Microinjection of IFA antibody induces intermediate filament aggregates in epithelial cell lines but perinuclear coils in fibroblast-like lines.

The murine monoclonal IFA antibody recognizes a conserved sequence present in almost all intermediate filament (IF) proteins. When IFA antibody was injected into 13 different primary or established cell lines, striking differences were detected between epithelial and fibroblastic cell lines. In epithelial cells keratin IFs were broken down within 4 h into numerous spheroid aggregates scattered throughout the cytoplasm. Keratin aggregates were first detected in the cytoplasmic periphery. In contrast, in fibroblastic cells, injection of IFA antibody led to the formation of perinuclear coils of vimentin. IFA antibody at a concentration of greater than 1 mg/ml had to be injected to initiate these transitions. When HeLa cells, which contain separate networks of vimentin and keratin filaments, were injected with IFA antibody, vimentin did not form perinuclear coils but was instead found together with keratin in aggregates. Electron micrographs of HeLa cells injected with IFA antibody showed that the aggregates have diameters between 0.5 and 2.6 microns and resembled the keratin aggregates observed in certain mitotic epithelial cells. Although the ultrastructural studies support an association of some aggregates with desmosomes, aggregates were, however, also induced by injection of IFA antibody into human keratinocytes in low calcium medium under conditions where desmosomes were not present.