Age-related decrease of immune function is well documented. The emergence of immune disorders is explained by many factors, including thymus dysfunction, decrease in the proportion and function of naive T cells, etc. According to conventional opinion, there are several approaches to prevent these changes, such as thymus rejuvenation, stem cells recovery, modulation of hormone production and others. In our investigations of heterochronic parabiosis have shown that benefits of young immune system like actively working thymus, presence of regular migration of young hematopoietic stem cells between parabiotic partners, and exchange of hormones were unable to restore immune system of the old partner. At the same time we have established a progressive immune impairment in young heterochronic partners. Experiments aimed to studying the life span of disconnected animals, which over 3 months coexisted in heterochronic parabiosis, showed opposite changes in life expectancy, namely – weak tendency to its increase in old and its significant decrease in the young partners. The mechanism of age changes in the immune system in this model, which may lead to reduced life expectancy, is not fully understood. The first age-related manifestation in young partners seen 3 weeks after surgery was the dramatic increase of rapidly renewing CD8+44+ cells population in the spleen. A detailed analysis of further changes revealed a progressive decline of most immunological functions observable up to 3 months after surgery. While assessing level of definite hormones in the blood serum, we registered the presence of synchronization processes in their production between partners, being in most cases imposed by old body. The paper analyzes possible mechanisms of induction of changes in the immune system and their relationship with changes in hormone levels. The data obtained assume the existence certain old organism’s factors which trigger aging thus preventing rejuvenation process.