Stratum spinosum

[2] This layer is composed of polyhedral keratinocytes.

[3] Their spiny (Latin, spinosum) appearance is due to shrinking of the microfilaments between desmosomes that occurs when stained with H&E.

[4] They have large pale-staining nuclei as they are active in synthesizing fibrillar proteins, known as cytokeratin, which build up within the cells aggregating together forming tonofibrils.

The stratum spinosum also contains Langerhans cells, which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer.

[6][7][8] Diffuse hyperplasia of the stratum spinosum is termed acanthosis.