Improved rat model of Pneumocystis carinii pneumonia: induced laboratory infections in Pneumocystis-free animals

Abstract

An immunosuppressed rat model of Pneumocystis carinii pneumonia is described that utilizes simple, noninvasive intratracheal (i.t.) inoculation of cryopreserved parasites and results in development of severe P. carinii pneumonia within 5 weeks. This is an improvement over the most commonly used models of P. carinii pneumonia that rely on immune suppression to activate latent P. carinii infections and that often require 8 to 12 weeks to produce heavy infections of P. carinii. It is also less labor intensive than more recent models requiring surgical instillation of parasites. Our report describes a series of preliminary studies to select an appropriate strain of rat; to determine suitable methods for inducing uniform immunosuppression, P. carinii inoculation, and laboratory maintenance of P. carinii; and to determine effective animal husbandry methods for maintaining animals free from serious secondary infections. Results of our more detailed studies demonstrate that animals receiving two or three i.t. inoculations of approximately 106 cryopreserved P. carinii organisms have a predictable course of disease progression which includes moderate P. carinii infections within 3 weeks, severe P. carinii pneumonia in 5 weeks, and a high percentage of mortality due to P. carinii pneumonia in 6 weeks. Parasites were distributed evenly between the right and left lungs, regardless of the number of P. carinii inoculations administered. Non-P. carinii-inoculated immunosuppressed control rats maintained in microisolator cages remained free ofP. carinii, thus providing an important control that is missing from many P. carinii pneumonia models. Most non-P. carinii-inoculated control animals and P. carinii-inoculated rats treated with trimethoprim-sulfamethoxazole that were housed in open caging in the same room containing heavily infected animals had no detectable infections after 5 to 6 weeks of immunosuppression; however, some had a small number of P. carinii in their lungs. Because heavy, reproducible infections are achieved 5 weeks after i.t. inoculation, because few animals are lost to secondary infections, and because animals can be maintained as noninfected contemporaneous controls, this animal model is useful for the maintenance of P. carinii strains, for studies of the transmission and natural history of P. carinii, for the production of large numbers of organisms for laboratory studies, and for the evaluation of potential anti-P. carinii drugs.

The Regulation of Pulmonary Immunity

“…Lung infections with two microorganisms, Mtb and Cryptococcus neoformans (Cne), are discussed in this section as examples of infections requiring intact CMI for resolution. Animal models of chronic lung infections with several other important pathogenic organisms have been studied, including Pneumocystis carinii (Walzer, 1984;Shel-lit0 et al, 1990;Harmsen and Stankiewicz, 1990;Boylan and Current, 1992), Histoplasma capsdatum (Baughman et al, 1986;Defaveri and Graybill, 1991;Fojtasek et al, 1993;Allendoerfer et al, 1993), Blastomyces dermitiditis (Morozumi et al, 1982;Moser et al, 1988;Frey et al, 1989;Williams et al, 1994), Paracoccidiodes braziliensis (Brummer et al, 1984;Defaveri et al, 1989), Coccidiodes immitis (Cox et al, 1988), Chlamydia trachomatis and psittaci (Williams et al, 1988), Rhodococcus equi (Kanaly et al, 1993), and Mycobacterium auiumintracellulare (Takashima and Collins, 1988). Although infection with Legionella pneumophila can cause an acute pneumonia in susceptible hosts, it is a facultative intracellular bacterium; CMI is thought to be necessary for resolution of the infection.…”

Uptake and Metabolism of L‐Serine by Pneumocystis carinii carinii

“…Evidence of significant metabolic ~~ ~ a Material remaining after processing lungs from an immunosuppressed uninfected rat using the same protocol for obtaining organisms from the lungs of immunosuppressed P. carinii-infected rats. 4.4 x lo9 nuclei in final preparation. 3.5 x lo9 nuclei in final preparation.…”

“…[26] organisms were isolated from female viral antibody-negative, methylprednisolone-immunosuppressed Lewis rats weighing 130-1 50 g (Harlan Sprague Dawley, Indianapolis, IN). The rats were intratracheally inoculated with 106-1 O7 organisms, as previously described [4,11,141. The animals were housed in filtered air facilities in microisolator cages, and were aseptically handled.…”

The impact of CMV on the respiratory burst of macrophages in response toPneumocystis carinii

“…Wistar male rats were immunosuppressed with dexamethasone 1 mg/l added to the drinking water, which was furthermore supplemented with tetracyclin 1 g/l to prevent secondary infections. After two weeks of immunosuppression the animals were inoculated intratracheally with P. carinii (obtained from the American Type Culture Collection), as previously described by Boylan and Current [8]. When pneumonia ensued, usually after 6±8 weeks, animals were sacrificed, the lungs were removed aseptically, and imprints of lung sections were examined for bacterial and fungal infections other than PCP.…”