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Abstract Neisseria meningitidis is normally a human nasopharyngeal commensal but is also capable of causing life-threatening sepsis and meningitis. N. meningitidis secretes several virulence-associated proteins including Neisserial autotransporter lipoprotein (NalP), an immunogenic, type Va autotransporter harboring an S8-family serine endopeptidase domain. NalP has been previously characterized as a cell-surface maturation protease which processes other virulence-associated meningococcal surface proteins, and as a factor contributing to the survival of meningococci in human serum due to its ability to cleave complement factor C3. Here, recombinant NalP (rNalP) fragments were purified and used to investigate the interaction of NalP with host cells. Flow cytometry and confocal microscopy demonstrated binding and uptake of rNalP into different human cell types. High-resolution microscopy confirmed that internalized rNalP predominantly localized to the perinuclear region of cells. Abolition of rNalP protease activity using site-directed mutagenesis did not influence uptake or sub-cellular localization, but inactive rNalP (rNalPS426A) was unable to induce an increase in human brain microvascular endothelial cell metabolic activity provoked by proteolytically-active rNalP. Our data suggests a more complex and multifaceted role for NalP in meningococcal pathogenesis than was previously understood which includes novel intra-host cell functions. Highlights • Recombinant NalP is internalized by a variety of human cell types. • Internalized NalP is localized predominantly to the perinuclear region of cells. • Exposure to NalP provokes increases in cell metabolic activity. • Effects on cell metabolic activity are dependent on NalP proteolytic activity. [ABSTRACT FROM AUTHOR]

Abstract: Actinobacillus pleuropneumoniae is a major respiratory pathogen of pigs; current vaccines provide only limited protection. AasP, a subtilisin-like serine protease, is a conserved outer membrane-localised autotransporter protein. We hypothesized that AasP would induce protective immunity and may thus constitute a useful component of a vaccine against A. pleuropneumoniae infection. Here we confirm experimentally that AasP is an antigenic in vivo-expressed protein. In pig protection studies, a detectable specific antibody response was induced in response to recombinant AasP. However, the vaccine was not capable of protecting pigs from colonization, infection or severe clinical disease resulting from challenge with the homologous A. pleuropneumoniae strain. [Copyright &y& Elsevier]