Complex sentence: Dendritic cells are present in small quantities in tissues in contact with the external environment, mainly the skin (where there is a specialized dendritic cell type called Langerhans cells) and the inner lining of the nose, lungs, stomach and intestines.
Split into simpler sentences: Dendritic cells are present in small quantities in tissues in contact with the external environment. This means they are present mainly in the skin (where there is a specialized dendritic cell type called Langerhans cells) and the inner lining of the nose, lungs, stomach and intestines.