Measurement of antineutrophil antibodies by flow cytometry: simultaneous detection of antibodies against monocytes and lymphocytes.

We describe a flow cytometric technique which detects the presence of antineutrophil antibodies (NABs) in human serum. The technique provides a qualitative as well as a semiquantitative screen and provides an excellent method for monitoring the presence of antineutrophil antibodies in patients with suspected autoimmune neutropenia. Using light-scatter gating, individual populations consisting of neutrophils, monocytes, and lymphocytes can be examined simultaneously for the presence of antibody. The methodology utilizes an indirect immunofluorescence technique with FITC-labeled goat antihuman F(ab')2 antibody and fixed leukocyte suspensions. Furthermore, by utilizing class-specific FITC-labeled second antibody, significant information can be ascertained regarding the class, cell specificity, and quantity of detected antibody. Formalin fixation of neutrophils prevented pinocytosis of the fluorochrome, significantly reducing background fluorescence. Twenty-five normal subjects provided baseline antibody levels for each class. Of 92 patients with suspected autoimmune neutropenia, 27 had class IgG alone and seven were positive for both IgG and IgM class NABs. During treatment, IgG levels varied. IgM NABs alone were detected in four patients. Fifty-four patients had undetectable antibody. Antibodies were detected against monocytes in several of the IgG-positive patients. Two sera contained both IgA and IgG NABs. One serum contained IgA and IgG antibodies against monocytes. No IgD antibodies were detected in any sera tested. Some sera tested contained antibodies against lymphocytes--however, only in those sera which also contained antibodies to other cell types.