Question

• Describe how cancer cells can avoid the immune system

Answer 1

There are a number of factors that contribute to tumor persistence despite having a normal host immune system. Immune editing is one of the key aspects why tumors evade surveillance causing the tumors to lie dormant in patients for years through “equilibrium” and “senescence” before re-emerging. In addition, tumors exploit several immunological processes such as targeting the regulatory T cell function or their secretions, antigen presentation, modifying the production of immune suppressive mediators, tolerance and immune deviation. Besides these, tumor heterogeneity and metastasis also play a critical role in tumor growth. A number of potential targets like promoting Th1, NK cell, ?? T cell responses, inhibiting Treg functionality, induction of IL-12, use of drugs including phytochemicals have been designed to counter tumor progression with much success.

It is only when these cells escape from the immune response that cancer develops. ... The former recognize components arising from the body itself and protect tissues from attack using the immune system. By contrast, effector T-cells specifically recognize foreign components and their function is to destroy them.

When the immune system loses its function of surveillance, tumor cells have the ability to form a tumor. Tumor cells that evade detection can be explained by the following proposed mechanisms:

• down-regulation of major histocompatibility class (MHC) I expression - allowing antigen to go unrecognized
• lack of co-stimulatory signals needed for antigen presentation - loss or alteration of the MHC molecule
• tumor secretion of immunosuppressive products inhibiting the body's immune response
• a tumor being immunogenic by expression of one or more antigens
• antigen modulation - where the antigen either enters the cell or leaves it completely, limiting the ability of the immune system to recognize the tumor cell as 'non-self'
• tumors do not give off inflammatory warning signals.