Monoclonal antibody with specificity for monocytes and neurons

We have characterized a monoclonal antibody, called UC45, that reacts with both monocytes and neurons. It was derived from a fusion of the NS-1 plasmacytoma cell line with spleen cells from a mouse immunized with human acute monoblastic leukemia cells. The antibody reacts weakly with viable monocytes in suspension but has specificity for fibrous projections, which are found on monocytes that have adhered to substrate. Other hemopoietically derived cells such as granulocytes and lymphocytes, and many tissue-culture lines, do not react with UC45 by cell-surface immunofluorescence. Similarly, UC45 reacts with the processes of both viable CNS and PNS neurons in tissue culture but with no other neural-tissue-derived cells. The monoclonal antibody has interspecies reactivity, in that it reacts with human, rat and mouse monocytes and neurons. The monocytes and neuronal antigen is present predominantly on a protein of 45 kd. Attempts to identify this protein on monocytes with conventional heteroantisera directed against fibronectin, complement components, fibrinogen, collagen, tubulin and actin have failed. A monoclonal antibody has therefore allowed identification of an antigen, unexpectedly shared by monocytes and neurons. The fact that it is found on cell processes of both cell types suggests that it may be performing some similar function for these cells, whose other activities differ substantially.