Chronological ageing and photoageing of dendritic cells

Ageing involves the whole organism, including the immune system. Age-depend ent alterations of immune functions are located in both the adaptive and in nate parts of the immune system. The most important cell type of the innate immune system are the dendritic cells, because their capacity to induce pr imary immune responses via professional antigen presentation is crucial for the initiation of the adaptive immune response. Evidence exists that dendr itic cells of the systemic immune system, represented by lymph-node and blo od-derived dendritic cells, as well as of local immunity, represented by La ngerhans cells of the skin, participate in ageing processes. In animal mode ls of older mice, dendritic cells of lymph nodes show degenerative characte ristics with decreased adhesion molecule expression, less dendrite formatio n, and reduced antigen trapping capacity, which together imply disruption o f functional activity. In contrast, dendritic cells generated from peripher al blood of elderly people were not impaired in their capacity to induce T- cell responses. Together, these findings indicate that in old individuals i n vivo dendritic cells of the systemic. immune system are reduced in their functional capacity to stimulate immune responses, whereas in vitro generat ed dendritic cells are fully functional, and therefore might be used in the rapeutic approaches to treat age-associated malfunctions of the immune syst em. Thus far, only morphological descriptions about age-associated changes of dendritic cells (in particular the Langerhans cells) of the skin exist. In the skin, effects of naturally occuring ageing have to be differentiated from UV-radiation-induced ageing processes. The hallmark of Langerhans cel l changes in natural as well as UV induced skin ageing is their reduction i n cell number within the epidermis. In addition, they show an atrophic morp hology with less dendrites, and less Birbeck granules. It is assumed that t hese morphological changes are associated with loss of dendritic cell funct ions, and that this contributes to age-associated development of skin cance r. Therapeutic strategies against natural and UV induced skin ageing should include a reduction of these changes of Langerhans cells in order to stren gthen the immunological functions of the body's outer surface.