The Role of Antibodies Against the Crude Capsular Extract in the Immune Response of Porcine Alveolar Macrophages to In Vitro Infection of Various Serovars of Glaesserella (Haemophilus) parasuis

Abstract

In Glässer’s disease outbreaks, Glaesserella (Haemophilus) parasuis has to overcome the non-specific immune system in the lower respiratory tract, the alveolar macrophages. Here we showed that porcine alveolar macrophages (PAMs) were able to recognize and phagocyte G. parasuis with strain-to-strain variability despite the presence of the capsule in virulent (serovar 1, 5, 12) as well in avirulent strains (serovar 6 and 9). The capsule, outer membrane proteins, virulence-associated autotransporters, cytolethal distending toxins and many other proteins have been identified as virulence factors of this bacterium. Therefore, we immunized pigs with the crude capsular extract (cCE) from the virulent G. parasuis CAPM 6475 strain (serovar 5) and evaluated the role of the anti-cCE/post-vaccinal IgG in the immune response of PAMs to in vitro infection with various G. parasuis strains. We demonstrated the specific binding of the antibodies to the cCE by Western-blotting assay and immunoprecipitation as well as the specific binding to the strain CAPM 6475 in transmission electron microscopy. In the cCE, we identified several virulence-associated proteins that were immunoreactive with IgG isolated from sera of immunized pigs. Opsonization of G. parasuis strains by post-vaccinal IgG led to enhanced phagocytosis of G. parasuis by PAMs at the first two hours of infection. Moreover, opsonization increased the oxidative burst and expression/production of both pro- and anti-inflammatory cytokines. The neutralizing effects of these antibodies on the antioxidant mechanisms of G. parasuis may lead to attenuation of its virulence and pathogenicity in vivo. Together with opsonization of bacteria by these antibodies, the host may eliminate G. parasuis in the infection site more efficiently. Based on these results, the crude capsular extract is a vaccine candidate with immunogenic properties.

TbpB-based oral mucosal vaccine provides heterologous protection against Glässer’s disease caused by different serovars of Spanish field isolates ofGlaesserella parasuis

“…Correspondingly, a moderated macrophage response in the lung tissue of immunized piglets likely reflected a more balanced and effective immune strategy. This reduction in the need for extensive inflammatory infiltration, coupled with minimized collateral tissue damage, was facilitated by the G. parasuis opsonization by post-vaccinal immunoglobulins, leading to effective phagocytosis by alveolar macrophages (28). This scenario underscores the efficacy of the vaccine not only in preventing severe disease and mortality, but also in modulating the immune response to minimize collateral tissue damage, thus offering a comprehensive protective mechanism against G. parasuis infection.…”

Screening of linear B-cell epitopes and its proinflammatory activities of Haemophilus parasuis outer membrane protein P2

“…Therefore, for virulent H. parasuis , escape is the first step in inducing Glässer disease. Previous studies have shown that antibody-mediated opsonization can facilitate the phagocytosis of virulent H. parasuis by PAMs, which prevents the development of the disease in the early stages of infection ( Matiaskova et al., 2021 ). In the present study, we found that there were six linear B-cell epitopes in the loop region of OmpP2 that were exposed to the surface of bacteria, distributed in loop2 (Pt5, Pt5-II), loop3 (Pt7/Pt7a, Pt9), loop4 (Pt11/Pt11a), loop5 (Pt14), and loop8 (Pt21), suggesting that these epitopes and corresponding antibodies may participate in the opsonization and phagocytosis resistant of H. parasuis .…”

Glaesserella parasuis serotype 5 breaches the porcine respiratory epithelial barrier by inducing autophagy and blocking the cell membrane Claudin-1 replenishment

“…Mitochondria-derived antimicrobial effectors like mROS primarily generated during mitochondrial metabolism aid in bacterial killing [34]. When G. parasuis infected, released ROS gathered at the bacterial site to resist the bacteria [35]. However, the aggregation of mitochondria oxidative catastrophe induces cell death and inflammation [36].…”

“…When G . parasuis infected, released ROS gathered at the bacterial site to resist the bacteria [ 35 ]. However, the aggregation of mitochondria oxidative catastrophe induces cell death and inflammation [ 36 ].…”