2. Apoptosis in a reactive lymph node (follicular hyperplasia)

Overview. Those rings are germinal centres.

Staining: HE

Organ: Lymph node

Description: We can see a normal-looking lymph node with several germinal centres. Inside the germinal centres we can see a “starry-sky” pattern. Apoptotic bodies, seen as small round eosinophilic masses with fragments of dense chromatin are also present. The “stars” in the starry-sky pattern are formed by large cells with pale cytoplasm, the tingible body macrophages.

Diagnosis: Follicular hyperplasia in response to antigen stimulation

Theory:

This slide shows a lymph node with active germinal centres. Recall from immunology that germinal centres are formed when a B-cell has been activated by an antigen. The B-cell divides into centroblasts that undergo affinity maturation inside the germinal centre. Every centroblast that doesn’t produce higher affinity antibodies will die by apoptosis. The apoptotic bodies are phagocytosed by a special type of macrophage called the tingible body macrophages. Some of the centroblasts will eventually become centrocytes.

Shown here is the starry-sky pattern inside the germinal centre. The mantle around the germinal centre is also shown.

Shown here is a tingible body macrophage, with an apoptotic body in its cytoplasm.