Related Experiment Video
Updated: Aug 7, 2026
Plunge Freezing: A Tool for the Ultrastructural and Immunolocalization Studies of Suspension Cells in Transmission Electron Microscopy
Published on: May 5, 2017
Ultrastructural immunocytochemical localization of lysozyme in human monocytes and macrophages
Abstract:
In order to investigate the mechanism of synthesis and secretion of lysozyme (LZ) by human mononuclear phagocytes, the ultrastructural localization of LZ was studied by a pre-embedding direct immunoperoxidase method. Blood monocytes showed a reaction product for LZ in cytoplasmic granules, whereas cultured monocytes showed the reaction product in phagosomes as well as granules at 5 h of culture and in numerous large granules at 3 days of culture. In Kupffer cells, LZ was present in cytoplasmic granules, vacuoles and phagosomes. Some Kupffer cells showed a positive reaction for LZ in the rough endoplasmic reticulum, perinuclear cisterna and Golgi apparatus. Macrophages in the lymph nodes contained LZ in cytoplasmic granules. Bone marrow macrophages contained numerous phagosomes with electron-dense degradation products of erythrocytes, but the reaction product for LZ could not be clearly identified. The present study demonstrated that LZ is present in the granules of human mononuclear phagocytes and released into phagosomes. An in-vitro culture study, furthermore, demonstrated that macrophages produce LZ-containing large granules distinct from those of monocytes. However, findings that indicate the synthesis and secretion of LZ by cultured monocytes, as suggested previously by other investigators, were not observed in this study.
Insights
This study investigated lysozyme (LZ) in human immune cells. Lysozyme is found in granules of monocytes and macrophages, and released into phagosomes, but synthesis by cultured monocytes was not confirmed.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Lysozyme (LZ) is a key enzyme in innate immunity.
- Human mononuclear phagocytes play a crucial role in host defense.
- Understanding LZ synthesis and secretion mechanisms is vital.
Purpose of the Study:
- To investigate the ultrastructural localization and mechanism of lysozyme synthesis and secretion.
- To examine LZ distribution in various human mononuclear phagocyte populations.
- To clarify the role of monocytes and macrophages in LZ production.
Main Methods:
- Pre-embedding direct immunoperoxidase method for ultrastructural localization.
- Study of blood monocytes, cultured monocytes, Kupffer cells, lymph node macrophages, and bone marrow macrophages.
- In-vitro culture of monocytes to observe changes over time.
Main Results:
- Lysozyme (LZ) was localized to cytoplasmic granules in monocytes and macrophages.
- LZ was observed in phagosomes of cultured monocytes, Kupffer cells, and lymph node macrophages.
- Kupffer cells showed LZ in rough endoplasmic reticulum, Golgi apparatus, and perinuclear cisterna, suggesting synthesis.
- Cultured monocytes did not show evidence of LZ synthesis and secretion as previously suggested.
Conclusions:
- Lysozyme (LZ) is present in granules of human mononuclear phagocytes and released into phagosomes.
- Macrophages produce distinct LZ-containing granules during in-vitro culture.
- Evidence for de novo synthesis and secretion of LZ by cultured monocytes was not observed in this study.
