Expression sites of the collectin SP-D suggest its importance in first line host defence: Power of combining in situ hybridisation, RT-PCR and immunohistochemistry

Surfactant proteins A and D are pattern recognition molecules that play a role in pulmonary host defence. In this paper, we describe for the first time the expression and localisation of both collectins in various porcine tissues using a combination of in situ hybridisation (ISH), RT-PCR and immunohistochemistry (IHC). SP-D was expressed in several tissues including lung, tongue, intestinal tract, thymus, skin, gall bladder and lacrimal gland. Focal SP-D expression was detected in oesophagus, stomach, kidney, liver, prostate and spleen with both histological techniques. These tissues tested negative with RT-PCR. In contrast, SP-A expression was limited to the lung as measured by ISH and IHC. Interestingly, analysis by RT-PCR showed that thymus, trachea, jejunum and duodenum are positive for the presence of SP-A mRNA. We conclude that the combination of different methods can be advantageous if tissue-specific expression is studied. The importance of SP-D in innate immune defence of the pig is underlined by its expression at the potential ports of entry of pathogens.