MATURATION OF CELLULAR DEFENSE IN THE RESPIRATORY-TRACT OF YOUNG CALVES

The maturation of respiratory tract defence was investigated in a long itudinal study of calves during the first 100 days of life. From day 7 , the proportions of the cell types identified in bronchoalveolar lava ge (BAL) fluid were similar to those found in adults, with a predomina nce of alveolar macrophages over polymorphonuclear neutrophils (PMNs) and lymphocytes. Functionally, bactericidal activity Of BAL cells was defective and for the first 21 days they supported intracellular bacte rial growth. At 24 hours of life, the movement of peripheral blood neu trophils to a chemotactic source was poor, but this increased rapidly during the first week of life. Like BAL cells, peripheral blood PMNS s upported intracellular bacterial growth for the first two weeks of lif e. These studies suggest that cellular defence mechanisms may be compr omised during the first week of life.