Ultrastructural localization of cationic proteins in human polymorphonuclear leukocytes

Area of Science:

• Cell Biology
• Immunology
• Biochemistry

Background:

• Arginine-rich cationic proteins in human polymorphonuclear leukocytes are implicated in antibacterial action and inflammation.
• The ammoniacal silver reaction is a key technique for detecting these proteins at the ultrastructural level.
• Previous methods using dilute formalin fixation limited optimal tissue preservation and reaction localization.

Purpose of the Study:

• To optimize the ammoniacal silver reaction for enhanced ultrastructural localization of arginine-rich cationic proteins.
• To investigate the precise cellular localization of these proteins within human polymorphonuclear leukocytes.
• To address discrepancies with previously published data regarding protein distribution.

Main Methods:

• Utilized a refined protocol involving sequential glutaraldehyde fixation, ammoniacal silver solution treatment, and osmium tetroxide postfixation.
• Applied the optimized technique to human polymorphonuclear leukocytes for ultrastructural analysis.
• Compared results with established methods and prior literature.

Main Results:

• Achieved superior tissue fixation and precise localization of the ammoniacal silver reaction product.
• Demonstrated that the reaction is exclusively localized within the large, crystalline cytoplasmic granules of eosinophils.
• Found all other cytoplasmic granules in neutrophils, eosinophils, and basophils to be devoid of the reaction product, contradicting previous studies.

Conclusions:

• The optimized ammoniacal silver reaction provides enhanced ultrastructural detection of arginine-rich cationic proteins.
• These proteins are specifically localized in eosinophil crystalline granules, suggesting a specialized role.
• The findings necessitate a re-evaluation of existing models for leukocyte function and protein distribution.