Background: Current methods for the detection of granulocyte antibodies require panels of freshly isolated cells. This makes these assays time-consuming, costly, and technically difficult.
Study design and methods: The immunofluorescence method of detecting the binding of antibodies to granulocytes was modified for use with a flow cytometer, and methods were tested to store granulocytes for use in that assay. Granulocytes were stored at 4 degrees C for 7 days under three conditions: 1 -percent formaldehyde-fixed cells were stored in Hanks' balanced salt solution (HBSS); untreated cells were stored in tissue culture medium (RPMI-1640); and cells were fixed and stored with a commercial white cell-storage solution (Cyto-Chex Reagent). Antigen stability was evaluated by using monoclonal antibodies (MoAbs) and alloantibodies. Serologic studies were done by an indirect immunofluorescence assay and assessed by flow cytometric analysis.
Results: On Day 2, only 2 to 7 percent of granulocytes stored in RPMI-1640 remained. On Day 7, 67 to 76 percent of granulocytes fixed in formaldehyde and stored in HBSS remained, and 47 to 87 percent of granulocytes stored in a white cell-storage solution remained. All antigens were detectable by the MoAbs and alloantisera on Day 7. However, nonspecific staining by the fluorescein isothiocyanate (FITC)-conjugated secondary antibody hindered interpretation of test results on Day 4. Non-specific staining occurred over time and was associated with increased cell permeability during storage. Two sources of nonspecific staining were identified. The first source was the FITC-conjugated secondary antibody; it was eliminated by switching to a phycoerythrin conjugate. The second source was factors in human serum; it was resolved by examining only viable, impermeable cells identified by using 7-aminoactinomycin-D.
Conclusion: Granulocytes and their antigens can be preserved for at least 7 days, but evaluation of antibody reactions was possible for only 4 days as a result of non-specific staining due to enhanced membrane permeability of dying cells.