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Morphological and functional characteristics of peritoneal mast cells from young rats
J S Marshall1, S Kawabori, L Nielsen
1Department of Pathology, McMaster University, Hamilton, Ontario, Canada.
Insights
Young rat mast cells have significantly less histamine and fewer granules than adult cells. These differences explain why young rats resist certain secretagogue effects.
Area of Science:
- Immunology
- Cell Biology
- Developmental Biology
Background:
- Neonatal and young rats exhibit resistance to specific secretagogues.
- Peritoneal mast cells (PMCs) are key players in allergic and inflammatory responses.
Purpose of the Study:
- To investigate the cellular and molecular differences in PMCs between young and adult rats.
- To elucidate the mechanisms underlying the resistance of young rats to certain secretagogues.
Main Methods:
- Comparative analysis of PMCs from 14-15-day-old (young) and adult rats.
- Histochemical staining (safranin O, berberine sulphate) and ultrastructural examination.
- Functional assessment of histamine release in response to various secretagogues (compound 48/80, nerve growth factor, substance P).
Main Results:
- Young rat PMCs contained ~10% of the histamine found in adult PMCs.
- Fewer granules and a higher prevalence of bilobed/indented nuclei were observed in young rat PMCs.
- Young rat PMCs showed significantly reduced histamine release to compound 48/80 and nerve growth factor, but similar release to substance P compared to adult cells.
Conclusions:
- Significant developmental differences exist in rat peritoneal mast cells.
- Lower histamine content, granule number, and altered nuclear morphology in young rat PMCs contribute to their resistance to specific secretagogues.
Abstract:
To study why neonatal and young rats are resistant to the effects of some secretagogues, such as compound 48/80 and 2.5-S nerve growth factor, we examined peritoneal mast cells from 14-15-day-old rats (young rats) and compared them to peritoneal mast cells from adults. Peritoneal mast cells from young rats contain approximately one-tenth of the amount of histamine observed in adult peritoneal mast cells. However, both cell populations contained similar low levels of the mucosal mast cell-associated protease rat mast cell protease II. Histochemical analysis of peritoneal mast cells from young rats using safranin O and berberine sulphate suggested that only a portion of the granules of these cells contained heparin. At an ultrastructural level the young rat peritoneal mast cell contains relatively few granules. The majority of mast cells from young rats have a bilobed or indented nucleus which is only rarely observed in adult cells. Functionally, the young rat peritoneal mast cell demonstrates a significantly reduced histamine release in response to the connective tissue mast cell-specific secretagogues compound 48/80 and 2.5-S nerve growth factor. In contrast, the percent histamine release in response to the neurotransmitter substance P, which degranulates both connective tissue mast cells and intestinal mucosal mast cells, was similar in the adult cells and the young rat cells. This study demonstrates substantial differences between the young rat and adult peritoneal mast cells which may explain the ability of very young animals to withstand large doses of certain secretagogues.