Our study, for the
first time, revealed localization of Ki67- or
LGR5-positive crypt cells in the small intestine of nursing and
weaned pigs, with or without PEDV infection. Intestinal stem cells
located in the villous crypts replace the apoptotic (normal process)
or necrotic (virus-induced) enterocytes shed at the villous tips and
are essential for maintenance of the intestinal epithelium (Saif
et al., 2012). The turnover rate of the intestinal epithelium may
depend on the stem cells and their proliferative levels in the
intestinal crypt. The turnover of enterocytes was slower in
neonatal nursing piglets vs. weaned pigs (Moon et al., 1973).
Our study suggests that a lack of LGR5-positive crypt stem cells and
lower numbers of proliferating crypt cells in the small intestine of
uninoculated nursing piglets might lead to the slower turnover of
enterocytes in nursing piglets vs. weaned pigs, possibly also
influencing the slower recovery from disease in nursing piglets.
After PEDV inoculation, however, the number of LGR5-positive
crypt stem cells and proliferation of intestinal crypt cells in nursing
piglets increased remarkably at PIDs 3 and 5, likely leading to
replacement of necrotic enterocytes shed from infected villi. On
the other hand, the uninoculated weaned pigs tested at PIDs
1–5 exhibited high numbers of proliferating intestinal crypt cells
and LGR5-positive crypt stem cells, likely contributing to the
rapid turnover rate of enterocytes. The high proliferation rates and
LGR5-positive scores in the intestinal crypts were maintained after
PEDV inoculation, ultimately influencing the rapid recovery from
disease in weaned pigs.