R P Gogolewski

Experimental Haemophilus somnus Pneumonia in Calves and Immunoperoxidase Localization of Bacteria

Pneumonia was produced in nine, conventionally reared calves by intrabronchial inoculation with Haemophilus somnus. Volumes of pneumonic lung were determined stereologically, following serial slicing of lungs fixed by vascular perfusion. Twenty-four hours after inoculation, consistent findings were: neutrophilic to fibrinoid vasculitis, degeneration of alveolar macrophages, necrotizing bronchiolitis, suppurative bronchopneumonia, lobular necrosis, and dilation and thrombosis of lymphatics. Bacteria were identified histologically by an immunoperoxidase technique and were either free in alveoli or associated with degenerate alveolar macrophages. The latter suggests that macrophage degeneration may be a result of bacteria/macrophage interaction. Immune complex deposition is unlikely to be the principal mechanism for the vasculitis because bacterial antigen was not generally found in necrotic vessel walls, and two colostrum-deprived, H. somnus antibody-negative calves also had neutrophilic vasculitis 12 to 24 hours after inoculation with the lowest dose of H. somnus used in the above experiment.

Haemophilus Somnus: Antigen Analysis and Immune Responses

Haemophilus sonrnus causes several disease syndromes in cattle and sheep but is also carried asymptomatically, especially on the genital mucosa. The factors involved in determining whether disease or asymptomatic carriage result are only beginning to be defined. Both host and bacteria contribute to the outcome of the dynamic interaction. To gain some insight into H. sonrnus/host interactions, it is necessary to consider what is known of the disease or asymptomatic conditions seen as well as current information on virulence factors and host immune response. This review constitutes the biased synthesis of the reviewers’ thoughts on available data relative to H. sonrnus infection.

Characterization of Two Haemophilus somnus Fc Receptors

Haemophilus somnus expresses two types of receptors that bind to the Fc region of bovine IgG, IgA and IgM. In this study, the relationship between these two types of Fc receptors is characterized. The high molecular mass receptors (350, 270 and 120 kDa) were secreted into the culture medium and were also in the insoluble protein fraction of the culture medium. The 41 kDa Fc receptor, which is a major outer-membrane protein, was only present in the insoluble protein fraction. Peptide mapping of the two types of Fc receptors suggests that the 41 kDa receptor is related to the high molecular mass receptor complex. Disulphide linkage is unlikely to be the mechanism of association of the 41 kDa receptor with the high molecular mass receptors since reducing agents had no effect on separating the individual receptors. Although the 41 kDa receptor is a major protein in the outer membrane of H. somnus, it does not react with convalescent bovine sera in Western blots. In contrast, convalescent bovine sera reacts intensely with the high molecular mass receptors in Western blots.