Human Ig-like transcript 4 (ILT-4) is a member of the inhibitory receptor family for immune function. Little is known about the expression levels of ILT-4 in tumor cells.
We have studied the expression levels of ILT-4 both in vitro in cancer cell lines and in vivo in tumor tissues from 70 patients with non-small cell lung cancer (NSCLC) by reverse transcriptase-polymerase chain reaction, fluorescence-activated cell sorting, and immunohistochemical analysis.
Three cancer cell lines (H1299, A549, and U1810) express ILT-4 messenger RNA, and only two cell lines (H1299 and A549) express ILT-4 protein on the cell surface. Approximately 37.1% of 70 tumor tissue samples express ILT-4, which is localized in the cell membrane and cytoplasm. In addition, tumor cells and stromal and plasma cells also express ILT-4. The number of infiltrating lymphoid cells in the tumor tissues that express B7-H3 was much lower than those that did not, but there is no significant correlation between ILT-4 expression and disease progression including nodal metastasis.
These findings suggest that ILT-4 is frequently expressed in both tumor and stromal cells of NSCLC, and it might play an important role in regulation of the host immune system.