Susceptibility of mice genetically deficient in SP-A or SP-D gene to Invasive Pulmonary Aspergillosis

Pulmonary surfactant proteins, SP-A and SP-D, are carbohydrate pattern recognition molecules of innate immunity, which significantly enhance phagocytosis and killing of Aspergillus fumigatus, a pathogenic fungus, by neutrophils and macrophages. The present study examined the susceptibility of immunosuppressed SP-A gene deficient (SP-A^-/-) or SP-D gene deficient (SP-D^-/-) mice to A. fumigatus conidia challenge compared to wild-type (WT) mice. A. fumigatus-challenged SP-A^-/- (SP-A^-/- IPA) mice showed less mortality (40%) than the WT-IPA mice (100%) and increased mortality (60%) following administration of SP-A with decreased TNF-α and IFN-γ to IL-4 ratio than SP-A^-/- IPA mice. The SP-D^-/- IPA mice (57.14%) showed similar mortality as WT-IPA mice (60%). However, the SP-D ^-/- IPA mice (42.86% mortality on day 2) died earlier than the WT-IPA mice (20% mortality on day 2), showed a higher hyphal density and tissue injury in lungs. Treatment with SP-D or a recombinant fragment of human SP-D rhSP-D reduced the mortality to 50% and 33%, respectively, concomitant with higher IFN-γ to IL-4 ratios in treated SP-D^-/- mice, compared to untreated control group. The results showed that SP-D gene deficient mice are more susceptible to IPA while SP-A gene deficient mice acquire resistance to IPA.