Surfactant protein D (
SP-D) is part of the innate immune system involved in lung homeostasis.
SP-D knockout mice show accumulations of foamy alveolar macrophages, alveolar
lipoproteinosis and
pulmonary emphysema. Three single nucleotide polymorphisms (SNPs) have been described in the coding sequence of the human
SP-D gene SFTPD. Clinical studies showed that the SNP SFTPD with a
nucleotide change from A to C resulting in a Met to Thr substitution at position 11 in the
protein (Met(11)Thr), is relevant. This study set out to create a humanised mouse model of the Met(11)Thr SNP. Transgenic mice lines expressing either Met(11) or Thr(11)
SP-D under the control of the ubiquitously expressed pROSA26 promoter in C57Bl/6
SP-D deficient mice (DKO) was created. Both Met(11) (142 ± 52 ng mL(-1) ) and Thr(11) (228 ± 76 ng mL(-1) ) mice lines expressed human
SP-D at almost similar levels. According to the literature this was within the range of
SP-D levels found in wildtype (WT) mice (253 ± 22 ng mL(-1) ). Met(11) or Thr(11)
SP-D in serum from transgenic mice bound
maltose in a
calcium-dependent manner, and binding was inhibited in the presence of
EDTA or
maltose. Bronchoalveolar lavage showed for both transgenic mice lines complementation of the DKO phenotype by restoring cell counts,
phospholipid levels and
protein content back to WT levels. Cytospins of BAL pellet cells showed a resemblance to WT but both mice lines showed some foamy alveolar macrophages. The stereological analysis showed for none of the mice lines a complete abrogation of emphysematous alterations. However, both Met(11) and Thr(11) mice lines were partially reverted back to a WT phenotype when compared with DKO mice, indicating important effects on
surfactant metabolism in vivo.