Detection of muramidase (lysozyme)-secreting leucocytes at the single-cell level by a protein A plaque assay.

Using a modification of the protein A plaque assay, muramidase (lysozyme)-producing leucocytes were detected as plaque-forming cells. In the presence of anti-muramidase Ig and complement the secreted lysozyme resulted in lysis of protein-A-coated target erythrocytes. By the use of a monolayer technique individual plaque-forming cells could be identified by staining procedures. Granulocytes as well as monocytes were found to produce muramidase and thus to form plaques. This method could serve as a useful tool when studying lysozyme secretion. Furthermore, by the use of appropriate antisera, this method could be employed for the study of any cell type (any secretion), provided enough molecules are being secreted.