Presented at the Neonatal Society 2004 Autumn Meeting.

Clark H, Knudsen L, Mackay R, Hawgood S, Reid K, Ochs M

MRC Immunohistochemistry Unit, Department of Biochemistry, University of Oxford, UK

Background: Current surfactant formulations for the treatment of RDS do not contain the innate immune molecules, surfactant protein A and surfactant protein D (SP-A and SP-D), though accumulating data point to the importance of these molecules in protecting the lung against infection and inflammation (1). Low surfactant protein D levels have been associated with an increased risk of developing neonatal chronic lung disease (2). The importance of SP- D in regulating inflammation in the lung has been clearly demonstrated in SP-D deficient mice which show a chronic pulmonary inflammation characterised by increased numbers of alveolar macrophages in the alveolar space, alveolar lipidosis, type II cell proliferation and hyperplasia and the spontaneous development of emphysema. We have previously shown that daily intranasal administrations of recombinant human SP-D to SP-D knock-out mice reduced numbers of alveolar macrophages and partially corrected the alveolar lipidosis (3).

Aim: The aim of the current study was to establish if the partial correction of these indices affected the development of the emphysema phenotype by carrying out detailed lung morphometric studies on treated and untreated mice.

Methods: SP-D knock-out mice, aged 3 weeks, 6 weeks and 9 weeks were treated daily for 5 out of 7 days with10 micrograms of recombinant fragment of human SP-D for 9, 6 and 3 weeks respectively. Mice were sacrificed at age 12 weeks and compared to saline treated control 12 weeks old knock-out mice. Lungs were inflation fixed at 20 cm of water in situ and detailed lung morphometry carried out according to recently published methodology (4).

Results: Consistent with our previously reported findings, replacement therapy with recombinant human SP-D reduced the number of alveolar macrophages accumulating in the SP-D deficient lung. The accumulation of excess surfactant phospholipids was similarly much reduced with very scanty foamy macrophages present. The number and volume of Type II cells was also smaller in the treated groups (n=6, p<0.01). Lung volumes were smaller in the treated mice and the number of alveoli was higher in the treated group, with a smaller mean linear intercept of distal air spaces (n=6, p<0.01). Overall lung volumes were significantly smaller in treated animals (n=6, p<0.01).

Conclusion: Treatment of SP-D deficient mice with a recombinant fragment of human SP-D for as little as 3 weeks from age 9 weeks significantly improved the degree of emphysema in SP-D knock-out mice.

References
1. Clark, H.W., K.B. Reid, and R.B. Sim,. Microbes Infect, 2000. 2(3): p. 273-8.
2. Beresford, M. and N. Shaw Pediatric Research, 2003. 53(4): p. 663-670.
3. Clark, H., et al., J Immunol, 2002. 169(6): p. 2892-9.
4. Ochs, M., et al., Am J Respir Crit Care Med, 2004. 169(1): p. 120-4.