Inhibition of bactericidal activity of anticapsular antibody by nonspecific antibodies reactive with surface-exposed antigenic determinants on Actinobacillus pleuropneumoniae

Abstract

In an attempt to understand the mechanism of serum resistance in ActinobaciUus pleuropneumoniae, in the present study we examined various interactions among the bacterial surface constituents, serum antibodies, and complement. Analysis of swine sera revealed the presence of anticapsular antibodies in convalescent-phase sera but not in preimmune sera. Both types of sera contained antibodies which reacted with each of 14 polypeptides present in saline extracts of the bacteria. Absorption of the preimmune sera with intact bacteria depleted antibodies to two of the polypeptides (27 and 32 kDa) and high-molecular-weight (>97.4,000) components which did not stain with Coomassie blue. Data derived from complement consumption and C3-binding experiments indicated that the organism was capable of initiating complement activation and binding C3 during incubation in preimmune and immune sera. Experiments designed to evaluate the bactericidal effectiveness of anticapsular antibody revealed that the purified antibody was bactericidal only when preimmune sera absorbed with intact bacteria were used as a source of complement. The bactericidal effects of anticapsular antibody and absorbed preimmune sera were inhibited in a dose-dependent manner by heat-inactivated preimmune sera and immunoglobulin G derived from the sera. The inhibitory activity of the preimmune sera was neutralized by preincubating the sera with column fractions of the saline extract which contained either the 27or the 32-kDa polypeptide. These results indicate that serum resistance in A. pleuropneumoniae 4074 could be related to inhibition of the bactericidal action of anticapsular antibody by nonspecific antibodies which recognize surface-exposed epitopes on the polypeptides.

Actinobacillus Species and their Role in Animal Disease

“…Analysis of the resistance, using sublethal polymyxin B to permeate the outer membrane and sensitize the bacteria, showed that A. pleuropneumoniae was serum-resistant through a quite different mechanism from that seen in strains of E. coli (Rycroft & Cullen, 1990b). Further investigations showed that the mechanism of resistance involved interference by blocking antibody to lipopolysaccharide and other antigens (Udeze & Kadis, 1992b;Ward & Inzana, 1994).…”

Infección por Actinobacillus pleuropneumoniae en un modelo murino = Actinobacillus pleuropneumoniae infection in a murine model

“…Tras la inoculación en ratones y cerdos, el LPS induce una neumonía intersticial, multifocal o consolidada, con infiltración de células inflamatorias, en la que la gravedad de las lesiones se relaciona con la dosis utilizada. Sin embargo, este factor endotóxico es incapaz de reproducir por sí solo el cuadro de lesión característico de la pleuroneumonía, ya que no origina hemorragias y la necrosis está menos difundida (Udeze et al, 1987;Jewen, 1994). Tampoco se consigue una protección adecuada frente a la enfermedad mediante la inmunización con LPS puro Inzana et al, 1988).…”

“…el modelo murino se ha utilizado frecuentemente como una alternativa experimental de primer nivel, en particular en los estudios de inmunidad y virulencia de A. pleuropneumoniae. La mayoría de los investigadores ha concluido, sin embargo que la susceptibilidad de este animal a la infección por A. pleuropneumoniae depende de la cepa o línea de ratón utilizadas y que este animal representa un modelo adecuado para el estudio de la fase aguda de la enfermedad, aunque no para la evaluación del proceso en su conjunto(Sebunya y Sanders, 1982, Fenwik et al, 1986Udeze et al, 1987; Inzana et al, 1988; Gomal, y…”