Abstract
IgM was the main immunoglobulin seen by immunofluorescence and immunoperoxidase techniques in the nasal and bronchial glands of lambs before suckling. After suckling IgG was found in tissues at all levels of the respiratory tract. Some IgA also was found after suckling but there was little evidence of transport into secretions. In adult sheep IgA- and IgG-containing cells were found in nearly equal numbers in the nasal mucosa but IgA cells exceeded by 2.5:1 in the bronchial mucosa and by 2:1 in the lung. IgA cells usually outnumbered IgM cells by more than 3:1 in all tissues. The numbers of all three classes of immunoglobulin-containing cells increased in sheep with chronic respiratory disease and, although the IgA:IgG ratio was reduced, IgA remained the major locally secreted immunoglobulin. Cytoplasmic staining of epithelial cells for IgA and IgM was seen most frequently in proliferating areas, which suggested that immature cells were engaged actively in immunoglobulin transport.