Immunology: Haematopoiesis and Bone Marrow Disorders

• Immunology

Haematopoiesis

• It is the site of circulating blood cell production in the bone marrow

Division of haematopoietic stem cells (HSC)

• One daughter cell remains in the bone marrow to renew the HSC pool; the other daughter cell matures into blood cells

Blood and Tissue Production in Bone Marrow

• Hematopoietic Stem Cells differentiate into: Multipotent Progenitors (MPPs), Common Lymphoid Progenitors (CLPs), and Common Myeloid Progenitors (CMPs)

Bone Marrow Disorders

• Leukemias are malignant diseases of the bone marrow that occur during haematopoietic development
• Lymphoid lineages develop into acute or chronic lymphoblastic leukemia (ALL/CLL).
• Myeloid lineages develop into acute or chronic myeloid leukemia (AML/CML)
• Myeloproliferative disorders are characterized by the overproduction of one type of blood cell, such as essential thrombocythaemia (platelets), polycythaemia vera (red blood cells), and myelofibrosis (fibroblasts).
• Myelodysplastic syndromes (MDS) are a spectrum of disorders involving the overproduction of one or more types of blood cells
• Multiple myeloma and Aplastic anemia are examples of MDS.

Lymph Node

• Activation of T and B cells occurs here
• The lymph node is connected to lymphatic and blood vessels

Lymph Node Structure

• The cortex (outer layer) of the node contains B-cell areas (follicles).
• The paracortex (middle layer) contains T cells and dendritic cells.
• Lymph vessels enter the nodes at the outer edge
• B and T cells leave the node via 'efferent' lymphatic vessels in the central 'medullary' region
• This important in pathogen responses occurs in the lymph node
• Dendritic cells present pathogenic peptides to T cells here
• T cell activation and differentiation happens at the lymph node
• Some T cells promote B cell activation in the lymph node

Immunity in the Gut

• Large intestine (colon) has 10^12 microorganisms per gram of luminal content
• There is a constant threat of potential pathogens
• Pathogens enter via intestinal mucosa
• Gut-associated lymphoid tissues are organized in Peyer's patches and mesenteric lymph nodes.
• Mucosal epithelium involves T cells, plasma cells, mast cells, dendritic cells, and macrophages
• Here, the epithelium has a barrier function
• Defects in barrier function can lead to the development and perpetuation of inflammation in inflammatory bowel disease (IBD)

Immunity in the Lungs

• The nasopharynx and tonsillar regions clear debris by inertial force (coughing and sneezing)
• The mucociliary surface captures and expels substances via upper airways
• Antimicrobial compounds include collectins and surfactant proteins
• These are recognized by innate immune cells and the complement system
• They also include antimicrobial peptide secretions
• The alveoli are the terminal branches of the lungs, where most of the gaseous exchange occurs
• Alveolar macrophages carry out phagocytosis and recruitment of other immune cells

This lesson covers haematopoiesis, the production of blood cells in the bone marrow, and the division of haematopoietic stem cells (HSC). It also discusses blood and tissue production in the bone marrow and various bone marrow disorders such as leukemias and myeloproliferative disorders.