Cellular garbage collection

Distinct methods of disposal of dead cells by the immune system have been described in a paper published online this week in Nature Immunology.

Billions of dead cells arise daily in the human body and their accumulation can trigger tissue pathology. Specialized cells, which act as cellular garbage collectors, are therefore necessary to remove these dead cells.

Greg Lemke and colleagues find that these immune system cells use different cellular receptors, collectively called TAM receptor tyrosine kinases, for this process. The TAM receptors, Mer and Axl, recognize proteins that latch onto the surface of dead cells, marking them for disposal. Mer functions predominantly under normal conditions to maintain tissue immune tolerance by removing dead cells. In contrast, Axl production is rapidly increased and takes over the removal process during inflammation.

The distinctions between Mer and Axl functions are important as current clinical therapies that target TAM receptors are being developed for cancer and autoimmune diseases.