Sources/Clones
Accurate (1A4), Biodesign (asm-1, A4), Biogenex (1A4), Cymbus Bioscience (asm-1), Dako (1A4), Enzo (CGA7), ICN (1A4), Immunotech (1A4), Medac (TCS), Novocastra (asm1), RDI (asm-1), Sigma (1A4) and Zymed (Z060).
Fixation/Preparation
Several of the antibody clones to a-smooth muscle actin (a-SMA) are immunoreactive in fixed paraffin-embedded sections. HIER does not significantly enhance staining.
Background
Cytoplasmic actins vary in amino acid sequences and can be separated by electrophoresis into six different isotopes, all having the same molecular weight of 42 kDa. Actins are found in muscle cells. While b and g actins may be present in muscle cells as well as most other cell types in the body, including non-muscle cells. Both striated and smooth muscle fibers differ in their expression of actin isotypes and this has formed the basis for the generation of antibodies directed at musclespecific actin subtypes. HHF35 (muscle-specific actin) identifies all four actin isoforms present in smooth muscle as well as skeletal muscle cells, pericytes, myoepithelial cells and myofibroblasts. In contrast, antibodies to a-SMA specifically identify the single a isoform characteristic of smooth muscle cells and those cells with myofibroblastic differentiation.
Applications
Antibodies to a-SMA are used in several diagnostic situations. These include the identification of myoepithelial cells, which are admixed, with epithelial cells in benign proliferative lesions of the breast, allowing their distinction from neoplastic proliferations. Myoepithelial cells also line benign ductules of the breast compared to their absence in neoplastic tubules (Raymond & Leong, 1991)a. -SMA is also a useful marker to identify myofibroblastic differentiation and has been used in studies of idiopathic pulmonary fibrosis (Ohta et al, 1995) and of the fibrogenic Ito cells in the liver (Enzan et al, 1994). In diagnostic pathology, a-SMA is used mostly as a discriminator of smooth muscle tumors in the identification of spindled and pleomorphic tumors (Jones et al, 1990). It is important to emphasize that this marker should not be used in isolation (Leong et al, 1997a). Because myogenic determinants are not always synthesized by normal and neoplastic cells simultaneously, the highest diagnostic yield is obtained with a panel of antibodies that include a-SMA, desmin and muscle-specific actin (Appendices 1.22 and 1.23). In the diagnostic context of the morphologically indeterminate spindle cell tumor, it should also be remembered that myofibroblasts may express these myogenic markers. However, expression of desmin tends to be focal and within scattered cells in myofibroblastic proliferations and these cell types show a thin and fragmented basal lamina compared to the thick, irregular and long runs of basal lamina around smooth muscle tumors (Leong et al, 1997b). Myofibroblastic proliferations may display a characteristic "tram track" pattern of distribution of muscle actins distributed in a subplasmalemmal location. Furthermore, smooth muscle cells may express low molecular weight cytokeratin. a-SMA positivity is also observed in adult and juvenile granulosa cell tumors, and in the theca externa and focally in the cortex-medulla of the ovary (Santini et al, 1995). The significance of muscle actin expression observed in mesotheliomas is presently unknown (Kung et al, 1995).
Comments
Clone 1A4 produces the best results in our hands. Immunoreactivity appears not to be enhanced by HIER or proteolytic digestion.
References
•Enzan H, Himeno H, Iwamura S, et al 1994. Immunohistochemical identification of Ito cells and their myofibroblastic transformation in adult human liver. Virchows Archives 424:249-256.
•Jones H, Steart PV, DuBoulay CE, Roche WR 1990. Alpha-smooth muscle actin as a marker of soft tissue tumors: a comparison with desmin. Journal of Pathology 162:29-33.
•Kung IT, Thallas V, Spencer EJ, Wilson SM 1995. Expression of muscle actins in diffuse mesothelioma. Human Pathology 26:565-570.
•Leong AS-Y, Wick MR, Swanson PE 1997a. Immunohistology and electron microscopy of anaplastic and pleomorphic tumors. Cambridge: Cambridge University Press, pp 64-68.
Leong AS-Y, Milios J, Leong FJ 1997b. Patterns of basal lamina immunostaining in soft-tissue and bony tumors. Applied Immunohistochemistry 5:1-7.
•Ohta K, Mortenson RL, Clark RA, et al 1995. Immunohistochemical identification and characterization of smooth muscle-like cells in idiopathic pulmonary fibrosis. American Journal of Respiratory & Critical Care Medicine 152:1659-1665.
•Raymond WA, Leong AS-Y 1991. Assessment of invasion in breast lesions using antibodies to basement membrane component and myoepithelial cells. Pathology 23:291-297.
•Santini D, Ceccarelli C, Leone O, et al 1995. Smooth muscle differentiation in normal human ovaries, ovarian stromal hyperplasia and ovarian granulosa-stromal cell tumors. Modern Pathology 8:25-30.
Bibliografia
Manual of diagnostic antibodies for immunohistology / Anthony S.-Y. Leong, Kumarasen Cooper, F. Joel W.-M. Leong.
Accurate (1A4), Biodesign (asm-1, A4), Biogenex (1A4), Cymbus Bioscience (asm-1), Dako (1A4), Enzo (CGA7), ICN (1A4), Immunotech (1A4), Medac (TCS), Novocastra (asm1), RDI (asm-1), Sigma (1A4) and Zymed (Z060).
Fixation/Preparation
Several of the antibody clones to a-smooth muscle actin (a-SMA) are immunoreactive in fixed paraffin-embedded sections. HIER does not significantly enhance staining.
Background
Cytoplasmic actins vary in amino acid sequences and can be separated by electrophoresis into six different isotopes, all having the same molecular weight of 42 kDa. Actins are found in muscle cells. While b and g actins may be present in muscle cells as well as most other cell types in the body, including non-muscle cells. Both striated and smooth muscle fibers differ in their expression of actin isotypes and this has formed the basis for the generation of antibodies directed at musclespecific actin subtypes. HHF35 (muscle-specific actin) identifies all four actin isoforms present in smooth muscle as well as skeletal muscle cells, pericytes, myoepithelial cells and myofibroblasts. In contrast, antibodies to a-SMA specifically identify the single a isoform characteristic of smooth muscle cells and those cells with myofibroblastic differentiation.
Applications
Antibodies to a-SMA are used in several diagnostic situations. These include the identification of myoepithelial cells, which are admixed, with epithelial cells in benign proliferative lesions of the breast, allowing their distinction from neoplastic proliferations. Myoepithelial cells also line benign ductules of the breast compared to their absence in neoplastic tubules (Raymond & Leong, 1991)a. -SMA is also a useful marker to identify myofibroblastic differentiation and has been used in studies of idiopathic pulmonary fibrosis (Ohta et al, 1995) and of the fibrogenic Ito cells in the liver (Enzan et al, 1994). In diagnostic pathology, a-SMA is used mostly as a discriminator of smooth muscle tumors in the identification of spindled and pleomorphic tumors (Jones et al, 1990). It is important to emphasize that this marker should not be used in isolation (Leong et al, 1997a). Because myogenic determinants are not always synthesized by normal and neoplastic cells simultaneously, the highest diagnostic yield is obtained with a panel of antibodies that include a-SMA, desmin and muscle-specific actin (Appendices 1.22 and 1.23). In the diagnostic context of the morphologically indeterminate spindle cell tumor, it should also be remembered that myofibroblasts may express these myogenic markers. However, expression of desmin tends to be focal and within scattered cells in myofibroblastic proliferations and these cell types show a thin and fragmented basal lamina compared to the thick, irregular and long runs of basal lamina around smooth muscle tumors (Leong et al, 1997b). Myofibroblastic proliferations may display a characteristic "tram track" pattern of distribution of muscle actins distributed in a subplasmalemmal location. Furthermore, smooth muscle cells may express low molecular weight cytokeratin. a-SMA positivity is also observed in adult and juvenile granulosa cell tumors, and in the theca externa and focally in the cortex-medulla of the ovary (Santini et al, 1995). The significance of muscle actin expression observed in mesotheliomas is presently unknown (Kung et al, 1995).
Comments
Clone 1A4 produces the best results in our hands. Immunoreactivity appears not to be enhanced by HIER or proteolytic digestion.
References
•Enzan H, Himeno H, Iwamura S, et al 1994. Immunohistochemical identification of Ito cells and their myofibroblastic transformation in adult human liver. Virchows Archives 424:249-256.
•Jones H, Steart PV, DuBoulay CE, Roche WR 1990. Alpha-smooth muscle actin as a marker of soft tissue tumors: a comparison with desmin. Journal of Pathology 162:29-33.
•Kung IT, Thallas V, Spencer EJ, Wilson SM 1995. Expression of muscle actins in diffuse mesothelioma. Human Pathology 26:565-570.
•Leong AS-Y, Wick MR, Swanson PE 1997a. Immunohistology and electron microscopy of anaplastic and pleomorphic tumors. Cambridge: Cambridge University Press, pp 64-68.
Leong AS-Y, Milios J, Leong FJ 1997b. Patterns of basal lamina immunostaining in soft-tissue and bony tumors. Applied Immunohistochemistry 5:1-7.
•Ohta K, Mortenson RL, Clark RA, et al 1995. Immunohistochemical identification and characterization of smooth muscle-like cells in idiopathic pulmonary fibrosis. American Journal of Respiratory & Critical Care Medicine 152:1659-1665.
•Raymond WA, Leong AS-Y 1991. Assessment of invasion in breast lesions using antibodies to basement membrane component and myoepithelial cells. Pathology 23:291-297.
•Santini D, Ceccarelli C, Leone O, et al 1995. Smooth muscle differentiation in normal human ovaries, ovarian stromal hyperplasia and ovarian granulosa-stromal cell tumors. Modern Pathology 8:25-30.
Bibliografia
Manual of diagnostic antibodies for immunohistology / Anthony S.-Y. Leong, Kumarasen Cooper, F. Joel W.-M. Leong.
