IMMUNOHISTOCHEMICAL LOCALIZATION OF LAMININ IN FETAL MOUSE LUNGS

Immunohistochemical localization of laminin was investigated in fetal lungs of mouse. The antigenicity of laminin was lost during the process of fixation and paraffin embedding, but restored well by the 60 min pepsin treatment. Laminin was already detected in Day 12 fetal lungs and clearly demarcated the tubule of the lung primordium. In Days 14 and 16 fetal lungs, laminin was fouad at the epitheliomesenchymal boundary of any portion of the tubule, and the proximal portion showed stronger immunoreaction than the distal portion. In Days 17 and 18 fetal lungs, the immunoreaction became generally weak, but the reaction products clearly demarcated the epitheliomesenchymal boundary. In both Day 14 and Day 16 fetal lungs, the effects of the pepsin treatment at different time intervals were explored. Without the pepsin treatment, no peroxidase reaction products were found on any part of the tissue section. When treated with pepsin for 15 min, the immunoreaction became positive at the distal portion of the tubule. After the pepsin treatment for 30 min, the immunoreaction became intense at the distal portion and appeared at the proximal portion of the tubule. The pepsin treatment for 60 min generally intensified the immunoreaction of laminin. However, after the pepsin treatment for 120 min, the immunoreactivity became rather weak at the distal portion of the tubule, but was unaltered or became stronger at the proximal portion and at the bronchus. These results indicate that the rapidly growing or expanding areas in the distal portion of the tubule of fetal lungs appear to be sustained often weakly by the basement membrane which is considered to be immature in its compositions, constituents or matrix assembly, while immunoreactive products of laminin in the basement membrane along the boundary between the undifferentiated epithelium and the adjacent mesenchyme appears consistently in a thick belt-shape.