Which type of cells are predominantly found in the stratum spinosum layer of the skin?

The stratum spinosum, which is the second layer of the epidermis, is predominantly populated by keratinocytes. These cells are vital for the production of keratin, a protein that provides strength and water-resistance to the skin. In the stratum spinosum, keratinocytes appear to have spiny projections due to desmosomal connections between them, contributing to the layer's mechanical strength and integrity.

While Langerhans cells are indeed present in the stratum spinosum, their role is more about immune response than making up the predominant cell type; they are a small population that participates in antigen presentation and helps protect the skin from pathogens. Melanocytes, which are responsible for producing melanin, are located in the stratum basale, the deepest layer of the epidermis. Fibroblasts are primarily found in the dermis, where they play a crucial role in the production of collagen and other extracellular matrix components. Therefore, the correct answer focuses on the predominant cell type, which is keratinocytes, within the stratum spinosum.