The specific immune response B and T lymphocytes

Immunity Non-specific system Specific system Cells Barriers Phagocytes Cells Lymphocytes Mast cells Humoral Neutrophils Macrophages Plasma cell Antibodies B Lymphocytes Memory cell Cell mediated T Lymphocytes Helper Killer Suppressor Cytokines

THE SPECIFIC IMMUNE SYSTEM This complex system has evolved to SPECIFICALLY identify and destroy foreign invaders. The system can remember an invasion and prepare itself for further attacks. The basis for this system is a group of highly specialised cells: LYMPHOCYTES

LYMPHOCYTES Lymphocytes are produced in the bone marrow before birth. They then mature and travel around the body. They are NOT phagocytic.

Lymphocyte (huge nucleus, very little cytoplasm)

Immunity Non-specific system Specific system Cells Barriers Phagocytes Cells Lymphocytes Mast cells Humoral Neutrophils Macrophages Plasma cell Antibodies B Lymphocytes Memory cell Cell mediated T Lymphocytes Helper Killer Suppressor Cytokines

The Specific Immune response Humoral response B Cells Cell Mediated response T Cells These are 2 different types of lymphocytes that work in different ways and are matured in different areas of the body

B Lymphocytes and humoral immunity • B lymphocytes (B cells) involves antibodies which are present in body fluids or ‘humour’ • Develop and mature in the bone marrow. • Takes place in the fetus • 10 million different types • Specific • Divide by mitosis – clones

B CELL ACTIVATION B cell receptor binds to specific antigen Memory cell remains in lymph nodes Antigen Plasma cells divide and release antibodies to the antigen

Two types of cell develop: Plasma cells • Secrete antibodies • Survive a few days • Make 2000 antibodies every second! • Responsible for immediate defence Primary immune response Memory cells • Live considerably longer than plasma cells (often decades!) • Don’t produce antibodies directly • On contact with antigen, rapidly divide and develop into plasma and memory cells. secondary immune response Immunological memory (Greater intensity and more rapid)

Complete your diagram stages as we go through these.

How do B lymphocytes work? • Remember that each B cell has a specific B cell receptor on its surface. • This receptor recognises a specific antigen. There will be at least one B cell in your body for every antigen that you encounter. • When a B cell receptor binds with the correct antigen, the B cell divides by mitosis to form MEMORY CELLS and PLASMA CELLS • Plasma cells release millions of antibodies to the antigen. However, this is termed HUMORAL IMMUNITY since the antibodies cannot penetrate cells

Immunity Non-specific system Specific system Cells Barriers Phagocytes Cells Lymphocytes Mast cells Humoral Neutrophils Macrophages Plasma cell Antibodies B Lymphocytes Memory cell Cell mediated T Lymphocytes Helper Killer Suppressor Cytokines

T lymphocytes and cell-mediated immunity • Respond to organisms own cells which have been invaded by non-self material, e. g. A virus or a cancer cell. • T lymphocytes develop and mature in the Thymus gland HOW ? Antigen-presenting cells • Macrophage cells

T lymphocytes • These cells are produced in the bone marrow and then move to the thymus, where they mature. • Each T cell has a specific receptor on its surface, the T cell receptor. This recognises a single SPECIFIC antigen. • In the thymus, T cells are exposed to the body’s antigens and are killed if they react.

• T lymphocytes only respond to antigens that are attached to body cell: Cell-mediated immunity. Types of T lymphocytes: • T helper cells secrete chemicals= cytokines • T cytotoxic cells (T killer cells) make holes in cell surface membrane using Perforins (proteins) • T suppressor cell Turns off action of other lymphocytes once pathogen has been eliminated from body.

Complete your stages for cell-mediated immunity

Copy and complete the following table into your notes: T lymphocyte B lymphocyte Lymphocyte type Site of Role in immunity development and maturation Plasma cell Memory cell T Helper cell T Cytotoxic cell T Suppressor cell

Tasks: Try the following question on B lymphocytes: Jan 2001

Testing understanding. . . • Tell the person you are sat next to how B lymphocytes form part of the immune response, Swap • The partner now needs to tell you how T lymphocytes form part of the immune response.

June 2004 – T Lymphocytes Q answers 4) a) • bone marrow; R marrow on own • phagocytes / neutrophils / PMNs / monocytes / macrophages; • thymus; • plasma cells / effector cells; • antibodies; 5

(b) 1. ref to antigen presentation / described; 2. receptors on T cell (surface) are complementary to antigen; R same shape 3. ref to specificity (in context of T cells); 4. clonal selection / described; 5. clonal expansion / clonal proliferation / T cells divide by mitosis; 6. R ‘T cells clone’ unqualified / ‘reproduction’ / ‘replication’ 7. T helper cells release, cytokines / lymphokines; 8. stimulate B cells to, divide / clone / differentiate (into plasma cells); 9. stimulate macrophages to carry out phagocytosis (more actively); 10. Tc / cytotoxic / killer (T) cells, search for / kill / attach to, infected (host) cells; 11. secrete, enzymes / toxins; 12. named enzyme / toxin; e. g. hydrolytic / protease / nuclease / H 2 O 2 / free radicals / perforin 13. active immunity; 14. memory (T) cells / immunological memory; 15. ref to secondary response; e. g. more rapid / greater AVP; e. g. suppressor cells AVP; e. g. function of suppressor cells 16. cell mediated response max 7 QWC – clear, well organised using specialist terms; 1