Patterns and mechanisms of immunosenescence in the tree swallow Tachycineta bicolor.

PALACIOS, M. G.; CUNNICK, J. E.; WINKLER, D. W.; VLECK, C. M.

Hamburgo, Alemania

Congreso; 24th International Ornithological Conference.; 2006

International Ornithological Council

Biological aging, or senescence, is one of the least understood components of a life-history. Most knowledge about patterns and mechanisms of senescence comes from laboratory studies of model organisms, and relatively little is known about its relevance for aging in free-living populations. Immunosenescence, an age-related decline in immune function, is well documented in humans and mammalian models, but not well known in birds. We assessed patterns and mechanisms of immunosenescence in a free-living tree swallow Tachycineta bicolor population in Ithaca, NY, USA. We measured cellular (acquired) and humoral (acquired and innate) immune function of adult individuals spanning 1-8 years in age. We used in vivo and ex vivo assays of immune function to understand underlying mechanisms. Proliferation of lymphocytes ex vivo in response to T-cell mitogens (PHA and ConA) decreased with age. This suggests reduced proliferative ability of T-lymphocytes might be one mechanism underlying the previously documented age-related decline in in vivo cellular immune response in this population. In contrast, proliferation of lymphocytes in response to a B-cell mitogen (LPS) did not change with age, in accordance with our lack of detection of immunosenescence in humoral immune responses, both innate and acquired. Studies with humans and mammalian models indicate that decreased ability of lymphocytes to proliferate upon stimulation is a hallmark of immunosenescence and that B-cell function does not decline with age as pervasively as T-cell function does. Our finding of immunosenescence in avian T-cell proliferation, but not in B-cell proliferation, is in accordance with these ideas. Our study suggests that deterioration in T-cell function might be an important mechanism underlying immunosenescence in birds. In future studies, we will examine other components of immune function and variation in rate of immunosenescence in species with diverse life spans.