Question

part vi. lymph nodes

given the images below that are taken at several different magnifications:

key: 1 - capsule; 2 - cortex; 3 - medulla; 4 - germinal center; 5 - medullary cords; 6 - lymphocytes

1. describe the particular locations of the t and b cells in lymph nodes.

Explanation:

Identify the structural regions of the lymph node

The lymph node is divided into three main histological regions: the outer cortex, the inner paracortex (deep cortex), and the central medulla. The key provided in the image identifies:

• 1: Capsule (outer connective tissue covering)
• 2: Cortex (outer region containing lymphoid follicles)
• 3: Medulla (inner region containing medullary cords and sinuses)
• 4: Germinal center (lightly staining central region within a cortical follicle)

Determine B cell localization

B cells are primarily organized into spherical aggregates called lymphoid follicles (or nodules) located in the outer cortex (labeled 2).

• In inactive (primary) follicles, B cells are densely packed.
• Upon activation by an antigen, these follicles develop germinal centers (labeled 4) where B cells rapidly proliferate, differentiate, and undergo somatic hypermutation.
• Therefore, B cells are located in the follicles/germinal centers of the outer cortex.

Determine T cell localization

T cells are primarily located in the paracortex (also known as the deep cortex or inner cortex), which lies directly between the outer cortex and the inner medulla.

• This region is rich in dendritic cells presenting antigens to T cells and contains high endothelial venules (HEVs) where lymphocytes enter the node from the blood.
• Additionally, some T cells (specifically helper T cells) migrate into the germinal centers of the outer cortex to assist B cells, and both T and B cells can be found migrating through the medullary cords (labeled 5) as they exit the node.

Answer:

In a lymph node, the specific locations of T and B cells are organized as follows:

• B cells are primarily located in the outer cortex, where they aggregate into structures called lymphoid follicles (nodules). Within active follicles, B cells are concentrated in the germinal centers (labeled 4), where they proliferate and mature.
• T cells are primarily located in the paracortex (also known as the deep cortex or inner cortex), which is the region situated between the outer cortex and the inner medulla.