Alveolar macrophage functions during the transition phase to active immunity in calves.

The first three to six months of the life of calves is the period during which active immunity is established. During this period, greater morbidity and mortality is caused by bronchopneumonia, because of the immaturity of the pulmonary immune system or the exaggerated cytotoxic response at subsequent infection. The aim of this study was to examine the maturity of the immune system during this phase of activation of acquired immunity in calves. For this purpose, the functions of phagocytosis and the reactive oxygen species (ROS) of alveolar macrophages CD14+ were evaluated. Further, the classes of immunoglobulins and the cytokines implicated in lymphocyte response patterns Th1 and Th2 in 10 healthy Holstein calves were quantified. Samples were taken from calves every 15 days, from the third to the sixth month of life. The alveolar macrophage CD14+ functions increased progressively until 150 days of age (phagocytosis, P=0.02, ROS, P=0.05), IgG1 and IgG2 isotype secretion reached an equilibrium, and the cytokine profiles were compatible with the Th1 response. At 165 days of age, there was a decrease in cellular function (phagocytosis P=0.02, ROS P=0.04) and an increase in IgG1 titers (P= 0.005) and IL-10 mRNA expression (P=0.09). At 180 days of life, we observed an IgG1 and IgG2 secretion balance, a decrease in IL-10mRNA expression, and an increase in IL-12 mRNA (P=0.04)and TNF-α mRNA expressions(P=0.0003) and alveolar macrophage oxidative metabolism were observed. These results indicate that the calves had an active immune response that was distinctive for the age group. The CD14+ response is more reactive at 150 days. A regulatory and/or humoral response begins at 165 days of life as the equilibrium of Th1 and Th2 profiles is reached at 180 days of life. This may be clinically relevant for the development of specific therapies and prophylactic measures for bronchopneumonia in calves at 135 to180 days of life.