Effect of Neisserial Porin in Immune Cell Apoptosis

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Neisserial porins (gonococcal Protein I [PIA or PIB] or meningococcal class 1 [PorA], 2 or 3 [PorB] proteins) are the major protein constituents of the Neisserial outer membrane. We have previously demonstrated that the Neisserial porins activate B lymphocytes, increasing the surface expression of the costimulatory ligand B7-2, which improves the B cell's ability to "costimulate" T lymphocytes. The induction of B7-2 expression is directly related to the porins' adjuvant ability. During the course of this work, we have discovered that the porins, when activating B cells, decreased the susceptibility of these B cells to activation induced cell death (AICD) or apoptosis. We found that the anti-apoptotic effect is due to a direct interaction of the porin with mitochondria (a central control point for apoptotic cell death). Immunoprecipitation experiments revealed that PorB interacts with the mitochondrial porin, VDAC. We hypothesize that this VDAC-Neisserial porin protein-protein interaction, which is similar to that of VDAC with the anti- apoptotic molecule Bcl-2, is responsible for the anti-apoptotic effect of the porins. This interaction results in an enhancement of cell survival and continued activation of B cells, which would potentiate the B cells' involvement in specific immune responses. Therefore, it is possible that this anti-apoptotic effect is a potential additional mechanism of the porins' immunopotentiating ability. This proposal will investigate the effect of Neisserial porins on the susceptibility of B cells, epithelial cells and other cell types to apoptosis. The basic aims include 1) examining the interaction of Neisserial porin with mitochondria and mitochondrial VDAC, 2) determining if alterations in cell culture conditions (especially serum withdrawal) can alter the effect of porins on apoptosis and whether this could be related to changes in cellular ATP levels and 3) determining the effect of intact Neisserial organisms on apoptosis and whether porin might play a role in this effect. These studies will yield significant findings that could both elucidate the immune stimulatory effect of Por (and potentially other bacterial components), allowing for the better use of Por as a vaccine adjuvant. In addition, these results can have significant implications in Neisserial pathogenesis, especially since we have new preliminary data that intact live meningococci can also protect cells from apoptosis.