Final answer:
T cells are crucial to the adaptive immune system because they activate B cells, directly attack and destroy infected cells, regulate immune responses, and establish immunological memory. The absence of T cells severely hampers the body's ability to respond to infections, as seen in conditions like HIV/AIDS, which deplete helper T cells.
Step-by-step explanation:
The assertion "no T cells, no immunity" underlines the critical role of T cells in the adaptive immune system's functioning. Adaptive immunity is composed of two main components: humoral immunity, which involves antibodies produced by B cells, and cellular immunity, which involves T cells directed against intracellular pathogens. T cells are essential for several reasons:
- T cells help activate B cells to produce antibodies and facilitate humoral immunity.
- Cytotoxic T cells (Tc) are specialized in attacking and destroying infected or cancerous cells, particularly crucial for combating viral infections that occur within host cells, beyond the reach of antibodies.
- Helper T cells (Th) orchestrate the immune response by releasing chemical signals that regulate the activity of other immune cells.
- The adaptive immune system also relies on T cells for the generation of immunological memory, leading to a more efficient and rapid response to subsequent encounters with the same pathogen.
Without T cells, the body lacks the cellular response to directly destroy infected cells and has impaired capability to create immunological memory, rendering the adaptive immune response severely compromised. In diseases such as HIV/AIDS, where T cell populations, particularly helper T cells, are depleted, patients suffer from severe immunodeficiency due to the inability of the adaptive immune system to function effectively.