Detection ofProtein Subunits ofFerritin InSituin Cells byImmunofluorescence

Antisera raised inrabbits against protein subunits ofratliver ferritin contain antibodies (IgG)that precipitate subunits andother antibodies (IgG)that precipitate undissociated ferritin andapoferritin. Removal ofthelatter antibodies fromIgG fractions ofimmuneserabyrepeated addition offerritin leaves antibodies that specifically precipitate subunits. Usingthese subunit-specific antibodies, we have demonstrated thepresence ofsubunit-positive sites incells byimmunofluorescence. Subunit-positive sites werebestdemonstrated inratsthathadbeenloaded with iron. Thesesites werediffusely spread through thecytoplasm ofhepatocytes and Kupffer cells inratlivers andofmacrophages andfibroblasts inratlivers and hearts. Withantibodies toferritin, thepresence offerritin wasdemonstrated in thesamekinds ofcells. Although, byimmunofluorescence, theintracellular localization offerritin-positiv e andsubunit-positive sites wassimilar, ferritin-positiv e immunofluorescence wasmostintense inPrussian blue-positive cytoplasmic granules in whichhighconcentrations offerritin werepresumed tobepresent onthebasis of electron microscopic studies. Ourfindings canbeinterpreted toindicate either the presence ofunassociated subunits oroffragments ofsubunits inthecytoplasm of theseveral kinds ofcells studied. Itisalso possible that partly assembled molecules offerritin orapoferritin inthese cells reacted withsubunit-specific antibodies. Subunit-specific antibodies maybeuseful forlocalizing sites ofassembly offerritin molecules atthelevel ofcell fine structure andforelucidation ofthebiosynthesis offerritin (AmJPathol 75:473-488, 1974).