Kynurenic Acid and Its Synthetic Derivatives Protect Against Sepsis-Associated Neutrophil Activation and Brain Mitochondrial Dysfunction in Rats.

Background and Aims: The systemic host response in sepsis is frequently accompanied by central nervous system (CNS) dysfunction. Evidence suggests that excessive formation of neutrophil extracellular traps (NETs) can increase the permeability of the blood-brain barrier (BBB) and that the evolving mitochondrial damage may contribute to the pathogenesis of sepsis-associated encephalopathy. Kynurenic acid (KYNA), a metabolite of tryptophan catabolism, exerts pleiotropic cell-protective effects under pro-inflammatory conditions. Our aim was to investigate whether exogenous KYNA or its synthetic analogues SZR-72 and SZR-104 affect BBB permeability secondary to NET formation and influence cerebral mitochondrial disturbances in a clinically relevant rodent model of intraabdominal sepsis. Methods: Sprague-Dawley rats were subjected to fecal peritonitis (0.6 g kg-1 ip) or a sham operation. Septic animals were treated with saline or KYNA, SZR-72 or SZR-104 (160 µmol kg-1 each ip) 16h and 22h after induction. Invasive monitoring was performed on anesthetized animals to evaluate respiratory, cardiovascular, renal, hepatic and metabolic parameters to calculate rat organ failure assessment (ROFA) scores. NET components (citrullinated histone H3 (CitH3); myeloperoxidase (MPO)) and the NET inducer IL-1ß, as well as IL-6 and a brain injury marker (S100B) were detected from plasma samples. After 24h, leukocyte infiltration (tissue MPO) and mitochondrial complex I- and II-linked (CI-CII) oxidative phosphorylation (OXPHOS) were evaluated. In a separate series, Evans Blue extravasation and the edema index were used to assess BBB permeability in the same regions. Results: Sepsis was characterized by significantly elevated ROFA scores, while the increased BBB permeability and plasma S100B levels demonstrated brain damage. Plasma levels of CitH3, MPO and IL-1ß were elevated in sepsis but were ameliorated by KYNA and its synthetic analogues. The sepsis-induced deterioration in tissue CI-CII-linked OXPHOS and BBB parameters as well as the increase in tissue MPO content were positively affected by KYNA/KYNA analogues. Conclusion: This study is the first to report that KYNA and KYNA analogues are potential neuroprotective agents in experimental sepsis. The proposed mechanistic steps involve reduced peripheral NET formation, lowered BBB permeability changes and alleviation of mitochondrial dysfunction in the CNS.

Divergent Effects of the N-Methyl-D-Aspartate Receptor Antagonist Kynurenic Acid and the Synthetic Analog SZR-72 on Microcirculatory and Mitochondrial Dysfunction in Experimental Sepsis.

Introduction: Sepsis is a dysregulated host response to infection with macro- and microhemodynamic deterioration. Kynurenic acid (KYNA) is a metabolite of the kynurenine pathway of tryptophan catabolism with pleiotropic cell-protective effects under pro-inflammatory conditions. Our aim was to investigate whether exogenously administered KYNA or the synthetic analog SZR-72 affects the microcirculation and mitochondrial function in a clinically relevant rodent model of intraabdominal sepsis. Methods: Male Sprague-Dawley rats (n = 8/group) were subjected to fecal peritonitis (0.6 g kg-1 feces ip) or a sham operation. Septic animals were treated with sterile saline or received ip KYNA or SZR-72 (160 µmol kg-1 each) 16 and 22 h after induction. Invasive monitoring was performed on anesthetized animals to evaluate respiratory, cardiovascular, renal, hepatic and metabolic dysfunctions (PaO2/FiO2 ratio, mean arterial pressure, urea, AST/ALT ratio and lactate levels, respectively) based on the Rat Organ Failure Assessment (ROFA) score. The ratio of perfused vessels (PPV) of the ileal serosa was quantified with the intravital imaging technique. Complex I- and II-linked (CI; CII) oxidative phosphorylation capacities (OXPHOS) and mitochondrial membrane potential (ΔΨmt) were evaluated by High-Resolution FluoRespirometry (O2k, Oroboros, Austria) in liver biopsies. Plasma endothelin-1 (ET-1), IL-6, intestinal nitrotyrosine (NT) and xanthine oxidoreductase (XOR) activities were measured as inflammatory markers. Results: Sepsis was characterized by an increased ROFA score (5.3 ± 1.3 vs. 1.3 ± 0.7), increased ET-1, IL-6, NT and XOR levels, and decreased serosal PPV (65 ± 12% vs. 87 ± 7%), ΔΨmt and CI-CII-linked OXPHOS (73 ± 16 vs. 158 ± 14, and 189 ± 67 vs. 328 ± 81, respectively) as compared to controls. Both KYNA and SZR-72 reduced systemic inflammatory activation; KYNA treatment decreased serosal perfusion heterogeneity, restored PPV (85 ± 11%) and complex II-linked OXPHOS (307 ± 38), whereas SZR-72 improved both CI- and CII-linked OXPHOS (CI: 117 ± 18; CII: 445 ± 107) without effects on PPV 24 h after sepsis induction. Conclusion: Treatment with SZR-72 directly modulates mitochondrial respiration, leading to improved conversion of ADP to ATP, while administration of KYNA restores microcirculatory dysfunction. The results suggest that microcirculatory and mitochondrial resuscitation with KYNA or the synthetic analog SZR-72 might be an appropriate supportive tool in sepsis therapy.

The incidence, mortality and timing of Pneumocystis jiroveci pneumonia after hematopoietic cell transplantation: a CIBMTR analysis.

Pneumocystis jiroveci pneumonia (PJP) is associated with high morbidity and mortality after hematopoietic stem cell transplantation (HSCT). Little is known about PJP infections after HSCT because of the rarity of disease given routine prophylaxis. We report the results of a Center for International Blood and Marrow Transplant Research study evaluating the incidence, timing, prophylaxis agents, risk factors and mortality of PJP after autologous (auto) and allogeneic (allo) HSCT. Between 1995 and 2005, 0.63% allo recipients and 0.28% auto recipients of first HSCT developed PJP. Cases occurred as early as 30 days to beyond a year after allo HSCT. A nested case cohort analysis with supplemental data (n=68 allo cases, n=111 allo controls) revealed that risk factors for PJP infection included lymphopenia and mismatch after HSCT. After allo or auto HSCT, overall survival was significantly poorer among cases vs controls (P=0.0004). After controlling for significant variables, the proportional hazards model revealed that PJP cases were 6.87 times more likely to die vs matched controls (P<0.0001). We conclude PJP infection is rare after HSCT but is associated with high mortality. Factors associated with GVHD and with poor immune reconstitution are among the risk factors for PJP and suggest that protracted prophylaxis for PJP in high-risk HSCT recipients may improve outcomes.

Essential requirements for setting up a stem cell processing laboratory.

The Graft Processing subcommittee of the Worldwide Network for Blood and Marrow Transplantation wrote this guideline to assist physicians and laboratory technologists with the setting up of a cell processing laboratory (CPL) to support a hematopoietic stem cell transplant program, thereby facilitating the start-up of a transplant program in a new location and improving patient access to transplantation worldwide. This guideline describes the minimal essential features of designing such a laboratory and provides a list of equipment and supply needs and staffing recommendations. It describes the typical scope of services that a CPL is expected to perform, including product testing services, and discusses the basic principles behind the most frequent procedures. Quality management (QM) principles specific to a CPL are also discussed. References to additional guidance documents that are available worldwide to assist with QM and regulatory compliance are also provided.

Immune reconstitution after unrelated cord blood transplantation.

Over the past years unrelated cord blood transplant (UCBT) has emerged as an effective alternative to unrelated donor blood and marrow transplantation. However, despite several advantages, its success is limited by the high incidence of opportunistic infections (OI), most of which are viral. Infection-related mortality is the primary cause of death after UCBT with most deaths occurring in the first 3-6 months post transplant. For several months, until recovery of the thymus is restored to support de novo T cell generation, protective antiviral immunity depends on the activity of post-thymic T cells infused within the cord blood (CB) grafts. However, almost all CB T cells are antigen inexperienced (naïve) lymphocytes that have been functionally altered by placental factors to protect pregnancy. CB T cells need to undergo in vivo priming, Th1/Tc1 maturation, and peripheral expansion before they can afford immunologic protection. This article provides an overview of what is currently known regarding the reconstitution of adaptive immunity following UCBT including our own data from prospective analyses of pediatric cohorts. Remarkable immunophenotypic changes are notable already in the first 2-3 weeks post-UCBT. These changes result from apparent 'homeostatic' peripheral T cell expansion in the lymphopenic environment. While we can identify patient- and graft-specific predictive factors, the concordant emergence of T cell subsets displaying the phenotype of Th1/Tc1 cytotoxic effector cells can be statistically linked to those UCBT recipients who will subsequently develop viral and other opportunistic infections. Antigen presenting dendritic cell reconstitution may also reflect alterations in immunocompetence due to OI and/or GVHD.

Combination treatment of bullous pemphigoid with anti-CD20 and anti-CD25 antibodies in a patient with chronic graft-versus-host disease.

In this case report we describe a novel treatment with two chimeric monoclonal antibodies (MoAb) targeting the autoimmune B cell clone responsible for bullous pemphigoid (BP) as a manifestation of steroid refractory chronic graft-versus-host disease (GVHD) that developed after unrelated cord blood transplantation. Monitoring the BP-specific circulating antibodies and CD25-expressing activated T lymphocyte subset led us to combine anti-CD20 (Rituximab) mediated B cell ablation with anti-CD25 (Daclizumab) therapy to block CD4(+) T cell help. Complete clinical and serologic response was achieved within 4 weeks of initiation of therapy allowing global immunosuppression to be dramatically reduced.

Graft-versus-leukemia-induced complete remission following unrelated umbilical cord blood transplantation for acute leukemia.

A 15-year-old female received an unrelated three of six HLA antigen matched umbilical cord blood (UCB) transplant for refractory, relapsed T-cell ALL. Conditioning consisted of TBI, melphalan, and anti-thymocyte globulin (ATG), with cyclosporin A (CsA) and solumedrol for GVHD prophylaxis. She engrafted and a day 34 bone marrow aspirate showed 100% donor cells and no evidence of leukemia. The post-transplant course was complicated by mild grade I acute GVHD involving skin, and limited chronic GVHD of the gut which resolved with the addition of 1 mg/kg/day of steroids to her CsA prophylaxis. One hundred and ninety days after transplantation the patient developed pancytopenia and was subsequently found to have a leukemic relapse. Immunosuppression was discontinued and she was started on G-CSF and erythropoietin. Moderate skin and gut GVHD developed which was treated with both topical and low-dose oral steroids. Over the next few weeks she became transfusion independent and a follow-up bone marrow aspirate showed complete remission. She continued in complete remission for 4 months, at which time localized leukemic relapse was found in a soft tissue breast mass in spite of continued bone marrow remission. While the patient ultimately died of progressive disease, this case demonstrates that mismatched UCB in conjunction with G-CSF is capable of generating a GVL effect that can induce a complete remission.

Comparison of immune reconstitution after unrelated and related T-cell-depleted bone marrow transplantation: effect of patient age and donor leukocyte infusions.

Unrelated bone marrow transplantation (BMT) is often complicated by fatal opportunistic infections. To evaluate features unique to immune reconstitution after unrelated BMT, the lymphoid phenotype, in vitro function, and life-threatening opportunistic infections after unrelated and related T-cell-depleted (TCD) BMT were analyzed longitudinally and compared. The effects of posttransplant donor leukocyte infusions to treat or prevent cytomegalovirus (CMV) or Epstein-Barr virus (EBV) infections on immune reconstitution were also analyzed. This study demonstrates that adult recipients of TCD unrelated BMTs experience prolonged and profound deficiencies of CD3(+), CD4(+), and CD8(+) T-cell populations when compared with pediatric recipients of unrelated BMT and adults after related BMT (P <.01), that these adults have a significantly increased risk of life-threatening opportunistic infections, and that the rate of recovery of CD4 T cells correlates with the risk of developing these infections. Recovery of normal numbers of CD3(+), CD8(+), and CD4(+) T-cell populations is similar in children after related or unrelated BMT. This study also demonstrates that adoptive immunotherapy with small numbers of unirradiated donor leukocytes can be associated with rapid restoration of CD3(+), CD4(+), and CD8(+) T-cell numbers, antigen-specific T-cell responses, and resolution of CMV- and EBV-associated disease after unrelated TCD BMT.

T-cell-depleted allogeneic bone marrow transplantation as postremission therapy for acute myelogenous leukemia: freedom from relapse in the absence of graft-versus-host disease.

Thirty-one consecutive patients with acute myelogenous leukemia (AML) in first complete remission and 8 with AML in second complete remission received T cell-depleted allogeneic bone marrow transplants from HLA-identical sibling donors. Patients received myeloablative cytoreduction consisting of hyperfractionated total body irradiation, thiotepa, and cyclophosphamide. Those patients at risk for immune-mediated graft rejection received additional immune suppression with antithymocyte globulin and methylprednisolone in the early peritransplant period. Patients with AML who underwent allogeneic T-cell-depleted bone marrow transplantations (BMT) in first or second remission have achieved respective disease-free survival (DFS) probabilities of 77% (median follow-up at approximately 56 months) and 50% (median follow-up at approximately 48 months). Ten of 31 patients transplanted in first remission were > or = 40 years old and have attained a DFS at 4 years of 70%. For patients with AML transplanted in first or second remission, the respective cause-specific probabilities of relapse were 3.2% or 12.5%, and those of nonleukemic mortality were 19.4% or 37.5%. There were no cases of immune-mediated graft rejection and no cases of grade II to IV acute graft-versus-host disease (GVHD). All survivors enjoy Karnofsky performance scores (KPS) of 100%, except 2 patients with KPS of 80% to 90%. T-cell-depleted allogeneic BMT can provide durable DFS together with an excellent performance status in the majority of patients with de novo AML. In addition, GVHD is not an obligatory correlate of the graft-versus-leukemia benefit or freedom from relapse afforded by allogeneic BMT administered as postremission therapy for AML. This study provides a basis for prospective comparison with other postremission therapies considered standard in the management of patients with this disease.

Retrovirally transduced human dendritic cells express a normal phenotype and potent T-cell stimulatory capacity.

Dendritic cells are attractive candidates for vaccine-based immunotherapy because of their potential to function as natural adjuvants for poorly immunogenic proteins derived from tumors or microbes. In this study, we evaluated the feasibility and consequences of introducing foreign genetic material by retroviral vectors into dendritic cell progenitors. Proliferating human bone marrow and cord blood CD34+ cells were infected by retroviral vectors encoding the murine CD2 surface antigen. Mean transduction efficiency in dendritic cells was 11.5% from bone marrow and 21.2% from cord blood progenitors. Transduced or untransduced dendritic cell progeny expressed comparable levels of HLA-DR, CD83, CD1a, CD80, CD86, S100, and p55 antigens. Granulocytes, macrophages, and dendritic cells were equally represented among the transduced and mock-transduced cells, thus showing no apparent alteration in the differentiation of transduced CD34+ precursors. The T-cell stimulatory capacity of retrovirally modified and purified mCD2-positive allogeneic or nominal antigen-pulsed autologous dendritic cells was comparable with that of untransduced dendritic cells. Human CD34+ dendritic cell progenitors can therefore be efficiently transduced using retroviral vectors and can differentiate into potent immunostimulatory dendritic cells without compromising their T-cell stimulatory capacity or the expression of critical costimulatory molecules and phenotypic markers. These results support ongoing efforts to develop genetically modified dendritic cells for immunotherapy.

Growth and differentiation of human dendritic cells from CD34+ progenitors.

Human dendritic cells can be generated from bone marrow CD34+ progenitors in the presence of GM-CSF and TNF alpha. The addition of a factor like c-kit-ligand optimizes the expansion of dendritic cells, as well as the other myeloid progeny grown under the same conditions, and facilitates their identification and characterization. In contrast to cord blood, where dendritic cells account for the majority of the class II MHC positive myeloid progeny, bone marrow CD34(+)-derived dendritic cells are less frequent than macrophages. When mature macrophages are depleted from days 5-6 cultures, terminally differentiated CD14+ HLA-DR dendritic cells as well as non-monocyte/macrophage CD14+ HLA-DR+ cells can be distinguished. The latter are post-CFU, bipotential, intermediate precursors that can terminally differentiate into either dendritic cells or macrophages depending on subsequent cytokine exposure. Human CD34+ progenitors isolated from bone marrow, as well as cord and peripheral blood, include CFU-DC that give rise to pure dendritic cell colonies in the combined presence of GM-CSF and TNF alpha. The different sources of CD34+ progenitors are not equivalent, however, with respect to frequency of CFU-DC growth. Cord blood is relatively enriched for dendritic cell progenitors. The developmental relationship of CFU-DC and CFU-GM, to the early developing dendritic cells and the bipotential intermediates observed in suspension culture, is not yet established.

Dendritic cells and macrophages can mature independently from a human bone marrow-derived, post-colony-forming unit intermediate.

CD34+ precursors in normal human bone marrow (BM) generate large numbers of dendritic cells alongside macrophages and granulocytic precursors when cultured for 12 to 14 days in c-kit ligand, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha (TNF-alpha). This study reports an intermediate cell type that develops by day 6, and has the potential to differentiate into either macrophages or dendritic cells. When the d6 progeny are depleted of mature macrophages and residual CD34+ precursors, a discrete CD14+ HLA-DR+ population persists in addition to immunostimulatory CD14- HLA-DR() dendritic cells. Half of the CD14+ HLA-DR+ population is in cell cycle (Ki-67+), but colony-forming units (CFUs) are no longer detectable. The calls are c-fms+, but lack myeloperoxidase and nonspecific esterase. They also possess substantial phagocytic and allostimulatory activity. These post-CFU, CD14+ HLA-DR+ intermediates develop into typical macrophages when recultured in the absence of exogenous cytokines. M-CSF supports up to approximately 2.5-fold expansion of macrophage progeny. In contrast, the combination of GM-CSF and TNF-alpha supports quantitative differentiation into dendritic cells, lacking c-fms, CD14, and other macrophage properties, and expressing HLA-DR, CD1a, CD83, CD80, CD86, and potent allostimulatory activity. Therefore, normal CD34+ BM precursors can generate a post-CFU bipotential intermediate in the presence of c-kit ligand, GM-CSF, and TNF-alpha. This intermediate cell type will develop along the dendritic cell pathway when macrophages are removed and GM-CSF and TNF-alpha are provided. Alternatively, it can differentiate along a macrophage pathway when recultured with or without M-CSF.

Identification of dendritic cell colony-forming units among normal human CD34+ bone marrow progenitors that are expanded by c-kit-ligand and yield pure dendritic cell colonies in the presence of granulocyte/macrophage colony-stimulating factor and tumor necrosis factor alpha.

Several cytokines, especially granulocyte/macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor alpha (TNF-alpha), have been identified that foster the development of dendritic cells from blood and bone marrow precursors in suspension cultures. These precursors are reported to be infrequent or to yield small numbers of dendritic cells in colony-forming assays. Here we readily identify dendritic cell colony-forming units (CFU-DC) that give rise to pure dendritic cell colonies. Human CD34+ bone marrow progenitors were expanded in semi-solid cultures with serum-replete medium containing c-kit-ligand, GM-CSF, and TNF-alpha. The addition of TNF-alpha to GM-CSF did not alter the number of typical GM colonies but did generate pure dendritic cell colonies that accounted for approximately 40% of the total colony growth. When the two distinct types of colonies were plucked from methylcellulose and tested for T cell-stimulatory activity in the mixed leukocyte reaction, the potency of colony-derived dendritic cells exceeded that of CFU-GM progeny from the same cultures by at least 1.5-2 logs. Immunophenotyping and cytochemical staining of the CFU-DC-derived progeny was also characteristic of dendritic cells. Other myeloid cells were not identified in these colonies. The addition of c-kit-ligand to GM-CSF- and TNF-alpha-supplemented suspensions of CD34+ bone marrow cells expanded CFU-DCs almost 100-fold by 14 d. We conclude that normal human CD34+ bone marrow cells include substantial numbers of clonogenic progenitors, distinct from CFU-GMs, that can give rise to pure dendritic cell colonies. These CFU-DCs can be expanded for several weeks by in vitro culture with c-kit-ligand, and their differentiation requires exogenous TNF-alpha in addition to GM-CSF. We speculate that this dendritic cell-committed pathway may in the steady state contribute cells to the epidermis and afferent lymph, where dendritic cells are the principal myeloid cell type, and may increase the numbers of these specialized antigen-presenting cells during T cell-mediated immune responses.

Expansion of immunostimulatory dendritic cells among the myeloid progeny of human CD34+ bone marrow precursors cultured with c-kit ligand, granulocyte-macrophage colony-stimulating factor, and TNF-alpha.

Human CD34+ bone marrow progenitors cultured in the presence of granulocyte-macrophage CSF (GM-CSF) develop along a myeloid pathway, and the addition of exogenous TNF-alpha leads to the differentiation of dendritic cells among the myeloid progeny. These bone marrow CD34+ -derived dendritic cell that develop during 2-wk culture have the same morphologic, phenotypic, and functional properties that distinguish mature dendritic cells in blood. c-kit ligand does not directly influence dendritic cell differentiation per se, but rather increases the total cell number in synergistic combination with GM-CSF and TNF-alpha. This degree of expansion translates into an effective yield of approximately 1.7 x 10(6) mature dendritic cells per single ml of normal adult human bone marrow, compared with approximately 10(6) dendritic cells usually obtained from 450 to 500 ml of peripheral blood. In addition to dendritic cells that constitute approximately 10 to 15% of the total myeloid progeny, the cultures contain monocytes/macrophages and intermediate granulocytic precursors. Monocytes/macrophages and dendritic cells together comprise all of the class II MHC-positive progeny. Sorted cells bearing the CD14+ HLA-DR+ phenotype of mature monocytes are at least 1.5 to 2 logs less active than CD14- HLA-DR+ dendritic cells as stimulators in the allogeneic MLR, even though both CD14+ and CD14- subpopulations share expression of several costimulatory ligands. The synergistic combination of c-kit ligand, GM-CSF, and TNF-alpha therefore expands substantial numbers of immunostimulatory CD14- HLA-DR+ dendritic cells from defined CD34+ progenitors in human bone marrow. This should facilitate the use of dendritic cells in the manipulation of T cell-mediated immune responses.

Progenitor recruitment and in vitro expansion of immunostimulatory dendritic cells from human CD34+ bone marrow cells by c-kit-ligand, GM-CSF, and TNF alpha.

Several cytokines have been identified that support the development of dendritic cells from murine and human precursor populations, most notably GM-CSF, TNF alpha, and IL-4. We have been interested in human bone marrow as a source of defined CD34+ progenitors to generate large numbers of autologous dendritic cells for use as adjuvants in immune based therapy. In serum-replete conditions with c-kit-ligand, GM-CSF, and TNF alpha, dendritic cells constitute approximately 10-15% of the myeloid progeny (equivalent to approximately 1.7 x 10(6) dendritic cells per single ml of starting bone marrow); and they develop together with granulocytic intermediates and monocytes in the same cultures. CD14- dendritic cells share expression of class II MHC and costimulatory ligands with CD14+ monocyte progeny, but only the CD14- HLA-DR+ dendritic cells are highly stimulatory of resting unprimed T cells. We have further identified a novel colony that develops in the presence of GM-CSF and TNF alpha alongside typical CFU-GM, which is comprised of dendritic cells mixed with < or = 15% monocytes (CFU-DC/mono). c-kit-ligand recruits and expands early progenitors responsive to the dendritic cell-differentiating effects of GM-CSF and TNF alpha, effecting a 100- to 1000-fold greater expansion of CFU-DC/mono by 14d and 21d respectively than does the combination of GM-CSF and TNF alpha without c-kit-ligand.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of endogenous and synthetic sex steroids on the clearance of antibody-coated cells.

Steroid hormones may influence the clinical expression of immunologic disease; however, their mechanism of action is uncertain. By using an experimental model, we studied the effect of sex steroids on the clearance of antibody-coated cells by macrophages in the spleen and liver. Progesterone significantly inhibited the clearance of IgG-coated E by splenic macrophages, whereas no effect was observed on the clearance of heat-altered E. This effect of progesterone was observed at serum concentrations which are attained during human pregnancy and the menstrual cycle. Furthermore, when splenic macrophages were isolated from progesterone-treated animals, they expressed decreased Fc gamma R activity. In addition, structural analogs of progesterone which have diminished glucocorticoid and progesterone activity retained this effect on macrophage Fc gamma R. In contrast, the estrogens estradiol and estriol as well as a structural estrogen analog with minimal estrogenic activity, 1,3,5(10)-estratrien-3,16 beta-diol, enhanced splenic macrophage Fc gamma R-dependent clearance. This action of estradiol could be partially inhibited by the antiestrogen tamoxifen. However, estradiol did not affect the C3-dependent clearance of IgM-coated E by hepatic macrophages. Concurrent administration of estradiol and progesterone demonstrated that the action of estradiol was predominant. These studies indicate that sex steroids alter splenic macrophage Fc gamma R function in vivo. This result may explain the alteration of disease activity in some human immunologic disorders during changes in hormonal state. Furthermore, analogs of progesterone and estrogen, as well as antiestrogens, which minimally affect the sex organs, retain the ability to alter splenic macrophage Fc gamma R function.