Structure of the perilobular sheath of the deep proventricular gland of the chicken: presence and possible role of myofibroblasts.

The morphology of the perilobular connective tissue of the deep proventricular gland of the chicken was examined, with special reference to myofibroblasts. Observations were made after immunohistochemical staining for alpha-vascular smooth muscle actin, gamma-enteric smooth muscle actin, and desmin, as well as by scanning and transmission electron microscopy. A perilobular sheath containing multiple layers of flat cells and an elastic network was observed around each lobule by scanning electron microscopy. The flat cells included myofibroblasts, fibroblasts, and a few smooth muscle cells. Myofibroblasts were immunopositive for alpha-vascular smooth muscle actin but immunonegative for gamma-enteric smooth muscle actin and desmin. Smooth muscle cells were immunopositive for gamma-enteric smooth muscle actin and desmin, as well as for alpha-vascular smooth muscle actin. Fibroblasts failed to bind any of the antibodies used in this study. The ultrastructural characteristics of myofibroblasts were intermediate to those of smooth muscle cells and fibroblasts. Small numbers of thin filaments and a few thick filaments were present in the myofibroblast cytoplasm. Dense bodies and caveolae were seldom observed. Cytoplasmic processes of the myofibroblasts extended along the bases of the lobules, and desmosomes and gap junctions interconnected the processes. Myofibroblasts in the sheaths may collaborate with fibers in the elastic network to prevent collapse of the glandular lobules.