Immune thrombocytopenia (ITP) is an immunological disease of children and adults characterized by a transient or permanent decline in the number of platelets in their peripheral blood. The clinical characteristics are isolated thrombocytopenia and varying degrees of bleeding (1). Based on the etiology of the disease, it is divided into primary and secondary ITP owing to underlying autoimmune diseases, hematologic malignancies, use of certain medications, or acute infections (2, 3). According to the International Working Group (IWG) guidelines, ITP is defined as newly diagnosed when remission is within 3 months of diagnosis, persistent if remission occurs between 3 and 12 months after diagnosis and includes patients not reaching spontaneous remission or not maintaining a complete response off therapy, or chronic when it lasts for more than 12 months (1).

Most pediatric ITP patients could achieve complete recovery when treated with systemic steroids, intravenous immunoglobulin (IVIG), or anti-D immunoglobulin, and some achieve complete remission with no treatment (3–5). However, 10–20% of children were progressing to the chronic stage in long-term follow-up (3, 4). The prognosis of patients with ITP who were diagnosed with chronic ITP is not as good as those diagnosed with non-chronic (6). Several retrospective studies have investigated predictors for the development of chronic ITP (7–11), such as age, gender, and platelet counts. The Nordic group devised a weighted prediction score to evaluate a brief and uneventful course of newly diagnosed ITP in children (12). A recent study simplified the rules for diagnosing chronic ITP by analyzing 6–8 clinical features and identifying children as being of low, intermediate, and high risk for getting ITP (13).

With the understanding of the mechanism of ITP, it was considered to be an autoimmune disease (14). The presence of antibodies against platelets has traditionally been considered to play a central role in ITP. For example, autoantibodies against platelet glycoprotein (GP)IIb/IIIa or (GP)Ib/IX could be detected in the majority of patients (15, 16). Furthermore, the cellular immune responses of patients with ITP have the characteristic immune tolerance disorder (17). The immune function was mainly activated by T cells at diagnosis for ITP patients and they might have same immune status for chronic ITP (18, 19). However, a recent study showed that the level of kappa-deleting recombination excision circles (KRECs) was different in chronic patients with ITP compared to non-chronic patients. This points to an overreaction of the development of B-cells as a role in the pathogenesis of ITP (20).

The replication of the cytomegalovirus (CMV), and Epstein Barr virus (EBV) in the leukocytes of patients, may impact varying degrees on their immunological processes (21, 22). A primary viral infection is usually asymptomatic. However, viral latency in macrophages, T lymphocytes CD8+, and the endocrine cells may occur after viral infection. Several studies have suggested that the CMV and EBV may be common causes of autoimmune thrombocytopenia due to the phenomenon of antigenic mimicry which stimulates the production of antiplatelet antibodies (17, 23–25). In addition, primary ITP is more common in children and is usually triggered by non-specific viral infections, such as upper respiratory or gastrointestinal virus infections. In some cases, it is triggered by acute infection of EBV, CMV, Rubella virus (RV), Varicella, and Mumps (26, 27). These results may provide more information on the immune mechanism involved and an analysis of the prognosis. Viral infections may play a role in the occurrence of ITP. However, the association between related virus infections and the duration of ITP is still not clear.

Our present study aimed to evaluate the predictive value of clinical features and viral infections of childhood ITP. Furthermore, our study analyzed the differences in immune function between children with ITP and those with and without herpes virus infection.

Evaluating the chronic course of ITP is essential for establishing an appropriate management plan and searching for an underlying etiology. Several clinical factors have been investigated to identify patients who are more susceptible to becoming chronic (6, 12, 13, 28, 29). Our study suggested that age and low levels of hemoglobin were adverse risk factors for chronic ITP, which was similar to previous studies. As described previously, many viruses, such as CMV, EBV, and RV, are involved in the pathogenesis of ITP because they stimulate the production of antiplatelet antibodies (26, 27). Our data showed that patients with herpes virus infection had lower PLT counts compared to patients without herpes virus infection. However, our results showed that chronic ITP had lower proportion of CMV IgM and HSV-2 IgG and the multivariate analysis showed that patients with herpes virus infection had a low risk of progressing to become chronic. Those results suggest that herpes virus may be the trigger of ITP and the chronic phase was not associated with herpes virus infection status (HSV-2 IgG). The study by Smalisz-Skrzypczyk et al. showed that CMV or EBV infections are common in children with ITP and these infections do not seem to have an appreciable bearing on the clinical course and the response to treatment of children with ITP (26). Viral infections were identified solely based on laboratory tests, and only a few patients had clinical symptoms that could be associated with a viral infection. In addition, in our study we only tested for antiviral antibodies and did not obtain copies of the virus DNA from the pediatric ITP patients.

Our study showed that the CD4+/CD8+ cells ratio between patients with and without herpes virus infection was significantly different. The results suggest that children with viral infections will have more disordered immune function, especially T cell mediated immune responses. However, another study demonstrated that KRECs levels are different in chronic patients compared to non-chronic patients, pointing to an overreaction of the development of B cells as a role in the pathogenesis of ITP (20). Furthermore, the low level of complement C3 was also observed in patients with herpes virus infection. Enhanced peripheral complement activation has long been considered as one of the major pathogenic elements of immune thrombocytopenia (30, 31). The present study sheds light on complement activation in the pathogenesis of ITP (32). In conclusion, our study suggested that patients with herpes virus infection had higher immune dysfunction. However, herpes virus infection status may not be an adverse risk factor for transforming to the chronic in long-term follow up.

Although many studies have confirmed that patients with viral infections have an increased probability of an adverse prognosis (33–35), other studies have showed that there were no obvious interactions between viral infections and the burden of disease (36, 37). In our study, most children selected IVIG as their initial treatment which may not increase the probability of the disease going into remission and not progressing to the chronic phase. The recent study showed that the use of IVIG could not reduce the incidence of the chronic phase (38). However, the study by Tamminga et al. showed that there was a lower rate of chronic ITP after IVIG treatment (29). The results of difference in two studies may be the difference in the deadline for follow-up (6 vs. 12 months). Patients' age was adverse risk factors for patients with ITP, which is consistent with a previous study and shows that clinical workers must be more aware of the clinical features of the patients (8, 17).

We were also aware of some limitations in our study. Although viral load by PCR was a more robust way of assessing acute infection status, the detection of viral load was carried out in clinical laboratory until recent 2 years in our hospital and could not provide this critical data. This is the reason why the viral load was absent in this retrospective study. The results of single center retrospective cohort studies are not generalizable to other populations. The sample size of patients included in the present study was not large. In conclusion, our study explored the association between antiviral antibodies and chronic childhood ITP. Childhood ITP with herpes virus infection may not be an adverse risk factor, causing transformation to the chronic phase. It provides new insights into ITP therapy and management in children.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Research Ethics Boards of the Second Affiliated Hospital & Yuying Children's Hospital of Wenzhou Medical University. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the minor (s)' legal guardian/next of kin for the publication of any potentially identifiable images or data included in this article.

X-QZ: study design. TL and G-lY: statistical analysis and manuscript draft. ZL, QX, M-mL, and Z-GC: clinical data review and acquisition. All authors contributed to the article and approved the submitted version.

This study was supported by grants provided Natural Science Foundation of Zhejiang Province, China (No. LY18H200006).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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