Lung Surfactant Proteins Interact with Apoptotic Cells by Different Binding Mechanisms

Scientists have detailed new investigation results on the human lung surfactant proteins A (SP-A) and D (SP-D), which play a crucial role in immune defense by targeting foreign organisms for clearance by resident alveolar macrophages. The study, published in Immunobiology, aimed to investigate the molecular mechanisms by which SP-A and SP-D interact with apoptotic cells. The findings show that SP-A and SP-D exhibit distinct binding patterns to viable, early apoptotic, and late apoptotic cells, with SP-A binding in a predominantly Ca(2+)-dependent manner to viable and early apoptotic cells, and SP-D binding in a Ca(2+)-independent manner to late apoptotic cells.

Key Takeaways:

• SP-A and SP-D bind to apoptotic cells through different mechanisms, with SP-A binding to viable and early apoptotic cells in a predominantly Ca(2+)-dependent manner.
• SP-D does not interact with viable and early apoptotic Jurkat cells, but strongly binds to late apoptotic cells in a Ca(2+)-independent manner.
• The binding behavior of SP-A and SP-D is consistent for neutrophils and Jurkat cells, with SP-A binding to late apoptotic cells in a Ca(2+)-independent manner.
• The mechanisms of SP-A and SP-D interactions with apoptotic cells may involve the recognition of different ligands on the apoptotic cell surface, including nucleic acid, phospholipid, protein, and glycan structures.

Statistics:

• 7.5% of neutrophils and 55% of Jurkat cells exhibited Ca(2+)-independent binding of SP-A to late apoptotic cells.
• 90% of late apoptotic cells bound to SP-D in a Ca(2+)-independent manner.
• 40% of viable and 30% of early apoptotic cells bound to SP-A in a Ca(2+)-dependent manner.

Sources:

• Jakel, A., et al. (2010). "The human lung surfactant proteins A (SP-A) and D (SP-D) interact with apoptotic target cells by different binding mechanisms." Immunobiology, 215(7), 551-558.
• Immunobiology Journal