In parabiosis studies, a young and old animal have their circulatory systems linked. This is shown to improve measures of aging in the old animal, such as regenerative capacity, stem cell activity, and so forth. There is considerable debate over the mechanisms involved, with the current balance of evidence favoring a dilution of harmful factors and signals present in old blood and tissues rather than a delivery of beneficial factors and signals present in young blood.
In the research reported here, the authors examine the effects of parabiosis on the function of aged kidneys. It is too early to say what this will add to the discussion of specific mechanisms, but speculation is certainly possible. Even given the consensus, it has to be said that the data looks a lot one might expect to see if young immune cells are coming in and doing a better job of reducing the senescent cell burden in an aged kidney than the native, old immune system is capable of achieving. Yet it is also possible that simply altering the balance of factors in the surrounding environment spurs more of these unwanted