A novel approach to immune thrombocytopenia intervention: modulating intestinal homeostasis

Abstract

Immune thrombocytopenia (ITP) is a prevalent hemorrhage condition that causes notable immune-related abnormalities. Recently discovered data has shown that the intestinal flora plays a crucial role in maintaining a balanced immune system. Furthermore, an imbalance in gut flora has the potential to increase the possibility of developing ITP. Moreover, some studies reported a strong link between inflammatory bowel disease (IBD) and ITP. In this review, we described the significance of gut immunity in ITP. In addition, we explored the associations between gut flora and ITP as well as IBD and ITP. Finally, we examined the effectiveness of existing therapies that regulate gut homeostasis and their impact on the prognosis of patients with ITP.

Introduction and background

The gastrointestinal tract (GI), the largest immune-regulated organ in the human body, is a major contributor to the overall immune response [1]. The intestinal immunological barrier contains lymphoid tissue, immunoglobulins, and released cytokines, serving as a crucial defense mechanism in the body. Lymphocytes are commonly classified into two main categories: organized lymphoid tissue and diffusely dispersed lymphocytes. The diffusely distributed lymphocytes consist of intestinal mucosal lamina propria lymphocytes (LPL) and intestinal intraepithelial lymphocytes (IEL)[2]. Of these, IEL—which primarily consist of T cells and NK cells—fast-track epithelial cell regeneration, eradicate virus-infected epithelial cells, and provide a robust defense against bacterial infections. T and B cells predominate among LPL, which are found in the mucosa’s lamina propria. Upon closer analysis of the cellular subpopulations within the intraepithelial basement membrane and mucosal lamina propria, it was observed that the amounts of IEL and LPL subpopulations increased substantially after immunization. Furthermore, lymphocytes exhibit increased activity, so confirming their crucial function in mucosal immunity.

Multiple GI-based lymphocytes and immune factors work in concert to protect the body against outside invaders. Furthermore, an estimated 40 trillion microorganisms, known as the gut flora, inhabit the gastrointestinal tract of humans. The gut microbiota is highly advantageous to the host and is closely linked to the host’s immune system. The gut microbiota consists of a wide group of bacteria that play a crucial role in regulating various bodily functions, including physiology, metabolism, immunity, and overall health [3]. The strong association between gut flora, host, and the environment generates a dynamic equilibrium that modulates the overall well-being of the organism.

Immune thrombocytopenia (ITP) diagnosis impies the low platelet count (< 100 000/mm^3) in the absence of other known thrombocytopenia causes. In ITP, antibody and cell-mediated processes lead to the increased platelet destruction and insufficient production [4]. The incidence rate of ITP is estimated to be around 1.6–3.9 cases per 100,000 individuals. The chance of developing ITP increases with advancing age, and women are more prone to experiencing ITP compared to males [5].

Intestinal immunity and ITP

Patients with immune ITP who are also afflicted with Helicobacter pylori (HP) infection encounter many abnormalities in their immune system. Specifically, there is a decrease in the number of CD4 + cells and CD4 + /CD8 + cells while the number of CD8 + cells increases. The synthesis of anti-platelet antibodies has also significantly increased. GI homeostasis makes use of the complementary functions of immune and non-immune cells. However, significant overexpression of inflammatory cells might upset this delicate equilibrium by increasing the exposure of non-immune cells to cytokines.

T-lymphocyte

Cellular immunity is significantly modulated by T cells. Treg and Th17 cells cooperate in the GI mucosal immune system to preserve a complex equilibrium that ensures the integrity of the intestinal immunological environment [6].

Treg cells are a subpopulation of T lymphocytes. ITP sufferers often have substantially reduced peripheral blood CD4 + CD25 + T regulatory cells [7, 8]. Furthermore, compared to uninfected people, HP-infected patients have higher numbers of CD4 + CD25 + T cells in their stomach and duodenum mucosa. These Treg cells exacerbate the infection by inhibiting the gastric mucosal immune response to HP.

Th1 cells release IL-2, IFN-γ, and TNF-α, which accelerate inflammatory mediators production like NO. ITP sufferers often exhibit enhanced Th1 cell population, suggesting a potential link to inflammatory responses (Fig. 1). Th17 cells are responsible for secreting IL-17, IL-21, IL-22, TNF-α, and IL-6. These immune cells fight off bacterial infections outside of cells quite effectively. Unfortunately, there is a clear correlation between the development of severe autoimmune diseases and increased Th17 cell activity [9]. Thl7 cytokines, namely, MCP-1 and MIP-2, produce chemokines that accelerate inflammatory cell invasion, thereby damaging the intestinal mucosa tissue [10]. In terms of gut function, these patients experience impaired motility, chemotaxis, membrane translocation, and metabolism. Immune dysregulation and inflammation are the underlying mechanisms. Escherichia coli (E. coli) bacteria possess the characteristics of strong adherence and invasiveness, which can be observed either within the intestinal mucosa or as a result of invasion. Furthermore, these bacteria can replicate inside macrophages and produce an excessive amount of TNF-α, which is a pro-inflammatory cytokine that plays a crucial role in regulating the immune system [11,12,13,14] (Fig. 2).

Fig. 1

In patients with ITP, Th1 cells increase and release IL-2, IFN-γ, and TNF-α, which accelerates NO and causes inflammation

Fig. 2

The E. coli role in ITP

Th17 and Treg cells have opposing roles in the inflammatory microenvironment. Tregs can transform into Th17 cells, which are detrimental to the immune microenvironment [15, 16]. ITP patients who also suffer from gastrointestinal infections encounter an imbalance in the Th17 to Treg cells ratio. This imbalance results from both a significant drop in the Treg cell number and an elevation of the Th17 cell population. Therefore, deviations from the Th17/Treg cell ratio could play a role in the development of ITP. Furthermore, patients with ITP who simultaneously have GI infections have abnormally high percentages of Th17 cells and IL-17.

Furthermore, the degree of infection is closely correlated with the number of these immune cells. In the intestinal lymph nodes of patients with inflammatory bowel disease (IBD), IL-17( +) Foxp3( +) T cells are frequently abundant. This demonstrates the critical function of Treg and Th17 cells in controlling the immune response in ITP patients’ intestines [17].

B lymphocytes

B cells secrete mucosal IgA to modulate gut flora. This restricts bacterial proximity to epithelial cells, thereby regulating intestinal mucosal immunity [18, 19]. Recent investigations suggested a potential connection between changes in sIgA content and the onset of IBD. It is hypothesized that increased sIgA content causes sIgA expression, which eliminates the inflammatory response in the intestines of IBD patients. Scientists demonstrated enhanced sIgA release within the gastric mucosa of chronic atrophic gastritis (CAG) and HP infection sufferers relative to HP-negative individuals. Alternatively, in an autoimmune disease model of intervention ITP mice, sIgA content was significantly reduced. This suggests a potential link between ITP, sIgA formation, and the immune system. Intestinal homeostasis is achieved through the complex network of harmonious interactions and functions that make up the intestinal barrier. However, if the balance is disrupted, immunological complications can aggravate and lower platelet counts even further.

One study collected fecal samples from 25 ITP children and 16 healthy volunteers to examine alterations in gut microbiota diversity and composition under those conditions. They found that the gut flora of ITP children was noticeably out of balance, with a significant elevation of the anaplasmosis phylum (Bacteroidetes) population. Additionally, there was a direct correlation between this rise and IgG levels. They concluded that the gut microbiota probably regulates ITP development through IgG [20].

DC cells

DC cells are antigen-presenting cells that critically modulate Th1/Th2 immune response and immune tolerance, which, in turn, may affect ITP development. Specifically, intestinal DC cells recognize pathogenic bacteria and react by enhancing the immune response or immunological tolerance. To minimize unnecessary inflammation and allergy responses, these intestinal DC cells often stay in a hyporesponsive state. Nonetheless, these cells play a crucial role in controlling intestinal immunological tolerance [21].

Mechanistic study of intestinal immunity and ITP

Compared with the model control group, the levels of VIP and PACAP in the brain, colon, and serum of rats in the prednisone group, except for serum PACAP, were elevated. In comparison to mice in the blank control group, the mesenteric lymphocytes of mice in the model control group had much greater levels of p53 protein expression. The expression of p53 protein in the rat mesentery was significantly decreased following prednisone intervention. Compared with the blank control group, the spleen cytokines IFN-γ and IL-17A were elevated, and IL-4 and IL-10 were reduced in the model control group. After prednisone intervention, IFN-γ and IL-17A were down-regulated, and IL-4 and IL-10 were up-regulated [22].

Intestinal flora and ITP

According to high-throughput sequencing research of fecal samples from ITP patients and healthy volunteers, there are notable differences in the makeup and diversity of the gut microbiota in ITP patients. Specifically, when comparing ITP patients to healthy controls, Bacteroides were increased, and Thick Walled Bacteroides were decreased. Moreover, the Thick Walled Bacteroides to Actinobacteria ratio was markedly reduced in ITP patients. Additionally, they observed a direct association between Thick Walled Bacteroides abundance and platelet counts, whereas an inverse relation was seen between Bacteroides abundance and platelet counts. All of these results pointed to a potential link between platelet counts and changed gut flora in ITP patients. Additionally, it was discovered that the dysbiosis of the gut microbiota may be related to the platelet activation status among ITP patients utilizing flow cytometry of the platelet activation markers PAC-1 (identifying activated GP IIb/IIIa complex) and CD62p (platelet surface P-selectin) [11].

Wang et al. performed an extensive macrogenomics assessment of fecal samples from 99 ITP patients and 52 healthy controls. They showed no significant variations in the ratios of thick-walled/anaplastic bacilli between the two groups. Actinobacteria, Aspergillus, and Clostridium wartsonii, on the other hand, were highly prevalent in ITP patients. These bacteria had an inverse relationship with platelet counts and a direct relationship with the length of ITP. The study also screened key bacterial species that serve as critical ITP indicators, such as Prevotella, Sporothrix mucococcus, Clostridium perfringens, and Bifidobacterium. In particular, before using these species for ITP diagnosis, more research with a bigger sample size is necessary to confirm the findings of this study [12]. An additional study revealed a close correlation between the dysbiosis of gut bacteria in ITP patients and an increase in Actinobacteria, Lactobacillus, and Streptococcus contents, accompanied by a concurrent drop in Bacteroide content.

Furthermore, it was discovered that the gut microbiota and metabolites have a close relationship with platelet counts. For instance, there is an inverse correlation between the Lactobacillus proportion and platelet counts. In contrast, there is a reasonably strong negative correlation between metabolites, lipids, lipid-like compounds, and platelet counts. Alternately, Bacteroides are directly associated with platelet counts. Based on this evidence, intestinal bacterial and metabolic alterations strongly influence platelet count. Additionally, the platelet proportion can potentially be enhanced among ITP patients by regulating the composition of intestinal bacteria and metabolites [23].

In one study, fecal bacteria 16S rRNA sequencing analysis, circulating plasma cytokine, and metabolite analysis involving 29 ITP patients and 33 healthy volunteers demonstrated a robust relationship between microbiota and fat metabolism among ITP patients. Thus, by controlling cytokine release and interfering with fat metabolism, gut microbiota can significantly affect the development of ITP [24].

HP and ITP

A study conducted in 1998 discovered that platelet counts in patients with ITP increased following the eradication therapy for HP, leading to the suspicion that HP may have generated secondary ITP. HP triggers the activation of B lymphocyte clones, leading to the production of autoantibodies that target platelets. Platelet membrane glycoprotein GPIIb/IIIa is the main target antigen of anti-platelet autoantibody (PAIg) in ITP patients. It was found that Hp plays a role in the pathogenesis of adult ITP induced by Hp by up-regulating the excitatory FcγR and down-regulating the inhibitory FcγR on the surface of mononuclear macrophages [25]. In 2021, HP was found to promote the destruction of platelets in ITP mice, and the underlying mechanism may be related to accelerating megakaryocyte apoptosis by activating the NF-κB/IL-17 pathway (Fig. 3) [26].

Fig. 3

Helicobacter pylori regulates the apoptosis of human megakaryocyte cells via NF-κB/IL-17 signaling

Mechanistic studies of intestinal flora and ITP

Patients with ITP exhibit changes in their gut flora both in terms of functionality and structure. Additionally, specific bacterial populations are linked to cytokines and bleeding. Possible processes may include the activation of inflammatory responses and the modulation of immune system functions. Both the functional and structural composition of the gut microbiota in ITP patients have been observed to be modified. The mechanisms underlying the imbalance of Th1/Th2 ratio in ITP are not well understood and need to be investigated further [10].

IBD and ITP

CD and ITP

In 2007, the novel ectodermal CD complication known as ITP was first described. ITP and CD are both autoimmune diseases with similar immunological pathogenesis. It is believed that TH1-type CD4 + cells and activated tissue macrophages are the primary causes of platelet immune destruction. The investigation, as mentioned above, demonstrated that both hormonal and immunoglobulin therapies are insufficient for CD and ITP management. This highlighted the productive nature of infliximab in managing ITP complicated by CD [27].

UC and ITP

In one study involving a 21-year-old male patient diagnosed with UC and ITP, following rejection of steroid therapy, the patient was administered mesalazine tablets 400 mg for 2 months, along with eltrombopag 50 mg orally four times a day for four months to address the ITP. The patient was closely monitored for treatment response, and a follow-up colonoscopy was conducted eight weeks after the start of treatment, which revealed a drastic reduction of sigmoid proctitis and improvement of platelet levels [28].

A 49-year-old male patient presented to a hospital seeking medical attention for a severe case of sudden inflammation of the colon and was prescribed hydrocortisone, which effectively alleviated his condition. Upon discharge, the patient was prescribed a daily dose of 60 mg of prednisone and 50 mg of azathioprine. During the follow-up period, the dosage of azathioprine was increased to 100 mg/day, while the dosage of prednisone was gradually decreased. After 3 months of treatment, the patient exhibited thrombocytopenia (30,000/μL), which failed to improve even after azathioprine suspension. At this point, the physical conducted a bone marrow aspirate and diagnosed the patient with ITP. To treat this, the patient was given prednisone, which partially improved his symptoms. This was followed up with mesalazine 3.2 g for UC and eltrombopag for a platelet count of approximately 50,000/μL. Haematological alterations must be considered among UC patients due to complication risks, such as bleeding. In the presence of thrombocytopenia, it is critical to consider an ITP possibility while ruling out side effects emerging from medications, especially immunosuppressive agents [29]. Precise diagnosis and appropriate therapy are essential in controlling this specific manifestation because they assist in managing the disease, reduce complications, and improve patient outcomes.

Both ITP and IBD

A study that investigated 32 ITP and IBD patients found that the majority of ITP cases started after an IBD diagnosis. However, these patients performed well under conventional ITP treatment. Patients with IBD typically experience an ordinary course of ITP development that responds well to pharmaceutical therapy and requires less splenectomy [30]. Based on a case report involving 14 children with IBD and ITP, 57.1% were initially diagnosed with ITP, and 35.7% were concurrently diagnosed with IBD. IBD treatment, other than steroids, does not significantly affect ITP progression. Among the two surgical patients, one experienced full ITP recovery following colectomy. ITP was mild but chronic in half of the patients. Furthermore, ITP did not specifically affect any patient’s IBD severity. Finally, there was no discernible effect of colectomy on ITP [31].

A separate study investigated a pediatric patient who exhibited both celiac disease and an uncommon instance of ITP. Despite adhering to a rigorous gluten-free diet, thrombocytopenia continued to persist. Therefore, further investigations are necessary to explore the intricate relationship between celiac disease and ITP [32] (Table 1).

Table 1 Clinical reports on IBD and ITP [27,28,29,30,31,32,33,34,35,36,37,38,39]

Children with ITP and IBD may be related to genetic, immune system development, and environmental factors. In addition to genetic and environmental factors, lifestyle, dietary habits, and psychological stress may have a more significant impact on the occurrence of ITP and IBD in adults. In adults, the patient’s overall health, complications, and drug interactions should be carefully taken into consideration. Children and adults may respond differently to treatment, with children potentially showing a better response, but also being more susceptible to treatment side effects. Treatment for children needs special attention to its effects on growth and development, while treatment options for adults need to take more account of chronic disease management and quality of life.

Mechanistic studies of IBD and ITP

Emerging evidence suggests an intricate association between IBD and Henoch-Schönlein purpura (HSP) and ITP. However, much of this relationship remains undetermined. To investigate further, data from the FinnGen project and the International IBD Genetics (IIBDG) Consortium were used in a two-sample Mendelian randomization analysis. This study evaluated a possible causative relationship between HSP, ITP, or secondary thrombocytopenia and IBD, including UC and CD. Furthermore, several sensitivity analyses were conducted to validate these findings. The studies revealed a strong causal relationship between IBD and HSP. Genetic analysis revealed a direct correlation between both UC and CD with ITP.

In addition, CD alone was associated with an increased risk of HSP. Nevertheless, there was no clear correlation observed between IBD and secondary thrombocytopenia. According to this research, there is a possible cause-and-effect relationship between IBD, HSP, and ITP, which can be controlled and used to manage and treat IBD [40].

Gut homeostasis and ITP intervention

Hormones

Corticosteroids have a significant ability to control the composition of gut microbiota, and this characteristic is employed when corticosteroids are used to treat ITP. In particular, patients with corticosteroid-resistant ITP have different gut flora compared to corticosteroid-sensitive patients. This is highly indicative that an altered gut microbiota is crucial to the development of hormone resistance among ITP patients. Hence, targeting the intestinal floral imbalance can potentially augment the efficacy of drug-resistant ITP patient management [12].

Probiotics

Diet-based therapies aid in intestinal flora regulation, which, in turn, restores human health [41]. Prior investigations reported S. pseudomallei oral administration to patients with autoimmune diseases strongly diminished Th17 contents, IL-6 synthesis, and enhanced Treg cell proliferation [42]. Furthermore, dietary yeast has been found to generate many advantageous cytokines in individuals with ITP by controlling the composition of the intestinal flora. Therefore, altering the diet to improve the composition of gut bacteria shows potential as an innovative method for the future management of ITP.

Fecal flora transplantation

Fecal flora transplantation is a well-established, safe, and effective procedure for treating diseases involving immune imbalance and dysfunction. Therefore, this can also be regarded as a potential treatment for various diseases of the hematological system. Currently, research is scarce on the advantages of fecal flora transplantation in hematological disorders. Nevertheless, limited data suggests a beneficial effect on conditions such as ITP, thereby demonstrating its effectiveness in enhancing hematological challenges [43].

One investigation obtained 37 fecal samples from ITP patients and 36 from healthy controls. Following 16S rRNA sequencing of these samples, they found a markedly higher concentration of crucial microbiota in the ITP group. They then divided the ITP group into three smaller groups, giving each group a different level of care. They were able to accurately forecast the microbiota and discern distinct bacterial profiles between the ITP-treated and healthy subjects by using a random forest model. Moreover, using microbial functional annotation and variance, they revealed that the drug treatment strongly influenced gut flora, which, in turn, induced autoimmune responses within the host using microbial metabolic networks. After the treatment, they noticed a reverse correlation between clinical indications and changes in the microbiome. ITP patients who underwent pharmacological treatment had significant modifications in the composition and number of their microbiome. Hence, it is possible to distinguish the microbiome of healthy individuals from that of patients with ITP. Moreover, identifying the primary distinct bacteria can potentially aid in the regulation of platelet count and address the surplus of red blood cells in individuals with ITP [44].

Conclusion

The etiology of ITP is closely connected to the immunological activity in the intestines. Nevertheless, the signaling networks that underlie it have not been fully understood. Therefore, further investigations are necessary to definitively validate and establish this connection, which has the potential to open up new opportunities for improving the clinical diagnosis and treatment of ITP. With advancements in intestinal flora assessment technology, multiple studies have uncovered a potential link between gut microbiota and ITP development. However, it is also imperative to examine the modulators of ITP-based intestinal flora alterations, as well as explore the association between gut flora and ITP, both in basic and clinical environments. This review identifies the primary causative organisms and signaling pathways involved in ITP pathology, which is crucial to the development of novel therapeutics for early intervention and treatment. In particular, ITP and other extraintestinal symptoms are frequently seen in patients with IBD. Probiotics, fecal microbial transplantation, and dietary-targeted intervention may, therefore, be promising means of enhancing intestinal homeostasis regulation in the treatment of such disorders, including ITP. The study on intestinal homeostasis in ITP is encouraging, and further research may identify novel therapeutic targets and approaches that could result in more efficient and individualized ITP patient care.