An anti-human monocyte/macrophage monoclonal antibody, reacting most strongly with macrophages in lymphoid tissue.

In this report, we have described monoclonal antibody (mAb) 24 which bound specifically to a 174,000 polypeptide present on 45 +/- 16% of human monocytes. Expression of the 24 molecule increased on monocytes when they were cultured. When tissues were examined using immunohistochemical techniques, macrophages (Mph) associated with skin and with lymphoid organs strongly expressed the mAb 24 molecule, whereas, Mph in nonlymphoid organs were only weakly positive. mAb 24 reacted with cells of Mph morphology plus cells of interdigitating appearance in T-cell areas, suggesting that these cells might belong to the Mph cell lineage. There was no reaction with other types of cells, such as Langerhans cells, osteoclasts, dendritic reticulum cells, and endothelial cells. The fact that the molecule recognised by mAb 24 is particularly associated with Mph in lymphoid tissue suggests that it might have a function in immune responses.