Biomedical subjects

R P Kimberly

Publications and source records attributed to R P Kimberly.

At least 19 recordsLinked to original sources

PubMed1996

Fc gamma RIIA alleles are heritable risk factors for lupus nephritis in African Americans.

Allelic variants of Fc gamma R confer distinct phagocytic capacities providing a mechanism for heritable susceptibility to immune complex disease. Human Fc gamma RIIa has two codominantly expressed alleles, R131 and H131, which differ substantially in their ability to ligate human IgG2. The Fc gamma RIIa-H131 is the only human Fc gamma R which recognizes IgG2 efficiently and optimal IgG2 handling occurs only in the homozygous state. Therefore, since immune complex clearance is essential in SLE, we hypothesized that Fc gamma RIIA genes are important disease susceptibility factors for SLE, particularly lupus nephritis. In a two-stage cross-sectional study, we compared the distribution of Fc gamma RIIA alleles in African Americans with SLE to that in African American non-SLE controls. A pilot study of 43 SLE patients and 39 controls demonstrated a skewed distribution of Fc gamma RIIA alleles, with only 9% of SLE patients homozygous for Fc gamma RIIa-H131 compared with 36% of controls (odds ratio, 0.18; 95% CI, 0.05-0.69, P = 0.009). This was confirmed with a multicenter study of 214 SLE patients and 100 non-SLE controls. The altered distribution of Fc gamma RIIA alleles was most striking in lupus nephritis. Trend analysis of the genotype distribution showed a highly significant decrease in Fc gamma RIIA-H131 as the likelihood for lupus nephritis increased (P = 0.0004) consistent with a protective effect of the Fc gamma RIIA-H131 gene. The skewing in the distribution of Fc gamma RIIA alleles identifies this gene as a risk factor with pathophysiologic importance for the SLE diathesis in African Americans.

Alleles↗

PubMed1995

The Ca2+ dependence of human Fc gamma receptor-initiated phagocytosis.

Differing roles for [Ca2+]i transients in Fc gamma R-mediated phagocytosis have been suggested based on the observations that antibody-opsonized erythrocyte phagocytosis by human neutrophils shows a [Ca2+]i dependence, while that by murine macrophages appears [Ca2+]i-independent. To explore whether this difference might reflect different receptor isoforms or different cell types, we studied the [Ca2+]i dependence of receptor-initiated phagocytosis by human Fc gamma RIIa and a panel of Fc gamma RIIa cytoplasmic domain mutants expressed in murine P388D1 cells and by human Fc gamma R endogenously expressed on human neutrophils and monocytes. Wild-type and point mutants of huFc gamma RIIa stably transfected into murine P388D1 cells have different capacities to initiate a [Ca2+]i transient, which are closely correlated with quantitative phagocytosis (r = 0.94, p < 0.0001). Phagocytosis both by huFc gamma RIIa in P388D1 cells and by huFc gamma RIIa endogenously expressed on neutrophils and blood monocytes shows [Ca2+]i dependence. Phagocytosis of antibody-opsonized erythrocytes by neutrophils demonstrated greater susceptibility to [Ca2+]i quenching compared with Fc gamma RIIa-specific internalization with E-IV.3, suggesting that the phagocytosis activating property of Fc gamma RIIIb in neutrophils also engages a [Ca2+]i-dependent element. In contrast, phagocytosis by human Fc gamma RIa, endogenously expressed on blood monocytes, is [Ca2+]i-independent. Despite the importance of a consensus tyrosine activation motif for both receptors, Fc gamma RIa and Fc gamma RIIa engage at least some distinct signaling elements to initiate phagocytosis. The recognition that both of the phagocytic receptors on murine macrophages and human Fc gamma RIa associate with the Fc epsilon RI gamma-chain, which contains a tyrosine activation motif distinct from that in the Fc gamma RIIa cytoplasmic domain, suggests that [Ca2+]i-independent phagocytosis is a property associated with the utilization of gamma-chains by Fc gamma R.

Amino Acid Sequence↗

PubMed1995

Receptors for immunoglobulin G. Molecular diversity and implications for disease.

Our knowledge about human Fc gamma receptors has increased dramatically within the last several years. Their structural diversity presents a rich framework within which to understand how immunoglobulins and immunoglobulin complexes activate such a broad range of cell programs relevant to autoimmune diseases. Alleles of Fc gamma receptors provide a new perspective within which to define the interplay between the qualitative and quantitative humoral immune response and host genotype and to identify heritable risk factors for disease susceptibility. With recent insights into the role of Fc gamma receptors in the pathophysiology of inflammatory lesions, we can also anticipate important advances in therapeutic intervention.

Animals↗

PubMed1995

Fc gamma receptor IIIb enhances Fc gamma receptor IIa function in an oxidant-dependent and allele-sensitive manner.

Two classes of receptors for IgG, Fc gamma RIIa and Fc gamma RIIIb, both of which exist in two allelic forms, are expressed on human neutrophils. Neutrophils from normal donors, homozygous for the different allelic phenotypes of Fc gamma RIIIb, have significantly different levels of Fc gamma receptor-mediated phagocytosis of IgG-opsonized erythrocytes (EA). However, the observation that Fc gamma RIIIb mediates phagocytosis of specific mAb-targeted erythrocytes poorly suggests that this receptor may influence EA internalization by Fc gamma RIIa in an allele-sensitive fashion. Donors homozygous for the NA1 allele of Fc gamma RIIIb showed greater activation of Fc gamma RIIa after Fc gamma RIIIb cross-linking than donors homozygous for the NA2 allele of Fc gamma RIIIb. This increase in receptor-specific internalization reflects both an increase in ligand binding by Fc gamma RIIa and an increase in internalization efficiency of targets bound. Activation of Fc gamma RIIa by Fc gamma RIIIb is transferable by supernatants from activated cells and is blocked by inhibitors of reactive oxygen species and the H2O2-myeloperoxidase-chloride system and by serine protease inhibitors. Thus, cross-linking of Fc gamma RIIIb, which leads to neutrophil degranulation and the generation of reactive oxygen intermediates, in turn alters Fc gamma RIIa avidity and efficiency. These oxidant-mediated changes in Fc gamma RIIa function provide a novel mechanism for receptors to collaborate in both an autocrine and paracrine fashion. The allele sensitivity of these effects suggests that Fc gamma receptor polymorphisms may be inherited disease susceptibility factors in host defense against infection and in the development of autoimmunity.

Adult↗

PubMed1994

Anti-neutrophil cytoplasmic antibodies engage and activate human neutrophils via Fc gamma RIIa.

The presence of anti-neutrophil cytoplasmic Abs (ANCA) in many patients with systemic vasculitis suggests that ANCA may play a role in disease pathogenesis. Neutrophils from patients with Wegener's granulomatosis often express ANCA target Ags (myeloperoxidase (MPO) and proteinase 3 (PR3)) on their surface, making these intracellular primary granule enzymes accessible to these autoantibodies. Similarly, normal neutrophils can be induced to translocate MPO and PR3 to the cell surface in vitro, and we demonstrate that murine mAb ANCA IgG, but not IgM, binds to the ANCA target and engages the Fc gamma RIIa ligand-binding site on the surface of human neutrophils. In contrast to ANCA IgM, ANCA IgG also induces an oxidative burst in neutrophils (oxidation of dihydrorhodamine = 91 +/- 15 fluorescence units with anti-PR3 IgG vs 17 +/- 2 with anti-PR3 IgM, p < 0.001). Blockade of the ligand-binding site of Fc gamma RIIa with an antibinding site mAb Fab significantly reduces this ANCA IgG-triggered production of reactive oxygen species (p < 0.01). Similarly, human ANCA bind the ANCA target, engage Fc gamma RIIa, and induce an oxidative burst in neutrophils. The allelic phenotype of Fc gamma RIIa strongly influences the Fc gamma receptor engagement by ligand, and Fc gamma RIIa homozygous donors differ by more than threefold in the quantitative production of reactive oxygen intermediates (ROI) (p < 0.01). Thus, engagement of Fc gamma RIIa by the Fc region of ANCA is one mechanism by which these autoantibodies activate receptor-mediated signal transduction systems in human neutrophils to initiate programs of inflammation and tissue injury. Fc gamma receptor alleles may represent heritable disease risk factors influencing the magnitude of such a process.

Antibodies, Antineutrophil Cytoplasmic↗

PubMed1994

Modulation of Fc gamma and complement receptor function by the glycosyl-phosphatidylinositol-anchored form of Fc gamma RIII.

Human neutrophils express two structurally distinct receptors for IgG, the transmembrane Fc gamma RII (CD32) and the glycosyl-phosphatidylinositol-linked Fc gamma RIII (CD16). To explore the respective functional roles of Fc gamma RII and Fc gamma RIII, we have used anti-receptor mAb fragments coupled with erythrocytes to quantify both individual and cooperative receptor functions. With individual receptor engagement, Fc gamma RII (E-IV.3) was much more efficient than Fc gamma RIIIB (E-3G8) in initiating phagocytosis (p < 0.001). However, when identical total numbers of receptors were engaged, co-ligation of Fc gamma RII and Fc gamma RIIIB resulted in a phagocytic response, which was: 1) greater than that for either receptor alone (> twofold Fc gamma RII alone (p < 0.001) and > 20-fold Fc gamma RIIIB alone (p < 0.001)); 2) greater than the sum of Fc gamma RII and Fc gamma RIIIB (p < 0.001); and 3) comparable to the phagocytic potential of Fc gamma RII in FMLP pre-activated neutrophils. This synergistic capacity of Fc gamma RIIIB also enabled CR phagocytosis. Furthermore, the capacity for Fc gamma RIIIB to interact synergistically with Fc gamma RII was preserved in FMLP-preactivated neutrophils. The activation of Fc gamma RII by Fc gamma RIIIB was associated with tyrosine phosphorylation of the Fc gamma RII cytoplasmic domain, which is essential for Fc gamma RII function and which, by analogy to the Ig alpha-chain of the B cell Ag receptor complex, the zeta-chain of CD3, and the gamma-chain of some Fc epsilon Rs and Fc gamma Rs, may enhance the binding and activation of Src or Syk family tyrosine kinases. Thus, Fc gamma RIIIB can affect multiple receptor families and play a role in achieving maximal Fc gamma R capacity, even in stimulated neutrophils in inflammatory sites.

Antibodies, Monoclonal↗

PubMed1994

Glucocorticoids.

Despite the continuing debate about the risks and benefits of glucocorticoid, their central role in the therapeutic armamentarium remains undisputed. Studies continue to unravel the complexity of their biologic effects on gene transcription, and careful clinical observation refines their therapeutic use. Although cloaked in controversy, some recent highlights include the possibility that high-dose intravenous methylprednisolone may affect the development of multiple sclerosis, the suggestion that prednisone may have little efficacy in the management of high-risk pregnancy in patients with antiphospholipid antibodies, and several observations that administration of calcium and vitamin D prevents bone loss in patients receiving steroids.

Animals↗

PubMed1994

The high affinity Fc gamma receptor (CD64) induces phagocytosis in the absence of its cytoplasmic domain: the gamma subunit of Fc gamma RIIIA imparts phagocytic function to Fc gamma RI.

The high affinity Fc gamma receptor, Fc gamma RI, is unique among the three classes of macrophage Fc gamma receptors not only in its affinity for IgG, but also in the structure of its cytoplasmic domain. Fc gamma RIIA and the gamma subunit of Fc gamma RIIIA have tyrosine-containing motifs within their cytoplasmic domains that are phosphorylated when crosslinked and that are required for phagocytosis by COS-1 cell transfectants. In contrast to these other Fc gamma receptors, Fc gamma RI does not contain cytoplasmic tyrosines and does not induce phagocytosis in COS-1 transfectants. We transfected wild-type (WT) and mutant (MT) Fc gamma RI lacking the cytoplasmic domain into COS-1 cells and murine macrophages and assessed phagocytosis using IgG-coated red blood cells (RBCs) and RBCs conjugated with Fab anti-human Fc gamma RI monoclonal antibody (mAb). Fc gamma RI, in contrast to Fc gamma RIIA, did not induce phagocytosis in COS cells. However, both WT and MT Fc gamma RI induced phagocytosis in murine macrophages, and phagocytosis was inhibited by the tyrosine kinase inhibitor tyrphostin 23. Human monocytes also phagocytosed Fc gamma RI-targeted RBCs, and activation of Fc gamma RI on monocytes with Fab anti-Fc gamma RI induced phosphorylation of Fc gamma RII on tyrosine residues. However, Fc gamma RI activation of Fc gamma RI-Fc gamma RIIA COS-1 cotransfectants did not induce tyrosine phosphorylation of Fc gamma RIIA, and coexpression of Fc gamma RI and Fc gamma RIIA in COS cells did not confer Fc gamma RI phagocytic capability. In contrast, coexpression in COS-1 cells of Fc gamma RI with the gamma subunit of Fc gamma RIIIA conferred phagocytic function to both Fc gamma RI and the MT Fc gamma RI lacking the cytoplasmic domain. Thus, Fc gamma RI does not require its cytoplasmic domain to mediate a phagocytic signal and interacts with the gamma subunit of Fc gamma RIIIA to induce phagocytosis.

Animals↗

PubMed1993

Human mononuclear phagocytes express adenosine A1 receptors. A novel mechanism for differential regulation of Fc gamma receptor function.

Using monoclonal anti-adenosine A1 receptor antibodies that bind the A1 receptor ligand binding site, we demonstrate that A1 receptors are expressed on cultured monocytes and rheumatoid synovial fluid mononuclear phagocytes. This finding is associated with the acquisition of reactivity with selective adenosine A1 receptor agonists and is temporally coordinated with the induction of adenosine A2 receptors on cultured monocytes. In a rapid, concentration-dependent fashion, these two distinct adenosine receptors modulate Fc gamma receptor-mediated phagocytosis, a response critical to the pathogenesis of immune complex diseases. Occupancy of A1 receptors by N6-cyclopentyladenosine (an A1-specific adenosine analogue) or mAb AA1 (an anti-A1 mAb) results in a potent stimulation that is blocked by adenosine receptor antagonists. This A1 receptor-induced enhancement of Fc gamma receptor-mediated phagocytosis is a consequence of preferential augmentation of Fc gamma RI function, suggesting distinct mechanisms for receptor-effector coupling of Fc gamma receptor families. In contrast, ligation of A2 receptors by A2-specific agonists decreases Fc gamma receptor-mediated phagocytosis in cultured monocytes. The opposing effects of adenosine A1 and A2 receptors allow for a concentration-dependent feed-back loop that responds more rapidly than effects elicited by other endogenous modulators. Low concentrations of adenosine are proinflammatory providing enhanced Fc gamma receptor function via A1 receptors, whereas higher concentrations that can occur with tissue damage are anti-inflammatory providing inhibition via A2 receptors. This rapid and potent modulation of Fc gamma receptor-mediated function suggests that adenosine is an important local regulator of the inflammatory response.

Adenosine↗

PubMed1992

Receptor specific probes for the study of Fc gamma receptor specific function.

Human leukocytes express three distinct families of receptors for the Fc region of IgG (Fc gamma R). We have prepared erythrocytes (E) coated with monoclonal anti-Fc gamma R antibodies for the study of receptor specific phagocytosis using biotin and streptavidin. In this technique, both the E and the monoclonal antibody (mAb) are biotinylated and coupling of the mAb to the E occurs through the use of streptavidin. The same biotin/streptavidin principle was used to prepare E coated with human IgG. Using this technique, receptor specific probes or probes coated with natural ligand (IgG) can be prepared rapidly with the use of small amounts of mAb or IgG. Finally, we have used these receptor specific probes to demonstrate that all three families of Fc gamma R (Fc gamma RI, Fc gamma RII and Fc gamma RIII) expressed on human monocytes and human macrophages are phagocytic receptors.

Antibodies, Monoclonal↗

PubMed1992

Functional characterization of non-human primate erythrocyte immune adherence receptors: implications for the uptake of immune complexes by the cells of the mononuclear phagocytic system.

Erythrocytes from primates express an immune adherence (IA) receptor that binds complement-opsonized immune complexes (IC) both in vivo and in vitro. We have analyzed the immunochemical and functional properties of the IA receptor from erythrocytes from species that have been used for in vivo IC clearance studies and have compared these properties to the human IA receptor (which is called complement receptor type 1, CR1). Erythrocytes from all species (chimpanzee, baboon, rhesus and cynomolgus monkey) bind antibody/double-stranded DNA IC when opsonized with autologous complement. However, IC which are bound to chimpanzee erythrocytes are not released upon addition of chimpanzee serum (which contains factor I activity), while IC bound to baboon erythrocytes and human erythrocytes are released upon addition of autologous serum. Anti-human CR1 monoclonal antibodies (mAb) E11 and HB8592 bind to erythrocytes from all species examined and the number of mAb epitopes per erythrocyte correlated with the number of IC that could bind to the erythrocyte under saturating conditions. However, a number of interesting differences between the species are observed with other mAb. The anti-CR1 mAb 1B4 and 3D9, which block recognition of ligand by CR1, did not bind to chimpanzee erythrocytes and bound partially to rhesus and cynomolgus monkey erythrocytes. In addition, the ability of autologous serum to induce release of erythrocyte-bound IC correlates with the presence of these epitopes. These findings, taken in context with previous clearance studies, suggest that serum-mediated release may not be required for the rapid transfer of the IC from the erythrocyte to the mononuclear phagocytic system.

Animals↗

PubMed1992

Functional capacity of Fc gamma receptor III (CD16) on human neutrophils.

Receptors for the Fc region of immunoglobulin G (IgG) are a structurally diverse group of molecules. Within the three Fc gamma R families (Fc gamma RI, Fc gamma RII and Fc gamma RIII), the presence of distinct genes and alternative splicing variants leads to a variety of receptor isoforms that are most strikingly different in the transmembrane and intracellular regions. An obvious example of structural variation in the transmembrane and cytoplasmic domains is observed in the Fc gamma RIII family. Fc gamma RIIIB, which is nearly identical to Fc gamma RIIIA in the extracellular domains, lacks both transmembrane and cytoplasmic protein domains and is anchored to the cell through a glycosyl phosphatidylinositol anchor. Analysis of Fc gamma RIII function presents a considerable challenge in understanding the role of different Fc gamma R receptors in polymorphonuclear neutrophil (PMN) function. While one hypothesis for the role of Fc gamma RIII in Fc gamma R-dependent PMN effector functions is that Fc gamma RIII serves as a binding molecule which focuses the IgG ligand for more efficient recognition and intracellular signaling by Fc gamma RII, recent observations from a number of laboratories suggest that Fc gamma RIII on PMN can transduce signals across the membrane independent of ligand-dependent engagement of Fc gamma RII. We will review these data and present recent data which suggest that the role of Fc gamma RIII extends beyond direct initiation of functions to a more complex role of synergistic receptor interactions. These findings will be reviewed in the context of the experimental approaches that have been used to examine the roles of Fc gamma RII and Fc gamma RIII on PMN function.

Antibodies, Monoclonal↗

PubMed1992

Glucocorticoid therapy for rheumatic diseases.

Glucocorticoids are an essential therapeutic agent in the management of many inflammatory, autoimmune, and other rheumatic diseases. Perhaps because of their remarkable potency and widespread use, the literature on steroid treatment has tended to be rather anecdotal. Nonetheless, new information, both on the mechanism of action and on the clinical application, continues to become available. The complexity of the biology of steroid-receptor engagement and gene regulation is unraveling, and carefully designed clinical studies are helping to refine clinical application. However, for the clinician, the need for careful observation and sound judgment with glucocorticoid use remains critically important.

Glucocorticoids↗

PubMed1992

Allelic polymorphisms of human Fc gamma receptor IIA and Fc gamma receptor IIIB. Independent mechanisms for differences in human phagocyte function.

Two different allelic polymorphisms among the isoforms of human Fc gamma receptors have been defined: the low-responder (LR)-high-responder (HR) polymorphism of huFc gamma RIIA expressed on both PMN and monocytes and the NA1-NA2 polymorphism of the neutrophil Fc gamma RIII (huFc gamma RIIIB). To address the issues of whether the LR-HR polymorphism has a significant impact on Fc gamma R-mediated functions in human blood cells and whether any differences in LR-HR might be related to higher Fc gamma R-mediated phagocytosis in NA1 donors, we examined Fc gamma R-specific binding and internalization by donors homozygous for the two huFc gamma RIIA alleles. PMN from LR homozygotes showed consistently higher levels of internalization of erythrocytes opsonized with pooled human IgG (E-hIgG). The absence of an LR-HR phagocytic difference with erythrocytes opsonized with either anti-Fc gamma RIIA MAb IV.3 or rabbit IgG, as opposed to E-hIgG, suggested that the Fc piece of the opsonin might be important for this LR-HR difference. Accordingly, we studied HR and LR homozygotes with human IgG subclass-specific probes. Both PMN (independent of huFc gamma RIIIB phenotype) and monocytes from LR donors bound and internalized erythrocytes coated with human IgG2 (E-hIgG2) efficiently, whereas phagocytes from HR donors did so poorly. E-hIgG2 internalization was completely abrogated by blockade of the ligand binding site of huFc gamma RIIA with IV.3 Fab, indicating that huFc gamma RIIA is essential for the handling of hIgG2 and that the mechanism of the LR-HR phagocytic difference is at the level of ligand binding to huFc gamma RIIA. In contrast, the difference in internalization of E-hIgG between NA1 and NA2 homozygous donors was independent of the huFc gamma RIIA phenotype and did not manifest differences in ligand binding. Thus, the two known allelic polymorphisms of human Fc gamma R have distinct and independent mechanisms for altering receptor function, which may influence host defense and immune complex handling.

Adult↗

PubMed1992

Novel Fc gamma receptor I family gene products in human mononuclear cells.

Unlike the human Fc gamma RII and Fc gamma RIII families, which exhibit considerable diversity at both the nucleic acid and protein levels, the human Fc gamma RI family has only a single recognized product expressed as a 70-kD cell surface receptor with high affinity for monomeric IgG (hFc gamma RIa1). Using both polymerase chain reaction-based amplification and Northern hybridization, we document multiple interferon-gamma-inducible hFc gamma RI RNA transcripts in human mononuclear cells and neutrophils. The sequences of two of these Fc gamma RI related transcripts indicate that they are alternatively spliced products of a second Fc gamma RI family gene, termed Fc gamma RIB. The cDNA derived from the larger of these transcripts, termed hFc gamma RIb1, encodes a surface molecule that is not recognized by Fc gamma RI specific monoclonal antibodies when transfected into COS-7 cells. Unlike the interferon-gamma-inducible hFc gamma RIA gene product, hFc gamma RIb1 does not bind monomeric IgG with high affinity. However, both hFc gamma RIa1 and hFc gamma RIb1 do bind aggregated human IgG. Previously unrecognized diversity within the hFc gamma RI family includes an interferon-gamma-inducible, putative low affinity Fc gamma receptor that may play an important role in the mechanism by which Fc gamma receptors participate in the humoral immune response.

Amino Acid Sequence↗

PubMed1992

Patients with systemic lupus erythematosus at risk for Pneumocystis carinii pneumonia.

We describe 6 cases of patients with systemic lupus erythematosus (SLE) who developed Pneumocystis carinii pneumonia. All were treated with high dose corticosteroids, and all developed the infection within 4 months of beginning new or revised cytotoxic therapy. All patients tested (5 of 6) were negative for human immunodeficiency virus (HIV). Those patients who developed Pneumocystis carinii pneumonia had more severe lymphocytopenia (median 595 vs 833/mm3) and received higher doses of corticosteroids (median prednisone dose = 43 vs 20 mg/day) than other patients with active SLE. A threshold lymphocyte count of 350/mm3 identified 4 of 6 cases but only 1 of 20 controls. Patients with SLE treated with high dose corticosteroids and cytotoxic drugs and with severe lymphocytopenia may be at increased risk for this opportunistic infection.

Adult↗

PubMed1991

Regulation of phagocytosis and [Ca2+]i flux by distinct regions of an Fc receptor.

The binding of multivalent immunoglobulin G complexes to Fc receptors (Fc gamma Rs) on macrophages activates multiple immune functions. A murine macrophage cell line, but not a fibroblast cell line, that was transfected with human Fc gamma RIIA mediated phagocytosis and an intracellular Ca2+ concentration ([Ca2+]i) flux upon cross-linking of human Fc gamma RIIA. Transfected macrophages that expressed a truncated receptor lacking 17 carboxy-terminal amino acids phagocytosed small antibody complexes. However, only wild-type transfectants phagocytosed labeled erythrocytes and fluxed [Ca2+]i. Thus, the cytoplasmic domain of human Fc gamma RIIA contains distinct functional regions.

Animals↗

PubMed1991

Intravenous anti-D treatment of immune thrombocytopenic purpura: analysis of efficacy, toxicity, and mechanism of effect.

The efficacy, toxicity, and mechanism of effect of intravenous Anti-D (Winrho) were studied in 43 Rh+ patients with immune thrombocytopenia purpura (ITP) who had not undergone splenectomy and in three already splenectomized patients. The mean platelet increase for the 43 nonsplenectomized patients was 95,000/microL (median 43,000/microL). Children had greater acute platelet responses than did adults. Human immunodeficiency virus status and duration of thrombocytopenia did not affect response. Maintenance treatment was given to patients as needed: the average interval between infusions was 24 days. The three splenectomized patients had no platelet response whatsoever. Toxicity was minimal; infusions were completed in less than 5 minutes. The generally accepted mechanism of effect of Anti-D has been Fc receptor blockade by substitution of antibody-coated red blood cells for antibody-coated platelets. Evidence is presented suggesting that the effect of IV Anti-D is not limited to Fc receptor blockade, including: (1) no correlation of parameters of hemolysis with platelet increase; (2) a 48- to 72-hour delay before platelet increase; (3) a tendency of the change in monocyte Fc receptor I expression to correlate with platelet increase; and (4) increased in vitro production of antibodies to sheep red blood cells following IV Anti-D infusion.

Adult↗