A murine respiratory infection model was used to study the mechanism of protective immunity to BordeteUla pertussis. We found that nude mice, which are deficient in T cells, developed a persistent infection and failed to clear the bacteria after aerosol inoculation. In contrast, normal adult nonimmune mice cleared a respiratory infection approximately 35 days after challenge. Before bacterial clearance, antipertussis antibody levels in serum were low or undetectable, whereas consistent antigen-specific T-cell responses were demonstrated throughout the course of infection. The in vitro responses detected in immune spleen cells were mediated by a

We showed recently that the human T-lymphotropic virus, type 1 (HTLV-1), spreads directly from cell to cell via a virological synapse. The HTLV-1 virological synapse resembles the immunological synapse; each is a specialized contact between a lymphocyte and another cell that contains organized protein microdomains, and each involves repolarization of the T-cell microtubule cytoskeleton. However, formation of the virological synapse is not triggered by T-cell receptor-mediated antigen recognition. On the basis of our previous data, we postulated that formation of the viral synapse was triggered by a conjunction of two signals, one from HTLV-1 infection of the T-cell and one from cell-cell contact. We have recently identified ICAM-1 engagement as a cellcontact signal that causes the microtubule polarization associated with the virological synapse. Here we used confocal microscopy of T-lymphocytes naturally infected with HTLV-1 or transfected with individual HTLV-1 genes to investigate the role of the viral transcriptional transactivator protein Tax. Polarization of the microtubules was induced by cell-cell contact or by cross-linking T-cell surface molecules with monoclonal antibodies adsorbed to latex beads. We show that Tax, which is mainly found in the nucleus, is also present at two specific extranuclear sites as follows: around the microtubule organizing center in association with the cis-Golgi and in the cell-cell contact region. We show that expression of Tax provides an intracellular signal that synergizes with ICAM-1 engagement to cause the T-cell microtubule polarization observed at the virological synapse.

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A murine respiratory challenge model was used to examine the induction of cellular and humoral immune responses and their role in protection against BordeteUla pertussis following immunization or previous infection. Spleen cells from mice convalescing from a B. pertussis infection exhibited extensive in vitro T-cell proliferation and secreted high levels of interleukin-2 (IL-2) and gamma interferon but not IL-4 or IL-5, a cytokine profile

SUMMARYIn studies of the mechanism of immunity to Bordetella pertussis in a murine respiratory infection model, we have previously demonstrated that natural infection of immunization with a whole cell vaccine induces a potent protective immune response, which is mediated by T-helper type-1 (Th1) cells. In contrast an acellular vaccine generates Th2 cells and is associated with delayed bacterial clearance following respiratory challenge. In the present study we have investigated the apparent Th1/Th2 cell dichotomy in acquired immunity and have examined the factors that affect their induction or detection. The cytokine profiles of B. pertussis-specific T cells in immune animals were determined using antigenstimulated ex vivo spleen cells or CD4T-cell lines and clones established in the presence of interleukin-2 (IL-2) or IL-4. Antigen-specific T cells derived from mice immunized with the acellular vaccine were almost exclusively of the Th2 cell type. In contrast, T-cell lines and clones established following respiratory infection or immunization with the whole cell vaccine were predominantly of the Th1 type. However, a proportion of T cells from convalescent mice, especially when cultured in the presence of IL-4, secreted IL-4 and IL-5 with or without detectable IL-2 and interferon-g (IFN-g), suggesting that Th0 or Th2 cells were also primed during natural infection in vivo. Furthermore, when mice were assessed 6 months after infection, spleen cells produced significant levels of IL-4 and IL-5, which were not evident at 6 weeks. The route of immunization and the genetic background of the mice were also found to influence the preferential priming of Th1 cells, and this was directly related to the level of protection against respiratory or intracerebral (i.c.) challenge. Our findings underline the critical role of CD4 Th1 cells in immunity to B. pertussis, but also demonstrate that a number of factors in the in vivo priming and in vitro restimulation can skew the apparent dominance of one Th cell type over another.