Problem 11 - Biology: Concepts and Applications

Question

_______ are targets of cytotoxic T cells. a. Extracellular virus particles in blood b. Virus-infected body cells or tumor cells c. Parasitic flukes in the liver d. Bacterial cells in pus e. Pollen grains in nasal mucus

Step-by-Step Solution

Answer

The correct answer is (b) Virus-infected body cells or tumor cells.

Step 1: Understand the Role of Cytotoxic T Cells

Cytotoxic T cells, also known as cytotoxic T lymphocytes (CTLs), play a crucial role in the immune system. Their primary function is to identify and destroy infected or abnormal cells within the body. These include virus-infected cells and cancerous or tumor cells.

Step 2: Examine the Options

Go through each option one by one: - Option (a) 'Extracellular virus particles in blood' refers to viruses outside of body cells, which are not targeted by cytotoxic T cells directly. - Option (b) 'Virus-infected body cells or tumor cells' are indeed the type of targets cytotoxic T cells are known to attack and destroy. - Option (c) 'Parasitic flukes in the liver' involve large multicellular parasites, which are generally dealt with by other parts of the immune system, such as eosinophils. - Option (d) 'Bacterial cells in pus' are extracellular bacteria and typically targeted by antibodies or phagocytes, not cytotoxic T cells. - Option (e) 'Pollen grains in nasal mucus' are external allergens attacked primarily by the immune responses involving antibodies.

Step 3: Identify the Correct Answer

Based on the function of cytotoxic T cells, only option (b) 'Virus-infected body cells or tumor cells' fits as their primary targets. Cytotoxic T cells recognize and destroy these cells through the presentation of abnormal antigens on the cell surface.

Key Concepts

Immune System

The immune system is the body's defense mechanism against infections and diseases. It is an intricate network of cells, tissues, and organs that work cooperatively to ward off foreign invaders, such as pathogens like bacteria, viruses, and parasites.
The immune system can be divided into two main types: the innate immune system and the adaptive immune system.

• The **innate immune system** is the body's first line of defense, providing a rapid but non-specific response.
• The **adaptive immune system**, on the other hand, is more specialized and slower to respond, but it targets specific pathogens that the body has encountered previously.

Cytotoxic T cells are a part of the adaptive immune system. They seek and destroy cells presenting problematic antigens, usually indicating infection or abnormal cell activity. They identify threats by recognizing these antigens through the major histocompatibility complex (MHC) class I molecules found on most cells.

Virus-Infected Cells

Virus-infected cells pose a significant challenge to the immune system because viruses replicate inside the host cells, making them less detectable by the body's defenses. However, cytotoxic T cells are equipped to deal with these infections efficiently.
When a cell is infected by a virus, it often presents viral antigens on its surface. This is a call for help to the immune system.

• Cytotoxic T cells recognize these antigens using their unique receptors.
• Upon recognition, they trigger a series of responses to destroy the infected cell, usually by releasing enzymes that induce apoptosis, or cell death.

This process effectively halts the spread of the virus, targeting it at its replication site, thereby stopping or slowing the infection. This is a vital process in viral control and maintaining health.

Tumor Cells

Tumor cells are abnormal cells that divide uncontrollably, which may form masses called tumors or spread throughout the body, leading to cancer. Similar to virus-infected cells, tumor cells can present antigens that cytotoxic T cells recognize as signals of something gone awry within the body.

• The immune system, particularly cytotoxic T cells, plays a crucial role in surveilling against abnormal cells by constantly monitoring and eliminating potential threats like emerging tumor cells.
• This process is known as immune surveillance.

When cytotoxic T cells detect tumor-specific antigens presented by MHC class I molecules, they initiate an immune response to destroy these cells. This action is crucial in preventing the development and spread of tumors, potentially leading to cancer if unchecked. Despite this, some tumor cells can evade the immune system by altering their antigen presentation, necessitating ongoing research to enhance immune response effectiveness in cancer therapies.