Expression of macrophages is increased with maturation, with higher expression on peritoneal and alveolar macrophages. Some expression has also been observed on peripheral blood lymphocytes. The antigen recognised has a broad tissue distribution. Clone 10F28 stains macrophages in a range of tissues, including the thymus, spleen periarteriolar lymphoid sheath (PALS), spleen red pulp and the Peyer’s patches.