Acquired and transient RBC CD55 deficiency (Inab phenotype) and anti-IFC

CD55 Facilitates Immune Evasion by Borrelia crocidurae, an Agent of Relapsing Fever

Relapsing fever, caused by diverse Borrelia spirochetes, is prevalent in many parts of the world and causes significant morbidity and mortality. To investigate the pathoetiology of relapsing fever, we performed a high-throughput screen of Borrelia-binding host factors using a library of human extracellular and secretory proteins and identified CD55 as a novel host binding partner of Borrelia crocidurae and Borrelia persica, two agents of relapsing fever in Africa and Eurasia. CD55 is present on the surface of erythrocytes, carries the Cromer blood group antigens, and protects cells from complement-mediated lysis. Using flow cytometry, we confirmed that both human and murine CD55 bound to B. crocidurae and B. persica. Given the expression of CD55 on erythrocytes, we investigated the role of CD55 in pathological B. crocidurae-induced erythrocyte aggregation (rosettes), which enables spirochete immune evasion. We showed that rosette formation was partially dependent on host cell CD55 expression. Pharmacologically, soluble recombinant CD55 inhibited erythrocyte rosette formation. Finally, CD55-deficient mice infected with B. crocidurae had a lower pathogen load and elevated proinflammatory cytokine and complement factor C5a levels. In summary, our results indicate that CD55 is a host factor that is manipulated by the causative agents of relapsing fever for immune evasion. IMPORTANCE Borrelia species are causative agents of Lyme disease and relapsing fever infections in humans. B. crocidurae causes one of the most prevalent relapsing fever infections in parts of West Africa. In the endemic regions, B. crocidurae is present in ~17% of the ticks and ~11% of the rodents that serve as reservoirs. In Senegal, ~7% of patients with acute febrile illness were found to be infected with B. crocidurae. There is little information on host-pathogen interactions and how B. crocidurae manipulates host immunity. In this study, we used a high-throughput screen to identify host proteins that interact with relapsing fever-causing Borrelia species. We identified CD55 as one of the host proteins that bind to B. crocidurae and B. persica, the two causes of relapsing fever in Africa and Eurasia. We show that the interaction of B. crocidurae with CD55, present on the surface of erythrocytes, is key to immune evasion and successful infection in vivo. Our study further shows the role of CD55 in complement regulation, regulation of inflammatory cytokine levels, and innate immunity during relapsing fever infection. Overall, this study sheds light on host-pathogen interactions during relapsing fever infection in vivo.

Lack of association between feline AB blood groups and retroviral status: a multicenter, multicountry study

OBJECTIVES

The relationship between blood group antigens and disease has been studied in humans. Blood types have been associated with both decreased and increased rates of various infections. In addition, blood group expression has been shown to vary with some cancers and gastrointestinal diseases. The objective of this study was to explore whether there is a relationship between blood type and retroviral infections in cats.

METHODS

Case records from a veterinary research laboratory, veterinary teaching hospitals and veterinary blood banks were retrospectively searched for cats where both blood type and retroviral status (feline leukemia [FeLV], feline immunodeficiency virus [FIV] or both) were listed (part 1). In addition, a sample of 33 cats with confirmed FIV infection was genotyped to determine blood groups (part 2).

RESULTS

In part 1, 709 cats were identified, 119 of which were positive for retroviral infection. Among all cases, 621 were type A (87.6%), 68 were type B (9.6%) and 20 were type AB (2.8%). There was no relationship between overall retroviral status (positive/negative) and blood type (P = 0.43), between FeLV status and blood type (P = 0.86) or between FIV status and blood type (P = 0.94). There was no difference in the distribution of blood types between cats that were healthy and typed as possible blood donors vs sick cats that were typed prior to a possible transfusion (P = 0.13). In part 2, of the 33 FIV-infected cats, all blood group genotypes were identified, although this test did not discriminate type A from type AB.

CONCLUSIONS AND RELEVANCE

No relationship was identified between feline retroviral status and blood type in this study. The relationship between blood type and other disease states requires further study in veterinary patients.

Complement and the prothrombotic state

In 2007 and 2009 the regulatory approval of the first-in-class complement inhibitor Eculizumab has revolutionized the clinical management of two rare, life-threatening clinical conditions: paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS). While being completely distinct diseases affecting blood cells and the glomerulus, PNH and aHUS remarkably share several features in their etiology and clinical presentation. An imbalance between complement activation and regulation at host surfaces underlies both diseases precipitating in severe thrombotic events that are largely resistant to anti-coagulant and/or anti-platelet therapies. Inhibition of the common terminal complement pathway by Eculizumab prevents the frequently occurring thrombotic events responsible for the high mortality and morbidity observed in patients not treated with anti-complement therapy. While many in vitro and ex vivo studies elaborate numerous different molecular interactions between complement activation products and hemostasis, this review focuses on the clinical evidence that links these two fields in humans. Several non-infectious conditions with known complement involvement are scrutinized for common patterns concerning a prothrombotic statues and the occurrence of certain complement activation levels. Next to PNH and aHUS, germline encoded CD59 or CD55 deficiency (the latter causing the disease Complement Hyperactivation, Angiopathic thrombosis, and Protein-Losing Enteropathy; CHAPLE), autoimmune hemolytic anemia (AIHA), (catastrophic) anti-phospholipid syndrome (APS, CAPS) and C3 glomerulopathy are considered. Parallels and distinct features among these conditions are discussed against the background of thrombosis, complement activation, and potential complement diagnostic and therapeutic avenues.

Increased expression of complement regulators CD55 and CD59 on peripheral blood cells in patients with EAHEC O104:H4 infection

Background

An outbreak of Shiga Toxin 2 (Stx-2) producing enterohemorrhagic and enteroaggregative E.coli (EAHEC) O104H4 infection in May 2011 caused enterocolitis and an unprecedented high 22% rate of hemolytic uremic syndrome (HUS). The monoclonal anti-C5 antibody Eculizumab (ECU) has been used experimentally in EAHEC patients with HUS but treatment efficacy is uncertain. ECU can effectively prevent hemolysis in paroxysmal nocturnal hemoglobinuria (PNH) caused by a lack of complement-regulating CD55 and CD59 on blood cells. We hypothesized a low expression of CD55 and CD59, as seen in PNH, might correlate with HUS development in EAHEC patients.

Methods

76 EAHEC patients (34 only gastrointestinal symptoms [GI], 23: HUS, 19: HUS and neurological symptoms [HUS/N]) and 12 healthy controls (HC) were tested for the expression of CD55 and CD59 on erythrocytes and leukocytes retrospectively. Additionally, the effect of Stx-2 on CD55 and CD59 expression on erythrocytes and leukocytes was studied ex vivo.

Results

CD55 expression on erythrocytes was similar in all patient groups and HC while CD59 showed a significantly higher expression in HUS and HUS/N patients compared to HC and the GI group. CD55 and CD59 expression on leukocytes and their subsets was significantly higher in all patient groups compared to HC regardless of treatment type. However, CD59 expression on erythrocytes was significantly higher in HUS and HUS/N patients treated combined with plasma separation (PS) and ECU compared to HC. Adding Stx-2 ex vivo had no effect on CD55 and CD59 expression on leukocytes from HC or patients.

Conclusion

HUS evolved independently from CD55 and CD59 expression on peripheral blood cells in EAHEC O104:H4 infected patients. Our data do not support a role for CD55 and CD59 in HUS development during EAHEC O104:H4 infection and point to a different mechanism within the complement system for HUS development in EAHEC patients.

Antigen loss from antibody-coated red blood cells

Clinically significant signs and symptoms of hemolysis can result from the transfusion of crossmatch incompatible blood, the development of anti-red blood cell (RBC) alloantibodies posttransfusion, or the development of autoantibodies to RBCs (ie, autoimmune hemolytic anemia). However, a less understood and poorly appreciated phenomenon is when an antibody induces the loss of its target antigen without significant damage to the cells themselves. This has been referred to as "depressed antigen," "antigen suppression," "weakened antigenicity," and "antigen loss." This phenomenon has been observed for multiple blood group antigens on human RBCs, in addition to antigens on leukocytes, platelets, neurons, and neoplastic cells. This review discusses the published human case reports of antigen loss in each of the contexts described above and describes several experimental models, including whole animal models and in vitro culture systems. Our current understanding of the cellular and molecular mechanisms is discussed, and the role of antigen loss phenomena in both normal immune function and in disease states is reviewed.

Case report and literature review: transient Inab phenotype and an agglutinating anti-IFC in a patient with a gastrointestinal problem

BACKGROUND

The Inab phenotype is a rare deficiency of all Cromer antigens. These antigens are carried on the decay-accelerating factor (DAF, CD55) molecule that is attached to the red blood cell (RBC) membrane by a glycosylphosphatidylinositol (GPI) anchor. Although typically inherited, an acquired and transient form of the Inab phenotype also exists. A patient with the triad of transient Inab phenotype, a direct-agglutinating anti-IFC, and gastrointestinal (GI) abnormalities is reported.

CASE REPORT

An 18-month-old boy with gastroesophageal reflux disease requiring a feeding tube, milk and soy intolerance, and severe growth retardation, as well as vision and hearing deficits from cytomegalovirus infection, was identified when pretransfusion testing revealed a potent panagglutinin (titer > 2000 at 4 degrees C). This antibody did not react with Dr(a-) and IFC RBCs, and the autocontrol was negative. The patient's RBCs lacked CD55 by flow cytometric techniques but had normal levels of CD59 and antigens such as Yt(a) and Emm, carried on GPI-linked proteins, thus excluding paroxysmal nocturnal hemoglobinuria. Several months after initial detection, the anti-IFC was virtually undetectable and his cells reacted weakly with anti-IFC, anti-Dr(a), and anti-CD55. RBCs from the propositus' parents and brother demonstrated normal CD55 and CD59 expression.

CONCLUSION

This is the first example of a direct-agglutinating anti-IFC. The cause of the transient depression in CD55 protein (and thus Cromer system antigens) and appearance of anti-IFC remains unknown, as does the relationship between the patient's GI system abnormalities and these serologic findings.

[Complement component deficiencies in human disease]

The complement system, composed of several plasma and membrane proteins, is an integral part of the innate immune system and plays a role in inflammatory response, destruction of infectious agents, elimination of immune complexes, and control of the specific (adaptive) immune response. Hereditary deficiencies of complement components are relatively rare and associated with susceptibility to a wide variety of clinical diseases. Complement components may be target of antibodies (anti-C1q, factor H, C3 alternative convertase, or C3NeF autoantibodies or anti-C1 inhibitor antibodies) that lead to acquired deficiencies. Testing the complement system is especially necessary in patients with autoimmune diseases, some kidney diseases, recurrent infections (especially meningococcal), and angioedema. Precise clinical descriptions of the phenotypes associated with these deficiencies and their molecular diagnosis are necessary to improve our understanding of the role that the complement system plays in the physiopathological mechanisms of these diseases and to propose the most specific treatment for them.

Membrane complement regulatory proteins

A number of proteins anchored on the cell surface function to protect host tissues from bystander injury when complement is activated. In humans, they include decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46), complement receptor 1 (CR1, CD35) and CD59. Although disease conditions directly attributable to abnormal function of these proteins are relatively rare, it has become evident from recent studies using animal models that membrane complement regulatory proteins are important modulators of tissue injury in many autoimmune and inflammatory disease settings. Evidence is also emerging to support a role of these proteins in regulating cellular immunity. In this article, we highlight recent advances on the in vivo biology of membrane complement regulatory proteins and discuss their relevance in human disease pathogenesis and therapeutics.

Correlation between serum estradiol in the follicular phase of the ovarian cycle and decay acceleration factor (DAF) expression on red blood cells and coxsackiervirus B-3 induced hemagglutination in young cycling women

Decay accelerating factor (DAF) is a widely distributed glycoprotein which aids in the inactivation of complement. DAF is also a cellular receptor for certain group B coxsackieviruses (CVB) and is responsible for the viral hemagglutinating activity for human red blood cells (RBC). Healthy, young female volunteers donated blood on days 11 and 22 of the ovarian cycle. Samples were categorized into luteal and follicular phases based on serum progesterone level (P4 either < 2.0 ng/mL, follicular; P4 > or = 2.0 ng/mL, luteal) and analyzed by flow cytomtery for DAF expression on RBC and CD21 + B lymphocytes. Cycling females showed significant variation in CVB-induced hemagglutination and % RBC or CD19 + cells which were DAF +. There was a strong correlation between serum estradiol levels and % RBC expressing DAF (P < 0.01) in the follicular, but not in the luteal ovarian phase. Infection of white blood cells with green-fluorescent protein CVB (GFP-CVB) showed a correlation between infectivity of CD19+ cells and DAF expression. This indicates that women may show differential susceptibility to CVB infection in the luteal and follicular phases of the ovarian cycle.