Blood Transfusion-Induced Immunomodulation

Abstract

Blood transfusion therapy is associated with many risks, including major or minor blood transfusion reaction, non-A non-B hepatitis, hepatitis B, and HIV infection. Blood transfusion may result in immunologic changes (immunomodulation) that are beneficial in some patients but harmful in others. After reports of increased renal allograft survival in patients receiving pretransplant transfusion [1], Gantt [2] questioned whether transfusion might diminish or retard the immune response. Clinical studies have shown a beneficial effect of blood transfusion on graft survival [3,4], but an adverse effect on cancer recurrence [5-10] and postoperative infection [10-14]. Approximately two thirds of 11,000 transfusions [15,16] given perioperatively are administered by anesthesiologists [17], and 26% are given inappropriately [18,19]. This review will focus on the immunomodulatory effects of transfusion therapy. It will begin with a brief review of the immune system and then discuss 1) the effect of transfusion therapy on modulating the immune system, and 2) transfusion-induced immunomodulatory effects on vascularized graft survival, cancer recurrence, and postoperative infections. Immune System Overview The major function of the immune system is to recognize various pathogens and respond to them. Although the immune system evolved to inactivate pathogens, it is now known that it also protects the body against the development of tumors and the rejection of foreign tissue. The immune system consists of an afferent (recognition) limb and an efferent (response) limb. The afferent limb is involved with alerting the host against the entry of foreign pathogens or foreign alloantigens. The afferent (response) limb may respond by cellular and/or humoral immunity and by secretion of lymphokines that modulate the immune response [20]. Human Lymphoid System The lymphoid tissue is responsible for most of the body's immune response and contains about 1012 lymphocytes, which produce approximately 1020 antibody molecules [21]. The mature lymphocytes circulate to lymph nodes, spleen, or tonsils and remain in these secondary locations until they are activated by antigens and antigen-presenting cells [20]. T Lymphocytes T lymphocytes (T cells) are so named because they are matured by the thymus. T cells become activated by antigens and by antigen-presenting cells (APCs) and are characterized by an antigen-binding molecule or T-cell receptor (TCR) on their surface. TCRs react with antigens that have been processed and presented by major histocompatibility complex (MHC) molecules on the surface of macrophages or APCs. The TCR and the CD3 chain form a complex that functions as the primary antigen recognition site on the cell surface Figure 1. In addition to the TCR/CD3 molecules, numerous accessory surface molecules are present Figure 2. They include the CD8 and CD4 molecules, which bind to MHC class I and class II molecules on the APCs Figure 1[22].Figure 1: Interaction of a peptide-major histocompatibility complex (MHC) complex on a presenting cell with a receptor on a T cell. The presenting cell can be a macrophage using a class II MHC or any tissue cell using a class I MHC. The T cells can be helper T lymphocytes carrying CD4 or cytotoxic T lymphocytes carrying CD8. The class I MHC binds CD8; class II binds CD4. The T-cell receptor not only has CD8 or CD4 molecules as components of its interaction system, it also has four different proteins that make up the CD3 complex; their role is uncertain. Also, bound to the CD4 or CD8 proteins is the lck protein tyrosine kinase, which can phosphorylate a CD3 component on tyrosine in response to an interaction of the T-cell receptor with MHC-peptide complex. The CD3 and lck proteins are apparently part of the response system used by T cells after encounters with an MHC-peptide complex antigen. (From Darnell J, Lodish H, and Baltimore D. Molecular cell biology. 2nd ed. Copyright (c) 1990 by Scientific American Books, Inc., New York, NY. Used with permission of W. H. Freeman and Company.)Figure 2: Cell surface markers involved in T-cell activation and adhesion. Depicted are a number of T-cell surface molecules and their known ligands on the surface of antigen-presenting cells and/or the extracellular matrix. Many of these molecules are also known to deliver intracellular signals capable of interacting with the activation signal delivered through the T-cell receptor (TCR). HA, hyaluronic acid; FN, fibronectin; LN, laminin; Ag, antigen; PTP prime ase, protein tyrosine phosphatase; circles with dots represent phosphotyrosine residues; fyn (p59fyn) and lck (p56lck), protein tyrosine kinases. (Adapted with permission from Rothstein DM. The cellular immune response. In: Anderson KC, Ness PM, eds. Scientific basis of transfusion medicine--implications for clinical practice. Philadelphia: WB Saunders, 1994;124-46.)MHC I and MHC II antigens are cell surface glycoproteins that are responsible for alloreactivity and therefore rejection. The gene complex for human MHC is known as the human leukocyte antigen (HLA) complex. MHC genes that encode the targets for cytotoxic T lymphocytes' (CTLs') self-recognition are called class I MHC genes. These genes code for class I antigens at HLA A, B, and C loci Table 1. Several thousand molecules of each HLA A, B, and C antigen are expressed on every nucleated cell in the body.Table 1: Class I and Class II Antigens: Structure and FunctionThe receptors on T cells recognize peptide fragments of antigens that are linear sequences of eight to 15 amino acids Figure 1. These peptides bind to MHC molecules on the cell's surface. The MHC molecules then present the peptides to a TCR. Class I MHC expresses peptides synthesized by the cell itself. These may be derived from normal self-proteins or from peptides from viral proteins made in a virusinfected cell Figure 3. Class II MHC binds exogenous protein which is endocytosed and broken down into peptide fragments.Figure 3: Antigen processing and presentation. Endogenously synthesized or intracellular proteins (e.g., viral gene products) are degraded into peptides that are transported to the endoplasmic reticulum. These peptides bind to class I major histocompatibility complex (MHC) molecules and are transported to the surface of the antigen-presenting cell. CD8+ T cells recognize the foreign peptide bound to class I MHC by way of the T-cell receptor complex. Extrogenous antigen (e.g., bacterial) is endocytosed and broken down into peptide fragments in endosomes. Class II molecules are transported to the endosome in association with the invariant chain, bind the peptide, and are delivered to the surface of the antigen-presenting cell, where they are recognized by CD4+ cells. (Adapted with permission from Hanto DW, Mohanakumar T. Transplant immunology. In: Greenfield LJ, Mulholland MW, Oldham KT, Zelenock GB, eds. Surgery--scientific principles and practice. Philadelphia: JB Lippincott, 1993;461-500.)T cells are divided into at least two subpopulations: CD-4 (helper) and CD-8 (killer) T-cells. The helper T lymphocytes, or TH cells, utilize the CD-4 molecules to bind the class II MHC-peptide complexes that have been presented by macrophage APCs. The TH cells recognize the antigen presented by the class II MHCs. The TH cells then secrete lymphokines that stimulate other cells involved in the immune response [23]. Cytokines are nonantibody mediators of cellular immunity produced by activated lymphocytes [24,25]. As shown by Table 2, an individual lymphokine or cytokine may have multiple actions, with effect on immunomodulation, angiogenesis, hematopoiesis, septic shock, or antiproliferative activity against tumor cells [20]. Cytokines are known to have multiple effects on both T cells and B cells. Cytokines stimulate TH cells through specific receptors on their surfaces. Activation of a TH cell by an encounter with peptide-MHC complex induces formation of an IL-2 receptor, which responds to the IL-2 it secretes by activating autocrine growth [25].Table 2: Partial List of Cytokines Secreted by TH Cells or Macrophages in Response to AntigenaAs B cells are maturing, they develop surface receptors for T-cell derived IL-2 and IL-4-6. These cytokines find receptors on activated B cells and stimulate growth of the B cells and their maturation to plasma cells. In summary, cytokines secreted by TH cells promote antibody production from B cells and stimulate both T- and B-cell growth and maturation. TH cell loss after HIV infection causes failure of the immune system in AIDS [26]. CTLs can be distinguished from TH cells because they express the CD8 surface protein. CTLs recognize foreign antigens in the context of class I MHC and the CD8 molecule. Antibodies deal with intact foreign materials, whereas CTLs deal with cell-bound peptides. A classic CTL target is a virus-infected cell that displays fragments of viral glycoproteins on its surface bound to class I MHC. CTLs attach to the target cell and secrete proteases that form ion channels that depolarize the cell, thereby destroying its ionic and osmotic balance, resulting in cell death [20]. A third T cell, the suppressor T cell (TS), suppresses B-cell activity and inhibits lymphocytotoxicity. The TS cell appears to be associated with a CD8 surface protein that is different from the CD8 protein associated with CTL cells [20]. B Lymphocytes B lymphocytes (B cells) originate in the bone marrow, mature into plasma cells, and are specialized for antibody production. During development, B cells pass through successive stages characterized by different patterns of cell surface marker expression and immunoglobulin (Ig) production. B lymphocytes express many different cell surface antigens Figure 4 as they pass from the pre-B cell to become activated B cells and then functional plasma cells [27]. These shortlived, noncirculating plasma cells are capable of producing 10 million antibody molecules an hour [28]. B-cell activation and response to antigen is directed by TH cells and their secreted cytokines. The B cell can decompose a protein into peptides in association with MHC class II molecules and display them in a manner similar to the way an APC displays peptides in association with MHC class I or II molecules Figure 5.Figure 4: Cell surface antigen expression. The stages of expression of some B-cell antigens are indicated by a solid line. Cytoplasmic but not surface expression is indicated by a dashed line. (Adapted with permission from Ord DC, Tedder TF. The humoral immune response. In: Anderson KC, Ness PM, eds. Scientific basis of transfusion medicine--implications for clinical practice. Philadelphia: WB Saunders, 1994;124-46.)Figure 5: The hapten-carrier complex activates B cells by first stimulating helper T (TH) cells. The hapten-carrier complex is a protein to which several hapten molecules have been covalently coupled. The hapten portion binds to a B cell but cannot by itself initiate B-cell proliferation. The B cell internalizes and digests the hapten-carrier complex, and portions of the carrier peptide are displayed on the B-cell surface as a complex with class II major histocompatibility complex (MHC) protein. A macrophage cell also internalizes carrier protein and displays peptide fragments on its surface in association with class II MHC. Then TH cells with appropriate receptors bind to the peptide-MHC complex displayed on the macrophage surface. Binding stimulates the TH cells, which then proliferate, recognize the identical peptide-MHC complex on the B cell, and secrete factors that stimulate the B cell to grow. (From Darnell J, Lodish H, Baltimore D. Molecular cell biology. 2nd ed. Copyright (c) 1990 by Scientific American Books, Inc., New York, NY. Used with permission of W. H. Freeman and Company).Antibody secretion by plasma cells requires a B lymphocyte to bind an antigen and then receive costimulation from TH cells in order to differentiate and become an active plasma cell. IL-2, IL-4, and IL-5 stimulate B-cell maturation into plasma cells. After the B lymphocyte binds an antigen to its receptor, it differentiates and secretes antibody molecules [20,29]. IgA-producing plasma cells are located in the gut and bronchial mucosa; IgG-producing plasma cells are located in bone marrow, spleen, and lymph nodes; IgM-producing plasma cells are located in the spleen and lymph nodes; and IgE plasma cells are found in gut, mesenteric, and bronchus lymphoid tissue. Each antibody molecule consists of two classes of polypeptide chains, light and heavy. Another type of activated B lymphocytes are memory B cells, which retain, for the life of the organism, a record of the antigens previously encountered so that a second encounter with the antigen can elicit a rapid, highly avid response [20]. Transfusion-Induced Immunomodulation Mechanism Exposure to allogenic tissue, including blood, can cause both allosensitization and immunosuppression [30,31]. The development of tolerance can be specific to the tissue donor; however, immune responses can be characterized in varying degrees by cross-reactivity or cross-specificity [32]. The best characterized clinical effect of transfusion-induced modulation is improved survival of renal allografts in previously transfused patients [3,4]. Transfusion-induced immunomodulation may be implicated as either a potential inhibitor of immunologic effector cells or as a stimulator of immunologic suppressor cells [30-34]. Some transfusion-induced down-regulated immune functions include decreased cytokine production, mitogen response, TH cells, natural killer (NK) cells, and lymphocyte numbers; decreased function and cellmediated cytotoxicity; and increased Ts cell number and function [5]. NK cells are cytotoxic lymphocytes, their activity is enhanced by IL-2, and they are a first-line defense against virus-infected cells [35]. In order to describe the transfusion effect, we will first discuss nonspecific immune suppression and antigen-specific immune suppression after transfusion. The component(s) of transfused blood responsible for these immunomodulatory effects is (are) uncertain; however, there are data to suggest that white cells or plasma are important in modifying the host immune defenses [30,32]. Compared to packed cells prepared in the late 1970s, current packed red cells contain less than 10% of the plasma and 5% of the white cells [36]. The decreased quantity of plasma and white cells present in today's packed red blood cells may be responsible for the apparent decrease in the ability of packed cells to provide a modulating effect. Nonspecific Immune Suppression after Blood Transfusions The mechanism(s) by which transfusions produce nonspecific immunomodulation is (are) unknown. One hypothesis is that transfusions overload the reticuloendothelial system and that iron salts cause the suppressive changes [37,38]. Prostaglandin E2 (PGE2) production and IL-2 metabolism also play a role in down-regulating immune responses. PGE2 production by monocytes is increased after transfusions [39,40]. PGE2 is known to down-regulate macrophage class II antigen expression [41] and inhibit IL-2 production and target cell response to IL-2 [33]. IL-2 production by TH lymphocytes is known to decrease after transfusion [42-44]. As discussed earlier, IL-2 is required for the activation and proliferation of B cells and for the generation of cytotoxic T cells; hence, a decrease in IL-2 production will result in a decrease in B-cell stimulation, antibody production, and impaired NK activity [45,46]. These nonspecific immunomodulatory effects after transfusion appear to be transient after one transfusion, but they become more pronounced and longlasting after multiple transfusions. Hemodialysis patients demonstrate increased nonspecific immune suppression up to 20 wk after transfusion [47]. Antigen-Specific Immunosuppression In 1984, Terasaki [48] advanced a new theory that the "function of transfusion was to immunize patients and not to induce tolerance, or to serve as a donor selection mechanism." He proposed that transfusions did immunize recipients; however, if they were receiving azathropine (AZA), the AZA partially eliminated the clone of lymphocytes which were stimulated by the transfusion. When the patient subsequently underwent transplantation, the transplanted organ acted as a secondary stimulus and high dose immunosuppression at the time of transplantation killed or inactivated remaining clones of reactive cells. This clonal depletion theory suggests that the transfusion and immunosuppression result in removing or incapacitating the cells that would reject the graft. Multiple donor-specific transfusions (DSTs) have also been thought to generate TS cells [49-51]. TS cells are thought to express a CD8 surface protein and are generated via-a multistep process that occurs over several days [52]. A third antigen-specific immunosuppressive mechanism after DST results from the generation of an antiidiotypic antibody. Jeme [53] proposed that TCRs or antibodies generated against the graft antigen in the primary immune response could act as "new" antigens. Antibodies formed against these "new" antigens are called antiidiotypic antibodies, and they compete for binding locations on the initial antibodies [54-56]. These antiidiotypic antibodies function as blocking antibodies to prevent the antibodies generated against the graft antigen in the primary immune response from combining with the graft antigen. Blood Transfusion and Organ Transplantation In the late 1960s, renal failure patients were often given transfusions for anemia. However, transfusion therapy became controversial when it was established that hyperacute rejection after kidney transplant was due to lymphocytotoxic antibodies arising from sensitization to HLA antigens. The most frequent causes of sensitization were identified as blood transfusion, pregnancy, and rejected grafts [23]. After the discovery of sensitization to HLA antigens, transfusions were avoided in patients on hemodialysis. In 1973, Opelz et al. [1] published the first study showing improved cadaveric graft survival rates in transfused recipients. Other investigators subsequently confirmed that transfused recipients had better graft survival rates [57-60]. Opelz and Terasaki [57] collected data on 870 transfused and 490 untransfused patients prior to transplantation and stratified them according to the type and number of blood components received (whole blood, packed red blood cells, or frozen blood). This study showed a 1 yr graft survival rate of 42% in patients who had not received prior transfusions and 71% in patients who had received more than 20 transfusions. At 4 yr, graft survival rates were 30% without and 65% with transfusion [57,58]. Beginning in 1978, many centers developed a policy of giving potential recipients three units of packed red blood cells at 15-day intervals [59,60]. Other prospective studies confirmed the earlier results with a 1-yr graft survival rate of 87% in transfused and 32% in nontransfused patients [60]. However, controversy remained over the type of blood product to be transfused, the number and timing of transfusions, and the sensitization rate. Opelz and Terasaki [57] reported that whole blood and packed cells, but not frozen blood, had a significant immunosuppressive effect. Others confirmed that packed cells, washed red blood cells, and other blood products were more effective than frozen red blood cells in improving graft survival [60,61]. Persijn et al. [60] showed that single unit transfusions, even if given years earlier, could prolong cadaveric kidney graft survival. Opelz et al. [58] found a corresponding increase in graft survival rates with increasing numbers of transfusions. Some studies show improvement in graft survival only in animals receiving whole blood transfusions at the time of transplantation [62]. Salvatierra et al. [49] reported the beneficial effect of DST in recipients of kidneys from living, related donors. These patients received three transfusions 2 wk apart from the prospective donor while continuously receiving AZA immunosuppression. As discussed earlier, DST in conjunction with AZA is thought to eliminate clones of reactive cells (clonal depletion theory). In summary, studies of the "transfusion effect" suggest that even a single transfusion may enhance renal graft survival. Optimal transfusion effect for most recipients of cadaver grafts is obtained with three to five transfusions of whole blood or packed red cells given before transplantation. The magnitude of the transfusion effect appears to be somewhat less than that for cyclosporin A. With the introduction of cyclosporin A, the beneficial effect of random transfusion has disappeared; however, the clinical importance of DST protocols has persisted in some situations [63-65]. The specific blood component(s) responsible for the transfusion effect has (have) not been identified; the duration of the effect is unknown and the mechanism is not established [66-69]. Although the transfusion issue is not completely resolved, most programs now avoid transfusion to the of sensitization to HLA antigens. Blood Transfusion and et al. reported that patients cancer of transfused blood and are the of patients who receive transfusion therapy. studies show that and 65% of patients for cancer of the or receive transfusions. The of transfusion-induced immunosuppression in these patients has a number of studies on the effect of transfusion on tumor recurrence after in cancer recurrence rates have been reported in most clinical and may be secondary to different tumor of of or blood transfusion. It has been that transfusion is a marker for other factors that to cancer However, many studies or of individual studies have found the cancer recurrence and blood transfusion to be by other In the studies to show a significant transfusion effect, most found a recurrence rate in transfused and to find did not find because of study Another has been a rate of cancer recurrence and death when plasma and blood products are transfused (whole blood or frozen to packed red cell transfusion who receive transfusions of three units or less of packed red blood cells have a recurrence rate and increased of survival after cancer Many but not studies the of transfusion-induced immunosuppression in the and of tumor transfusion-induced tumor growth rate is found in these immune system is a and Transfusion A adverse effect of blood transfusion on cancer recurrence rate was first reported by and Other also reported a effect of blood transfusion on the rate of cancer recurrence when transfused and untransfused studies the transfusion and cancer recurrence were two were because of and the and intervals were in the remaining studies Table Table The of the studies showed a significant increase in cancer recurrence in transfused patients with an of and intervals of Figure The found in is similar to that reported in found apparent for the of a transfusion effect in the three of these studies from would increase the of the resulting of of the with of these was not 3: With and Blood 4: from Table of cancer recurrence with transfusion. of increased of with of to a increased of cancer recurrence with transfusion. Transfusion of plasma and blood components (whole blood, frozen has been shown to increase cancer recurrence and death rates when to red cell only transfusion et al. reported response to antigens after cancer in patients given whole blood to given red blood cells. et al. that cancer recurrence was after whole blood transfusion. or more units of packed red blood cells the recurrence rate. The recurrence rate was found in patients given a transfusion of three units or less of packed red cells or in given transfusion. et al. recurrence of cancer in patients receiving to transfusions. They reported in recurrence both had survival rates than patients receiving transfusion. In a to the and that of the 15 study were This that et al. in a white cell blood transfusion with an and found significant in cancer recurrence In a prospective study that packed red cells) but not transfusion is a significant of an increased cancer recurrence rate. in survival rates and transfusion has been reported for patients is a of NK cell function in after blood With the of one study blood transfusion has been to be associated with a after of cancer and after of primary cancer In the study the survival rate of cancer at in untransfused patients was to in a who received at least a transfusion of whole blood or packed cells. for and Transfusion of 10 a in the transfused et al. patients with I cancer and reported a survival rate of for transfused patients for untransfused and reported that patients with I and II had survival rates of and in untransfused patients and in transfused patients that blood transfusion, and were significant et al. found a significant adverse transfusion effect on survival rates studies adverse transfusion were studies with and are apparent for the these and After and Transfusion were a significant adverse effect after blood transfusion and two showed effect. In a of their data and five other et al. reported a for recurrence after transfusion to be a important adverse effect of transfusion of blood products on tumor recurrence in patients with advanced and and reported a recurrence rate of cancer of 65% the rate for cancer was 71% et al. reported that the survival rate was or packed red cell and the survival rate was with transfusion of five or more units of packed cells. Transfusion and studies were the first five reported a and for I an increased of recurrence or a decreased survival rate after blood transfusion. et al.