• Rh serologic phenotype-matched transfusions from minority donors do not prevent all Rh alloimmunization in patients with SCD.• Variant RH genes are common in patients with SCD and contribute to Rh alloimmunization and transfusion reactions.Red blood cell (RBC) transfusion is a key treatment of patients with sickle cell disease (SCD) but remains complicated by RBC immunization. In the present study, we evaluated the effects of antigen matching for Rh D, C, and E, and K and transfusion from African American donors in 182 patients with SCD. Overall, 71 (58%) chronic and 9 (15%) episodically transfused patients were alloimmunized. Fifty-five (45%) chronic and 7 (12%) episodically transfused patients were Rh immunized. Of 146 antibodies identified, 91 were unexplained Rh antibodies, one-third of which were associated with laboratory evidence of delayed transfusion reactions. Fifty-six antibodies occurred in patients whose RBCs were phenotypically positive for the corresponding Rh antigen and 35 in patients whose RBCs lacked the antigen and were transfused with Rh-matched RBCs. High-resolution RH genotyping revealed variant alleles in 87% of individuals. These data describe the prevalence of Rh alloimmunization in patients with SCD transfused with phenotypic Rh-matched African American RBCs. Our results suggest that altered RH alleles in both the patients and in the donors contributed to Rh alloimmunization in this study. Whether RH genotyping of patients and minority donors will reduce Rh alloimmunization in SCD needs to be examined. (Blood. 2013;122 (6):1062-1071

Background: Red cell transfusions remain a mainstay of therapy for patients with sickle cell disease (SCD), but pose significant clinical challenges. Guidance for specific indications and administration of transfusion, as well as screening, prevention, and management of alloimmunization, delayed hemolytic transfusion reactions (DHTRs), and iron overload may improve outcomes. Objective: Our objective was to develop evidence-based guidelines to support patients, clinicians, and other healthcare professionals in their decisions about transfusion support for SCD and the management of transfusion-related complications. Methods: The American Society of Hematology formed a multidisciplinary panel that was balanced to minimize bias from conflicts of interest and that included a patient representative. The panel prioritized clinical questions and outcomes. The Mayo Clinic Evidence-Based Practice Research Program supported the guideline development process. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to form recommendations, which were subject to public comment. Results: The panel developed 10 recommendations focused on red cell antigen typing and matching, indications, and mode of administration (simple vs red cell exchange), as well as screening, prevention, and management of alloimmunization, DHTRs, and iron overload. Conclusions: The majority of panel recommendations were conditional due to the paucity of direct, high-certainty evidence for outcomes of interest. Research priorities were identified, including prospective studies to understand the role of serologic vs genotypic red cell matching, the mechanism of HTRs resulting from specific alloantigens to inform therapy, the role and timing of regular transfusions during pregnancy for women, and the optimal treatment of transfusional iron overload in SCD.

In humans, NH 3 transport across cell membranes is facilitated by the Rh (rhesus) family of proteins. Human Rh C glycoprotein (RhCG) forms a trimeric complex that plays an essential role in ammonia excretion and renal pH regulation. The X-ray crystallographic structure of human RhCG, determined at 2.1 Å resolution, reveals the mechanism of ammonia transport. Each monomer contains 12 transmembrane helices, one more than in the bacterial homologs. Reconstituted into proteoliposomes, RhCG conducts NH 3 to raise internal pH. Models of the erythrocyte Rh complex based on our RhCG structure suggest that the erythrocytic Rh complex is composed of stochastically assembled heterotrimers of RhAG, RhD, and RhCE.ammonia channel | comparative modeling | membrane protein | rhesus factor | X-ray structure

Ammonia excretion from the gill in teleost fish is essential for nitrogen elimination. Although numerous physiological studies have measured ammonia excretion, the mechanism of ammonia movement through the membranes of gill epithelial cells is still unknown. Mammalian Rh glycoproteins are members of a family of proteins that mediate ammonia transport in bacteria, yeast, and plants. We identified the Rh glycoprotein homologs, fRhag, fRhbg, fRhcg1, and fRhcg2, of the pufferfish, Takifugu rubripes. Northern blot, in situ hybridization, and immunohistochemistry revealed that the pufferfish erythroid Rh glycoprotein homologue fRhag was present in red blood cells and the hematological organs (spleen and kidney) in fish. All four pufferfish Rh glycoproteins are specifically localized in the gill and line the pillar cells, pavement cells, and the mitochondrion-rich cells. Heterologous expression in Xenopus oocytes showed that they mediate methylammonium (an analog of ammonium) transport. These results suggest that pufferfish Rh glycoproteins are involved in ammonia excretion from the gill. These findings challenge the classic view that ammonia excretion in the fish gill occurs by passive diffusion.