However , Page et al. cell responses in coinfected mice were comparable to those in animals solely infected withPbANKA. Our data suggest thatM. tuberculosiscoinfection is not able to change the outcome ofPbANKA-induced disease, most likely because the inflammatory response induced by the parasite rapidly dominates in mice previously infected withM. tuberculosis. == INTRODUCTION == Malaria is the most common and most deadly parasitic infection in the world. The vector-borne disease is caused by apicomplexan parasites of the genusPlasmodiumand transmitted byAnophelesmosquitoes. Clinical manifestations in humans Bay 11-7821 range from self-resolving malaria to life-threatening disease. Malaria tropica, the most severe form, is caused byPlasmodium falciparumand accounts for the majority of malaria-related deaths. A fine balance between pro- and anti-inflammatory immune responses is required for parasite clearance without the induction of host pathology associated with life-threatening complications such as respiratory distress, metabolic acidosis, severe malarial anemia, and cerebral malaria (CM). The precise mechanisms and factors predisposing to CM are far from being understood. Human studies are obviously limited by the fact that cerebral Bay 11-7821 pathology can be analyzed only postmortem. By utilizing susceptible mouse strains, it is possible to study the events that lead to cerebral pathology. Infection of C57BL/6 mice withPlasmodium bergheiANKA (PbANKA) causes experimental cerebral malaria (ECM), which shares many characteristics with the human disease (1, 2). While the exact mechanisms that lead to the development of both human and experimental CM are not fully understood, it is thought that the combination of sequestration of parasitized red blood cells (pRBCs) and a strong inflammatory immune response involving cytokines such as gamma interferon (IFN-), lymphotoxin alpha (LT-), tumor necrosis factor alpha (TNF-), and both CD8+and CD4+T cells causes CM (310). While CD4+T cells are required during the early induction phase of ECM, CD8+T cells mediate late-stage immunopathology and seem to directly contribute to blood-brain barrier damage (4, 11). In fact , antigen-specific CD8+T cells seem to be of major importance as they are activated duringPbANKA infection in the spleen and migrate to the brain just before the onset of neurological symptoms (12). A recent study recognized for the first time a conserved and highly immunogenic CD8 epitope which is cross-presented by brain microvessels duringPbANKA infection (13). It has been postulated that a certain number of Rabbit polyclonal to ITLN1 parasites in the brain is required for the full activation of cytotoxic CD8+T cells (13, 14), suggesting that, indeed, coinciding parasite and CD8+T cell sequestration causes ECM. Several groups have shown that the modulation of parasite burden protects against ECM (4, 8, 15, 16). This might at least in part be explained by the reduced availability Bay 11-7821 of parasite antigen in the brain microvasculature (13). We and others have found some degree of nonspecific protection against rodentPlasmodiumparasites in the presence of mycobacterial infection (1721). This protective effect is mainly reflected by reduced parasitemia in coinfected compared to singly infected mice and is believed to be mediated by the mycobacterium-induced proinflammatory immune response (17, 19, 20). Of interest, simultaneous infection of C57BL/6 mice withPbANKA and the closely relatedPbK173 strain, which does not induce cerebral symptoms, could protect mice from the development of ECM (16). In this coinfection model, early IFN- production induced byPbK173 has been associated with protection from ECM (16). Mycobacterium tuberculosis, Bay 11-7821 the causative agent of tuberculosis (Tb), is coendemic withP. falciparumin many regions in the world, andM. tuberculosisis a potent inducer of type I (Th1) immune responses (22), including large amounts of IFN-, the hallmark Th1 cytokine which is crucial for protection. Therefore , we were interested to see whether coinfection withM. tuberculosiswould actually reduce the risk of development ofPbANKA-induced ECM in susceptible C57BL/6 mice. In order to study this, we used a murine coinfection model where mice were infected withM. tuberculosisfollowed by inoculation withPbANKA. Contrary to our hypothesis, we found no impact of concurrentM. tuberculosisinfection on the outcome ofPbANKA infection in C57BL/6 mice. All mice developed similar levels of parasitemia and Bay 11-7821 succumbed to ECM. The immunological environments in spleen and brain did not differ between singly infected and coinfected animals; instead, the overall cytokine and T cell responses in coinfected mice were comparable to those in animals solely infected withPbANKA. Our study demonstrates that a preexisting proinflammatory immune environment does not necessarily have a beneficial effect on the outcome of concurrent malaria. Moreover, our data indicate that the elicited.