Cells of immune system

Cells of immune system

1. TOPIC: CELLS OF IMMUNE SYSTEM HAFIZ M WASEEM UE LAHORE PAKISTAN

2. Contents Hematopoiesis Lymphoid cells NK Cells (Natural Killer Cells) B Lymphocytes T Lymphocytes Myeloid Cells Neutrophils Basophils Eosinophils Monocytes Macrophages Dendritic cells

3. Introduction White blood cells or leucocytes serve as defenders against infections. Leucocytes originate in the bone marrow. Leucocytes are classified by morphology, number of nuclei lobes and presence or absence of cytoplasmic granules. Hematopoietic stem cell in the bone marrow give rise to two major lineages: Myeloid Lineage: Platelets, erythrocytes, eosinophils, basophils, neutrophils, monocytes and dendritic cells. Lymphoid Lineage: T and B lymphocytes, NK (Natural Killer) cells and some dendritic cells.

4. Hematopoiesis

5. Monocytes Survive only a day or so before they enter the tissue to mature into macrophages. Circulate freely in blood. Involved in phagocytosis and intracellular killing of microorganisms. Monocytes are antigen processing and presenting cells. Help other WBCs and regulate immunity against foreign substances. Macrophages When monocytes enter the tissues and become macrophages. Enlarge and increase production of intracellular lysozymes . Can live for years in tissue, highly motile. Activated macrophages recognize and remove unwanted particulate matter including products of inflammation and invading organism.

6. Neutrophils Approximately 60% of the peripheral blood. Neutrophils have multi-lobed nuclei and cytoplasmic granules that stain with both acidic and basic dyes. Neutrophils play an essential role during an inflammatory response. They are rapidly mobilized from the circulation into damaged tissues. In tissues, they are active phagocytes. They destroy ingested microorganism.

7. Eosinophils Eosinophils are major effector cells in the immune system. Eosinophils constitute 1-3% of circulating leucocytes. Eosinophils have bi-lobed nuclei and cytoplasmic granules that stain with acid dye eosin. Act as host defense against nematodes and other parasitic infections and are active participants in many immune responses. Eosinophils can also be damaging as part of the inflammatory process of allergic disease. Eosinophil accumulation and inappropriate activation causes symptoms and pathology in allergic asthma.

8. Basophils Basophils have bilobed nuclei and cytoplasmic granules that stain with the basic dye methylene blue. Found in low numbers in the blood (less than 1%). They are nonphagocytic . Involved in allergic reactions. Mast cells Similar importance in allergic reactions as basophils but only found in tissues. Contain granules with preformed mediators to be released after stimulation. Secrete heparin, histamine and prostaglandins.

9. B Lymphocytes Produce antibodies with specificity for antigens and display it on their surfaces to function as BCRs. Plasma B cells: Terminally differentiated B cells that secrete immunoglobulins . Memory B cells: Stronger secondary immune response. Activation of B cell can switch to produce a different class of antibody with the same antigen specificity.

10. T Lymphocytes T lymphocytes develop in the thymus. Critical in B cell-antibody production. Mature T cells display either CD4 or CD8. Type 1 helper T cells: Interacts with mononuclear phagocytes and helps them destroy intracellular pathogens. Type 2 helper T cells: Interacts with B cells and helps them to divide, differentiate and make antibody. Cytotoxic T Cells: Responsible for the destruction of host cells that have become infected by viruses or other intracellular pathogens. Regulatory T cells: Help to control the development of immune responses and limit reactions against self tissues.

11. Natural Killer Cells Functionally cytotoxic representing an innate population that kill virally infected or tumor target cells. They do not need to recognize foreign antigens presented on the target cell. NK cells do not have a specific cell receptor. Target recognition occurs by a Killer Inhibitory Receptor which assess MHC I molecules on the target cell surface. MHC 1 molecule is lacking on infected and tumor targets. Kill targets by releasing perforin which damages target cell membranes. It induces apoptosis in the target cell.

12. Dendritic cells Arise both from the myeloid and lymphoid lineages. Abundant at interfaces between the external and internal environments (skin, lining of the gastrointestinal tract), where they encounter invading pathogens. Antigen presenting cells. Dendritic cells are very efficient at activation of T cells.

13. Conclusion The immune system has evolved to protect us from pathogens. Phagocytes and lymphocytes are key mediators of immunity. Phagocytes internalize pathogens and degrade them. Lymphocytes have receptors that recognize specific molecular components of pathogens and have specialized functions. B cells make antibodies, cytotoxic T lymphocytes kill infected cells and helper T cells coordinate the immune response by direct cell to cell interactions and the release of cytokines. The immune system may fail. This can be a result of immunodeficiency, hypersensitivity or dysregulation leading to autoimmune diseases.

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