Answer
Cellular immunity, also known as cell-mediated immunity, is a crucial component of the immune system that involves the activation of T lymphocytes (T cells) to recognize and destroy infected or abnormal cells. There are several classes of T lymphocytes, each with distinct functions in cellular immunity:
1. **Cytotoxic T cells (CD8+ T cells)**:
Function: Cytotoxic T cells are responsible for directly killing infected or abnormal host cells. They recognize antigens presented on the surface of these target cells in the context of major histocompatibility complex class I (MHC-I) molecules. Upon recognition, cytotoxic T cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (programmed cell death) in the target cells. This helps eliminate intracellular pathogens, such as viruses, and cancerous or otherwise damaged cells.
2. **Helper T cells (CD4+ T cells)**:
Function: Helper T cells play a critical role in coordinating the immune response by secreting cytokines that activate other immune cells. They recognize antigens presented on the surface of antigen-presenting cells (APCs) in the context of major histocompatibility complex class II (MHC-II) molecules. Helper T cells differentiate into several subsets, including Th1, Th2, Th17, and T follicular helper (Tfh) cells, each of which promotes specific immune responses. For example, Th1 cells help activate cytotoxic T cells and macrophages to combat intracellular pathogens, while Th2 cells are involved in stimulating antibody production by B cells.
3. **Regulatory T cells (Tregs)**:
Function: Regulatory T cells play a crucial role in maintaining immune tolerance and preventing excessive immune responses that could lead to autoimmune diseases or tissue damage. They suppress the activation and function of other immune cells, including T cells and antigen-presenting cells. Tregs help prevent immune reactions against self-antigens and control immune responses to external antigens, thereby preventing immune overactivity.
4. **Memory T cells**:
Function: Memory T cells are long-lived T cells that remain after the initial immune response has subsided. They "remember" specific antigens they have encountered before. If the same antigen is encountered again in the future, memory T cells can quickly mount a rapid and robust immune response. This mechanism provides immunological memory and contributes to the effectiveness of vaccines, as vaccinated individuals develop memory T cells that respond more rapidly and efficiently to pathogens.
These four classes of T lymphocytes work in a coordinated manner to provide a multifaceted and effective cellular immune response against infections and abnormal cellular conditions.
Work Step by Step
Cellular immunity, also known as cell-mediated immunity, is a crucial component of the immune system that involves the activation of T lymphocytes (T cells) to recognize and destroy infected or abnormal cells. There are several classes of T lymphocytes, each with distinct functions in cellular immunity:
1. **Cytotoxic T cells (CD8+ T cells)**:
Function: Cytotoxic T cells are responsible for directly killing infected or abnormal host cells. They recognize antigens presented on the surface of these target cells in the context of major histocompatibility complex class I (MHC-I) molecules. Upon recognition, cytotoxic T cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (programmed cell death) in the target cells. This helps eliminate intracellular pathogens, such as viruses, and cancerous or otherwise damaged cells.
2. **Helper T cells (CD4+ T cells)**:
Function: Helper T cells play a critical role in coordinating the immune response by secreting cytokines that activate other immune cells. They recognize antigens presented on the surface of antigen-presenting cells (APCs) in the context of major histocompatibility complex class II (MHC-II) molecules. Helper T cells differentiate into several subsets, including Th1, Th2, Th17, and T follicular helper (Tfh) cells, each of which promotes specific immune responses. For example, Th1 cells help activate cytotoxic T cells and macrophages to combat intracellular pathogens, while Th2 cells are involved in stimulating antibody production by B cells.
3. **Regulatory T cells (Tregs)**:
Function: Regulatory T cells play a crucial role in maintaining immune tolerance and preventing excessive immune responses that could lead to autoimmune diseases or tissue damage. They suppress the activation and function of other immune cells, including T cells and antigen-presenting cells. Tregs help prevent immune reactions against self-antigens and control immune responses to external antigens, thereby preventing immune overactivity.
4. **Memory T cells**:
Function: Memory T cells are long-lived T cells that remain after the initial immune response has subsided. They "remember" specific antigens they have encountered before. If the same antigen is encountered again in the future, memory T cells can quickly mount a rapid and robust immune response. This mechanism provides immunological memory and contributes to the effectiveness of vaccines, as vaccinated individuals develop memory T cells that respond more rapidly and efficiently to pathogens.
These four classes of T lymphocytes work in a coordinated manner to provide a multifaceted and effective cellular immune response against infections and abnormal cellular conditions.
