Figure 1.

SP-D can undergo several post-translational modifications leading to changes in both structure and function. SP-D is capable of multimerization depending on the local environment. The most common isoform is the dodecameric structure, which is thought to have anti-inflammatory properties through binding via its C-type lectin domain. However, in an inflammatory or more acidic environment, the dodecameric form can change to a trimeric or monomeric isoform. The monomers and trimers are believed to have pro-inflammatory properties through binding via its collagen-like domain. When pathogens are present, the C-type lectin domain is occupied by its corresponding ligand and thus incapable of eliciting its anti-inflammatory signaling.