Lecture 9 Flashcards
Secondary Lymphoid Organs
Sites of Adaptive Immune Cells
1. Lymph nodes: screens the lymphatic fluids
2. Spleen: screens the blood
3. MALTs: screens the mucosal surfaces
Lymph Nodes
- Variable sized ‘bean-shaped’ tissues
- Inline Lymphatic filters
- Immune surveillance of the Lymphatics
Three functional regions
- Cortex
a. Lymphoid Nodules (Follicles) - Paracortex
- Medulla
a. MS: Medullary Sinuses
includes histiocytes
b. MC: Medullary Cords
Ab-secreting plasma cells
Lymph Nodes (Roles)
- Provides a site concentrate B- and T- cells
- Increases the efficiency of screening for antigens
- Optimizes B- and T- cell activation
Lymph Nodes (Seeding)
- Naïve lymphocytes (from the bone marrow and thymus) enter the cortex via the vascular supply
High Endothelial Venules
- Most endothelial cells are squamous (flat)
- High Endothelial Venules are cuboidal in stature and comparatively taller
- High Endothelial Venules facilitate the translocation of naïve lymphocytes out of the venules and into the sinusoidal spaces of the lymph node cortex
Lymph Node (Concentration)
Naïve Lymphocytes segregate and concentrate
1. B-Cells: concentrate in follicles (in the cortex)
2. T-Cells: concentrate in the paracortex
Lymph Nodes
- Lymph enters the Node via the Afferent Lymphatics
- Lymph starts in the subcapsular sinus
- Lymph percolates through the body of the node
Cortex (Follice)
- B-Cells
- Follicular Dendritic Cells
Follicular Dendritic Cells
Distinct from the hematopoietic-derived dendritic cells
1. Promote the retention of B-Cells within the Lymph Node Cortex Follicle
2. Promotes the productive movement and interactions of B-Cells within the Lymph Node Cortex Follicle
Primary Follicles
NO germinal centers
Secondary Follicles
Have germinal centers
Differentiation of B-Cells into Plasma Cells
Initial Step in B-Cell Activation
1. Antigen-specific binding to B-Cell Receptor
2. Occurs within the follicle
Differentiation of B-Cells into Plasma Cells
Two Fates of Activated B-Cells:
1. Immediately begin developing into plasma cells in a primary focus and the medulla
2. Proliferate into a germinal center within the follicle where the B-cells undergo further enhancement
Enhancement of B-Cells in the Germinal Center
Antigen-specific B-Cells proliferate
1. B-Cell Receptor genes undergo somatic hypermutation
2. B-Cell Receptor genes undergo somatic class switch recombination selection
3. B-cells with the highest antigen binding affinity are selected (survive fate)
4. Cells differentiate into Plasma Cells (Ab-producing)
5. Plasma Cells take up residence in the medulla or return to the bone marrow
