Veterinary Immunology: Tumor Immunity and Recognition Mechanisms

What is the primary difference between normal cells and tumor cells?

Tumor cells lose control of cell growth due to multiple mutations.

What triggers the immune response to tumor cells?

Tumor cells may express abnormal proteins that can be recognized by the immune system.

Why are tumor antigens often not attacked by the immune system?

Abnormal molecules are not presented appropriately to cytotoxic T cells.

What type of cells can occasionally attack tumor cells?

Natural Killer (NK) cells, cytotoxic T cells, activated macrophages, or antibodies.

How are Natural Killer (NK) cells activated?

By interferons from virus-infected cells and IL-12 from macrophages.

What is a key characteristic of NK cells?

They do not express antigen-specific receptors but use different combinations of receptors to bind abnormal cells.

Where are NK cells primarily located in the body?

In secondary lymphoid organs, with few in the bone marrow and none in the thymus.

What receptors do NK cells express instead of conventional antigen receptors?

NK cells express CD56, CD2, CD16, CD178 (fas ligand), and CD40 ligand.

What mechanism do NK cells use to kill abnormal cells?

They use perforin to create holes in the tumor cell membrane and secrete enzymes that trigger apoptosis.

What role do macrophages play in tumor immunity?

They secrete tumor necrosis factors and have direct antitumor action by releasing cytotoxic molecules.

How do hyperactivated macrophages induce apoptosis in tumor cells?

By binding tumor necrosis factors to receptors on tumor cells.

What do macrophages detect on tumor cells for phagocytosis?

Phosphatidyl-serine expressed on the surface of tumor cells.

What is the role of cytotoxic T cells in tumor immunity?

They are important for controlling virally induced tumors but not spontaneous tumors.

What is a reason cytotoxic T cells may not encounter tumor cells?

Naïve cytotoxic T cells are confined to the bloodstream and secondary lymphoid organs.

What is antibody-mediated immunity in relation to tumors?

Antibodies to tumor cells can be found in tumor-bearing animals and may lead to tumor cell lysis.

What is antibody-dependent cellular cytotoxicity (ADCC)?

A mechanism where effector cells bind to antibodies on tumor cells via their Fc receptors.

What is one mechanism by which tumors evade the immune response?

High mutation rates lead to differences in cell surface molecules, making them less antigenic.

What are tumor-specific suppressor cells?

Cells that inhibit the host immune response in animals with tumors.

How can excess circulating tumor antigens affect immunity?

They can soak up specific anti-tumor antibodies, diverting immune effector cells away from the tumor.

What effect can prostaglandins released by tumors have on the immune system?

They can inhibit the immune functions of macrophages.

What is the significance of MHC class I molecules in NK cell activity?

MHC class I molecules on healthy cells provide inhibitory signals to NK cells, preventing them from attacking.

What happens when NK cells encounter cells lacking MHC class I molecules?

NK cells are activated to attack and kill those cells.

What is the role of gamma interferon produced by NK cells?

It primes macrophages for enhanced immune response.

What is the relationship between tumor cells and the immune system regarding antigen presentation?

Tumor cells often fail to present antigens effectively, leading to reduced immune recognition.

What is the impact of metastasis on cytotoxic T cell activation?

Metastasis allows T cells to encounter tumor cells in lymph nodes, increasing activation chances.

What is the role of complement in antibody-mediated tumor immunity?

Complement can lyse free tumor cells but is less effective against cells in solid tumors.