SUMMARY:Anthrax is considered a serious biowarfare and bioterrorism threat because of its high lethality, especially by the inhalation route. Rhesus macaques (Macaca mulatta) are the most commonly used nonhuman primate model of human inhalation anthrax exposure. The nonavailability of rhesus macaques necessitated development of an alternate model for vaccine testing and immunologic studies. This report describes the median lethal dose (LD 50 ) and pathology of inhalation anthrax in cynomolgus macaques (Macaca fascicularis). Gross and microscopic tissue changes were reviewed in 14 cynomolgus monkeys that died or were killed after aerosol exposure of spores of Bacillus anthracis (Ames strain). The LD 50 and 95% confidence intervals were 61,800 (34,000 to 110,000) colony-forming units. The most common gross lesions were mild splenomegaly, lymph node enlargement, and hemorrhages in various organs, particularly involving the meninges and the lungs. Mediastinitis, manifested as hemorrhage or edema, affected 29% of the monkeys. Microscopically, lymphocytolysis occurred in the intrathoracic lymph nodes and spleens of all animals, and was particularly severe in the spleen and in germinal centers of lymph nodes. Hemorrhages were common in lungs, bronchial lymph nodes, meninges, gastrointestinal tract, and mediastinum. These results demonstrate that the Ames strain of B. anthracis is lethal by the inhalation route in the cynomolgus macaque. The LD 50 of the Ames strain of B. anthracis was within the expected experimental range of previously reported values in the rhesus monkey in an aerosol challenge. The gross and microscopic pathology of inhalation anthrax in the cynomolgus monkey is remarkably similar to that reported in rhesus monkeys and humans. The results of this study are important for the establishment of an alternative nonhuman primate model for evaluation of medical countermeasures against inhalational anthrax. (Lab Invest 2003, 83:1201-1209.A nthrax is caused by Bacillus anthracis, a Grampositive, aerobic or facultative anaerobic, rodshaped spore-forming bacterium. Infection follows dermal, gastrointestinal, or inhalation routes of entry, each with slightly different clinical manifestations; however, the final outcome, regardless of portal of entry, is often septicemia. The inhalation route is most lethal, with nonspecific initial clinical signs such as fever, malaise, headache, nausea, and vomiting. The spores are phagocytosed by pulmonary macrophages and germinate in the draining mediastinal and thoracic lymph nodes. Rapid progression to chest pain and respiratory distress leads to an almost 100% case fatality rate in humans. The incubation period in humans varies from 12 hours to 5 days, depending on the dose received, and can be longer following exposure to low doses or removal of therapeutics. Death is thought to be due to effects of the two major anthrax exotoxins, lethal toxin and edema toxin. Species differ in susceptibility, with ruminants most susceptible and carnivores generally less susceptible. Hig...

Monocrotaline (MCT) is an 11-membered macrocyclic pyrrolizidine alkaloid (PA) that causes a pulmonary vascular syndrome in rats characterized by proliferative pulmonary vasculitis, pulmonary hypertension, and cor pulmonale. Current hypotheses of the pathogenesis of MCT-induced pneumotoxicity suggest that MCT is activated to a reactive metabolite(s) in the liver and is then transported by red blood cells (RBCs) to the lung, where it initiates endothelial injury. While several lines of evidence support the requirement of hepatic metabolism for pneumotoxicity, the mechanism and relative importance of RBC transport remain undetermined. The endothelial injury does not appear to be acute cell death but rather a delayed functional alteration that leads to disease of the pulmonary arterial walls by unknown mechanisms. The selectivity of MCT for the lung, as opposed to that of other primarily hepatotoxic PAs, appears likely to be a consequence of the differences in hepatic metabolism and blood kinetics of MCT. A likely candidate for a reactive metabolite of MCT is the dehydrogenation product monocrotaline pyrrole (MCTP). Secondary or phase II metabolism of MCT through glutathione (GSH) conjugation has been characterized recently and appears to represent a detoxification pathway. The role of inflammation in the progression of MCT-induced pulmonary vascular disease is uncertain. Both perivascular inflammation and platelet activation have been proposed as processes contributing to the response of the vascular media. This review presents the experimental evidence supporting these hypotheses and outlines additional questions that arise from them.

Yersinia pestis, the causative agent of plague, possesses multiple virulence determinants encoded on its three plasmids and on its chromosome. We evaluated the role of the protein capsule F1 in virulence an immunity against plague. Strains lacking F1, either those that are naturally occurring or those with genetically defined nonpolar mutations in the structural gene, retained their virulence for mice and nonhuman primates. However, both active immunization with F1, from either a recombinant vector or Y. pestis, and passive immunization with F1 monoclonal antibody protected mice from experimental infection with wild-type F1-positive organisms. These results suggest that protective immunogens like F1 need not be essential for virulence. The rare isolation of virulent F1-negative organisms from F1-immunized animals infected with F1-positive strains supports this conclusion and also suggests that, in addition to F1, an optimal vaccine against plague should include essential virulence factors as immunogens.

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The immune mechanisms by which early host-mycobacterium interaction leads to the development of severe tuberculosis (TB) remain poorly characterized in humans. Here, we demonstrate that severe TB in juvenile rhesus monkeys down-regulated many genes in the blood but up-regulated selected genes constituting gene networks of Th17 and Th1 responses, T cell activation and migration, and inflammation and chemoattractants in the pulmonary and lymphoid compartments. Overexpression (450–2740-fold) of 13 genes encoding inflammatory cytokines and receptors (IL-22, CCL27, MIP-1α, IP-10, CCR4, CCR5, and CXCR3), immune dysfunctional receptors and ligands (PD1 and PDL2), and immune activation elements (IL-3, IFN-β, TIM1, and TLR2) was seen in tissues, with low antigen-specific cellular responses. Thus, severe TB in macaques features unbalanced up-regulation of immune-gene networks without proportional increases in antigen-specific cellular responses.