Stephen W. Hosea

Replacement Therapy in Hereditary Angioedema: Successful Treatment of Acute Episodes of Angioedema with Partly Purified C1 Inhibitor

Although considerable progress has been made during the past two decades in the use of androgens to prevent attacks of hereditary angioedema, replacement of the deficient C1-inhibitor protein would provide a useful menas of treatment once an attack has begun. We studied the clinical use of C1 inhibitor that was partly purified on a large scale from pooled plasma. The in vivo efficacy and safety of this protein concentrate were evaluated during 11 intravenous infusions in eight patients with hereditary angioedema. Three patients received the C1-inhibitor preparation during an asymptomatic period. Increases in serum C4 activity provided evidence of the biologic activity of the infused inhibitor. Intravenous administration of the concentrate during acute abdominal or laryngeal attacks of hereditary angioedema in five patients resulted in abatement of symptoms in addition to increased serum C4 activity. No untoward effects of the intravenous administration of the C1 inhibitor were observed in these eight patients. Thus, this C1-inhibitor preparation seems to offer the potential for safe, effective replacement therapy and may provide a means of controlling an attack of hereditary angioedema that is in progress.

Opsonic Requirements for Intravascular Clearance after Splenectomy

We investigated the opsonic requirements for intravascular clearance of pneumococci in guinea pigs and of sensitized erythrocytes in human beings after splenectomy. The impaired clearance of injected pneumococci in splenectomized guinea pigs was corrected by immunization. This improvement in clearance was due to increased hepatic sequestration of organisms. There was a significant delay in antibody-mediated clearance of autologous erythrocytes sensitized with IgG (P < 0.001), although the rate of complement-mediated clearance in splenectomized patients was normal. A fourfold increase in sensitizing antibody resulted in a significant improvement in clearance that was due to increased hepatic sequestration (P < 0.005). One patient who had an intact spleen and who had previously received Thorotrast (thorium oxide) had impaired antibody-mediated clearance despite increased sensitization. These observations suggest that, after splenectomy the remaining macrophages of the reticuloendothelial system require increased amounts of antibody to mediate efficient intravascular clearance of opsonized particles.

Role of Complement Activation in a Model of Adult Respiratory Distress Syndrome

The adult respiratory distress syndrome is characterized by arterial hypoxemia as a result of increased alveolar capillary permeability to serum proteins in the setting of normal capillary hydrostatic pressures. Because bacterial sepsis is prominent among the various diverse conditions associated with altered alveolar capillary permeability, we studied the effect of bacteremia with attendant complement activation on the sequestration of microorganisms and the leakage of albumin in the lungs of guinea pigs. Pneumococci were injected intravenously into guinea pigs and their localization was studied. Unlike normal guinea pigs, complement-depleted guinea pigs did not localize injected bacteria to the lungs. Preopsonization of organisms did not correct this defect in pulmonary localization of bacteria in complement-depleted animals, suggesting that a fluid-phase component of complement activation was required. Genetically C5-deficient mice showed no pulmonary localization of bacteria. C5-sufficient mice demonstrated the usual pulmonary localization, thus further suggesting that the activation of C5 might be important in this localization. The infusion of activated C5 increased alveolar capillary permeability to serum proteins as assayed by the amount of radioactive albumin sequestered in the lung. Neutropenic animals did not develop altered capillary permeability after challenge with activated C5. Thus, complement activation through C5, in the presence of neutrophils, induces alterations in pulmonary alveolar capillary permeability and causes localization of bacteria to the pulmonary parenchyma. Complement activation in other disease states could potentially result in similar clinical manifestations.

Long-Term Therapy of Hereditary Angioedema with Danazol

We treated 69 patients who had hereditary angioedema with danazol to alleviate attacks of mucocutaneous angioedema involving the skin, oropharynx, and gastrointestinal tract, and we documented the continued efficacy of danazol for long-term treatment (1 to 6 years) of hereditary angioedema. Significant dose-related, adverse reactions occurred, including weight gain, myalgias, headaches, microscopic hematuria, abnormal liver function tests, anxiety, altered libido, alopecia, dizziness, and nausea. Alterations in menstrual function were consistently observed. About 10% of patients noted masculinizing side effects, such as acne, hirsutism, and voice deepening. We recommend downward titration of danazol dosage to achieve control of attacks and minimize adverse reactions. Periodic monitoring of patients on long-term danazol therapy is essential to avoid undesirable toxicity.

A quantitative analysis of the interactions of antipneumococcal antibody and complement in experimental pneumococcal bacteremia.

The mechanism of protection of type-specific antipneumococcal antibody and complement in bacteremia was investigated with purified rabbit antibody and a guinea pig model of pneumococcal bacteremia. IgG and IgM were isolated from the sera of rabbits immunized with type 7 pneumococci (Pn), and their binding to Pn was quantitated. The number of antibody-binding sites on the pnuemococcal capsule was also determined. Pn were incubated with various amounts of the immunoglobulin preparations before intravenous injection into nonimmune guinea pigs. Whereas 120 molecules of IgM per Pn were sufficient to enhance bloodstream clearance of Pn, 1,400 molecules of IgG per bacterium were required to produce this effect. As the amount of either IgG or IgM added to the Pn was increased, the rate of bloodstream clearance accelerated. In striking contrast, greater than 1,000 molecules of IgM had no effect on the rate of clearance in C4-deficient guinea pigs, which cannot activate complement via the classic pathway. Similarly, 5,000 molecules of IgG had only minimal effect in C4-deficient guinea pigs, and 24,000 molecules of IgG had no effect in guinea pigs depleted of complement by cobra venom factor. Thus, the in vivo opsonic effects of both IgG and IgM anticapsular antibody are mediated via their ability to activate complement. IgG anti-pneumococcal cell wall antibody, raised by intravenous injection of rabbits with unencapsulated Pn, had no effect on the rate of bloodstream clearance of Pn or on the polymorphonuclear leukocyte killing of type 7 Pn in an in vitro bacterial assay. Because the opsonic effects of anticapsular antibody required complement activation, the ability of anticell wall IgG to activate complement was compared with the two classes of anticapsular antibody. As judged by depletion of C3 and C4 from guinea pig serum, as well as by the fixation of radiolabeled C3 to Pn, IgM anticapsular antibody was the best complement activator. However, anticell wall IgG was somewhat more active than anticapsular IgG in each of these tests of complement activation and fixation. When equivalent amounts of C3 were fixed to Pn by each of the three antibodies, Pn sensitized with IgG and IgM anticapsular antibodies caused immune adherence, whereas Pn sensitized with anticell wall IgG did not. This may explain the failure of anticell wall antibody of mediate complement-dependent phagocytosis of Pn in vivo or in vitro. Although anticell wall IgG is capable of activating complement and fixing C3 to Pn, it is not opsonic; the most likely reason is that the nonopsonic antibody mediates C3 deposition in sites on the Pn that cannot interact efficiently with phagocytic cell C3 receptors.

The role of the spleen in experimental pneumococcal bacteremia.

The importance of the spleen in host defense against pneumococcal bacteremia has been suggested by a number of experimental models as well as the occurrence of the syndrome of overwhelming pneumococcal sepsis in asplenic individuals. We studied the mechanism of splenic protection against pneumococcal bacteremia using a guinea pig model. Rates of removal of pneumococci from the blood stream in normal and splenectomized guinea pigs were compared with the extent of hepatic and splenic sequestration of radiolabeled organisms for three different types of pneumococci. A relationship was found between the virulence of a pneumococcus for normal guinea pigs, the extent to which it is cleared by the spleen, and the magnitude of the defect in blood stream sterilization induced by splenectomy. The spleen plays an increasingly important role in the clearance of progressively more virulent organisms, for which hepatic clearance cannot compensate. Thus, the division between hepatic and splenic clearance of bacteremia is a key determinant of the outcome of experimental pneumococcal infection.

Response of Variant Hereditary Angioedema Phenotypes to Danazol Therapy: GENETIC IMPLICATIONS

Hereditary angioedema (HAE), an auto-somal dominant disorder characterized by attacks of episodic edema is associated with decreased functional levels of the C1 esterase inhibitor. Approximately 85% of patients have lowered antigen levels of a normal inhibitor protein. 15% of patients have normal or elevated antigenic levels of functionless protein. We have examined the response to danazol therapy of patients with the variant HAE phenotypes possessing the abnormal protein in an effort to determine if these patients possess a normal structural C1 inhibitor allele. Four patients with a variant HAE phenotype were treated successfully with danazol. In two patients, distinguished by the presence of a functionless, albumin-bound, C1 inhibitor (phenotype 2), phenotypic analysis of the danazol response by bidirectional immunoelectrophoresis revealed the appearance of the normal C1 inhibitor gene product during danazol therapy. This relatively cathodal C1 inhibitor peak appears in conjunction with the development of nearly normal functional activity. All of the functional C1 inhibitory activity which appeared in the phenotype 2 treatment serum was associated with the electrophoretically normal inhibitor. This normal protein could be separated from the functionless inhibitor protein by immunoadsorption and molecular sieve chromatography. Danazol therapy of the two patients with an electrophoretically normal, functionless C1 inhibitor (phenotype 3) also resulted in a clinical remission associated with development of a significant increment in functional serum C1 inhibitory activity and C1 inhibitor protein. These findings demonstrate that these two HAE phenotypic variants are heterozygous for the normal serum C1 inhibitor, a finding which was not apparent before phenotypic analysis of this serum during danazol therapy. These data provide strong evidence for a basic similarity between the common form of HAE and its phenotypic variants. They also suggest that a structural gene lesion may result in the abnormalities of serum C1 inhibitor function and disease expression in all three of these HAE phenotypes.

The use of conglutinin in a quantitative assay for the presence of cell bound C3bi and evidence that a single molecule of C3bi is capable of binding conglutinin

We have developed a quantitative assay for cell surface C3bi using 125I-labeled conglutinin. Conglutinin was purified to homogeneity from bovine serum and radiolabeled with 125I Bolton Hunter reagent. Conditions of time, temperature, ionic strength, and cell concentration that optimized the binding of conglutinin to erythrocytes bearing C3bi were then determined. The interaction between conglutinin and C3bi under these conditions was highly specific, since EAC4b3b, EAC4b3d, EAC4b3b-beta IH, and EAC4b treated with serum did not bind radioconglutinin significance better with EA or EAC4b. Using this assay, was examined the kinetics of inactivation of both human and guinea pig C3b bound to erythrocytes and showed that, for both, maximum conglutinin binding occurred after EAC4b3b had been incubated with a source of beta 1H and C3INA for 10 to 20 min at 37 degrees C.l We showed a linear relationship between the number of molecules of C3bi per erythrocyte and the amount of conglutinin bound for both guinea pig and human C3bi. The affinity of conglutinin for cell-bound C3bi was shown to be independent of C3bi density on the erythrocyte surface, and the Kd for conglutinin binding to erythrocytes bearing human C3bi was determined to be 1.3 X 10(-8) M. The number of conglutinin binding sites per erythrocyte as calculated from Scatchard plots was equal to the number of C3bi molecules on the cell surface as determined by direct assay using 125I-labeled C3. Moreover, for both human and guinea pig C3bi, the plot of log (cell surface C3bi) vs log (conglutinin bound) had a slope of 1. These findings imply that a single molecule of C3bi is capable of binding a molecule of conglutinin under the conditions of our assay.