The porin (PorB) of Neisseria gonorrhoeae is an intriguing bacterial factor owing to its ability to translocate from the outer bacterial membrane into host cell membranes where it modulates the infection process. Here we report on the induction of programmed cell death after prolonged infection of epithelial cells with pathogenic Neisseria species. The underlying mechanism we propose includes translocation of the porin, a transient increase in cytosolic Ca 2⍣ and subsequent activation of the Ca 2⍣ dependent protease calpain as well as proteases of the caspase family. Blocking the porin channel by ATP eliminates the Ca 2⍣ signal and also abolishes its pro-apoptotic function. The neisserial porins share structural and functional homologies with the mitochondrial voltage-dependent anion channels (VDAC). The neisserial porin may be an analogue or precursor of the ancient permeability transition pore, the putative central regulator of apoptosis.

A characteristic of human pathogenic Neisseriae is the production and secretion of an immunoglobulin (Ig)A1-specific serine protease (IgA1 protease) that cleaves preferentially human IgA1 and other target proteins. Here we show a novel function for native IgA1 protease, i.e., the induction of proinflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-8 from peripheral blood mononuclear cells. The capacity of IgA1 protease to elicit such cytokine responses in monocytes was enhanced in the presence of T lymphocytes. IgA1 protease did not induce the regulatory cytokine IL-10, which was, however, found in response to lipopolysaccharide and phytohemagglutinin. The immunomodulatory effects caused by IgA1 protease require a native form of the enzyme, and denaturation abolished cytokine induction. However, the proteolytic activity is not required for the cytokine induction by IgA1 protease. Our results indicate that IgA1 protease exhibits important immunostimulatory properties and may contribute substantially to the pathogenesis of neisserial infections by inducing large amounts of TNF-α and other proinflammatory cytokines. In particular, IgA1 protease may represent a key virulence determinant of bacterial meningitis.