The present study assessed the HSP-70 serum levels in newly diagnosed and chronic ITP and compared their expressions to the healthy controls. Our findings showed that the HSP-70 levels in newly diagnosed and chronic ITP children were significantly increased compared to the healthy control group. In addition, the chronic ITP group demonstrated significantly elevated HSP-70 levels compared to the newly diagnosed ITP group. In addition, a positive correlation was observed between the levels of HSP-70 and the thrombocyte counts.

HSP-70 has been reported to play varying roles in the progression of various inflammatory diseases. The molecule has been confirmed to regulate intracellular homeostasis and is released into the extracellular environment as a response to acute myocardial infarction (AMI) [10]. Increased circulating HSP-70 has been discussed as a myocardial damage marker post-AMI, which is linked with the inflammatory responses [11], and might also enhance the heart failure progression. Furthermore, HSP70 was significantly increased post-AMI and was directly linked to severe cardiac events [10]. However, some studies indicated that high HSP-70 levels might have athero-protective impacts [12], and exosomes from healthy humans might offer cardio-protection in cardiac ischemia and reperfusion through HSP70-mediated effects [13].

In a study involving asthmatic patients, remarkably elevated HSP-70 autoantibodies were reported to be associated with asthma. A significant positive correlation was further reported between HSP-70 and the severity of asthma symptoms [14]. Contrastingly, some studies also reported that HSP-70 plays an auto-protective role in lung injury and asthma. Furthermore, HSPs autoantibodies have been confirmed to have notable roles in the pathogenesis and prognosis of various other diseases. For instance, Shinghai and colleagues confirmed antibodies against HSPS in autoimmune liver disease patients and hypothesized that anti-HSP70 presence indicates the disease activity of primary biliary cirrhosis [14].

No literature has, however, reported the role of HSP-70 in the development of childhood immune thrombocytopenia. Certain parameters provide information about platelets, overall referred to as platelet indices, and they include the platelet distribution width (PDW), mean platelet volume (MPV) and the platelet large cell ratio (PLCR) [15]. In platelets, various HSP-70-linked genes have been specified for the trafficking and sequestration of proteins. Classical endoplasmic reticulum chaperone, BiP/Grp78, is one member of the HSP70 family that has been categorized in the cytosol of the platelet, in circulation and on the surface of the platelet, whereby it has antithrombotic function through pro-coagulant tissue factor sequestration on the surface of the platelet [16].

More recent findings have indicated that the platelet HSP90/Hsp70 system has been hypothesized to modulate intracellular trafficking and multidrug resistance MDR4/ABCC4 localization [17]. The HSP members additionally play essential roles in the assembly of actinomyosin filament, an important step in the change of platelet shape and spreading [18]. For instance, HSP27 has been implicated as a downstream p38 MAPK target in the assembly of the cytoskeleton, and phosphorylation of HSP27 is important for the secretion of platelet granules [19]. Taken together, these reports indicate the HSP70 intracellular and extracellular functions and associated chaperones in trafficking, assembly of protein and platelets regulation. In this investigation, Hsp-70 concentration was positively correlated with the platelets counts.

ITP has imbalances in pro- and anti-inflammatory mechanisms [20]. According to various studies, pro-inflammatory CD4 + T-helper 17 cells that generate interleukin 17 have a pathogenic function in an active autoimmune infection [21]. Contrastingly, regulatory T cells constituting 5–10% of the peripheral CD4 + T cells have an important function in self-tolerance, inhibit antibody- and cell-mediated immunity responses and protect the host from autoimmunity [22]. Among the most unique aspects of the physiology of T-regs is their opposing feature against pro-inflammatory Th17 cells and suppressing their autoimmune capability in a particular way [20]. According to Nishimoto et al., about 36% of the Tregs-deficient mice became thrombocytopenic for about 5 weeks. IgG antiplatelet antibodies were reported in these thrombocytopenic mice, and the transfer of purified T-regs into the experimental mice alleviated the thrombocytopenia [23].

At present, HSPs have been regarded as toxic autoantigens and have an association between autoimmunity and infection. Nevertheless, growing evidence has indicated that HSPs such as HSP-70 might demonstrate anti-inflammatory characteristics in some circumstances. HSPs that have anti-inflammatory properties, such as HSP-70, specifically affect the presence or the functional activities of these immune-regulatory cells, especially since these stress genes are reported ligands for toll-like receptors (TLRs) [24]. The TLRs are normally expressed on the regulatory T cells, and the TLRs ligation on CD4 + CD25 + T cells initiates a tenfold rise in their inhibitory activity [25].

Our findings show that HSP-70 is elevated in childhood ITP. This observation confirms that Hsp-70 can play an immunosuppressive role, which has also been reported by previous literature. As an immunosuppressant, HSP-70 has been shown to pass through a lipid bilayer, an ability-linked phosphatidylserine presence. Additional sphingolipids, including globotriaosylceramide also induce the insertion of HSP-70 into a membrane, confirming that HSP-70 might be present in the tumor membranes [26].

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population that expands during inflammation, cancer and infection, with a significant ability to suppress T cell responses [27]. According to Chalmin and colleagues' findings in humans and mice, membrane-related HSP-70 present in tumor-derived exosomes (TDEs) inhibited tumor immune regulations by enhancing the suppressive roles of MDSCs. TDEs contained in the supernatant of tumor cells of three cancer cell lines could mediate T cell-dependent immunomodulatory functions of MDSCs. It was identified that the TDEs factor that induced activation of MDSCs was the inducible TDE cell surface-expressed HSP-70 (HSPA1A) [27]. These observations indicated that immunosuppressive effects of tumor cells include their ability to induce functional MDSCs by producing exosomes that express HSP-70. The limitation of this study is that it did not investigate the HSP-70 expression in ITP patients' tissues and lacked in vivo studies to investigate the association of HSP-70 with other important inflammatory factors, such as TNF-α and IL-4. Furthermore, a longitudinal study is needed to determine whether levels of HSP-70 in ndITP change once they develop either chronic ITP or go into remission. Another limitation is the possibility that thrombocytopenia itself leads to higher levels of HSP-70 in circulation.