Dose–response analysis demonstrates that a higher concentration (10 μm) of galectin-1 is required to induce T cell apoptosis, indicating that dimerization of galectin-1 is necessary for induction of apoptosis [55, 56]. However, increased deposition of galectin-1 on MUC-16/CA-125 in ovarian carcinoma results in facilitated dimerization and efficient presentation of galectin-1 leading to the death of tumour-infiltrating T cells even at a very low concentration [57]. In fact, sequestration of galectin-1 by MUC-16 is so efficient that despite overexpression of galectin-1 by ovarian cancer cells, the serum
concentration is lower than that of normal individuals [58]. Association of galectin-3, a relative of galectin-1, with MUC-2 in colon carcinoma cells prevents Smad inhibitor tumour apoptosis and promotes proliferation and growth of the Doxorubicin tumour [57, 58]. Further, galectin-3, by interacting with cancer-associated MUC-1 via TF, promotes cancer cell adhesion to endothelium by revealing epithelial adhesion molecules that are otherwise concealed by MUC-1 [59]. Inefficient tumour lysis characterizes most of the mucin overexpressing cancers. For instance, overexpression of MUC-4/SMC or MUC-16 inhibits lymphokine-activated killer
(LAK) cells-mediated tumour lysis by masking the surface antigens on the tumour target cells [60, 61]. Efficient lyses of tumour cells by immune effectors require a clear distinction in their approach when it comes to mucin-expressing tumours. For one, mucins are superbly
designed to protect the cells from both internal and external insults, and the penetration of mucin barrier and access to the tumour cells require both physical and physiological overturns. For example, expression of mucin antigens and membrane-spanning glycoprotein, Cancer Antigen (CA)-125, in ovarian cancer exerts immunosuppressive Lck effects by entrapping/shedding effectors of the complement cascade and attenuates complement lysis of antibody-sensitized cells [62, 63]. Furthermore, lysis of episialin− melanoma cells by CLTs and LAKs involves a broad spectrum of adhesion molecules, whereas only LFA-1/ICAM-1 and CD2/LFA-3 pathways are exclusively utilized for the lysis of episialin + melanomas, blocking of which results in complete inhibition of cytolytic ability [64]. Similarly, innate immune response is capable of recognizing chemotactic signals of secreted MUC-1 from DA3 mammary tumours expressing MUC-1/Sec phenotype. Secretary MUC-1 is capable of recruiting 3–4 times as many macrophages/APC as transmembrane phenotype (MUC-1/TM) and is mainly due to upregulation of MCP-1 (CCL-2) by MUC-1/Sec expression [65]. Naturally, DA3/sec tumours are more susceptible to CTL-mediated rejection than DA3/TM tumours and therefore fail to develop in Balb-c mice [65]. Recruitment of macrophages and monocytes involves interaction of GluNAc residues of mucin with calcium-type human macrophage lectin.