No abstract

Guinea pig eosinophils were positively identified in bronchoalveolar lavage populations and in the lung granulomas of Mycobacterium tuberculosis-infected guinea pigs. It is possible that the rapid influx of these cells, and their subsequent degranulation during acute pulmonary tuberculosis, may play a key role in the susceptibility of this animal model.The guinea pig (Cavia porcellus) is widely used in research into tuberculosis given its similarities to humans in the pathological process (7,12). After exposure to aerosol infection (ϳ50 CFU), this animal develops a potent granulomatous response characterized at first by a florid influx of lymphocytes and mononuclear phagocytes, followed more slowly by increasing lesion necrosis, fibrosis, and mineralization. As a result of this process, lesions become very large, causing extensive lung involvement and damage, killing the animal in about 15 to 20 weeks after exposure to infection.It has traditionally been assumed (2, 5) that the increasing necrosis in guinea pig lung lesions is mediated by mechanisms of acquired immunity, given the similarities to tissue-damaging delayed-type hypersensitivity. However, in a recent study (13) our investigators proposed a contrary hypothesis based upon our observation that elements of this necrosis are in fact demonstrable in very early lesions and clearly arise long before acquired T-cell-mediated immunity has had an opportunity to emerge. These small pockets of necrosis in very early lung lesions, which coalesce and form the initial lesion core structure, appear to arise from the degranulation of granulocytes that can be observed in these lesions over the first 5 to 10 days. Such granulocytes have been described in the guinea pig previously, but they have been given a variety of names, including "heterophils" and "pseudoeosinophils" (8,12). In this brief report, we provide evidence that indicates that these particular granulocytes have, in fact, the characteristics of true eosinophils and thus should be regarded as such.To establish a low-dose lung infection, specific-pathogenfree outbred Hartley strain guinea pigs (Charles River Breeding Laboratories, Inc., Wilmington, Mass.) were infected with approximately 50 CFU of Mycobacterium tuberculosis H37Rv (ATCC 27294; American Type Culture Collection, Rockville, Md.) via the respiratory route in a Madison infection chamber (University of Wisconsin College of Engineering Shops, Madison, Wis.). Between 1 and 5 weeks postchallenge, the animals were euthanized humanely by an intraperitoneal injection of 3 ml of sodium pentobarbital (Fort Dodge Laboratories, Inc.).To obtain the bronchoalveolar lavage (BAL) cell population, BAL was performed by instilling ice-cold 12 mM lidocaine (10 ml) in phosphate-buffered saline (pH 7.4) with 2% heat-inactivated fetal bovine serum (FBS; Atlanta Biologicals, Norcross, Ga.) into the lungs. Lavage cells were washed twice in RPMI 1640 (Irvine Scientific, Santa Ana, Calif.) with 1% FBS by centrifugation at 320 ϫ g for 10 min at 4°C. After the second wash, t...

In this study, we focused on three leukocyte-rich guinea pig cell populations, bronchoalveolar lavage (BAL) cells, resident peritoneal cells (PC), and splenocytes (SPC). BAL cells, SPC, and PC were stimulated either with live attenuated Mycobacterium tuberculosis H37Ra or with live or heat-killed virulent M. tuberculosis H37Rv (multiplicity of infection of 1:100). Each cell population was determined to proliferate in response to heat-killed virulent H37Rv, whereas no measurable proliferative response could be detected upon stimulation with live mycobacteria. Additionally, this proliferative capacity (in SPC and PC populations) was significantly enhanced upon prior vaccination with Mycobacterium bovis BCG. Accordingly, in a parallel set of experiments we found a strong positive correlation between production of antigen-specific bioactive tumor necrosis factor alpha (TNF-␣) and prior vaccination with BCG. A nonspecific stimulus, lipopolysaccharide, failed to induce this effect on BAL cells, SPC, and PC. These results showed that production of bioactive TNF-␣ from mycobacterium-stimulated guinea pig cell cultures positively correlates with the vaccination status of the host and with the virulence of the mycobacterial strain.Tuberculosis (TB) is a pandemic disease that represents a major public health, social, and economic problem throughout the world. Mycobacterium tuberculosis, the causative agent of TB, is estimated to have infected nearly one-third of the world's population, annually causing approximately 8 million cases and claiming the lives of nearly 2 million people. Although combination drug therapies are available for this deadly disease, the only realistic hope of eradicating this ancient killer is through the development of a standard, universally efficacious form(s) of vaccination. Although the current TB vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG), has yielded widely divergent results in several human field trials, considerable protection can be afforded by BCG in the guinea pig model of TB (30). Accordingly, the mechanisms of vaccine-induced protection in the guinea pig model can teach us important lessons about TB immunology and vaccinology that can fuel our search for a superior vaccine.Effective vaccination against an intracellular pathogen such as M. tuberculosis requires the induction of cell-mediated immunity, which is characterized by the bidirectional interactions between T lymphocytes and cells of the monocyte/macrophage lineage. The specificity of this interaction is governed by the T-cell antigen receptor, which recognizes small peptide frag-

Transforming growth factor ␤ (TGF-␤) is a cytokine which has been shown to suppress the antimycobacterial immune responses of humans and experimental animals. In this study, the contributions of TGF-␤ to cytokine production in vivo were investigated by using the established guinea pig model of tuberculous pleurisy.