The identification of amyloid P-component (protein AP) in normal cultured human fibroblasts.

The amyloid protein, AP, has not previously been detected in normal or nonamyloidotic tissues. In this study, human fibroblasts were examined for the presence of AP by immunofluorescence technique. Normal human skin fibroblasts were cultured in Eagle's minimum essential medium for varying periods of time. Antiserum was prepared in rabbits using AP isolated from amyloid-rich tissues. Using indirect immunofluorescence and anti-AP, fluorescent material was found to be distributed in a punctate pattern throughout the cytoplasm with sparing of the nucleus. The fluorescent reaction was speicifically inhibited by absorption of anti-AP with AP-positive serum but not by addition of AP-negative human cord serum. Thus, AP may have a fibroblast origin and a relationship to normal connective tissue.