Langerhans cell

The Langerhans cell lives in the epidermis, the outermost layer of the skin. It is a dendritic cell, meaning it has arms that reach out among the cells around it, and it is the skin's first line of cellular immune defense. Its job is antigen presentation.

An antigen is the fragment of something foreign that the defense system uses to recognize it. The Langerhans cell captures it in the skin and carries it to the lymph nodes, and to display it the cell loads its surface with major histocompatibility complex class I and II molecules, which work as the counter where it shows what it found. It is a patrol that collects the sample and takes it to where it is identified.

It comes from the bone marrow, the factory for blood cells, and it contains Birbeck granules and tennis racket shaped cytoplasmic organelles. Electron microscopy, the kind that uses beams of electrons instead of light, can be useful in recognizing it.