Overview
This lecture explores lymphocytes, their types, functions, characteristics, significance in the immune system, and clinical implications.
Types of Lymphocytes
- Lymphocytes are a type of white blood cell essential for immune defense.
- There are three main lymphocyte types: T cells, B cells, and natural killer (NK) cells.
- T cells are formed in the thymus and are defined by the T cell receptor, which recognizes antigens.
- B cells develop in the bone marrow and have B cell receptors on their surface to bind antigens.
- NK cells are cytotoxic and can destroy virally infected or cancerous cells.
Functions of Lymphocytes
- Lymphocytes attack infectious agents, toxins, and abnormal cells, helping prevent disease and tumor growth.
- They distinguish between self and foreign tissue, which can cause tissue rejection in transplants.
- NK cells detect and kill infected or abnormal cells quickly, providing innate immune responses.
- Some lymphocytes provide general immune responses, while others target specific microorganisms previously encountered.
Structure and Laboratory Features
- Lymphocytes are small (7-8 micrometers), some larger types reach 10-20 micrometers.
- They have a central nucleus and lack grain-like particles found in other white blood cells.
- Their nucleus stains blue or purple with Wright stain in lab tests.
Clinical Significance and Normal Ranges
- Normal adult lymphocyte count: 1,000–4,800 per microliter of blood; in children: 3,000–9,500 per microliter.
- High lymphocyte counts may indicate viral/bacterial infections, autoimmune diseases, or lymphatic cancers.
- Low counts often occur after trauma, surgery, or infections like HIV, which destroys T cells.
- CD4 and T cell levels help track HIV progression to AIDS.
- Lymphocyte counts assist in diagnosing immune system disorders and infections.
Key Terms & Definitions
- Lymphocyte — a white blood cell vital for immune defense.
- T cell — lymphocyte originating in the thymus, recognizes antigens via T cell receptor.
- B cell — lymphocyte from bone marrow, recognizes antigens via B cell receptor.
- Natural Killer (NK) cell — lymphocyte that kills infected or abnormal cells.
- Antigen — substance that induces an immune response.
- Cytotoxic — ability to kill cells.
- Wright stain — dye used to visualize blood cells in laboratory tests.
Action Items / Next Steps
- Review normal lymphocyte ranges for adults and children.
- Study the differences between T cells, B cells, and NK cells.
- Understand lymphocyte changes in disease conditions such as infections and HIV/AIDS.