Introduction
The immune system is made up of a variety of cells with specialized roles in defense against infections and maintaining tolerance to the body’s own cells. Natural Killer (NK) cells and Natural Killer T (NKT) cells are two types of lymphocytes involved in immune responses. B-cell tolerance, on the other hand, is a mechanism that prevents the immune system from attacking the body’s own tissues. Let’s explore both in simple language.
a) Compare NK and NKT Cells
1. What are NK Cells?
- Natural Killer (NK) cells are a part of the innate immune system.
- They are responsible for killing virus-infected cells and tumor cells without needing prior activation or recognition of specific antigens.
2. What are NKT Cells?
- Natural Killer T (NKT) cells are a unique type of immune cell that shares features of both NK cells and T-cells.
- They are part of the adaptive immune system but respond quickly like innate immune cells.
Comparison Table
| Feature | NK Cells | NKT Cells |
|---|---|---|
| Type of Immunity | Innate | Innate and Adaptive |
| Antigen Specificity | Non-specific (no receptors for specific antigens) | Specific (have T-cell receptors) |
| Target | Virus-infected and tumor cells | Cells presenting lipid antigens via CD1d molecules |
| Receptors | Have NK cell receptors (e.g., KIR, NKG2D) | Have both NK and T-cell receptors |
| Function | Direct killing of abnormal cells | Regulate immune response and produce cytokines |
b) Mechanism of B-cell Tolerance
B-cell tolerance is a mechanism that ensures B-cells do not attack the body’s own tissues. It helps prevent autoimmune diseases.
Types of B-cell Tolerance
- Central Tolerance: Occurs in the bone marrow during B-cell development.
- Peripheral Tolerance: Occurs in the body after B-cells have matured and entered circulation.
1. Central Tolerance Mechanism
- When immature B-cells in the bone marrow bind strongly to self-antigens, they are either:
- Deleted: Undergo apoptosis (cell death).
- Receptor Editing: Modify their receptors to stop recognizing self-antigens.
- Anergic: Become inactive and non-functional.
2. Peripheral Tolerance Mechanism
- Some self-reactive B-cells may escape the bone marrow. In the peripheral tissues, they are controlled by:
- Anergy: B-cells become functionally inactive.
- Clonal Deletion: Self-reactive B-cells are destroyed.
- Regulation by T-regulatory cells: These cells suppress self-reactive B-cells.
Why is B-cell Tolerance Important?
- Prevents autoimmunity (where the immune system attacks the body’s own tissues).
- Maintains immune system balance and protects self-tissues.
Conclusion
NK and NKT cells play distinct but complementary roles in immune defense. NK cells work in innate immunity to destroy infected or cancerous cells, while NKT cells bridge innate and adaptive immunity. B-cell tolerance ensures the immune system does not turn against the body, helping to prevent autoimmune diseases. Together, these systems keep our immune response strong yet balanced.