LO: Identify the primary and secondary lymphoid organs and their functions

Primary

• Development and maturation of adaptive immune cells (lymphocytes)
• Bone marrow - B cells
• Thymus gland - T cells

Secondary

• Mature lymphocytes meet pathogens
• Spleen, adenoids, tonsils, appendix, lymph nodes

Lymph nodes

• Strategically located around the body
• 'Meeting place' for immune cells
• pathogens from infected tissue sites are picked up by dendritic cells and arrive at the closest lymph node
• Circulating T and B lymphocytes enter node and congregate at specific regions (cortex/paracortex)
• If they encounter a "matching" dendritic cell - they are activated and proliferate
• Architecture and size of node changes in response to activation of lymphocytes

LO: Describe how adaptive and innate immune cells are generated in the bone marrow and briefly outline their main functions

Haematopoiesis

• Making of blood

flowchart TD
	A[Multipotent stem cell]
	B[Myeloid progenitor]
	C[Lymphoid progenitor]
	D[Plasma cell]
	E[NK cell]
	F[Red blood cells]
	G[Macrophage dendritic cell]
	H[ ]:::empty
	I[ ]:::empty
	J[ ]:::empty
	K[ ]:::empty
	
	A --- H
	H --> B
	H --> C
	B --- I
	I --> Megakaryocyte
	I --> Erthroblast
	I --> Myeloblast
	Megakaryocyte --> Platelets
	Erthroblast --> Reticulocyte
	Reticulocyte --> F
	Myeloblast --- J
	J --> Monocyte
	Monocyte --> G
	J --> Neutrophil
	J --> Basophil
	J --> Eosinophil
	C --- K
	K --> B-lymphocyte
	B-lymphocyte --> D
	K --> T-lymphocyte
	K --> E
	
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Monocytes

• Monocytes circulating in blood migrate to tissues where they differentiate into macrophages
• Alveolar macrophages: lung
• Histiocytes: connective tissue
• Mesangial cells: kidneys
• Microglial cells: brain
• Kupffer cells: liver
• Osteoblast: bone

Macrophages

• Phagocytosis
• Antigen presentation - activation of adaptive immune system

Dendritic cells

• Better antigen presenting cells (APCs) than macrophages because of lower degradation potential - antigen preservation
• Antigen uptake in peripheral tissues
• Migration to lymph nodes and antigen presentation

Granulocytes

Neutrophil

• Polymorphonuclear neutrophils (PMN)
• 95% of circulating granulocytes
• Short-lived
• Major component of pus
• First line of defence against pathogens
• Recruitment to site of infection by interleukin-8 (chemotaxis)

Eosinophils, basophils and mast cells

• Killing of parasites
• Target recognition via Immunoglobulin E (IgE, an antibody)
• Degranulation and release of toxic contents
• Cytokine release leads to inflammation
• Eosinophils and basophils circulating in blood
• Mast cells resident in tissues

Natural killer cells (NK cells)

• Cytotoxic granules containing perforin and granzymes
• Recognise and destroy abnormal cells
• Detection via lack of Major Histocompatibility Complex (MHC) class 1 molecules

B Lymphocytes

• Express surface-bound B cell receptor specific for particular antigen
• After binding to antigen B cells proliferate and differentiate into antibody-secreting plasma cells

T Lymphocytes

• Express T cell receptor specific for particular antigen
• T helper 1 (Th1) cells help macrophages digest pathogens
• T helper 2 (Th2) cells help B cells to produce antibodies
• Cytotoxic T cells kill virus-infected cells

LO: Describe the process of antigen presentation

LO: Describe the different cells of the innate immune response and how they respond to infection