**Core Concept**
Langerhans cells are a type of dendritic cell located in the epidermis, the outermost layer of the skin. They play a crucial role in the immune system by processing and presenting antigens to T-cells, thereby initiating an immune response.

**Why the Correct Answer is Right**
Langerhans cells express major histocompatibility complex (MHC) class II molecules on their surface, which allows them to present antigens to CD4+ T-cells. This process involves the uptake of antigens by Langerhans cells, their processing into peptide fragments, and the presentation of these fragments in the context of MHC class II molecules. This presentation of antigens to T-cells is essential for the initiation of an adaptive immune response against pathogens and foreign substances.

**Why Each Wrong Option is Incorrect**
**Option B:** Langerhans cells are not responsible for pigment production in the skin. Melanocytes, another type of cell in the epidermis, synthesize melanin and transfer it to surrounding keratinocytes, which then produce the pigment.
**Option C:** Langerhans cells do not synthesize keratin. Keratinocytes, the predominant cell type in the epidermis, produce keratin, a key structural protein that provides strength and rigidity to the skin.
**Option D:** Langerhans cells are not sensory neurons. Sensory neurons, also known as nerve endings, are specialized cells that detect stimuli and transmit signals to the central nervous system. They are not involved in the immune response or the presentation of antigens.

**Clinical Pearl / High-Yield Fact**
Langerhans cells are named after Paul Langerhans, the German pathologist who first described them in 1868. They are a critical component of the skin's immune system, and their dysfunction has been implicated in various skin disorders, including psoriasis and atopic dermatitis.

**✓ Correct Answer: A. Antigen presenting cells**