35. An important role of Fas and mediate elimination of tumor cells by killer lymphocytes. In a study of 35 primary lung and colon tumors, half the tumors were found to have amplified and overexpressed a gene for a “secreted protein” that binds to Fas ligand. The main reason for survival of these tumor cells by this “secreted Fas- ligand binding protein” may be attributed to its
    (1) decoy receptor activity.
    (2) anti-proliferative activity.
    (3) cellular defense activity against cytotoxic killing.
    (4) anti-contact inhibition activity.

The main reason for the survival of tumor cells by the “secreted Fas-ligand binding protein” is its:

(1) decoy receptor activity.

Explanation

• Tumor cells can evade immune surveillance by producing a secreted protein that binds Fas ligand (FasL) without transmitting the apoptotic signal. This protein acts as a decoy receptor, neutralizing FasL and preventing it from binding to Fas receptors on tumor cells, thus protecting the tumor cells from FasL-mediated apoptosis induced by killer lymphocytes.​

• This decoy mechanism allows tumor cells to survive and continue proliferating despite the immune attack.

• Other options such as anti-proliferative or anti-contact inhibition activities do not explain the survival mechanism related to Fas ligand binding.