Human lung cancer cell lines express cell membrane complement inhibitory proteins and are extremely resistant to complement-mediated lysis; a comparison with normal human respiratory epitheliumin vitro, and an insight into mechanism(s) of resistance

Abstract

SUMMARYHuman lung cancer expresses cell membrane complement inhibitory proteins (CIP). We investigated whether human lung cancer cell lines also express cell-membrane CIP molecules and whether the biology of CIP molecules in these cell lines differs from that of CIP in normal human respiratory epithelium in culture. The cell lines ChaGo K-1 and NCI-H596 were compared with normal human nasal epithelium in primary cultures in respect to the level of cell membrane CIP expression of membrane cofactor protein (MCP; CD46), decay-accelerating factor (DAF; CD55) and CD59, in respect to the level of cell resistance to complement-mediated lysis, and in respect to the contribution of cell membrane CIP to cell resistance against complement-mediated lysis. We found, using flow cytometry, that both human lung cancer cell lines expressed MCP, DAF and CD59, as did normal nasal epithelial cells. However, normal cells showed a large subpopulation of low DAF-expressing cells (60% of all cells) and a smaller subpopulation of high DAF-expressing cells (40%), while the lung cancer cell lines showed only one cell population, of high DAF expression. In addition, both lung cancer cell lines expressed higher MCP levels, and NCI-H596 cells showed higher levels of CD59. Cell resistance to complement-mediated lysis of both lung cancer cell lines was much higher than that of normal cells. Fifty percent normal human serum, under the same concentrations of complement activators, induced lysis of less than a mean of 10% of lung cancer cells, while lysing up to a mean of 50% of nasal epithelial cells. Lung cancer cell resistance to complement was due to its ability to prevent significant activation of complement upon its cell membrane, as manifested by a failure of complement activators to increase cell membrane deposition of C3-related fragments. The exact mechanism for this resistance remains obscure. Unexpectedly, neutralizing antibodies, anti-MCP and anti-DAF were entirely ineffective and anti-CD59 was only slightly effective (18% mean cell lysis) in increasing the susceptibility of the lung cancer cell lines to complement, while the same antibodies were very effective in facilitating complementmediated lysis of the normal nasal epithelial cells (50% mean cell lysis with CD59 MoAb). On the other hand, detachment of DAF and CD59 by phosphatidylinositol-specific phospholipase C (PIPLC) from the lung cancer cell lines abrogated their resistance to lysis. We suggest that the biology of cell membrane CIP molecules in human lung cancer cell lines is different from that of CIP in normal respiratory epithelial cells. Human lung cancer cell lines are able to prevent significant complement activation upon its cell membrane and are therefore especially resistant to complement-mediated lysis. Complement resistance may serve this common and highly lethal human cancer as an escape mechanism from the body's immunosurveillance and prevent effective immunotherapy with tumour-specific MoAbs.Keywords CD46 CD55 CD59 complement inactivators nasal epithelium lung...

Down-Regulation of Human Complement Factor H Sensitizes Non-Small Cell Lung Cancer Cells to Complement Attack and Reduces In Vivo Tumor Growth

“…Only when we neutralized simultaneously factor H and CD59, an inhibitor of the MAC formation, cell lysis increased, both in H1264 and A549 cells. As previously reported, blockade of CD59 alone also increased complement-mediated cytotoxicity (28). We conclude that both factor H and CD59 play a major role in the protection of H1264 and A549 lung cancer cells against complement activity.…”

“…To make the most of this strategy, the interaction between the complement system and the tumor cell needs to be clarified. Upon activation of the classical pathway of complement, lung cancer cells show a high resistance to complement-mediated cytotoxicity compared with normal respiratory epithelial cells (28). Immunohistochemical analysis has also revealed that lung tumors have minimal deposition of C3b and apparently lack activation of the lytic membrane attack complex (30).…”

“…Intense C3 deposition in the absence of subsequent complement activation may indicate the presence of inactive C3 fragments on the cell membrane due to the action of C3 convertase inhibitors, such as the mCRPs CD46 and CD55. However, Varsano et al (28) observed that neutralizing Abs anti-CD46 and anti-CD55 were entirely ineffective in increasing the susceptibility of the lung cancer cells to complement. Interestingly, the neutralization of the same inhibitors increased significantly the level of complement-mediated lysis in normal nasal epithelial cells (28), showing a different behavior from malignant cells.…”

“…However, Varsano et al (28) observed that neutralizing Abs anti-CD46 and anti-CD55 were entirely ineffective in increasing the susceptibility of the lung cancer cells to complement. Interestingly, the neutralization of the same inhibitors increased significantly the level of complement-mediated lysis in normal nasal epithelial cells (28), showing a different behavior from malignant cells. Our present data suggest that factor H may be responsible for this inhibitory activity in lung cancer cells.…”

“…Human NSCLC cells are highly resistant to the activation of the classical pathway of complement as compared with normal cells (28). Factor H, CD46, and CD55 are complement regulators that inhibit C3 convertases, key enzymes in the activation cascade of complement.…”