Anti-C1 domain antibodies that accelerate factor VIII clearance contribute to antibody pathogenicity in a murine hemophilia A model

Essentials Inhibitor formation remains a challenging complication of hemophilia A care. The Bethesda assay is the primary method used for determining bleeding risk and management. Antibodies that block factor VIII binding to von Willebrand factor can increase FVIII clearance. Antibodies that increase clearance contribute to antibody pathogenicity.

SUMMARY

Background The development of neutralizing anti-factor VIII (FVIII) antibodies remains a challenging complication of modern hemophilia A care. In vitro assays are the primary method used for quantifying inhibitor titers, predicting bleeding risk, and determining bleeding management. However, other mechanisms of inhibition are not accounted for in these assays, which may result in discrepancies between the inhibitor titer and clinical bleeding symptoms. Objectives To evaluate FVIII clearance in vivo as a potential mechanism for antibody pathogenicity and to determine whether increased FVIII dosing regimens correct the associated bleeding phenotype. Methods FVIII-/- or FVIII-/- /von Willebrand factor (VWF)-/- mice were infused with anti-FVIII mAbs directed against the FVIII C1, C2 or A2 domains, followed by infusion of FVIII. Blood loss via the tail snip bleeding model, FVIII activity and FVIII antigen levels were subsequently measured. Results Pathogenic anti-C1 mAbs that compete with VWF for FVIII binding increased the clearance of FVIII-mAb complexes in FVIII-/- mice but not in FVIII-/- /VWF-/- mice. Additionally, pathogenic anti-C2 mAbs that inhibit FVIII binding to VWF increased FVIII clearance in FVIII-/- mice. Anti-C1, anti-C2 and anti-A2 mAbs that do not inhibit VWF binding did not accelerate FVIII clearance. Infusion of increased doses of FVIII in the presence of anti-C1 mAbs partially corrected blood loss in FVIII-/- mice. Conclusions A subset of antibodies that inhibit VWF binding to FVIII increase the clearance of FVIII-mAb complexes, which contributes to antibody pathogenicity. This may explain differences in the bleeding phenotype observed despite factor replacement in some patients with hemophilia A and low-titer inhibitors.

Endogenous glucocorticoids modulate experimental anti-glomerular basement membrane glomerulonephritis

The influence of endogenous glucocorticoids (GC) on glomerular injury was studied in a rat model of heterologous anti-glomerular basement membrane (GBM) glomerulonephritis (GN). Sprague-Dawley rats underwent adrenalectomy (ADX) or sham-operation 3 days prior to i.v. administration of both nephritogenic (100 microgram/g) and subnephritogenic (50 microgram/g) doses of sheep anti-rat GBM globulin. Administration of a subnephritogenic dose of anti-GBM globulin resulted in GN in adrenalectomized animals only. Similarly, ADX performed prior to administration of anti-GBM in the nephritogenic dose range resulted in exacerbation of GN compared with sham-operated animals (24 h protein excretion: 190.8 +/- 32.8 versus 42.5 +/- 2.6 mg/24 h; P < 0.005). In ADX animals receiving subnephritogenic doses of anti-GBM injury was manifested by abnormal proteinuria (62.7 +/- 5.8 mg/24 h), accumulation of neutrophils which peaked at 6 h (7.2 +/- 1.37 neutrophils per glomerular cross-section (neut/gcs)) and macrophage accumulation in glomeruli at 24 h (6.8 +/- 1.2 macrophages/gcs). Sham-adrenalectomized animals given the same dose of anti-GBM globulin developed minimal or no glomerular injury: urinary protein excretion (8.7 +/- 1.5 mg/24 h, P < 0.001); neutrophils (0.2 +/- 0.04 neutrophils/gcs, P < 0.001); macrophages (1.2 +/- 0.5 macrophages/gcs, P < 0.001). The increased cellular recruitment to glomeruli in adrenalectomized animals was associated with glomerular endothelial P-selectin expression. P-selectin expression was not detected in sham-operated rats after anti-GBM injection. Complement deposition in glomeruli was minimal in both groups. Physiologic GC replacement of ADX rats receiving subnephritogenic-dose anti-GBM reversed the observed susceptibility to GN development, with urinary protein excretion (7.8 +/- 1.12, P < 0.005) and no detectable P-selectin expression or leucocyte accumulation in glomeruli. These results suggest that endogenous GC modulate heterologous anti-GBM nephritis in rats and that this may be attributable, in part, to regulation of P-selectin expression.

IgG and complement-mediated tissue damage in the absence of C2: evidence of a functionally active C2-bypass pathway in a guinea pig model

In vitro complement-mediated lysis of heavily sensitized sheep erythrocytes by C4-deficient (C4D) guinea pig and C2-deficient (C2D) human sera was demonstrated some years ago. It was postulated that these "complement-bypass" pathways resulted from activation of C1 and components of the alternative pathway. We used normal, C2D, and C4D guinea pigs in a Forssman shock model to test the in vivo relevance of the C2- and C4-bypass pathways of complement activation. High concentrations of both anti-Forssman Ab and C2D or C4D guinea pig serum induced efficient lysis of sheep erythrocytes in vitro. The most efficient lysis was observed when IgG Ab and C2D guinea pig serum were used. Blocking either the classical pathway (treatments with EGTA-Mg2+ or soluble recombinant complement receptor type 1 (sCR1)) or the alternative pathway (treatment with heating at 50 degrees C, sCR1, or soluble recombinant CR1 lacking the first of the four long homologous repeat sequences (sCR1[desLHR-A])) inhibited lysis; both pathways were required for lysis of sheep erythrocytes by C2D and C4D guinea pig sera. i.v. injection of anti-Forssman Ab in normal guinea pigs resulted in rapid death from pulmonary shock, whereas C4D guinea pigs had no adverse effect. Surprisingly, C2D guinea pigs either died in a delayed fashion or had a sublethal reaction. sCR1 treatment prevented Forssman shock in both normal and C2D guinea pigs, whereas sCR1[desLHR-A] prevented Forssman shock only in C2D animals. Our results suggest that the C2-bypass pathway occurs in vivo to produce tissue damage. Activation of complement in the absence of C2 appears to be far more efficient than in the absence of C4.

Effects of anti-B7 monoclonal antibodies on humoral immune responses

The costimulatory interaction between CD28 on T cells and B7-related molecules on antigen presenting cells plays an important role in a broad range of functions of the immune system, including protective immunity, tolerance induction, allograft rejection, and the development of autoimmune diseases. Monoclonal antibodies to B7-1 and B7-2 have been used in vivo to examine the mechanisms underlying these processes and to evaluate costimulation antagonism as an approach to treatment of chronic autoimmune diseases. To determine whether anti-B7 mAb might elicit, or inhibit, a host immune response that could influence the effects of these antibodies in vivo, we assessed the immune response to rat anti-B7-1 and anti-B7-2 mAb in healthy (BALB/c) mice and in lupus-prone NZB/NZW F1(B/W) mice. In BALB/c mice, low doses (1-10 microg) of mAb to B7-1 and mAb to B7-2 elicited brisk immune responses that occurred earlier and were significantly greater than the immune response to an isotype-matched control rat mAb to ovalbumin. In contrast, at higher doses (100-500 microg), both anti-B7 mAb, but not the control mAb, blocked the mouse anti-rat response. No such blockade occurred in B/W mice, who generated a significant mouse anti-rat response even at very high doses of anti-B7 mAb (1,000-4,000 microg). Blockade of the immune response to the anti-B7 mAb in BALB/c mice apparently did not reflect generalized immune suppression, because high doses of these mAb had little, if any effect on the humoral immune response to another antigen. These findings indicate that: (1) mAb to B7-1 and B7-2 can elicit either a potent immune response or no immune response at all depending upon the dose administered; (2) blockade of the immune response to anti-B7 mAb may be more difficult in the setting of autoimmunity; and (3) neither anti-B7-1 nor anti-B7-2 causes generalized suppression of humoral immunity.

Effects of a novel elastase inhibitor, ONO-5046, on nephrotoxic serum nephritis in rats

ONO-5046 is a potent, specific and intravenously active inhibitor of neutrophil elastase. To examine the role of elastase in glomerulonephritis, we tested the effects of ONO-5046 on nephrotoxic serum (NTS) nephritis in a rat model of the disease in humans. Rats were administered ONO-5046 or phosphate-buffered saline (PBS) intraperitoneally 24 hours prior to injection of NTS, and they were then given equal doses of ONO-5046 or PBS three hours and 1, 2, 3, 4, 5 and 6 days later. Compared with the control groups, ONO-5046 significantly reduced proteinuria and hematuria, and suppressed the formation of crescentic glomeruli in a dose-dependent manner. Our results suggest that neutrophil elastase participates in NTS nephritis by degrading glomerular basement membrane proteins, and that the elastase inhibitor, ONO-5046, suppresses crescentic formation and glomerular injury caused by elastase.

In vitro accommodation of porcine endothelial cells by low dose human anti-pig antibody: reduced binding of human lymphocytes by accommodated cells associated with increased nitric oxide production

Transplanted xenografts, protected from rejection by depletion of xenoreactive natural antibodies (XNA) and complement, can sometimes survive when complement levels and titres of anti-graft antibodies return to baseline; this phenomenon is called accommodation. We have previously reported that low concentrations of human IgG induce a change in the phenotype of immortalised porcine endothelial cells (IPEC) consistent with the development of accommodation. The cells acquired a resistance to lysis by human complement and showed a reduced expression of VCAM. In this study, we extend these findings by showing that VCAM expression falls on several IPEC clones and on primary porcine endothelial cells. Moreover, we show that these accommodated cells bind fewer human lymphocytes compared to controls, implying that leukocyte traffic through accommodated endothelium may be altered compared to that through normal endothelium. Finally we show that during the induction of accommodation, porcine endothelial cells produce greater amounts of nitric oxide than controls, due to the expression of inducible nitric oxide synthase (iNOS). We speculate that nitric oxide may be an important mediator in accommodation.

Heterophilic antibodies produce spuriously elevated concentrations of the MB isoenzyme of creatine kinase in a selected patient population

Dual-site murine antibody-based immunoassays are commonly used in clinical laboratories to quantitate the MB isoenzyme of creatine kinase (CK-MB). Because the serum level of CK-MB is a relatively specific and sensitive indicator of myocardial ischemic damage, accurate quantitation is essential for a correct diagnosis. Heterophile antibodies (eg, human anti-murine antibodies) can interfere with these assays, however, and produce erroneous results. A subpopulation of 19 surgical patients with colorectal carcinoma who had received injections of an 125I-labeled murine monoclonal antibody directed against a tumor-associated glycoprotein was studied. Serum specimens from eight patients (42%) showed a marked increase in the level of CK-MB and normal total CK concentrations. The increased concentrations of CK-MB, which were attributed to interference by human antimurine antibodies, were substantially reduced in these specimens after a heterophile blocking reagent was added. However, this reagent did not significantly alter the serum level of CK-MB in patients who had clinical evidence of acute myocardial ischemia.

Effect of an antidiencephalon immune serum on pain and sleep in primary fibromyalgia

The results of a double-blind, randomized, therapeutical trial with SER282, an antidiencephalon immune serum (Serolab, Lausanne, Switzerland), in 36 women, aged 24-56 years, with primary fibromyalgia are presented. Treatment was ambulatory and consisted of either SER282 (20 mg/ml) or amitryptiline (AMI, 50 mg) or placebo (PL) over an 8-week treatment course. Clinical and sleep EEG polygraphic data were obtained at baseline and after 4 and/or 8 weeks of therapy. Compared to an important PL response and moderate analgesia with AMI, pain and associated symptoms improved moderately with SER282. In contrast, polysomnographic recordings showed that SER282 tended to promote stage 4 sleep, while AMI and PL had few--if any--effect on sleep. These results are discussed together with the clinical characteristics of the patients and the relations between pain, associated symptoms, and sleep parameters in our patient population.

Attempts to induce immune-mediated cerebral arterial injury for an experimental model of moyamoya disease

To examine the possible role of immune complex-mediated reactions in moyamoya disease, a novel experimental system using a serum sickness vasculitis model combined with intracisternal administration of antibodies or antigens was developed. Twenty-eight male Japanese white rabbits were divided into four experimental groups. Group I was treated twice with intravenous injections of heterologous serum. In group II, intracisternal administration of antibodies or antigens was combined with the second injection of serum. Group III received a single intravenous injection of antigens simultaneously with intracisternal administration of antibodies. Group IV was a technical control group. Cerebral arteritis, although likely in the initial process, was induced only in groups II and III. This study suggests that the cerebral arteries rarely develop arteritis in a serum sickness model alone. The cerebral arteries may require additional intracisternal administration of antibodies or antigens to induce in situ deposition of immune complexes around them.

The effect of three novel thromboxane A2 receptor antagonists (S-1452, AA-2414 and ONO-3708) on the increase in pulmonary pressure caused by Forssman anaphylaxis in guinea-pigs

The effects were studied of three novel thromboxane A2 (TXA2) receptor antagonists (S-1452, AA-2414 and ONO-3708) on the increase in pulmonary pressure caused by Forssman anaphylaxis in guinea-pigs. Three TXA2 antagonists at doses of between 1 and 10 mg/kg administered orally 1 h before the challenge clearly inhibited the pulmonary pressure increase. At a dose of 10 mg/kg, all three antagonists inhibited the pulmonary pressure increase caused by leukotriene D4 (LTD4) and U-46619, but not that caused by histamine. The decrease in peripheral platelet counts caused by Forssman anaphylaxis was also clearly inhibited by the three TXA2 antagonists. However, the decreased peripheral leukocyte counts were unaffected by the three agents. The decrease in serum complement activity (CH50) was inhibited by S-1452 and AA-2414 at a dose of 10 mg/kg. In bronchoalveolar lavage fluid (BALF), significant increases in eosinophils and neutrophils were observed after Forssman anaphylaxis. Three TXA2 antagonists at a dose of 10 mg/kg (except for AA-2414 on eosinophils) did not affect the changes of leukocyte counts in BALF. Moreover, increases in the TXB2 and 6-keto-PGF1 alpha levels of the BALF brought about by Forssman anaphylaxis were unaffected by the three TXA2 receptor antagonists. Histamine and LTD4 were not changed in the BALF after Forssman anaphylaxis. These results indicate the efficacy of TXA2 receptor antagonists on the increase in pulmonary pressure caused by Forssman anaphylaxis in guinea-pigs by direct antagonism to released TXA2.

[Modification of the regulatory effects of thymocytes on hematopoiesis in irradiated mice as affected by heterologous immunoglobulin G and low-dose ionizing radiation]

The administration of heterologous immunoglobulin G (IgG) and/or exposure of mouse thymocyte donors to 1 and 2 Gy radiation were shown to change the regulatory effects of thymus lymphocytes on the recovery of haemopoiesis in syngeneic recipients irradiated with a median lethal dose of 6 Gy. Thymocytes of exposed (2 Gy) donors produced a stimulatory effect on the restoration of the myelokaryocytes number and increased the number of endogenous splenic colonies and bone marrow CFUs in animals exposed to a median lethal dose, whereas the administration of IgG to thymocyte donors given 2 Gy eliminated the stimulatory effect of thymocytes on the number of myelokaryocytes, and the amount of CFUs in irradiated recipients decreased.

Effects of Forssman antibody on renal function of the guinea pig

When guinea pigs were injected with rabbit anti-sheep red blood cell antiserum (Forssman antibody) by the intra arterial (i.a.) route (abdominal aorta at the level of the renal arteries), they developed renal disfunction. A diminished glomerular filtration rate associated with a 27% increase in the fractional excretion of K+ was observed. No alterations were noted in the fractional excretion of water and NA+.

Production of cell-mediated immune response to herpes simplex virus by immunization with anti-idiotypic heteroantisera

Three BALB/c monoclonal antibodies capable of neutralizing herpes simplex virus type 1 (HSV-1) were used to prepare rabbit anti-idiotypic antisera. Affinity-purified antibodies from four of these rabbits were used to immunize mice by repeated subcutaneous injection over a period of 6 to 7 weeks: the mice were then challenged with HSV-1 subcutaneously in the ear pinna. Measurement of ear swelling showed that prior administration of anti-idiotypic serum could generate dose-dependent delayed-type hypersensitivity responses.

Nephropathy produced by Forssman antibody in guinea pigs: an experimental model of mesangial injury

In the present work the involvement of the kidneys of guinea pigs injected with rabbit anti-sheep red blood cell antiserum (Forssman antibody) was studied. The antibody was introduced by a catheter into the abdominal aorta close to the openings of renal arteries. Glomerular lesions were observed 6 h following the injection: increased cellularity at the expense of polymorphonuclear and mononuclear cells, widened mesangial regions, deposits of fuchsinophilic material in the mesangium and capillary loops. By immunofluorescence the antibody was detected in the mesangial region extending to adjacent capillary loops, but it was not possible to demonstrate the presence of complement with certainty. The presence of subepithelial nodules on the glomerular basement membrane and deposits in the mesangium was demonstrated by electron microscopy. These findings suggest that this glomerulopathy induced by Forssman antibody may be a simple and reproducible model for the study of mesangial lesions.

[Immunological treatment of digitalis poisoning with heterologous antibodies]

Our own experience with the production of digoxin-specific antibody preparations from the sheep and the results of the experimental and clinical use are briefly reviewed. Advantages, risks and unsolved problems of therapy with glycoside-specific antibodies are discussed.

Effects of heterologous anti-erythrocyte antibodies on the generation cycle of erythroblasts in rats

An injection of anti-rat erythrocyte rabbit serum or its 7S globulin fraction into rats resulted in immunohemolytic anemia associated with a positive anti-gloublin test examined with anti-rabbit gammaglobulin serum. However, an injection of 19S globulin fraction from the anti-erythrocyte serum failed to cause immunohemolytic anemia, although it induced a transient decrease in red cell count. These results indicate that 7S antibodies are responsible for the induction of anti-globulin test positive, experimental immunohemolytic anemia. The ferrokinetic and stathmokinetic studies revealed the prolongation of generation time of basophilic and polychromatic erythroblasts in rats injected with anti-erythrocyte serum or its 7S globulin fraction. The results from in vitro [3H] thymidine incorporation experiments also confirmed this prolongation. The analysis of in vivo [3H] thymidine labeling of erythroblasts in rats which were given the 7S GLOBULIN ANTIBODIES SUGGESTED THE PROLONGATION OF THE G1 time of the erythroblasts. These results suggest that the effects of anti-erythrocyte antibodies on the generation cycle of erythroblasts are to prolong their G1 time and keep them dormant.