Conditions were established whereby nuclear or cytoplasmic immunocytochemical localization of lactoferrin was observed in the human peripheral blood granulocyte. A positive nuclear staining reaction was obtained when cells were either not fixed or treated with most fixatives. However, treatment of blood smears with formaldehyde-acetone prior to the immunocytochemical localization gave a cytoplasmic staining reaction. A method was developed that allowed the authors to examine proteins obtained from granulocyte nuclei isolated from fixed cells. Only a trace amount of lactoferrin was detected n the electrophoretically separated nuclear proteins obtained from granulocytes treated for 1 min with formaldehyde-acetone. However, lactoferrin was a major protein component in nuclei isolated from untreated cells, cells treated with other fixatives, or cells preincubated in buffered saline prior to formaldehyde-acetone fixation. Formaldehyde-acetone treatment of nuclear materials containing lactoferrin did not extract lactoferrin or mask it from detection, thus indicating that lactoferrin found in the mature neutrophilic granulocyte nucleus is most likely acquired from other cellular organelles during tissue processing.
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