HLA-DRB1 alleles and Jk(a) immunization

Harnessing the potential of red blood cells in immunotherapy

Red blood cell (RBC) transfusion represents one of the earliest and most widespread forms of cellular therapy. While the primary purpose of RBC transfusions is to enhance the oxygen-carrying capacity of the recipient, RBCs also possess unique properties that make them attractive vehicles for inducing antigen-specific immune tolerance. Preclinical studies have demonstrated that RBC transfusion alone, in the absence of inflammatory stimuli, often fails to elicit detectable alloantibody formation against model RBC antigens. Several studies also suggest that RBC transfusion without inflammation may not only fail to generate a detectable alloantibody response but can also induce a state of antigen-specific non-responsiveness, a phenomenon potentially influenced by the density of the corresponding RBC alloantigen. The unique properties of RBCs, including their inability to divide and their stable surface antigen expression, make them attractive platforms for displaying exogenous antigens with the goal of leveraging their ability to induce antigen-specific non-responsiveness. This could facilitate antigen presentation to the host's immune system without triggering innate immune activation, potentially enabling the induction of antigen-specific tolerance for therapeutic applications in autoimmune disorders, preventing immune responses against protein therapeutics, or reducing alloreactivity in the setting of transfusion and transplantation.

Impact of human leucocyte antigen class II polymorphism on anti-red blood cell antibody development: Correlations and indications

BACKROUND AND OBJECTIVES

Blood transfusion therapy is vital for many patient groups. They can cause many complications, and the development of anti-red blood cell (RBC) antibodies is of significant importance. Molecules of class II human leucocyte antigens (HLA) are one of the several factors that influence antibody development in patients.

MATERIALS AND METHODS

In this study, we investigated 108 patients who developed antibodies against different erythrocyte antigens and 115 patients on multiple transfusion therapies who did not develop anti-RBC antibodies. The HLA loci HLA-DRB1 and HLA-DQB1 were typed using commercial molecular assays routinely used in HLA laboratories.

RESULTS

An increased frequency of the HLA-DRB1*04 allele group was observed in patients who developed antibodies. Additionally, HLA-DRB1*09 was also significant for anti-E development and in patients with multi-specific alloimmunization. It was found that the HLA-DRB1*07 allele group is associated with antibodies to antigents of the Rh and MNS systems but also lacks an association with anti-K development. The HLA-DRB1*11 and -DRB1*01 allele groups displayed a protective mechanism for anti-E development, similar to that of HLA-DQB1*02 for anti-K.

CONCLUSION

There is an association between various HLA class II alleles and anti-RBC development.

Investigating the Correlation Between HLA-II Gene Polymorphism and RhE Alloimmunization in Pregnant Chinese Women

The Rhesus (Rh) blood group is a significant and complicated biological system in humans. Incompatible transfusion or pregnancy with Rh antigens can lead to the production of alloantibodies, among which the anti-E antibody is prevalent. The relationship between Anti-E antibody and HLA-II gene polymorphism in Chinese pregnant women is worth exploring. Our aim in this study was to verify the correlation between HLA-II gene polymorphisms and RhE alloimmunization in pregnant Chinese women through HLA-II typing and DR-RhE structural prediction. In total, 94 anti-E-negative pregnant women and 103 anti-E-positive pregnant women were enrolled from Southwest China Second Hospital, and HLA-II genotyping was performed using next-generation sequencing. NetMHCpan software was used to predict the binding of E -derived anchoring peptides to HLA-DRB1 molecules. AlphaFold was used to analyze the differences in antigen presentation based on the structure of major histocompatibility complex peptides. The HLA-DRB1*09:01-DQA1*03:02-DQB1*03:03 haplotype showed a significant positive association with anti-E. One E-derived anchoring peptide (219FWPSVNSPL227) was predicted to bind to the HLA-DRB1*09:01 molecule. The interaction between the 60Ser of DR9 and 226pro of RhE comprised one hydrogen bond. This study demonstrated that HLA-II haplotypes are associated with allo-anti-E antibodies in pregnant women from Sichuan Province, China. The HLA-DRB1*09:01-DQA1*03:02-DQB1*03:03 phenotype may enhance the formation of anti-E alloantibodies, and the HLA-DRB1*09:01 molecule may play a key role in alloimmunity.

HLA Class II regulation of immune response in sickle cell disease patients: Susceptibility to red blood cell alloimmunization (systematic review and meta-analysis)

BACKGROUND AND OBJECTIVES

Sickle cell disease (SCD) patients are commonly treated with red blood cell (RBC) transfusion. Pretransfusion tests commonly involve limited serological antibody testing. RBC alloimmunization to RBC antigens is a frequently encountered complication seen in chronically transfused patients. Genetic factors such as the human leukocyte antigen (HLA) are known to influence and regulate immune responses. HLAs are highly polymorphic and play an essential role in regulating immune responses, including RBC alloimmunization. The aim of this study was to conduct a systematic review and meta-analysis to evaluate the association between HLA Class II allelic polymorphisms with the possible risk of developing RBC alloantibodies.

MATERIALS AND METHODS

Four databases were systematically searched for relevant studies between the years 2000 and 2021 following the PRISMA guidelines. Four articles met the eligibility and quality criterion, and three alleles, HLA-DRB1*04, HLA-DRB1*15 and HLA-DQB1*03, that were found to be potentially associated with an increased risk in alloantibody formation were included.

RESULTS

The primary outcome measure was alloimmunization by RBC antigen exposure in multiply transfused SCD patients. The total estimate of alloimmunization of the SCD patients was 2.33 (95% CI, 1.58-3.44), demonstrating susceptibility to RBC alloantibody formation. Heterogeneity between the studies was insignificant, suggesting the differences associated with random sampling errors. The results showed that SCD patients carry an increased risk of producing RBC alloantibodies.

CONCLUSION

A strategy to prevent RBC alloimmunization is genotyping for genetically susceptible SCD patients receiving multiple transfusions. Early identification of genetic variants that can potentially increase the risk of RBC alloimmunization could aid in the screening process and selection of phenotypically matched RBC units.

Relationship between B-cell epitope structural properties and the immunogenicity of blood group antigens: Outlier properties of the Kell K1 antigen

BACKGROUND

The immunogenicities of polypeptide blood group antigens vary, despite most being created by single amino acid (AA) substitutions. To study the basis of these differences, we employed an immunoinformatics approach to determine whether AA substitution sites of blood group antigens have structural features typical of B-cell epitopes and whether the extent of B-cell epitope properties is positively related to immunogenicity.

STUDY DESIGN AND METHODS

Fifteen structural property prediction programs were used to determine the likelihood of β-turns, surface accessibility, flexibility, hydrophilicity, particular AA composition and AA pairs, and other B-cell epitope properties at AA substitution sites of polypeptide blood group antigens.

RESULTS

AA substitution sites of Lu^a , Jk^a , E, c, M, Fy^a , C, and S were each located in regions with at least two structural features typical of B-cell epitopes. The substitution site of K, the most immunogenic non-ABO/D antigen, scored the lowest for most B-cell epitope properties and was the only one not predicted to be part of a linear B-cell epitope. The most immunogenic antigens studied (K, Jk^a , Lu^a , E) had B-cell epitope structural properties determined by the fewest programs; the least immunogenic antigens (e.g., Fy^a , S, C, c) had B-cell epitope properties according to the most programs.

DISCUSSION

Counter to prediction, the immunogenicity of polypeptide blood group antigens was not positively related to B-cell epitope structural features present at their AA-substitution sites. Instead, it tended to be negatively related. The AA-substitution site of the most immunogenic non-ABO/D antigen, K, had the least B-cell epitope features.

An insight in Salmonella typhi associated autoimmunity candidates' prediction by molecular mimicry

Autoimmune diseases develop when the immune system targets healthy cells and tissues of an individual. In developing countries, S. typhi (a gram-negative pathogenic bacteria) remains a major public health issue. This study aimed to employ bioinformatics analyses to determine the 3D structural-based molecular mimicry and sequence of S. typhi and human host proteins. In addition, to classify possible antigenic microbial peptides homologous to human peptides and comprehend the molecular basis of S. typhi-related autoimmune disorders. Protein sequences were obtained from the NCBI database, and redundancy was removed using the CD-HIT tool. The BLASTp comparative sequence analysis was followed for molecular mimicry identification of human and S. typhi protein sequences. The PathDIP database was utilized to simulate essential physical relationships between proteins and curated pathways for metabolic processes. Subsequently, the IEDB database was used to find cross-reactive MHC class-II binding epitopes that could trigger an autoimmune reaction. SPARKS-X computational biology resource was also used to determine the structural homology between human and S. typhi peptides. The BLASTp study showed that S. typhi and the human host have several proteins holding considerable sequence similarities based on a set threshold of e ≤ 10-6 and bit score ≥100. The PathDIP putatively identified that these proteins enriched in a total of 68 metabolic pathways by a significant P-value (P < 0.005). The PSORTb analysis predicted that 26 out of these proteins are cytosolic, 1 predicted to be periplasmic protein, and 1 predicted to be localized in the cytoplasmic membrane. IEDB data analysis predicted many S.typhi and human homologs epitopes as a good binder of human HLA, i.e. DRB1*01:01, DPA1*03:01/DPB1*04:02, and DQA1*01:02/DQB1*06:02 with IC₅₀ < 50 nM. Finally, the docking data demonstrated that homolog lead epitopes promisingly interact with HLA and immune TLR4 receptors by exhibiting the best docking scores and molecular interactions. The analyses ultimately identified several potential candidate proteins and peptides that could cause S.typhi infection-mediated autoimmune diseases in humans.

Marginal zone B cells mediate a CD4 T-cell-dependent extrafollicular antibody response following RBC transfusion in mice

Red blood cell (RBC) transfusions can result in alloimmunization toward RBC alloantigens that can increase the probability of complications following subsequent transfusion. An improved understanding of the immune mechanisms that underlie RBC alloimmunization is critical if future strategies capable of preventing or even reducing this process are to be realized. Using the HOD (hen egg lysozyme [HEL] and ovalbumin [OVA] fused with the human RBC antigen Duffy) model system, we aimed to identify initiating immune factors that may govern early anti-HOD alloantibody formation. Our findings demonstrate that HOD RBCs continuously localize to the marginal sinus following transfusion, where they colocalize with marginal zone (MZ) B cells. Depletion of MZ B cells inhibited immunoglobulin M (IgM) and IgG anti-HOD antibody formation, whereas CD4 T-cell depletion only prevented IgG anti-HOD antibody development. HOD-specific CD4 T cells displayed similar proliferation and activation following transfusion of HOD RBCs into wild-type or MZ B-cell-deficient recipients, suggesting that IgG formation is not dependent on MZ B-cell-mediated CD4 T-cell activation. Moreover, depletion of follicular B cells failed to substantially impact the anti-HOD antibody response, and no increase in antigen-specific germinal center B cells was detected following HOD RBC transfusion, suggesting that antibody formation is not dependent on the splenic follicle. Despite this, anti-HOD antibodies persisted for several months following HOD RBC transfusion. Overall, these data suggest that MZ B cells can initiate and then contribute to RBC alloantibody formation, highlighting a unique immune pathway that can be engaged following RBC transfusion.

HLA-DRB1 molecules and the presentation of anchor peptides from RhD, RhCE, and KEL proteins

BACKGROUND

Antigens from the Rh and Kell systems are recognized as the most immunogenic in clinical practice. This study evaluated the possible molecular mechanisms involved in the interaction of antigenic peptides with the DRB1 molecules, which help to explain the high frequency of anti-K and association of D + C antibodies in transfusion and incompatible pregnancy.

STUDY DESIGN AND METHODS

We included 201 patients with antibodies against antigens from the Rh and Kell systems and compare them with 174,015 controls. HLA-DRB1 genotyping and in silico analysis were performed. The NetMHCIIpan software was used to identify RhD-, RhCE-, and KEL-derived anchor peptides that bind to DRB1 molecules.

RESULTS

HLA-DRB1*15 is associated with an increased risk of D, C, E, and K alloimmunization, while the HLA-DRB1*01 and *12 alleles are overrepresented in patients with anti-C and anti-D, respectively. In silico analysis showed that three polymorphic points (60I, 68S, and 103S) common to C and D antigens can be presented by several DRB1 molecules, including DRB1*15:01. The DRB1*09:01 molecule, although not showing statistical significance, was able to interact strongly with almost all five anchor peptides from the sequence containing the polymorphic determinants of E antigen, except 217-WMFWPSVNS-225.

CONCLUSION

The DRB1*15 molecule has specific physicochemical characteristics in residues 11P and 13R in the P4 pocket that can favor the response to various antigenic peptides. Anti-K alloimmunization is unrestricted for interaction with specific DRB1 molecules, which suggests that almost all individuals in our population have DRB1 molecules capable of binding to KEL-derived anchor peptides and produce anti-K when stimulated.

Back to base pairs: What is the genetic risk for red bloodcell alloimmunization?

Red blood cell (RBC) alloimmunization is a serious complication of blood transfusions, challenging selection of compatible units for future transfusions. Genetic characteristics may be associated with the risk of RBC alloimmunization and may therefore serve to identify high-risk patients. The aim of this systematic review was to summarize the available evidence on genetic risk factors for RBC alloimmunization. Electronic databases were searched up to April 2020 for studies (Search terms included transfusion, alloimmunization and genetic). A total of 2581 alloimmunized cases and 26,558 controls were derived from 24 studies. The alleles that were most frequently studied and that demonstrated significant associations in a meta-analysis with alloimmunization to the Duffy^a antigen were HLA-DRB1*04 (Odds Ratio 7.80 (95%CI 4.57-13.33)), HLA-DRB1*15 (OR 3.76 (95%CI 2.14-6.59)), and HLA-DRB1*03 (OR 0.12 (95%CI 0.05-0.29)). Furthermore, significant associations with anti-K formation was found for the alleles HLA-DRB1*10 (OR 2.64 (95%CI 1.41-4.95)), HLA*DRB1*11 (OR 2.11, (95%CI 1.34-3.32)), and HLA-DRB1*13 (OR 1.71 (95%CI 1.26-2.33)). Overall, the available evidence was of moderate to low quality, hampering interpretation of reported results. There is an urgent need for high quality evidence on genetic risk factors for RBC alloimmunization.

Red blood cell alloimmunization and sickle cell disease: a narrative review on antibody induction

The high prevalence of red blood cell (RBC) alloantibodies in people with sickle cell disease (SCD) cannot be debated. Why people with SCD are so likely to form RBC alloantibodies, however, remains poorly understood. Over the past decade, a better understanding of non-ABO blood group antigen variants has emerged; RH genetic diversity and the role this diversity plays in RBC alloimmunization is discussed elsewhere. Outside of antigen variants, the immune systems of people with SCD are known to be different than those of people without SCD. Some of these differences are due to effects of free heme, whereas others are impacted by hyposplenism. Descriptive studies of differences in white blood cell (WBC) subsets, platelet counts and function, and complement activation between people with SCD and race-matched controls exist. Studies comparing the immune systems of alloimmunized people with SCD to non-alloimmunized people with SCD to race-matched controls without SCD have uncovered differences in T-cell subsets, monocytes, Fcγ receptor polymorphisms, and responses to free heme. Studies in murine models have documented the role that recipient inflammation plays in RBC alloantibody formation, with human studies reporting a similar association. Murine studies have also reported the importance of type 1 interferon (IFNα/β), known to play a pivotal role in autoimmunity, in RBC alloantibody formation. The goal of this manuscript is to review existing data on factors influencing RBC alloantibody induction in people with SCD with a focus on inflammation and other immune system considerations, from the bench to the bedside.

Frequent transfusion and specific HLA-DRB1 alleles correlate independently with Miltenberger blood group alloimmunization in dialysis patients

Anti-"Mi^a " is the most frequent irregular RBC antibody in Taiwan due to high prevalence of Miltenberger antigens. Dialysis patients, a special patient group that needs frequent transfusions of RBCs, may have the greatest risk for developing anti-"Mi^a " antibodies. The aim of this study was to investigate the association between specific HLA-DRB1 alleles and Mi alloimmunization among dialysis patients. A cohort of 267 maintenance dialysis patients who had ever received at least one RBCs transfusion was enrolled. Anti-"Mi^a " was identified in patients' serum using the manual polybrene technique and HLA-DRB1 genotyping was carried out using polymerase chain reaction and sequence-specific oligonucleotide probe nonradioactive hybridization. Twenty-one (7.9%) of patients had positive anti-"Mi^a " tests and had received significantly more units of RBC transfusions than those without anti-"Mi^a " antibodies (11.3 ± 14.5 U vs 4.5 ± 10.1 U, P = .005). DRB1*04, *07, and *09 alleles were also more prevalent in patients with anti-"Mi^a " compared to those without Mi III alloimmunization. The multivariate logistic regression analysis showed that the number of RBC transfusions and the presence of DRB1*04, *07, and *09 phenotypes correlated independently with Mi III immunization (Odds ratios [OR] 1.05 (P = .001) for each unit of RBCs transfused; ORs 4.80 (P = .006), 12.29 (P = .005), and 5.42 (P = .003) for presence of DRB1*04, *07, and *09, respectively). This study is the first to demonstrate markedly high prevalence of Mi III alloimmunization in dialysis patients of Taiwan. Extending Mi III matching for RBC transfusions in susceptible dialysis patients may help to reduce the risk of Mi III alloimmunization in this patient population.

Identification of genetic biomarkers for alloimmunization in sickle cell disease

Most sickle cell disease (SCD) patients rely on blood transfusion as their main treatment strategy. However, frequent blood transfusion poses the risk of alloimmunization. On average, 30% of SCD patients will alloimmunize while other patient groups form antibodies less frequently. Identification of genetic markers may help to predict which patients are at risk to form alloantibodies. The aim of this study was to evaluate whether genetic variations in the Toll-like receptor pathway or in genes previously associated with antibody-mediated conditions are associated with red blood cell (RBC) alloimmunization in a cohort of SCD patients. In this case-control study, cases had a documented history of alloimmunization while controls had received ≥20 RBC units without alloantibody formation. We used a customized single nucleotide polymorphism (SNP) panel to genotype 690 SNPs in 275 (130 controls, 145 cases) patients. Frequencies were compared using multiple logistic regression analysis. In our primary analysis, no SNPs were found to be significantly associated with alloimmunization after correction for multiple testing. However, in a secondary analysis with a less stringent threshold for significance we found 19 moderately associated SNPs. Among others, SNPs in TLR1/TANK and MALT1 were associated with a higher alloimmunization risk, while SNPs in STAM/IFNAR1 and STAT4 conferred a lower alloimmunization risk.

Transfusion-related red blood cell alloantibodies: induction and consequences

Blood transfusion is the most common procedure completed during a given hospitalization in the United States. Although often life-saving, transfusions are not risk-free. One sequela that occurs in a subset of red blood cell (RBC) transfusion recipients is the development of alloantibodies. It is estimated that only 30% of induced RBC alloantibodies are detected, given alloantibody induction and evanescence patterns, missed opportunities for alloantibody detection, and record fragmentation. Alloantibodies may be clinically significant in future transfusion scenarios, potentially resulting in acute or delayed hemolytic transfusion reactions or in difficulty locating compatible RBC units for future transfusion. Alloantibodies can also be clinically significant in future pregnancies, potentially resulting in hemolytic disease of the fetus and newborn. A better understanding of factors that impact RBC alloantibody formation may allow general or targeted preventative strategies to be developed. Animal and human studies suggest that blood donor, blood product, and transfusion recipient variables potentially influence which transfusion recipients will become alloimmunized, with genetic as well as innate/adaptive immune factors also playing a role. At present, judicious transfusion of RBCs is the primary strategy invoked in alloimmunization prevention. Other mitigation strategies include matching RBC antigens of blood donors to those of transfusion recipients or providing immunomodulatory therapies prior to blood product exposure in select recipients with a history of life-threatening alloimmunization. Multidisciplinary collaborations between providers with expertise in transfusion medicine, hematology, oncology, transplantation, obstetrics, and immunology, among other areas, are needed to better understand RBC alloimmunization and refine preventative strategies.

Recipient priming to one RBC alloantigen directly enhances subsequent alloimmunization in mice

Individuals that become immunized to red blood cell (RBC) alloantigens can experience an increased rate of antibody formation to additional RBC alloantigens following subsequent transfusion. Despite this, how an immune response to one RBC immunogen may impact subsequent alloimmunization to a completely different RBC alloantigen remains unknown. Our studies demonstrate that Kell blood group antigen (KEL) RBC transfusion in the presence of inflammation induced by poly (I:C) (PIC) not only enhances anti-KEL antibody production through a CD4⁺ T-cell-dependent process but also directly facilitates anti-HOD antibody formation following subsequent exposure to the disparate HOD (hen egg lysozyme, ovalbumin, fused to human blood group antigen Duffy b) antigen. PIC/KEL priming of the anti-HOD antibody response required that RBCs express both the KEL and HOD antigens (HOD × KEL RBCs), as transfusion of HOD RBCs plus KEL RBCs or HOD RBCs alone failed to impact anti-HOD antibody formation in recipients previously primed with PIC/KEL. Transfer of CD4⁺ T cells from PIC/KEL-primed recipients directly facilitated anti-HOD antibody formation following (HOD × KEL) RBC transfusion. RBC alloantigen priming was not limited to PIC/KEL enhancement of anti-HOD alloantibody formation, as HOD-reactive CD4⁺ T cells enhanced anti-glycophorin A (anti-GPA) antibody formation in the absence of inflammation following transfusion of RBCs coexpressing GPA and HOD. These results demonstrate that immune priming to one RBC alloantigen can directly enhance a humoral response to a completely different RBC alloantigen, providing a potential explanation for why alloantibody responders may exhibit increased immune responsiveness to additional RBC alloantigens following subsequent transfusion.

Marginal Zone B Cells Induce Alloantibody Formation Following RBC Transfusion

Red blood cell (RBC) alloimmunization represents a significant immunological challenge for some patients. While a variety of immune constituents likely contribute to the initiation and orchestration of alloantibodies to RBC antigens, identification of key immune factors that initiate alloantibody formation may aid in the development of a therapeutic modality to minimize or prevent this process. To define the immune factors that may be important in driving alloimmunization to an RBC antigen, we determined the specific immune compartment and distinct cells that may initially engage transfused RBCs and facilitate subsequent alloimmunization. Our findings demonstrate that the splenic compartment is essential for formation of anti-KEL antibodies following KEL RBC transfusion. Within the spleen, transfused KEL RBCs are found within the marginal sinus, where they appear to specifically co-localize with marginal zone (MZ) B cells. Consistent with this, removal of MZ B cells completely prevented alloantibody formation following KEL RBC transfusion. While MZ B cells can mediate a variety of key downstream immune pathways, depletion of follicular B cells or CD4 T cells failed to similarly impact the anti-KEL antibody response, suggesting that MZ B cells may play a key role in the development of anti-KEL IgM and IgG following KEL RBC transfusion. These findings highlight a key contributor to KEL RBC-induced antibody formation, wherein MZ B cells facilitate antibody formation following RBC transfusion.

Complement serves as a switch between CD4+ T cell-independent and -dependent RBC antibody responses

RBC alloimmunization represents a significant immunological challenge for patients requiring lifelong transfusion support. The majority of clinically relevant non-ABO(H) blood group antigens have been thought to drive antibody formation through T cell-dependent immune pathways. Thus, we initially sought to define the role of CD4+ T cells in formation of alloantibodies to KEL, one of the leading causes of hemolytic transfusion reactions. Unexpectedly, our findings demonstrated that KEL RBCs actually possess the ability to induce antibody formation independent of CD4+ T cells or complement component 3 (C3), two common regulators of antibody formation. However, despite the ability of KEL RBCs to induce anti-KEL antibodies in the absence of complement, removal of C3 or complement receptors 1 and 2 (CR1/2) rendered recipients completely reliant on CD4+ T cells for IgG anti-KEL antibody formation. Together, these findings suggest that C3 may serve as a novel molecular switch that regulates the type of immunological pathway engaged following RBC transfusion.

The Role of the Immunological Synapse in Differential Effects of APC Subsets in Alloimmunization to Fresh, Non-stored RBCs

Background: Each year, over 5 million red blood cell (RBC) transfusions are administered to patients in the USA. Despite the therapeutic benefits of RBC transfusions, there are associated risks. RBC-specific alloantibodies may form in response to antigenic differences between RBC donors and recipients; these alloantibodies can be a problem as they may mediate hemolysis or pose barriers to future transfusion support. While there is currently no reliable way to predict which RBC recipients will make an alloantibody response, risk factors such as inflammation have been shown to correlate with increased rates of RBC alloimmunization. The underlying mechanisms behind how inflammation mediates alloantibody production are incompletely defined.

Methods: To assess erythrophagocytosis, mice were treated with PBS or inflammatory stimuli followed by a transfusion of allogeneic RBCs labeled with a lipophilic dye. At multiple time points, RBC consumption and expression of activation makers by leukocytes was evaluated. To determine which antigen presenting cell (APC) subset(s) were capable of promoting allogeneic T cell activation, sorted leukocyte populations (which had participated in erythrophagocytosis) were co-cultured in vitro with allogeneic CD4+ T cells; T cell proliferation and ability to form immunological synapses with APCs were determined.

Results: Upon transfusion of fresh allogeneic RBCs, multiple APCs consumed transfused RBCs. However, only CD8+ and CD11b+ dendritic cells formed productive immunological synapses with allogeneic T cells and stimulated proliferation. Importantly, allogeneic T cell activation and RBC alloantibody production occurred in response to RBC transfusion alone, and transfusion in the context of inflammation enhanced RBC consumption, the number of immune synapses, allogeneic T cell proliferation, and the rate and magnitude of alloantibody production.

Conclusions: These data demonstrate that regardless of the ability to participate in RBC consumption, only a subset of APCs are capable of forming an immune synapse with T cells thereby initiating an alloantibody response. Additionally, these data provide mechanistic insight into RBC alloantibody generation.

Relationship of epitope glycosylation and other properties of blood group proteins to the immunogenicity of blood group antigens

BACKGROUND

The intrinsic properties of polypeptide blood group antigens that determine their relative immunogenicities are unknown. Because size, composition, charge, dose, and epitope glycosylation affect the immunogenicity of other polypeptides, we examined whether similar properties were related to the immunogenicity of blood group antigens.

STUDY DESIGN AND METHODS

Amino acid (AA) sequences of antithetical blood group antigens were searched for N- and O-glycosylation sites. Regression analysis was carried out to determine whether blood group protein properties, including total and ectodomain size, red blood cell (RBC) antigen site density, number of mismatched AAs between an antigen and its closest homolog, and differences in mass, charge, and hydrophobicity of the mismatched AAs, were related to immunogenicity.

RESULTS

The immunogenicities of non-RhD polypeptide antigens were directly related to the total and ectodomain sizes of their carrier proteins. A negative power relationship existed between RBC antigen site density and immunogenicity, such that the most immunogenic antigens had the lowest site density. The strong immunogenicity of RhD was related to the number of AA mismatches between RhD and RhCE, to their cumulative hydrophobicity and electrostatic mismatch scores, and the cumulative AA mass difference. No N- or O-glycosylation differences were predicted for antithetical or homologous antigens, other than a previously known N-glycosylation difference between K and k.

CONCLUSION

Epitope glycosylation appeared not to be a determinant of immunogenicity for blood group antigens, except possibly for K. The immunogenicity of blood group antigens was positively related to total and ectodomain sizes of blood group proteins and negatively related to antigen site density. Such findings should be considered hypothesis generating for future, more definitive studies.

Morbid Sequences Suggest Molecular Mimicry between Microbial Peptides and Self-Antigens: A Possibility of Inciting Autoimmunity

Understanding etiology of autoimmune diseases has been a great challenge for designing drugs and vaccines. The pathophysiology of many autoimmune diseases may be attributed to molecular mimicry provoked by microbes. Molecular mimicry hypothesizes that a sequence homology between foreign and self-peptides leads to cross-activation of autoreactive T cells. Different microbial proteins are implicated in various autoimmune diseases, including multiple sclerosis, human type 1 diabetes, primary biliary cirrhosis and rheumatoid arthritis. It may be imperative to identify the microbial epitopes that initiate the activation of autoreactive T cells. Consequently, in the present study, we employed immunoinformatics tools to delineate homologous antigenic regions between microbes and human proteins at not only the sequence level but at the structural level too. Interestingly, many cross-reactive MHC class II binding epitopes were detected from an array of microbes. Further, these peptides possess a potential to skew immune response toward Th1-like patterns. The present study divulges many microbial target proteins, their putative MHC-binding epitopes, and predicted structures to establish the fact that both sequence and structure are two important aspects for understanding the relationship between molecular mimicry and autoimmune diseases. Such findings may enable us in designing potential immunotherapies to tolerize autoreactive T cells.

Nonclassical FCGR2C haplotype is associated with protection from red blood cell alloimmunization in sickle cell disease

Red blood cell (RBC) transfusions are of vital importance in patients with sickle cell disease (SCD). However, a major complication of transfusion therapy is alloimmunization. The low-affinity Fcγ receptors, expressed on immune cells, are important regulators of antibody responses. Genetic variation in FCGR genes has been associated with various auto- and alloimmune diseases. The aim of this study was to evaluate the association between genetic variation of FCGR and RBC alloimmunization in SCD. In this case-control study, DNA samples from 2 cohorts of transfused SCD patients were combined (France and The Netherlands). Cases had a positive history of alloimmunization, having received ≥1 RBC unit. Controls had a negative history of alloimmunization, having received ≥20 RBC units. Single nucleotide polymorphisms and copy number variation of the FCGR2/3 gene cluster were studied in a FCGR-specific multiplex ligation-dependent probe amplification assay. Frequencies were compared using logistic regression. Two hundred seventy-two patients were included (130 controls, 142 cases). The nonclassical open reading frame in the FCGR2C gene (FCGR2C.nc-ORF) was strongly associated with a decreased alloimmunization risk (odds ratio [OR] 0.26, 95% confidence [CI] 0.11-0.64). This association persisted when only including controls with exposure to ≥100 units (OR 0.30, CI 0.11-0.85) and appeared even stronger when excluding cases with Rh or K antibodies only (OR 0.19, CI 0.06-0.59). In conclusion, SCD patients with the FCGR2Cnc-ORF polymorphism have over a 3-fold lower risk for RBC alloimmunization in comparison with patients without this mutation. This protective effect was strongest for exposure to antigens other than the immunogenic Rh or K antigens.

Taming the immune system through transfusion in oncology patients

Blood transfusion is a clinical replacement therapy with many successes with some benefit and, also, some harm. Cancer is a multifaceted disease potentially associated with the immune system's weakness where the cancerous tumor cells escape from the immune system. Allogeneic blood transfusion, through five major mechanisms including the lymphocyte-T set, myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), natural killer cells (NKCs), and dendritic cells (DCs) can help the recipient's defense mechanisms. On the other hand, the role for each of the listed items includes activation of the antitumor CD8+ cytotoxic T lymphocytes (CD8+/CTL), temporal inactivation of Tregs, inactivation of the STAT3 signaling pathway, the use of bacteria to enhance the antitumor immune response and cellular immunotherapy. The above issues are concisely addressed in this manuscript based on a literature survey on this topic carried out by the first author.

Antigen Density Dictates Immune Responsiveness following Red Blood Cell Transfusion

Although RBC transfusion can result in the development of anti-RBC alloantibodies that increase the probability of life-threatening hemolytic transfusion reactions, not all patients generate anti-RBC alloantibodies. However, the factors that regulate immune responsiveness to RBC transfusion remain incompletely understood. One variable that may influence alloantibody formation is RBC alloantigen density. RBC alloantigens exist at different densities on the RBC surface and likewise exhibit distinct propensities to induce RBC alloantibody formation. However, although distinct alloantigens reside on the RBC surface at different levels, most alloantigens also represent completely different structures, making it difficult to separate the potential impact of differences in Ag density from other alloantigen features that may also influence RBC alloimmunization. To address this, we generated RBCs that stably express the same Ag at different levels. Although exposure to RBCs with higher Ag levels induces a robust Ab response, RBCs bearing low Ag levels fail to induce RBC alloantibodies. However, exposure to low Ag-density RBCs is not without consequence, because recipients subsequently develop Ag-specific tolerance. Low Ag-density RBC-induced tolerance protects higher Ag-density RBCs from immune-mediated clearance, is Ag specific, and occurs through the induction of B cell unresponsiveness. These results demonstrate that Ag density can potently impact immune outcomes following RBC transfusion and suggest that RBCs with altered Ag levels may provide a unique tool to induce Ag-specific tolerance.

Association of HLA-DRB1 and HLA-DQB1 with red-blood-cell alloimmunization in the Czech population

BACKGROUND AND OBJECTIVES

Alloimmune antibodies against red-blood-cell (RBC) antigens induced in susceptible individuals (responders) by transfusion, pregnancy or transplantation may have serious clinical consequences. The aim of this study was to investigate association of alloimmunization against selected RBC antigens with HLA-Class II.

MATERIALS AND METHODS

A total of 230 responders (106 monoresponders and 124 multiresponders) were enrolled into the study. HLA-DRB1 and HLA-DQB1 variants were determined by PCR-SSO and their frequencies compared between the patients (patient subgroups) and 375 ethnically and regionally matched controls.

RESULTS

Development of multiple RBC antibodies was associated with HLA-DRB1*15 and HLA-DQB1*06 allelic groups in the patients, with the relationship being particularly apparent in those with anti-C+D antibodies. Furthermore, DRB1*13 and DQB1*06 were more frequent in multiresponders with anti-E+c antibodies and DRB1*03 and DQB1*02 in those with anti-E+Cw.

CONCLUSION

For the first time, we confirmed the association of HLA-DRB1*15 with RBC antibody multiresponder status and found HLA-Class II associations for three frequent RBC antibody combinations. Our data support the concept that HLA restriction plays an important role in the response to RBC alloantigens.

Red blood cell alloimmunization in patients with sickle cell disease: correlation with HLA and cytokine gene polymorphisms

BACKGROUND

The reason for the difference in susceptibility to red blood cell (RBC) alloimmunization among patients with sickle cell disease (SCD) is not clearly understood and is probably the result of multiple factors. Our hypothesis is that genetic polymorphisms are associated with RBC alloimmunization.

STUDY DESIGN AND METHODS

We investigated the possible association of susceptibility to RBC alloimmunization with polymorphisms of HLA and cytokines genes in 161 SCD patients prior exposed to RBC transfusion. Cytokine gene polymorphisms were analyzed by polymerase chain reaction (PCR) and TaqMan assays. HLA Class I genotyping was performed using PCR-specific sequence of oligonucleotides. Polymorphism frequencies were compared using the Fisher's exact test.

RESULTS

Our results revealed increased percentage of the A allele and the GA genotype of the TNFA -308G/A cytokine among alloimmunized patients when compared to nonalloimmunized patients (A allele, 16.4% vs. 6.8%, p = 0.004; GA genotype, 32.8% vs. 11.7%, p = 0.0021). In addition, the IL1B -511T allele and the IL1B -511TT and CT genotype frequencies were overrepresented among alloimmunized patients (T allele, 53.0% vs. 37.5%, p = 0.0085; CT + TT genotypes, 81.82% vs. 60.87%, p = 0.0071). In relation to HLA Class I, we found a higher frequency of HLA-DRB1*15 among patients alloimmunized to Rh antigens when compared to nonalloimmunized patients (15.63% vs. 6.98%, p = 0.044).

CONCLUSION

Brazilian SCD patients with the TNFA, IL1B, and HLA-DRB1 gene polymorphisms were at increased risk of becoming alloimmunized by RBC transfusions. These findings may contribute to the development of future therapeutic strategies for patients with SCD with higher susceptibility of alloimmunization.

The HLA-DRB1*15 phenotype is associated with multiple red blood cell and HLA antibody responsiveness

BACKGROUND

Once a patient has produced a red blood cell (RBC) antibody, there is an increased risk of additional antibody formation after subsequent RBC exposure. Recently, we observed that HLA-DRB1*15 was overrepresented in 379 multiple RBC antibody responders compared to controls or 562 patients with a single RBC antibody (odds ratio [OR], 1.7; 95% confidence interval [CI], 1.3-2.3). In this study we evaluated whether the HLA-DRB1*15 represents a responder phenotype against HLA and/or RBC antigens.

STUDY DESIGN AND METHODS

HLA-DRB1*15 frequencies in single and multiple antibody responders were compared between three groups of individuals: 1) those with HLA antibodies, 2) those with RBC antibodies, and 3) those with both RBC and HLA antibodies.

RESULTS

A total of 3959 immunized patients (female-to-male ratio, 2.3) had been HLA-DRB1 typed. Among the 3275 individuals with HLA antibodies, the frequency of the DRB1*15 phenotype differed significantly from 19.7% in patients with a panel reactivity (PRA) of not more than 20% to 26.9% in patients with PRA of more than 80% (OR, 1.5; 95% CI, 1.2-1.9). This association between DRB1*15 and multiresponsiveness was mainly due to pregnancy-induced HLA immunization. In the 257 individuals with RBC and HLA antibodies, the frequency of DRB1*15 was 4.2 times (95% CI, 1.1-16) higher in those with multiple RBC antibodies and HLA-PRA of more than 50% compared to only single RBC responders with PRA of less than 20%.

CONCLUSION

The HLA-DRB1*15 phenotype is associated with broad RBC and HLA immunization.

Protective effect of HLA-DQB1 alleles against alloimmunization in patients with sickle cell disease

BACKGROUND

Alloimmunization or the development of alloantibodies to Red Blood Cell (RBC) antigens is considered one of the major complications after RBC transfusions in patients with sickle cell disease (SCD) and can lead to both acute and delayed hemolytic reactions. It has been suggested that polymorphisms in HLA genes, may play a role in alloimmunization. We conducted a retrospective study analyzing the influence of HLA-DRB1 and DQB1 genetic diversity on RBC-alloimmunization.

STUDY DESIGN

Two-hundred four multi-transfused SCD patients with and without RBC-alloimmunization were typed at low/medium resolution by PCR-SSO, using IMGT-HLA Database. HLA-DRB1 and DQB1 allele frequencies were analyzed using logistic regression models, and global p-value was calculated using multiple logistic regression.

RESULTS

While only trends towards associations between HLA-DR diversity and alloimmunization were observed, analysis of HLA-DQ showed that HLA-DQ2 (p=0.02), -DQ3 (p=0.02) and -DQ5 (p=0.01) alleles were significantly higher in non-alloimmunized patients, likely behaving as protective alleles. In addition, multiple logistic regression analysis showed both HLA-DQ2/6 (p=0.01) and HLA-DQ5/5 (p=0.03) combinations constitute additional predictor of protective status.

CONCLUSION

Our data suggest that particular HLA-DQ alleles influence the clinical course of RBC transfusion in patients with SCD, which could pave the way towards predictive strategies.

Phenotypic differences of CD4(+) T cells in response to red blood cell immunization in transfused sickle cell disease patients

Alloimmunization against red blood cells (RBCs) is the main immunological risk associated with transfusion in patients with sickle cell disease (SCD). However, about 50-70% of SCD patients never get immunized despite frequent transfusion. In murine models, CD4(+) T cells play a key role in RBC alloimmunization. We therefore explored and compared the CD4(+) T-cell phenotypes and functions between a group of SCD patients (n = 11) who never became immunized despite a high transfusion regimen and a group of SCD patients (n = 10) who had become immunized (at least against Kidd antigen b) after a low transfusion regimen. We studied markers of CD4(+) T-cell function, including TLR, that directly control lymphocyte function, and their spontaneous cytokine production. We also tested responders for the cytokine profile in response to Kidd antigen b peptides. Low TLR2/TLR3 expression and, unexpectedly, strong expression of CD40 on CD4(+) T cells were associated with the nonresponder status, whereas spontaneous expression of IL-10 by CD4(+) T cells and weak Tbet expression were associated with the responder status. A Th17 profile was predominant in responders when stimulated by Jb(k) . These findings implicate CD4(+) T cells in alloimmunization in humans and suggest that they may be exploited to differentiate responders from nonresponders.

The Influence of Clinical and Biological Factors on Transfusion-Associated Non-ABO Antigen Alloimmunization: Responders, Hyper-Responders, and Non-Responders

In the context of transfusion medicine, alloimmunization most often refers to the development of antibodies to non-ABO red blood cell (RBC) antigens following pregnancy, transfusion, or transplantation. The development of RBC alloantibodies can have important clinical consequences, particularly in patients who require chronic transfusions. It has been suggested that alloimmunization is more common in some clinical circumstances and patient populations than in others. As such, individuals that develop alloantibodies are frequently referred to as 'responders' in the medical literature. In contrast, individuals that do not develop alloantibodies despite repeated exposures to non-self blood group antigens have been referred to as 'non-responders'. The purpose of this article is to review the phenomenon of RBC alloimmunization in the context of responders and non-responders to: i) establish a basic framework for alloimmunization as reported across several diverse patient populations; ii) more fully explore literature reports which support the concept of responders/non-responders regarding blood group antigen alloimmunization; iii) summarize the mechanisms that have been shown to predispose an individual to alloimmunization to determine how these factors may differentiate 'responders' from 'non-responders'; and iv) briefly discuss some practical approaches to prevent alloimmunization in patients who may be prone to alloantibody development.

Factors Influencing RBC Alloimmunization: Lessons Learned from Murine Models

Red blood cell (RBC) alloimmunization may occur following transfusion or pregnancy/delivery. Although observational human studies have described the immunogenicity of RBC antigens and the clinical significance of RBC alloantibodies, studies of factors influencing RBC alloimmunization in humans are inherently limited by the large number of independent variables involved. This manuscript reviews data generated in murine models that utilize transgenic donor mice, which express RBC-specific model or authentic human blood group antigens. Transfusion of RBCs from such donors into nontransgenic but otherwise genetically identical recipient mice allows for the investigation of individual donor or recipient-specific variables that may impact RBC alloimmunization. Potential donor-related variables include methods of blood product collection, processing and storage, donor-specific characteristics, RBC antigen-specific factors, and others. Potential recipient-related variables include genetic factors (MHC/HLA type and polymorphisms of immunoregulatory genes), immune activation status, phenotype of regulatory immune cell subsets, immune cell functional characteristics, prior antigen exposures, and others. Although murine models are not perfect surrogates for human biology, these models generate phenomenological and mechanistic hypotheses of RBC alloimmunization and lay the groundwork for follow-up human studies. Long-term goals include improving transfusion safety and minimizing the morbidity/mortality associated with RBC alloimmunization.

Responder individuality in red blood cell alloimmunization

Many different factors influence the propensity of transfusion recipients and pregnant women to form red blood cell alloantibodies (RBCA). RBCA may cause hemolytic transfusion reactions, hemolytic disease of the fetus and newborn and may be a complication in transplantation medicine. Antigenic differences between responder and foreign erythrocytes may lead to such an immune answer, in part with suspected specific HLA class II associations. Biochemical and conformational characteristics of red blood cell (RBC) antigens, their dose (number of transfusions and pregnancies, absolute number of antigens per RBC) and the mode of exposure impact on RBCA rates. In addition, individual circumstances determine the risk to form RBCA. Responder individuality in terms of age, sex, severity of underlying disease, disease- or therapy-induced immunosuppression and inflammation are discussed with respect to influencing RBC alloimmunization. For particular high-risk patients, extended phenotype matching of transfusion and recipient efficiently decreases RBCA induction and associated clinical risks.

Molecular matching for Rh and K reduces red blood cell alloimmunisation in patients with myelodysplastic syndrome

BACKGROUND

Matching for Rh and K antigens has been used in an attempt to reduce antibody formation in patients receiving chronic transfusions but an extended phenotype matching including Fy(a) and Jk(a) antigens has also been recommended. The aim of this study was to identify an efficient transfusion protocol of genotype matching for patients with myelodysplastic syndrome (MDS) or chronic myelomonocytic leukaemia. We also examined a possible association of HLA class II alleles with red blood cell (RBC) alloimmunisation.

MATERIALS AND METHODS

We evaluated 43 patients with MDS undergoing transfusion therapy with and without antibody formation. We investigated antigen-matched RBC units for ABO, D, C, c, E, e, K, Fy(a), Fy(b), Jk(a), Jk(b), S, s, Do(a), Do(b) and Di(a) on the patients' samples and on the donor units serologically matched for them based on their ABO, Rh and K phenotypes and presence of antibodies. We also determined the frequencies of HLA-DRB1 alleles in the alloimmunised and non-alloimmunised patients.

RESULTS

Seventeen of the 43 patients had discrepancies or mismatches for multiple antigens between their genotype-predicted profile and the antigen profile of the units of blood serologically matched for them. We verified that 36.8% of patients had more than one RBC alloantibody and 10.5% of patients had autoantibodies. Although we were able to find a better match for the patients in our extended genotyped/phenotyped units, we verified that matching for Rh and K would be sufficient for most of the patients. We also observed an over-representation of the HLA-DRB1*13 allele in the non-alloimmunised group of patients with MDS.

DISCUSSION

In our population molecular matching for C, c, E, e, K was able to reduce RBC alloimmunisation in MDS patients. An association of HLA-DRB1*13 and protection from RBC alloimmunisation should be confirmed.

Red blood cell alloimmunization mitigation strategies

Hemolytic transfusion reactions due to red blood cell (RBC) alloantibodies are a leading cause of transfusion-associated death. In addition to reported deaths, RBC alloantibodies also cause significant morbidity in the form of delayed hemolytic transfusion reactions. These alloantibodies may also cause morbidity in the form of anemia, with compatible RBC units at times being unable to be located for highly alloimmunized patients, or in the form of hemolytic disease of the newborn. Thus, preventing RBC alloantibodies from developing in the first place, or mitigating the dangers of existing RBC alloantibodies, would decrease transfusion-associated morbidity and mortality. A number of human studies have evaluated the impact on RBC alloimmunization rates of providing partially phenotypically or genotypically matched RBCs for transfusion, and a number of animal studies have evaluated the impact of single variables on RBC alloimmunization. The goal of this review is to take a comprehensive look at existing human and animal data on RBC alloimmunization, focusing on strategies that may mitigate this serious hazard of transfusion. Potential factors that impact initial RBC alloimmunization, on both the donor and recipient sides, will be discussed. These factors include, but are not limited to, exposure to the antigen and an ability of the recipient's immune system to present that antigen. Beyond these basic factors, coexisting "danger signals," which may come from the donor unit itself or which may be present in the recipient, also likely play a role in determining which transfusion recipients may become alloimmunized after RBC antigen exposure. In addition, to better understanding factors that influence the development of RBC alloantibodies, this review will also briefly discuss strategies to decrease the dangers of existing RBC alloantibodies.

HLA-DRB1*07:01 allele is primarily associated with the Diego a alloimmunization in a Brazilian population

BACKGROUND

The Diego blood group presents a major polymorphic site at Residue 854, causing a proline (Di(b) antigen) to leucine (Di(a) antigen) substitution. Di(a) alloimmunization has been observed among Asian and Native South American populations. Considering that Brazilians represent a genetically diverse population, and considering that we have observed a high incidence of Di(a) alloimmunization, we typed HLA-DRB1 alleles in these patients and performed in silico studies to investigate the possible associated mechanisms.

STUDY DESIGN AND METHODS

We studied 212 alloimmunized patients, of whom 24 presented immunoglobulin G anti-Di(a) , 15 received Di(a+) red blood cells and were not immunized, and 1008 were healthy donors. HLA typing was performed using commercial kits. In silico analyses were performed using the TEPITOPEpan software to identify Diego-derived anchor peptide binding to HLA-DRB1 molecules. Residue alignment was performed using the IMGT/HLA for amino acid identity and homology analyses.

RESULTS

HLA-DRB1*07:01 allele was overrepresented in Di(a) -alloimmunized patients compared to nonimmunized patients and to healthy donors. Two motifs were predicted to be potential epitopes for Di(a) alloimmunization, the WVVKSTLAS motif was predicted to bind several HLA-DR molecules, and the FVLILTVPL motif exhibited highest affinity for the HLA-DRB1*07:01 molecule. Pocket 4 of the DRB1*07:01 molecule contained specific residues not found in other HLA-DRB1 molecules, particularly those at Positions 13(Y), 74(Q), and 78(V).

CONCLUSION

Individuals carrying the HLA-DRB1*07:01 allele present an increased risk for Di(a) alloimmunization. The identification of susceptible individuals and the knowledge of potential sensitization peptides are relevant approaches for transfusion care, diagnostic purposes, and desensitization therapies.

HLA-DRB1 associations in individuals with single and multiple clinically relevant red blood cell antibodies

BACKGROUND

A minority of red blood cell (RBC) alloantigen-exposed persons form antibodies. Responders are at high risk of developing additional antibodies upon subsequent transfusions. Several studies showed an association between particular HLA-DRB1 phenotypes and the development of specific RBC antibodies. This study evaluates the presence of HLA-DRB1 antigens in individuals with single or multiple RBC antibody specificities to explore whether the response against RBC antigens is associated with a summation of particular HLA-DRB1 susceptibility antigens.

STUDY DESIGN AND METHODS

Frequencies of HLA-DRB1 alleles in individuals with antibodies against clinically relevant antigens were compared to a large population cohort to calculate odds ratios (ORs) for alloimmunization to different RBC antigens.

RESULTS

The study cohort consisted of 941 individuals (female-to-male ratio, 3.8) possessing 1462 antibody specificities elicited by transfusion, pregnancy, transplantation, or a combination of these. Besides confirmation of known associations, new associations were identified for anti-E with DRB1*09 and for anti-S with DRB1*07 (ORs, 3.7 and 8.7, respectively). Multiple antibody formation was in a minority of cases associated with the presence of multiple DRB1 susceptibility genes. In multiple responders DRB1*15 was present in almost 40% of cases compared to approximately 25% in single-antibody responders and in the control population.

CONCLUSION

This study suggests that HLA-DRB1 restriction plays an important role for a first RBC antibody response but multiple antibody formation seems less dependent on the presence of particular HLA restriction genes, while HLA-DRB1*15 may represent a susceptibility phenotype enhancing formation of multiple RBC antibody specificities.

[Red-blood-cell allo-immunization]

Red blood cell allo-immunization is the immune response of an individual to foreign red blood cell antigens not present on the surface of their own cells. The aim of that paper is to clarify the different factors influencing the antibody response against red blood cell antigens.

Effects of genetic, epigenetic, and environmental factors on alloimmunization to transfused antigens: Current paradigms and future considerations

Transfused red blood cells, platelets, or coagulation factors have the capacity to induce alloantibodies, which once formed, can be a clinical barrier to future transfusion therapy and/or transplantation. Large observational studies over the last 50 years have characterized some of the general properties of transfusion induced alloimmunization, which appear to vary to a considerable extent from what is generally observed for human responses to other immunogens, such as microbial pathogens and vaccines. Transfused cells and factor only induce immune responses in the minority of recipients. There are data to suggest that differences in the unit may play a role. However, there are clearly differences in recipient biology, as once a recipient makes one antibody they are much more likely to make additional antibodies; indeed, recipients have been categorized as "responder" and "non-responder" by the field. Recent mechanistic studies have begun to define potential causes for such differences in alloimmunization from patient to patient, but much progress needs to be made to understand how, why, and in whom alloimmunization occurs. This review gives a general background on immunology in the context of transfusion, summarizes recent progress in the field, and discusses future directions for exploration. Particular attention is paid to the general concept that the human immune system is melded by the wide range of antigens encountered in our environment, and that the effects of such on the immune system may have a profound effect upon response to transfused cells.

Risk Factors for Alloimmunisation after red blood Cell Transfusions (R-FACT): a case cohort study

INTRODUCTION

Individuals exposed to red blood cell alloantigens through transfusion, pregnancy or transplantation may produce antibodies against the alloantigens. Alloantibodies can pose serious clinical problems such as delayed haemolytic reactions and logistic problems, for example, to obtain timely and properly matched transfusion blood for patients in which new alloantibodies are detected.

OBJECTIVE

The authors hypothesise that the particular clinical conditions (eg, used medication, concomitant infection, cellular immunity) during which transfusions are given may contribute to the risk of immunisation. The aim of this research was to examine the association between clinical, environmental and genetic characteristics of the recipient of erythrocyte transfusions and the risk against erythrocyte alloimmunisation during that transfusion episode. METHODS AND ANALYSIS STUDY DESIGN: Incident case-cohort study.

SETTING

Secondary care, nationwide study (within the Netherlands) including seven hospitals, from January 2005 to December 2011.

STUDY POPULATION

Consecutive red cell transfused patients at the study centres.

INCLUSION

The study cohort comprises of consecutive red blood cell transfused patients at the study centre. EXCLUSION: Patients with transfusions before the study period and/or pre-existing alloantibodies.Cases defined as first time alloantibody formers; Controls defined as transfused individuals matched (on number of transfusions) to cases and have not formed an alloantibody.

STATISTICAL ANALYSIS

Logistic regression models will be used to assess the association between the risk to develop antibodies and potential risk factors, adjusted for other risk factors.

ETHICS AND DISSEMINATION

Approval at each local ethics regulatory committee will be obtained. Data will be coded for privacy reasons. Patients will be sent a letter and an information brochure explaining the purpose of the study. A consent form in presence of the study coordinator will be signed before the blood taking commences. Investigators will submit progress summary of the study to study sponsor regularly. Investigators will notify the accredited ethics board of the end of the study within a period of 8 weeks.

Long-Term follow up after intra-Uterine transfusionS; the LOTUS study

BACKGROUND

The Leiden University Medical Center (LUMC) is the Dutch national referral centre for pregnancies complicated by haemolytic disease of the fetus and newborn (HDFN) caused by maternal alloimmunization. Yearly, 20-25 affected fetuses with severe anaemia are transfused with intra-uterine blood transfusions (IUT). Mothers of whom their fetus has undergone IUT for HDFN are considered high responders with regard to red blood cell (RBC) antibody formation. Most study groups report high perinatal survival, resulting in a shift in attention towards short- and long-term outcome in surviving children.

METHODS/DESIGN

We set up a large long-term observational follow-up study (LOTUS study), in cooperation with the Sanquin Blood Supply Foundation and the LUMC departments of Obstetrics, Neonatology and ImmunoHematology & Bloodtransfusion.The first part of this study addresses several putative mechanisms associated with blood group alloimmunization in these mothers. The second part of this study determines the incidence of long-term neurodevelopment impairment (NDI) and associated risk factors in children treated with IUT. All women and their life offspring who have been treated with IUT for HDFN in the LUMC from 1987-2008 are invited to participate and after consent, blood or saliva samples are taken. RBC and HLA antigen profile and antibodies are determined by serologic or molecular techniques. Microchimerism populations are tested by real time polymerase chain reaction (RT PCR).All children are tested for their neurological, cognitive and psychosocial development using standardised tests and questionnaires. The primary outcome is neurodevelopmental impairment (NDI), a composite outcome defined as any of the following: cerebral palsy, cognitive or psychomotor development < 2 standard deviation, bilateral blindness and/or bilateral deafness.

DISCUSSION

The LOTUS study includes the largest cohort of IUT patients ever studied and is the first to investigate post-IUT long-term effects in both mother and child. The results may lead to a change in transfusion policy, in particular future avoidance of certain incompatibilities. Additionally the LOTUS study will provide clinicians and parents better insights in the long-term neurodevelopmental outcome in children with HDFN treated with IUTs, and may improve the quality of antenatal counselling and long-term guidance.