Quantitation of NGF activity in supernatants from stimulated eosinophils.

Eosinophils were incubated with medium alone (med) or stimulated with sIgA + antihuman sIgA monoclonal antibody + IL-5 (IL-5 + sIgA-IC) for 24 hours as described above; the replicate culture contained sIgA + antihuman sIgA monoclonal antibody + IL-5, but no eosinophils. Supernatants were collected and used for the PC-12 cell biologic assay as described in “Materials and methods.” The NGF activities of the supernatants were semiquantitated by using a standard curve generated by PC-12 cells incubated with serial dilutions of recombinant NGF. Each dot represents different experiments using eosinophils from 6 different donors. Inset graph shows an example of a standard curve. PC-12 cells were incubated with serial dilutions of NGF (closed circle) or NT-3 (closed square) for 24 hours, and the numbers of cells with neurite elongation were determined. Note that NT-3 does not promote neurite elongation of PC-12 cells.