Postnatal development of leukocyte subset composition and activity in dogs

The aim of the presentation is to summarise our data on the counts and activity of circulating canine leukocytes at birth and on their changes in the first 3 months of life. On day 1, neutrophil counts were almost three times higher than lymphocyte counts. During the first week of life, a decrease of neutrophil and an increase of lymphocyte counts, resulting in a predominance of lymphocytes, were observed. Neutrophil counts reached values comparable with those in adults in 1 month. Lymphocyte counts were higher than those in adults during the first 3 months. From birth to the age of 3 months, the phagocytic activity of neutrophils was nonsignificantly higher than in young adults. When compared with adults, the peripheral blood of new-born pups contained a lower proportion of T lymphocytes (detected by CD3 and CD5 markers), with a very low percentage of CD8(+) cells and a higher proportion of CD21(+) B lymphocytes. The counts of individual subsets levelled out during the first 3 months of life, although the proportion of CD21(+) B cells remained higher all the time. Lymphocytes of new-born pups were able to respond to nonspecific mitogen stimulation. Spontaneous proliferation in vitro was higher during the first week of life. Although in vitro stimulation of lymphocytes with Concanavalin A in some pups was comparable with that of adult dogs, mean activity was weaker. Pups with zero or very low levels of maternal antibodies were able to develop specific immune responses to a parvovirus antigen as early as at 2 weeks of age. On the basis of these data, we assume that pups are born with an immune system that can respond to external stimuli. Nevertheless its development continues in the postnatal period and some parameters differ from adult values for at least 3 months after birth.