Compensation of CD55 Underexpression on Red Blood Cells of ß-Thalassemia Major Patients.

ß-Thalassemia (ß-thal), is an autosomal recessive disorder caused by mutations at the ß gene locus. ß-Thalassemia major (ß-TM) is a severe form of the disease, characterized by severe hypochromic and hemolytic anemia with an increased need for transfusion. Hemolysis is caused by intoxication, whereas mechanical removal of the affected cells caused by macrophage. Immunological implications are also reported and occur via antibodies and complement. We found previously that complement inhibitor receptor CD55 is underexpressed in these patients. This study concerns the compensatory mechanisms of this diminished expression upon flow cytometry analysis of CD55 and CD59 on the red blood cells (RBCs) of ß-thal patients. This study was conducted on 24 patients and 10 healthy controls. Full history and transfusion data was obtained, then a complete blood count (CBC) and flow cytometry analysis of CD55 and CD59 on erythrocytes were carried out. Within our 24 patients, we found a diminished expression of CD55 with a normal expression of CD59. The percentage of cells that express CD55 was significantly different from that of the controls. The mean fluorescence intensity (MFI) of CD55 and CD59 with correlation studies reveals that different factors affect the underexpression of CD55 and also revealed compensatory changes of the defect to minimize the hemolysis occurring in ß-thal patients. Compensation of CD55 underexpression in the deficient patients occurred when an increase in the MFI of both the receptor CD55, on the positive cells, and another complement inhibitor receptor CD59.

Red blood cells alloimmunization and autoimmunization among transfusion-dependent beta-thalassemia patients in Alexandria province, Egypt.

BACKGROUND: Beta thalassemia is considered a severe, progressive anemia, which needs regular transfusions for life expectancy. One of the most important complications of regular blood transfusions is autoimmunization and alloimmunization, which increases the need for transfusion. This study was performed to investigate the frequency of auto- and allo-antibodies in beta thalassemia patients in Alexandria, Egypt. MATERIALS AND METHODS: Blood samples of fourteen beta thalassemia patients were collected and tested for autosensitization with direct antiglobulin test (DAT). The positive DAT blood sample undergone antibody elution then identification. Plasma of the patients were also investigated for allosensitization by testing against cell panel reagents. RESULTS: DAT was positive in 45% of the patients. Eluted antibodies were identified in 6 cases of 10, they were Kp(b) and Lu(b), and one positive test was unidentified. Alloantibodies were detected in 42.5% of the cases. The identified antibodies were anti-D (4.76%), anti-c (4.76%), anti-K (4.76%), anti-Kp(a) (9.52%), anti-Kp(b) (19.05%), anti-Lu(a) (9.52%), anti-Lu(b) (19.05%), and anti-Bg(a) (4.76%). A total 23.81% of the alloantibodies were unidentified. DISCUSSION: This study observes that autoimmunization and alloimmunization were more frequent among poly transfused beta thalassemia Egyptian patients. The presence of these clinically significant alloantibodies is a bad indicator for situation of blood transfusion. There is need for use an effective strategies to provide a safe blood for those patients by using leukodepleted blood and more compatible blood with extended phenotyping.

Expression of CD55 on red blood cells of ß-thalassemia patients.

CD55 is a complement regulatory protein expressed by cells to protect them from bystander lysis by complement. It prevents the formation of C3/C5 convertase. In ß-thalassemia (ß-thal), the defective hemoglobin (Hb) production makes red blood cells (RBCs) lyse early and frequently. Loss of CD55 expression in those patients compromises the complement regulatory function, thereby accelerating RBC lysis. In this study, we aimed to evaluate the expression of CD55 on erythrocytes of ß-thal patients. Flow cytometry analysis of CD55 was conducted on RBCs of 21 ß-thalassemia major (ß-TM) patients, 11 ß-thalassemia intermedia (ß-TI) patients and 10 healthy volunteers. The results showed a significant decrease in CD55 expression in ß-TM (57.5 ± 16.7%), while there was a slight decrease in ß-TI patients (81.8 ± 3.8%) in comparison with that of the normal controls (88.7 ± 0.8%). The diminished expression of CD55 was not accompanied by decrease in CD59 expression in ß-thal patients (97.2 ± 2.3%). This could suggest a mechanism (could be genetic) responsible for low CD55 expression. It may be related to defective Hb genes in thalassemia, but it does not relate to cell membrane changes.