Biomedical subjects
A P Kaplan
Publications and source records attributed to A P Kaplan.
Mechanisms of autoimmune activation of basophils in chronic urticaria.
BACKGROUND: Approximately 35% to 40% of patients with chronic urticaria possess a circulating antibody directed to the alpha subunit of the high-affinity type I IgE receptor (FcepsilonRI), which is detectable by using histamine release assays or immunoblotting. Prior reports suggest that purified IgG may not directly activate basophils but rather does so through complement activation. OBJECTIVE: We sought to further elucidate the mechanism by which this antibody causes basophil histamine release, including the role of complement, and to reassess the relationship of functional versus binding assays. METHODS: We incubated human basophils with patient serum, patient IgG, or patient IgG plus normal serum as a complement source and measured histamine release for each condition. IgG fractions were neutralized with cloned alpha subunit to determine whether histamine release decreased proportionately. We also screened sera from 260 patients to compare histamine release with immunoblotting results. RESULTS: We initially tested 35 sera from patients with chronic urticaria by using basophils from 2 atopic donors and one nonreleaser with rabbit anti-IgE. No histamine was released from the nonreleaser, yet all donors responded identically to monocyte chemotactic protein 1, indicating a requirement for IgE or the IgE receptor. Basophil histamine release was markedly augmented by complement if release by IgG alone was low. Incubation of purified IgG with an increasing concentration of cloned alpha subunit gradually reduced the histamine-releasing capability in patients with positive or negative immunoblot results. Of 260 patients tested, 43% had positive histamine release results, and 47% had positive immunoblot results, yet there was no correlation when individual patients were assessed. CONCLUSION: A subpopulation of patients with chronic urticaria possess IgG antibody directed to the alpha subunit of FcepsilonRI. This IgG activates basophils, which is dependent on or augmented by complement. Binding assays for the FcepsilonRI alpha subunit, such as immunoblotting, are not currently feasible as a screening method. A functional assay is required.
Late asthmatic reactions provoked by intradermal injection of T-cell peptide epitopes are not associated with bronchial mucosal infiltration of eosinophils or T(H)2-type cells or with elevated concentrations of histamine or eicosanoids in bronchoalveolar fluid.
BACKGROUND: Isolated late asthmatic reactions can be provoked by intradermal challenge of allergen-derived T-cell peptide epitopes. OBJECTIVE: The purpose of this study was to determine whether the isolated LAR is associated with the local accumulation of inflammatory cells, the expression of T(H)2 cytokines, and the production of pharmacologic mediators. METHODS: A randomized, placebo-controlled, crossover study design was used. The investigation involved bronchial and skin biopsies and bronchoalveolar lavage (BAL) fluids from 8 cat-allergic subjects who developed significant late asthmatic reactions 6 hours after intradermal injection of Fel d 1 chain 1-derived peptides (FC1Ps). RESULTS: Immunostaining of bronchial biopsy specimens showed no changes in the numbers of eosinophils, neutrophils, basophils, mast cells, CD3(+), CD4(+) or CD8(+) T cells, CD25(+) cells or macrophages, or cells mRNA(+) for IL-4, IL-5, or IL-13 when the FC1P day was compared with the diluent control day. There were also no significant differences in eosinophil numbers, either in BAL fluids or in peripheral blood after FC1P challenge. Furthermore, there were no significant alterations in the concentrations of histamine, histamine-releasing factors, or eicosanoids (LTC(4)/D(4)/E(4), PGD(2), PGE(2), TXB(2), PGF(2alpha)) in BAL fluids. FC1Ps induced a significant (P <.05) elevation in CD8(+) cells in the skin and an unexpected decrease in IL-5 in BAL fluids (P =.043). CONCLUSION: Part of the asthma process might involve T cell-dependent airway narrowing with no requirement for IgE, mast cells, or infiltrating inflammatory cells.
Chemokines, chemokine receptors and allergy.
Chemokines are a group of cytokines that are responsible for the influx of blood cells, including T and B lymphocytes, monocytes, neutrophils, eosinophils and basophils, in allergic and other inflammatory conditions. They function as G protein-coupled chemotactic factors which also activate the cells with which they interact. Certain chemokines function within the afferent arm of the immune system, in which antigen is processed and antibody formation initiated, and others are active within the effector pathways of cellular immunity and late-phase allergic reactions. Th2 lymphocytes, which are critical for allergy, employ the CC chemokine receptors CCR4 and CCR8 with the ligands thymus- and activation-regulated chemokine (TARC), macrophage-derived chemokine (MDC) and I-309, respectively. The chemokine receptor CCR3 and ligands monocyte chemoattractant protein (MCP)-3, MCP-4, regulated upon activation normal T cell expressed and secreted (RANTES) and eotaxins I and II are of particular relevance for the recruitment and activation of eosinophils. Th1 reactions depend upon interferon gamma-induced CXC chemokines interferon- inducible protein (IP)-10, interferon-inducible T cell-alpha chemoattractant (iTAC) and monokine induced by interferon-gamma (MiG), which bind to chemokine receptor CXCR3.
Activation of the kinin-forming cascade on the surface of endothelial cells.
Activation of the plasma kallikrein-kinin forming cascade takes place upon incubation with human umbilical vein endothelial cells. The mechanism by which initiation occurs is uncertain. Zinc-dependent binding of plasma proteins to gC1qR, cytokeratin 1, and perhaps u-PAR is requisite for activation to take place. We demonstrate here that during a 2 hour incubation time plasma deficient in either factor XII or high molecular weight kininogen (HK) fails to activate, as compared to normal plasma, but with more prolonged incubation, factor XII-deficient plasma gradually activates while HK-deficient plasma does not. Our data support both factor XII-dependent (rapid) and factor XII-independent (slow) mechanisms; the latter may require a cell-derived protease to activate prekallikrein and the presence of zinc ions and HK.
Factor XII-dependent contact activation on endothelial cells and binding proteins gC1qR and cytokeratin 1.
Although proteins of the kinin-forming pathway are bound along the surface of endothelial cells, the mechanism of activation of this proteolytic cascade is unclear. Endothelial cell surface proteins, gC1qR and cytokeratin 1, are capable of binding Factor XII and high molecular weight kininogen (HK) in a zinc-dependent reaction thus we considered the possibility that these proteins might catalyze initiation of the cascade. Incubation of Factor XII, prekallikrein, and HK with gC1qR or cytokeratin 1 leads to a zinc-dependent and Factor XII-dependent conversion of prekallikrein to kallikrein. We also demonstrate that normal plasma is capable of activating upon interaction with the cells whereas plasma deficient in Factor XII, prekallikrein and HK do not activate. Normal plasma activation was inhibitable by antibody to gC1qR and cytokeratin 1. Thus, gC1qR and cytokeratin 1, represent potential initiating surfaces for activation of the plasma kinin-forming cascade and may do so as a result of their expression along cell surfaces.
C1 inhibitor deficiency: hereditary and acquired forms.
C1 inhibitor deficiency can be hereditary or acquired. The hereditary disorder has two types, each of which is inherited as a dominant disorder, with genetic mechanisms leading either to low levels of normal C1 INH and little or no mutant problem as a result of mRNA or protein synthetic defects or degradative mechanisms (Type I) or with point mutations and synthesis of a functionless protein product with transinhibition of the normal allele (Type II). The acquired disorder with low C1q is due to C1 INH consumption associated with lymphoma or connective tissue disease (Type I) and/or autoimmune mechanisms (Type II). The swelling of all types is due to absence of inhibition of the plasma kinin forming cascade with liberation of bradykinin while complement activation, a critical marker of the disorder, is not responsible for the swelling. Treatment employs androgenic compounds, antifibrinolytic agents, or replacement therapy.
Acquired C1 esterase inhibitor deficiency.
Explore the source record for details and available documents.
Diagnostic tests for urticaria and angioedema.
Explore the source record for details and available documents.
Zinc-dependent activation of the plasma kinin-forming cascade by aggregated beta amyloid protein.
Beta Amyloid proteins (Abeta) of 38, 40, and 42 amino acids long were assessed for their ability to activate the plasma kinin-forming cascade in vitro. Incubation with a mixture of Factor XII (Hageman Factor), prekallikrein, and high-molecular-weight kininogen (HK) led to conversion of prekallikrein to kallikrein that was dependent on zinc ion. No activation occurred if Factor XII was omitted. There was rapid generation of bradykinin equal to the molar HK input indicating complete cleavage. Incubation of aggregated Abeta with diluted human plasma also led to prekallikrein activation and HK cleavage. Activation of the cascade by Abeta (1-38) was dependent upon its preincubation time in buffer, suggesting that aggregation of Abeta is required, and studies with Abeta (1-40) revealed time-dependent aggregation by microscopy and augmented zinc-dependent binding of both Factor XII and HK to aggregated Abeta. These data demonstrate that aggregated Abeta can bind and activate proenzymes of the plasma kinin-forming cascade in a zinc-dependent reaction to release bradykinin and is of sufficient potency to do so at physiologic concentrations of each protein and in the presence of naturally occurring protease inhibitors.
Cytokeratin 1 and gC1qR mediate high molecular weight kininogen binding to endothelial cells.
High molecular weight kininogen (HK) attaches to endothelial cells by separate sites on the heavy and light chains and requires 15-50 microM zinc. Previously identified binding proteins include gC1qR, cytokeratin 1, and the urokinase plasminogen activator receptor; however, their relative contributions to binding are not yet clarified. We have prepared affinity columns to which were coupled either cleaved HK or peptide LDCNAEVYVVPWEKKIYPTVNCQPLGM derived from heavy-chain domain 3. Endothelial cell membranes were solubilized and chromatographed in the presence or absence of zinc ion, the bound proteins were eluted, and active fractions were identified by dot blot using biotinylated HK, SDS/PAGE, and Western blot analysis. The peptide containing column eluate revealed but one band at 68 kDa if zinc ion was present which was identified as cytokeratin 1 by amino acid sequencing of an internal peptide. The HK affinity column revealed bands at 68 kDa (cytokeratin 1), 33 kDa (gC1qR), and 66 kDa (unidentified). HK or domain 3-derived peptide bound to the 68 kDa band; prekallikrein and Factor XII did not. HK or Factor XII bound to the 33-kDa band if zinc was present while no binding to the 66 kDa band was observed. Antibody to cytokeratin 1 inhibited HK binding to endothelial cells by 30%, antibody to gC1qR inhibited HK binding to endothelial cells by 72%, and a mixture of both inhibited binding by 86%. Our data suggest HK binding by interaction of the heavy-chain domain 3 with cytokeratin 1 and the light chain with gC1qR.
A double-blind, placebo-controlled trial of fexofenadine HCl in the treatment of chronic idiopathic urticaria.
BACKGROUND: Symptoms of chronic idiopathic urticaria (CIU) include relentless itching and painful wheals, which can be physically and psychologically debilitating. Half of all patients with urticaria have angioedema, which is often disfiguring. OBJECTIVE: To evaluate the safety and efficacy of fexofenadine HCl for the treatment of CIU symptoms. METHODS: In this 4-week, multicenter, placebo-controlled study, 439 patients with moderate to severe pruritus and urticaria received 1 of 4 oral doses of fexofenadine HCl (20, 60, 120, or 240 mg twice a day) or placebo. Patients reflectively assessed (over the previous 12 hours) the severity of pruritus, the number of wheals, and the interference with sleep (7 AM) and normal activities (7 PM) due to urticaria. Efficacy measures included a change from baseline of daily mean pruritus score (MPS), daily mean number of wheals (MNW) score, daily mean total symptom score (MTSS) (ie, the sum of the wheal and pruritus scores), and mean interference with sleep and daily activities due to urticaria. RESULTS: All 4 doses of fexofenadine were statistically superior to placebo (P </=.0238) for MPS, MNW score, and MTSS. Patients receiving fexofenadine HCl also experienced significantly less interference with sleep and daily activities than patients receiving placebo (P </=.0001). Efficacy results were similar in the 60-, 120-, and 240-mg groups and were quantitatively better than those in the 20-mg group. Adverse events were mild and occurred with similar incidence in all treatment groups. CONCLUSIONS: Fexofenadine HCl is well tolerated and is statistically superior to placebo in reducing signs and symptoms of CIU and in ameliorating interference with sleep and daily activities due to urticaria. Doses of 60 mg twice a day or greater are most effective.
Complement dependence of histamine release in chronic urticaria.
BACKGROUND: IgG autoantibodies directed to the alpha-subunit of the IgE receptor have been identified in 30% to 45% of patients with chronic urticaria. However, the exact mechanism by which histamine secretion is initiated is uncertain. OBJECTIVE: Histamine release from cutaneous mast cells may occur by cross-linking the IgE receptor or by activation of complement. Our goal is to distinguish these 2 possibilities. METHODS: We incubated human cutaneous mast cells with patient sera, decomplemented sera, or purified patient IgG. The IgG was also added to pooled normal serum or to sera deficient in either C2 or C5, and its ability to activate mast cells was assessed. Mast cells were incubated with human IgE myeloma to saturate alpha-subunits to determine the effect on histamine release. RESULTS: Patient sera released histamine (18.26% +/- 4.39%), but purified IgG from patients (5.5% +/- 4.3%) did not. Addition of the patient IgG to normal sera rendered the sera positive for histamine-releasing activity (18.4% +/- 4.3%), whereas control IgG or patient IgG added to C2- or C5-deficient sera did not release histamine. Histamine release with decomplemented patient sera was also diminished (8.34% +/- 4.3%). Preincubation of mast cells with a C5-blocking peptide decreased histamine release but was not statistically significant; there was a significant decrease after preincubating mast cells with IgE myeloma. CONCLUSION: The degranulation of mast cells by IgG autoantibodies in patients with chronic urticaria requires binding to the IgE receptor and activation of the classical complement cascade. Saturation of the IgE receptor with IgE inhibits such degranulation, presumably by preventing binding of the requisite IgG.
Interaction of factor XII and high molecular weight kininogen with cytokeratin 1 and gC1qR of vascular endothelial cells and with aggregated Abeta protein of Alzheimer's disease.
High molecular weight kininogen (HK) attaches to endothelial cells at separate sites on the heavy and light chains by a process which requires 15-50 microM zinc. Previously identified binding proteins include gClqR, cytokeratin 1, and the urokinase plasminogen activator receptor (U-par), however, their relative contribution to binding are not yet clarified. We have purified the binding proteins by affinity chromatography, in the presence of zinc ion, and identified cytokeratin 1 and gC1qR by amino acid sequencing of an internal peptide and by immunoblot as heavy chain and light chain binding proteins, respectively. Antibody to cytokeratin 1 inhibited HK binding to endothelial cells by 30%, antibody to gClqR inhibited HK binding to endothelial cells by 72%, and a mixture of both inhibited binding by 86%. The binding and activation of the proteins of the kinin-forming cascade along the cell surface is zinc-dependent. Similarly, proteins of the plasma kinin-forming cascade can be activated by binding to aggregated A(beta) protein of Alzheimer's disease. Activation of the cascade using purified proteins or upon addition of Abeta to plasma requires aggregation of A(beta) and the reactions are zinc-dependent. In plasma, HK is cleaved and bradykinin is liberated. The data demonstrate that aggregated A(beta) can bind and activate proenzymes of the plasma kinin-forming cascade to release bradykinin and these reactions are dependent on zinc ion.
Platelet glycoprotein Ib: a zinc-dependent binding protein for the heavy chain of high-molecular-weight kininogen.
Domains 3 and 5 of high-molecular-weight kininogen (HK) have been shown to bind to platelets in a zinc-dependent reaction. However, the platelet-binding proteins responsible for this interaction have not been identified. We have focused on the platelet-binding site for the heavy chain (domain 3), which we approached using a domain 3-derived peptide ligand and isolated binding proteins by affinity chromatography. The domain 3-derived peptide, thrombin, HK, factor XII, as well as antibody to glycocalicin (the N-terminal portion of the alpha chain of GPIb) recognized a protein at 74 kD. We also isolated the thrombin receptor (PAR 1) at 45 kD, however, none of the above-mentioned ligands bound to this protein. Isolation of platelet membrane proteins using a monoclonal anti-glycocalicin antibody column revealed the same HK binding protein at 74 kD, which was reactive with anti-GPIb and represents a GPIb fragment. By photoaffinity labeling, HK interacted with membrane GPIb, which was then isolated in native form (135 kD) along with gC1qR, a ligand for the HK light chain. Finally, (125)I-HK binding to platelets was significantly inhibited by the anti-GPIb antibody. These results suggest that the GPIb alpha chain, a known thrombin binding protein, is also one of the zinc-dependent platelet membrane binding sites for HK domain 3.
Effect of neurotropin on the binding of high molecular weight kininogen and Hageman factor to human umbilical vein endothelial cells and the autoactivation of bound Hageman factor.
Bradykinin is generated by activation of the plasma kallikrein-kinin (K-K) cascade and contributes to the symptoms of allergic reactions and the perception of pain. Neurotropin is a biological material obtained from inflamed rabbit skin inoculated with vaccinia virus, which is widely used clinically in Japan as an effective agent for these disorders. Factor XII (FXII) and high molecular weight kininogen (HK), two critical constituents of the plasma K-K cascade, bind to endothelial cells, and bound FXII is autoactivated in the presence of zinc ions. We have investigated the effects of Neurotropin on the interactions of FXII and HK with endothelial cells. Neurotropin inhibited the binding of both proteins to cultured human umbilical vein endothelial cells (HUVEC) and inhibited autoactivation of FXII upon HUVEC in a concentration-dependent manner. These data suggest that the ameliorating effects of Neurotropin in allergic disorders and pain syndromes may be related to this ability to inhibit activation of the K-K cascade and, consequently, the formation of bradykinin.
Bradykinin formation. Plasma and tissue pathways and cellular interactions.
Explore the source record for details and available documents.
Comparative studies of functional and binding assays for IgG anti-Fc(epsilon)RIalpha (alpha-subunit) in chronic urticaria.
BACKGROUND: Recent data suggest that a subpopulation of patients with chronic urticaria have an autoimmune disorder that is caused by the presence of antibodies to the IgE receptor. The actual incidence of these antibodies is uncertain. OBJECTIVE: We sought to assess the incidence of autoimmunity to the IgE receptor in patients with chronic urticaria and to compare functional and binding assays. METHODS: We isolated skin mast cells and studied a large number of patient sera (68) for their ability to activate these cells and isolated basophils. We then compared the results with those obtained by immunoblotting using cloned alpha-subunit of the IgE receptor. RESULTS: Sera from patients with chronic urticaria released significant histamine (> 15% of basal) on incubation with basophils (48%) and mast cells (46%). By immunoblotting we obtained positive results in 64% of subjects tested and also identified a small subpopulation that is active on cells but does not bind Fc(epsilon)RIalpha. CONCLUSION: Our data suggest that approximately 45% to 50% of patients with chronic urticaria have a cutaneous autoimmune disorder. Immunoblotting may provide a rapid screening method for anti-Fc(epsilon)RIalpha detection in such patients.