorating this thrombocytopenia.

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