Evolution of phagocytic function in monocytes and neutrophils blood cells of healthy calves.

The immune system of newborn calves is immature and must mature gradually. Understanding how this immunity is established may define different profiles. Twelve healthy calves were monitored during 8 time periods to assess the innate immune system during the first 90d. Blood samples were collected, and the blood phagocytes, identified by the expression of CD14 and CH138 surface molecules, were evaluated for phagocytic functionality (Staphylococcus aureus and Escherichia coli stained with propidium iodide) and the intracellular production of reactive oxygen species (2,7'-dichlorofluorescein diacetate oxidation). Functional changes in the CD14+ and CH138+ cells occurred at 40d of age, with sporadic increases in phagocytosis intensity and reactive oxygen species production, and decreased phagocytosis occurred at 60d of age. Therefore, fewer phagocytes were active from 40d of age, although those that were active performed their roles with greater efficacy. That change presumably occurred because the calf phagocytes began to support the immune response without the influence of passive immunity. The animals failed to reach the stability needed to complete the maturation of the innate immune response by 90d of age. These data are applicable for healthy calves only.