Mucormycotic infection in mice following prolonged incubation of sporesin vivoand the role of spore agglutinating antibodies on spore germination

Abstract

Following intranasal inoculation of mice, Rhizomucor pusillus spores are gradually cleared from the lung, with the clearance complete at 30 days. Incubation of R. pusillus spores in vivo for up to 14 days after intranasal inoculation resulted in pulmonary mucormycosis when the mice were then treated with cortisone. Spore-agglutinating IgM antibodies were detected in normal adult mice and R. pusillus-inoculated but not cortisone-treated mice. There was no correlation between antispore antibody titers and spore germination in vitro. The absence of germinated R. pusillus in inoculated but non-cortisone-treated mice appears to be due to a reversible inhibition of spore germination rather than destruction of spores by the host. The factor(s) that restrict spore germination are reversible and do not appear to be spore agglutinating antibodies.Our previous studies established an animal model of pulmonary mucormycosis (phycomycosis) in cortisone-treated mice, resulting in disease that is similar to human mucormycotic infections [12]. It was shown that viable but non-germinated Rhizomucor pusillus spores remain for long periods of time only in lung tissue of nonpredisposed (non-cortisone-treated) animals, whereas germination and infection occurs rapidly in cortisone-treated mice. Cortisone can inhibit the restriction of spore germination, and is known to interfere with various processes in inflammatory and immunologic reactions [2,7].There is evidence of acquired immunity in experimental mucormycotic infection [3]: mice previously exposed to sub-lethal doses of spores showed a high resistance to subsequent intravenous challenge with Absidia ramosa. However, vaccination with non-viable A. ramosa spores did not induce significant protective immunity to the fungus. Additionally, the passive transfer of antibody increased the resistance of cortisone-treated mice to pulmonary and disseminated mucormycosis produced by R. pusillus although spore germination and infection occurred [11]. The role of naturally acquired antispore antibodies on spore germination has not been investigated.The purpose of this study was to determine whether and for how long spores maintain the ability to germinate in vivo when the animal is subsequently cortisonetreated and what effect naturally acquired antibodies to R. pusillus spores have on spore germination in vitro.

Specific susceptibility to mucormycosis in murine diabetes and bronchoalveolar macrophage defense against Rhizopus.

“…The observation that spore germination occurred only in diabetic mice following intranasal inoculation confirms earlier studies in which germination did not occur in the lungs of normal mice (12,13,36). Moreover, we found that germination of spores occurred only in bronchoalveolar lavage fluids recovered from diabetic mice.…”

“…We have previously shown that the factor(s) which restrict spore germination are reversible and are not antispore antibodies (13). Our findings of limited spore germination in normal mouse sera and increasing spore germination in diabetic sera extend these observations to the critical step involving conversion of R. oryzae to its tissue-invasive growth phase.…”

“…There are a variety of studies, however, with conflicting data to explain the apparent propensity of diabetics to develop mucormycotic infections (3)(4)(5). Numerous animal models using various predisposing agents and routes of inoculation have been used (6)(7)(8)(9)(10)(11)(12)(13). Often these models resulted in susceptibility to a variety of opportunistic organisms and differed markedly from mucormycosis, which typically occurs in uncontrolled human diabetics (2).…”

Systemic zygomycosis

“…Normal monocytes have a similar inhibitory effect on hyphal metabolism to that of neutrophils (Diamond et al, 1982), but those from patients with chronic granulomatous disease of childhood are ineffective, suggesting that the oxidative mechanisms of microbe damage (Ramasarma, 1982) are more important than the non-oxidative ones. Macrophages from diabetics bind zygomycete hyphae less avidly than do those from normal patients (Waldorf et al, 1984a). Isolated lymphocytes, on the other hand, have no effect on the metabolism of the cultured hyphae (Diamond et al, 1982).…”

“…Cortisone administration enhances spore germination (Waldorf et al, 1984b), and greatly reduces the lethal dose (Kitz et al, 1983).…”