Leukocytes and Immune Responses Quiz

Leukocytes (White Blood Cells)

• Monocytes are transformed into macrophages in tissues.
• Lymphocytes are involved in immune responses.
• Lymphocytes are classified as T and B cells.
• T-lymphocytes differentiate in the thymus gland.
• B-lymphocytes differentiate in the liver, spleen, and bone marrow.
• T-lymphocytes (85% of lymphocytes) are involved in cell-mediated immunity.
• T-lymphocytes secrete Interferon γ (glycoprotein that acts as an antiviral agent).
• T-lymphocytes contain lysosomes with antifungal agents.
• Cytotoxic T cells (T-killer cells) are a type of T cell.
• T cell receptors bind to specific antigens, and cytotoxic substances are released into foreign cells (bacteria, viruses, tissue cells).
• Cytotoxic T cells attack cells of transplanted organs and cancerous cells.
• B-lymphocytes (15% of lymphocytes) are involved in humoral immunity.
• B-lymphocytes secrete IgA, Interferon α & β.
• Activated B cells proliferate and transform into plasma cells (antibodies production).
• Activated B cells also transform into memory cells (B memory cells) that produce antibodies for the same antigens.

Leukocytes Disorders

• Leukocytosis is an increase in leukocyte numbers, often seen in bacterial infections.
• Leukopenia is a decrease in leukocyte numbers, often seen in the early stages of viral infections.
• Leukemia is a cancer of white blood cells, characterized by leukocytosis.

Thrombocytes (Platelets)

• Thrombocytes are produced in the bone marrow by fragmentation of the cytoplasm of megakaryocytes.
• About 1/3 of the marrow output of platelets is trapped in the spleen.
• The normal platelet count is 150,000-400,000/µL (250,000).
• Platelets have a lifespan of 7-10 days.
• Platelets are removed from circulation by the tissue macrophage system, primarily in the spleen.
• Thrombopoietin, produced by the liver and kidney, is the major regulator of platelet production.
• Platelet cytoplasm contains contractile proteins (actin and myosin), dense granules (contain serotonin and ADP secreted in response to platelet activation), and α-granules (contain secreted proteins like platelet-derived growth factor (PDGF) that stimulates wound healing, fibrin stabilizing factor (factor XIII), and other clotting factors).
• Platelet cytoplasm stores large quantities of Ca++.

Functions of Thrombocytes

• Thromboxane A attracts more platelets to injured vessels through chemotaxis.
• Growth factors increase the growth and number of endothelial cells.
• Plasma thromboplastin activates the intrinsic pathway for fibrin formation.
• Platelet-derived growth factor (PDGF) stimulates wound healing.

Blood Coagulation (Clotting)

• Haemostasis is the process of forming clots in the walls of damaged blood vessels to prevent blood loss (haemorrhage, bleeding) and maintain blood in a fluid state within the vascular system.
• Haemostasis involves three main steps: vascular spasm, formation of a platelet plug, and blood coagulation.
• Blood coagulation involves a cascade of reactions that activate coagulation factors, most of which are proteins synthesized by the liver in inactive form.
• Vitamin K is needed for the synthesis of coagulation factors II, VII, IX, and X.
• Activated coagulation factors act as proteolytic enzymes that activate other inactive enzymes.
• Many of the coagulation reactions require Ca++ and platelet phospholipids.

Intrinsic Pathway (of Blood Coagulation)

• The intrinsic pathway is initiated by contact of coagulation factors with collagen and kallikrein.
• This pathway involves the activation of XII, XI, IX, and X coagulation factors.

Extrinsic Pathway (of Blood Coagulation)

• The extrinsic pathway is initiated by tissue thromboplastin (released from damaged tissues).
• This pathway involves the activation of VII and X coagulation factors.

Common Pathway (of Blood Coagulation)

• Both the intrinsic and extrinsic pathways converge on the common pathway, leading to the activation of prothrombin (factor II) into thrombin.
• Thrombin converts fibrinogen into fibrin, which forms a mesh-like structure that traps blood cells and forms a clot.
• Factor XIII stabilizes the fibrin clot.

Anticoagulants

• Natural anticoagulants include:
  • Endothelium factors: smoothness of the endothelium (XII with collagen), glycocalyx (mucopolysaccharides).
  • Heparin
  • α-Macroglobulin
• Synthetic anticoagulants include:
  • Na-Citrate
  • Na-Fluoride
  • Ca-oxalates
  • EDTA
  • Heparin
• Anticoagulants prevent blood clotting.

The Plasma

• Plasma is the liquid component of blood.
• Plasma transports nutrients, gases, wastes, hormones, and other substances throughout the body.

Plasma Components

• Plasma is composed of:
  • Water (90-92%)
  • Proteins (6-7%)
    • Albumin, fibrinogen, and globulins.
  • Other components (2-3%), including: fats, carbohydrates (glucose), electrolytes, gases (O2, CO2), chemical messengers.

Plasma Proteins

• Plasma proteins are produced by the liver (except for immunoglobulins).
• Plasma proteins are produced by the rough endoplasmic reticulum (ER) in hepatocytes and exported into the blood via the Golgi complex.
• Plasma proteins have various functions, including:
  • Maintain blood pH slightly alkaline by binding excess H+ in the blood.
  • Provide a source of amino acids if required by being broken down by macrophages.
  • Act as carriers for small molecules and transport them to tissues via protein carriers.
  • Help maintain the colloid osmotic pressure of the blood, which is important in maintaining body fluid balance.

Albumin

• Albumin regulates the osmotic pressure of the blood (and hence moderates the osmotic pressure of body fluids).
• Albumin transports hormones and minerals.
• Hypoalbuminaemia can lead to edema.

Fibrinogen

• Fibrinogen is involved in blood coagulation.
• Soluble fibrinogen can form an insoluble fibrin clot.

α-1-antitrypsin

• α-1-antitrypsin is found in low concentrations in plasma.
• α-1-antitrypsin neutralizes digestive trypsin.

Globulins

• Globulins participate in the immune system (e.g. immunoglobulins) and also act as transport proteins (T4 and Vitamin A).
• Types of globulins:
  • α-Globulins: transport thyroxin (T4) and vitamin A.
  • β-Globulins: (transferrin) transport iron.
  • γ-Globulins: immunoglobulins (Igs).

γ-Globulins (Antibodies)

• γ-globulins are also called immunoglobulins.
• Immunoglobulins are produced by B lymphocytes.
• Antibodies are responsible for the body's humoral immune function, recognizing pathogens via specific receptors and neutralizing them through various mechanisms.

Haemostasis and Blood Coagulation

• Haemostasis is the process of forming clots in the walls of damaged blood vessels to prevent blood loss (haemorrhage, bleeding) and maintain blood in a fluid state within the vascular system.

Thrombocytopenia

• Thrombocytopenia is a low platelet count, which can cause bleeding (haemorrhage).
• Thrombocytopenia can be caused by:
  • Decreased production due to bone marrow failure, leukemia, or autoimmune disease.
  • Enlarged spleen.

Thrombocytosis

• Thrombocytosis is a high platelet count, which can cause thrombosis (blood clot formation).
• Thrombocytosis can be caused by:
  • Myeloproliferative disorders
  • Inflammation
  • Iron deficiency
  • Drugs (aspirin)
  • Splenectomy

Test your knowledge on leukocytes, including lymphocytes and their roles in the immune system. This quiz covers the transformation of monocytes, the differentiation of T and B cells, and their specific functions in immunity. Challenge yourself to recall key concepts about the types of T-cell responses and the roles of B-lymphocytes.