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Ontogeny of the inflammatory response in the fetal rat
Insights
Fetal rats exposed to bacteria or turpentine showed inflammatory responses, with younger fetuses (16 days gestation) exhibiting infiltrates of polymorphonuclear (PMN) and mononuclear (MN) cells. Gestational age significantly influenced the inflammation magnitude and character.
Area of Science:
- Developmental Biology
- Immunology
- Pathology
Background:
- The fetal inflammatory response is crucial for development and defense.
- Understanding fetal immune system maturation is key to predicting responses to injury or infection.
- Limited data exists on the early inflammatory capacity of the fetal rat peritoneum.
Purpose of the Study:
- To investigate the fetal rat's peritoneal inflammatory response to sterile irritants and bacteria.
- To determine the influence of gestational age on the magnitude and character of the inflammatory response.
- To characterize the cellular infiltrate and phagocytic activity in response to induced inflammation.
Main Methods:
- Fetal rats at 16, 17, and 18 days gestation were injected with turpentine or Streptococcus faecalis in India ink.
- Peritoneal tissues and exudates were collected at 24, 48, and 96 hours post-injection.
- Histological examination assessed cellular infiltrates, tissue injury, and phagocytosis.
Main Results:
- Inflammation, characterized by polymorphonuclear (PMN) and mononuclear (MN) cell infiltrates, was observed as early as 24 hours in 16-day gestation fetuses injected with bacteria.
- Phagocytosis of ink particles and bacteria by inflammatory cells, serosal cells, and mesenchymal cells was evident.
- A more pronounced granulocytic response and extensive inflammation were noted in older fetuses (17-19 days gestation).
- Turpentine induced variable tissue injury, and gestational age was a more critical factor than lesion duration.
Conclusions:
- The fetal rat peritoneum can mount an inflammatory response to sterile irritants and bacteria.
- Gestational age is a primary determinant of the fetal inflammatory response's intensity and nature.
- The fetal immune system demonstrates phagocytic capabilities even at early gestational ages.
Abstract:
Fetal rats of 16, 17 and 18 days gestation (dg) were injected with turpentine or Streptococcus faecalis in 1% India ink. Specimens of peritoneal tissues and exudates were collected at 24, 48 and 96 h after injection. Inflammation was present in some of the youngest animals (16 dg) 24 h after injection with bacteria. The response consisted of infiltrates of polymorphonuclear (PMN) and mononuclear (MN) cells in tissues adjacent to the peritoneum. Inflammatory cells were also found within the peritoneal cavity. Phagocytosis of ink particles and bacteria was noted in these cells and in cells of the serosa and adjacent mesenchyme. Free peritoneal cells were not seen in littermate controls. Phagocytosis was also noted in PMNs and MNs in the exudates collected at 48 h. A more marked granulocytic response was seen in animals sacrificed 24 h following bacteria-ink injection at 17 dg. Inflammation was more extensive and consistent by 19 dg. The reaction to turpentine was associated with the variable degree of tissue injury noted in histologic sections. The gestational age at time of injection was a more important determinant of the magnitude and character of response than was the duration of the lesion.