The nature of the factors that can induce age-related changes in the immune system of young partners during Heterochronic Parabiosis is unknown. Plasma is a possible carrier of aging inducers .
Old plasma injections lead to the increase in the number of CD4+8+ splenocytes. There is no significant changes in the thymus mass and subpopulations. Thus, old plasma has little effect on the immune system of young mice.
Whole microparticle fraction removal leads to changes in the old plasma activities. Particularly, mitogen-induced splenocyte proliferation and DN population of thymocytes are increased.
This may indicate that the plasma from old donors has specific factors which promote immune cell hyperproliferation. Microparticles prevent this proliferation and serve as stabilizers.
Alternatively plasma from old mice may have rejuvenation effect of proliferation activity of immune cells, and exactly microparticles may be the key aging-promoting factor in the plasma.