THE ROLE OF IMMUNE SYSTEM IN TUMOR IMMUNITY

What is Immunity?

Immunity refers to the body’s natural defense against pathogens, such as bacteria, viruses, and other foreign substances. When a person is exposed to a pathogen, their immune system mounts a response to fight off the infection. This response involves the production of antibodies, which are proteins that specifically target and neutralize the pathogen, as well as the activation of immune cells, such as white blood cells, which help to eliminate the pathogen from the body.

There are several different types of immunity, including:

1. Innate immunity: This is the body’s first line of defense against pathogens. It is present from birth and provides immediate protection against infection.

2. Adaptive immunity: This type of immunity develops over time and is specific to particular pathogens. It involves the production of antibodies and the activation of immune cells to fight off infection.

3. Passive immunity: This type of immunity is acquired through the transfer of antibodies from one individual to another, such as through breastfeeding or the use of antibody-rich products like immunoglobulin.

It’s important to note that immunity is not the same as tolerance, which is the ability of the immune system to distinguish between harmful and harmless substances.

 

Antigens associated with tumors

Antigens are substances that can trigger an immune response in the body. In the context of cancer, tumor-associated antigens (TAAs) are proteins or other molecules that are specifically expressed on the surface of cancer cells. These antigens can be recognized by the immune system as foreign, leading to an immune response that targets the cancer cells.

There are several types of TAAs that have been identified, including:

1. Tumor-specific antigens: These are antigens that are only expressed on cancer cells and not on normal cells. Examples include MAGE-A and NY-ESO-1.

2. Tumor-associated antigens: These are antigens that are expressed on both cancer cells and normal cells, but at higher levels on cancer cells. Examples include HER2/neu and EGFRvIII.

3. Tumor-specific shared antigens: These are antigens that are expressed on all cancer cells of a specific type, but not on normal cells. Examples include Wilms’ tumor 1 (WT1) and PLAP (placental-like alkaline phosphatase).

 

Mechanism of tumor immunity

Tumor immunity refers to the body’s natural defenses against cancerous cells. Our immune system is capable of recognizing and eliminating abnormal cells that have the potential to become cancerous. The immune system’s ability to distinguish between healthy and cancerous cells is crucial in preventing the growth and spread of tumors.

There are several mechanisms that contribute to tumor immunity, including:

1. Surveillance by the immune system: The immune system constantly monitors the body for any abnormal cells that may have the potential to become cancerous. This surveillance is carried out by immune cells such as natural killer cells and T cells.

2. Antigen presentation: When the immune system detects abnormal cells, it presents them to immune cells called antigen-presenting cells (APCs). APCs process the abnormal cells and present their antigens (proteins) to T cells, which then recognize and attack the cancerous cells.

3. T cell activation: T cells, such as cytotoxic T cells and helper T cells, play a crucial role in eliminating cancerous cells. Cytotoxic T cells directly kill infected cells, while helper T cells assist in activating other immune cells to fight the cancer.

4. Cytokine production: Cytokines are signaling molecules that help coordinate the immune response. They can activate or suppress the activity of immune cells, and they can also recruit immune cells to the site of infection.

5. Adaptive immunity: Adaptive immunity is a specific and targeted response to cancerous cells. It involves the activation of immune cells that are specific to the cancer cells, and it can result in long-lasting immunity to the cancer.

In summary, the mechanism of tumor immunity involves the recognition and elimination of cancerous cells by the immune system. The immune system uses various mechanisms, such as surveillance, antigen presentation, T cell activation, cytokine production, and adaptive immunity, to defend against cancer.

 

Overview of Carcinoembryonic antigen and alpha-fetoprotein

Carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) are two tumor markers commonly used in clinical practice for the diagnosis, monitoring, and management of certain types of cancer. These markers are proteins that can be detected in the blood or other body fluids and their levels may be elevated in individuals with specific types of cancer.

CEA is a glycoprotein that was first discovered in 1965 and is normally produced during fetal development. It is primarily found in the cells lining the gastrointestinal tract, but it can also be present in other tissues such as the lung, breast, and pancreas. Elevated levels of CEA have been associated with various types of cancer, including colorectal, pancreatic, lung, breast, and ovarian cancers.

AFP, on the other hand, is a protein that is predominantly produced by the liver during fetal development. Its levels decrease significantly after birth but can rise again in certain pathological conditions such as liver cancer (hepatocellular carcinoma) or germ cell tumors. AFP is also used as a marker for monitoring pregnancies, as its levels can be elevated in pregnant women carrying babies with neural tube defects or certain chromosomal abnormalities.

Both CEA and AFP are measured through blood tests. The levels of these tumor markers can provide valuable information about the presence and progression of cancer. However, it is important to note that elevated levels of CEA or AFP do not necessarily indicate the presence of cancer. Other non-cancerous conditions such as inflammation or certain benign tumors can also cause an increase in these markers.

The use of CEA and AFP in cancer diagnosis and management has several clinical applications. These include:

1. Screening and early detection: CEA and AFP tests can be used as screening tools to detect certain types of cancer at an early stage when treatment options are more effective. For example, CEA testing is commonly used for colorectal cancer screening in individuals at high risk or with a family history of the disease. AFP testing is primarily used for the early detection of liver cancer in individuals with chronic liver disease or other risk factors.

2. Diagnosis and staging: Elevated levels of CEA or AFP can provide additional evidence to support the diagnosis of certain types of cancer. These markers can also be used to determine the stage or extent of the disease, which helps in planning appropriate treatment strategies. For instance, CEA levels are often measured in colorectal cancer patients to assess tumor burden and monitor response to treatment.

3. Monitoring and prognosis: CEA and AFP levels can be monitored over time to evaluate the response to treatment and detect any recurrence or progression of the disease. A decrease in marker levels may indicate a positive response to therapy, while an increase may suggest treatment failure or disease recurrence. Additionally, high baseline levels of CEA or AFP have been associated with a poorer prognosis in some cancers, providing valuable prognostic information.

It is important to note that while CEA and AFP are useful tools in cancer management, they are not definitive diagnostic tests on their own. Other diagnostic methods such as imaging studies (e.g., CT scans, MRI) and tissue biopsies are often necessary for accurate diagnosis and staging.

In summary, carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) are tumor markers that can be detected in the blood or other body fluids. Elevated levels of these markers have been associated with certain types of cancer and can be used for screening, diagnosis, monitoring, and prognosis evaluation. However, it is crucial to interpret these results in conjunction with other clinical findings and diagnostic tests for accurate assessment.