The influence of age and gender on the immune system: a longitudinal studyin Labrador Retriever dogs

While aging studies employing a cross-sectional design have been informativ e in documenting many age-related alterations in immune function between di fferent age cohorts within a population, longitudinal studies are invaluabl e for verifying changes at the level of the individual and for defining the precise periods of life during which particular changes occur. In the pres ent study, a battery of immunological parameters were evaluated in a group of Labrador Retrievers as part of a comprehensive longitudinal aging study. Twenty-three dogs (14 females, 9 males; from 4 to 11 years of age) were ev aluated annually for total WBC counts, lymphocyte subset distributions, nat ural killer cell activity and neutrophil phagocytic activity, and biannuall y for lymphoproliferative activity. An age-related decline in absolute numb ers of lymphocytes, T-cells, CD4-cells and CD8-cells was observed in both g enders. The distribution of lymphocyte subsets shifted with age, most drama tically in the females; percentages of B-cells declined while those of T-ce lls increased. Changes in percentages of CD4- and CD8-cells over the 8-year period were not dramatic; in females, percentages of CD8-cells increased s ignificantly in early- to mid-life and then stabilized. Lymphoproliferative responses to mitogens declined over time in both genders. Males demonstrat ed higher levels of NK cytolytic activity than females; a marginal decline in activity with age was observed. No significant a-e-related changes in th e phagocytic capacity of PMN were observed. These longitudinal findings hel p to discriminate between those immune parameters which change most dramati cally in early-life versus those which either change more dramatically late r in life or change gradually over the entire span of life. In addition the y identify significant gender differences in several parameters and corrobo rate our previously published cross-sectional aging data in the same specie s. (C) 2001 Elsevier Science B.V. All rights reserved.