Flow injection fluorescence microscopy applied to a rapid cell surface immunoassay

A perfusion system for fluorescence microscopy that utilized a flow injection system was developed and used to study cell surface antibody binding on viable cells grown in monolayer cultures on coverslips. A polyclonal cell-specific antiserum used to probe the cell surface was monitored by indirect immunofluorescence. The flow injection system was completely automatic and allowed controlled perfusion of cell surfaces with the desired sequence of antibodies. The individual steps of the indirect assay were studied to determine the binding behavior of the primary cell surface antibody, the labeled second antibody, and control of nonspecific binding. Under stopped flow conditions, the second antibody was maximally bound within 10 min, while constant mixing of the second antibody solution over the cells resulted in maximal binding within as little as 6 min. A primary antibody contact time of 2 min followed by a wash and then exposure to the second antibody for 2 min showed that this fast automated procedure could distinguish specific from nonspecific binding of cell surface antibodies to the same set of cells for several repeated exposures. The flow injection fluorescence microscopy system can be automated to allow screening for cell surface antibodies and to study their interaction with specific cell surface antigens.