Transfusion-dependent patients, particularly those with β-thalassemia major, require lifelong regular red blood cell (RBC) transfusions to maintain adequate hemoglobin levels and prevent severe anemia. Although transfusion therapy significantly improves survival and quality of life, it is associated with several immunological complications, the most important of which is red cell alloimmunization. Alloimmunization occurs when the recipients immune system recognizes foreign antigens on donor RBCs and produces alloantibodies against them, which may lead to hemolytic transfusion reactions, difficulty in finding compatible blood and increased transfusion requirements (1). The incidence of RBC alloimmunization in transfusion-dependent patients varies widely but remains a major clinical challenge in transfusion medicine (2).

Recent advances in molecular hematology have highlighted the importance of microRNAs (miRNAs) in regulating immune responses and hematopoiesis. MicroRNAs are small non-coding RNA molecules that regulate gene expression at the post-transcriptional level and play a key role in both innate and adaptive immunity (3). Among them, microRNA-155 (miR-155) has emerged as a critical regulator of inflammatory pathways, antigen presentation, and lymphocyte activation. It modulates immune cell differentiation and cytokine production, thereby influencing immune responses to foreign antigens (4, 5).

In patients with β-thalassemia, miR-155 is also implicated in erythropoiesis and ineffective red cell production, suggesting its involvement in both hematologic and immunologic pathways of the disease. Increased expression of miR-155 has been reported in thalassemic erythroid cells and is associated with altered erythroblast proliferation and differentiation (6).

Importantly, recent studies suggest that miR-155 may contribute to the development of alloimmunization in transfusion-dependent patients.

Transfusion-dependent patients, particularly those with β-thalassemia major, require lifelong regular red blood cell (RBC) transfusions to maintain adequate hemoglobin levels and prevent severe anemia. Although transfusion therapy significantly improves survival and quality of life, it is associated with several immunological complications, the most important of which is red cell alloimmunization. Alloimmunization occurs when the recipients immune system recognizes foreign antigens on donor RBCs and produces alloantibodies against them, which may lead to hemolytic transfusion reactions, difficulty in finding compatible blood and increased transfusion requirements (1). The incidence of RBC alloimmunization in transfusion-dependent patients varies widely but remains a major clinical challenge in transfusion medicine (2).

Recent advances in molecular hematology have highlighted the importance of microRNAs (miRNAs) in regulating immune responses and hematopoiesis. MicroRNAs are small non-coding RNA molecules that regulate gene expression at the post-transcriptional level and play a key role in both innate and adaptive immunity (3). Among them, microRNA-155 (miR-155) has emerged as a critical regulator of inflammatory pathways, antigen presentation, and lymphocyte activation. It modulates immune cell differentiation and cytokine production, thereby influencing immune responses to foreign antigens (4, 5).

In patients with β-thalassemia, miR-155 is also implicated in erythropoiesis and ineffective red cell production, suggesting its involvement in both hematologic and immunologic pathways of the disease. Increased expression of miR-155 has been reported in thalassemic erythroid cells and is associated with altered erythroblast proliferation and differentiation (6).

Importantly, recent studies suggest that miR-155 may contribute to the development of alloimmunization in transfusion-dependent patients.

Therefore, investigating the association between miR-155 expression and RBC alloimmunization may provide valuable insights into the molecular mechanisms underlying immune dysregulation in transfusion-dependent patients and may help identify novel biomarkers for predicting alloimmunization risk.

Inclusion Criteria:

1- Confirmed transfusion-dependent . 2-Regular RBC transfusion history 3- Age ≥5 years

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Exclusion Criteria:

• 1- Autoimmune diseases 2- Active infections or inflammatory conditions. 3- Immunosuppressive therapy Ý

Include patients with chronic blood transfusion and not recive anti immune drugs Not with malignancy diseases