Where are Langerhans cells primarily found in the body?

Langerhans cells are specialized dendritic cells that play a crucial role in the immune response within the skin. They are primarily located in the stratum spinosum layer of the epidermis. This is significant because the stratum spinosum is where keratinocytes begin to connect with each other, forming a strong barrier. The presence of Langerhans cells in this layer allows them to effectively capture and present antigens to T cells, which is essential for initiating immune responses against pathogens that may penetrate the skin.

The other layers mentioned do not host a significant number of Langerhans cells. For instance, the stratum corneum is primarily made up of dead keratinized cells that provide a barrier and are not conducive to the presence of living immune cells. The stratum lucidum, found only in thicker skin like the palms and soles, is also composed of dead cells and lacks Langerhans cells. The stratum granulosum focuses on the process of keratinization and does not serve as a primary site for immune response. Thus, the stratum spinosum is the correct answer, as it is rich in Langerhans cells and plays a vital role in skin immunity.