In order to look into the ageing of the canine immune system we investigate
d age-related changes and associated gender-related differences in paramete
rs of innate and acquired immunity in German Shepherd dogs. We obtained the
following findings: white blood cell counts, peripheral blood lymphocytes,
lymphocyte proliferative activity and interleukin-2 (IL-2) serum concentra
tions were significantly lower in the group of old animals, whereas the con
centrations of gamma-globulins and the functional activity of the complemen
t system were significantly higher in the elderly. Phagocytic and bacterici
dal activity of polymorphonuclear cells, as well as their 'killing function
', the serum cytokine-like activities of tumour necrosis factor-ct and the
plasma concentrations of immunoglobulin G, as well as of alpha- and beta-gl
obulins, were not significantly affected by age, whereas natural killer-cel
l activity and the serum cytokine-like activities of IL-1 were significantl
y higher only in the group of female old animals. With regard to gender-rel
ated differences, lymphocyte proliferative activities as well as plasma con
centrations of alpha-globulin were significantly higher in the group of fem
ale animals, whereas the absolute numbers of segmented neutrophils were sig
nificantly lower. Species analogies with regard to ageing as presumed to ex
ist between man and laboratory rodents also seem to be applicable to the do
g. The observed age-related changes in the canine immune system are probabl
y among the main causes for the multimorbidity of old age, affecting life e
xpectancy and mortality in the dog and should be recognized and considered
by the attending veterinarian.