Monoclonal Antibody to Secretory Component

Background
Secretory component is an ~80 kDa glycoprotein important in mucosal immunity. Secretory component is the extracellular cleaved ectodomain of the polymeric immunoglobulin (Ig) receptor (pIgR) which transports Igs across mucosal membranes into secretions (reviewed in Johansen, 2011). IgA is the main immunoglobulin in secretions and pIgR is highly expressed in intestinal epithelial cells (ECs). Dimeric IgA (dIgA) manufactured by antibody producing plasma cells in the intestinal lamina propria binds to pIgR at the basolaterial membrane surface of ECs. pIgR-dIgA complexes are internalized and transcytosed across ECs to the apical surface. Secretory component is then proteolytically cleaved off from the pIgR and released into the lumen together with dIgA. Secreted IgA (SIgA) consists of dIgA + secretory component. SIgA protects the mucosa from microbial invasion, and bound Secretory component enhances immune function by inhibiting SIgA proteolytic degradation.

The SC05 antibody clone reacts with both free and bound secretory component (Bartek, 1989); it does not react in western blots of cell lines that lack secretory component. The antibody is useful for studying the distribution and level of both free and bound secretory component. Secretory component is differentially expressed in epithelium, and the antibody is a useful marker for identifying subpopulations of epithelial cells and epithelial differentiation (Fichorova, 1997 & 1998). Secretory component antibodies have also been part of antibody marker panels for differential identification of glandular carcinomas (Brown, 1993; Harris, 1981; Kalhounou, 2010). The Secretory component antibody is a useful research tool for studying mucosal immunity, inflammation, remodeling, differentiation and tumorigenesis, all processes associated with differential secretory component expression (Bartek, 1990; Johansen, 2011). Since the presence of secretory component implies immunological function, the antibody can help identify cells regulating immunological processes (Fichorova, 1999). The antibody can also be used to indirectly assess SIgA expression since SIgA contains bound secretory component (Vancikoa, 2003).

Antigen
Partially purified secretory component from human colostrum was used as immunogen to generate the antibody (Bartek, 1988 & 1989). The antibody reacts with a reduction-resistant epitope present in both free and SIgA bound Secretory Component. However, the exact epitope recognized by the antibody has not been mapped.

Application Notes
The optimal dilution for a specific application under a given set of experimental conditions should be determined by the investigator.

Immunohistochemical staining of formalin/paraffin tissues is enhanced by unmasking of the target epitope with trypsin at 1 mg/ml PBS for 5 min at 37 degrees C. Note: enzyme digestion may be better than citrate buffer based epitope unmasking according to Brown, 1993. However, we have found antigen retrieval with Heat Induced Epitope Retrieval (HIER) in Citrate buffer (pH6.0) also works well. In this case, de-paraffinized tissue sections should be boiled in this buffer for 5 minutes followed by cooling at room temp for 20 minutes.

Reference
1. Kalkounou I, V Smyrniotis, I Vassilious, D Voros, A Kondi-Pafiti. Hellenic J Surg 82:155-160 (2010).  IHC (P): thyroid neoplasms.
2. Gologan A, M Acquafondata, R Dhir, AR Sepulveda. Arch Pathol Lab Med 132:1295-1301 (2008). IHC (P): gastric adenocarcinomas and intestinal metaplasia (Figs 1-4, Tables 1-3).
3. Brown RW, GM Clark, AK Tandon, DC Allred. Mutliple –marker immunohistochemical phenotypes distinguishing malignant pleural mesothelioma pulmonary adenocarcinoma. Hum Pathol 24:347-354 (1993).
4. Harris JP, MA South. Secretory Component; A glandular epithelial cell marker. Am J Pathol 105:47-53 (1981).
5. Matysiak-Budnik T, IC Moura, M Arcos-Fajardo et al. JEM 205:143-154 (2008).
6. Bartek J, J Bartkova, J Taylor-Papadimitriou. Histochem J 22:537-544 (1990).  IHC (P): human breast, Fig 3C, D.  Note: Tissues were fixed in methacarn and embedded in paraffin.
7. Fichorova RN, JC Rheinwald, DJ Anderson. Bio Reprod 57:847-855 (1997). IHC (F) and ICC: epithelial tissue and tumorigenic (HeLa), immortalized and primary cell lines all originating from the vagina or cervix, Figs 2, 3 & Table 2,
8. Fichorova RN, DJ Anderson. Bio Reprod 60:508-514 (1999). IHC (F) and ICC: epithelial tissue and cell lines all originating from the vagina or cervix, Fig 3A-F.
9. Tang Q-J, K-Z Tao, Y Liu, X-J Sun, M-Y Gene, C-L Jiang. J Mol Histol 36:331-335 (2005). IHC (P): Fig 1 (rat small intestine); Immunoelectron microscopy: Fig 2 (rat small intestine).  On the electron microscope level, Secretory Component localized to the Paneth cells where it was detected in rough endoplasmic reticulum, Golgi complexes, basal membranes, and Secretory granules.
10. Polosukhin VV, JM Cates, WE Lawson, R Zaynagetdinov, AP Milstone, PP Massion, S Ocak, LB Ware, JW Lee, RP Bowler, AV Konov, SH Randell, TS Blackwell. Am J Resir Crit Care Med 184:317-327 (2011). IHC (P): lung, see publications for details.
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