Paneth cells and antibacterial host defense in neonatal small intestine

Abstract

Paneth cells are specialized epithelia in the small bowel that secrete antimicrobial proteins. Paneth cells are vital to the innate immunity of the small bowel in adult mammals, but their role during neonatal infection of the small bowel is not well established. Dithizone selectively damages Paneth cells, and when dithizone-treated newborn rats are infected enterally with Escherichia coli, the numbers of E. coli cells in their jejunal and ileal lavage fluid are significantly increased compared to controls. The data support that Paneth cells are necessary for neonatal antibacterial defense.

FIG. 1.

The appearance of Paneth cells in the ileal crypts 24 h after newborn rats received either intraperitoneal dithizone (75 mg/kg) in 25 mM lithium carbonate buffer or L₂CO₃ buffer alone. Photomicrographs are ileal sections stained with hematoxylin and eosin (magnification, ×1,000). The arrows identify individual Paneth cells. Paneth cells were examined for the content and the nature of their eosinophilic granules by using a Lickert score of 1 to 3, with 3 being best. (A) Crypt with two Paneth cells in a rat pup treated with i.p. dithizone; the Paneth cell was assigned a score of 2, while the Paneth cell on the right had a score of 1. (B) Paneth cell of a pup given i.p. L₂CO₃ buffer; this Paneth cell was given a score of 3. (C) The same Paneth cell as in panel B, except the incident light has been changed to show the autofluorescence of the cytoplasmic granules. Only epithelia with this autofluorescence were judged to be Paneth cells.

FIG. 2.

Effect of dithizone treatment on the numbers of Escherichia coli cells in small bowel specimens recovered from newborn rats. The x axis shows the CFU of E. coli per bowel mass. The y axis identifies the control groups (saline [NaCl] and Li₂CO₃ buffer) and the treatment group (dithizone). (A) Findings in small bowel lavage fluid; (B) the results seen in small bowel homogenates. The internal legend (A) signifies which studies involve jejunum or ileum. The statistical significance for comparisons between the dithizone group and the saline and Li₂CO₃ buffer controls is shown within the bars.