Page 750 - Veterinary Immunology, 10th Edition

suckling foal, its level in foal serum drops to a very low level by 6
VetBooks.ir weeks of age. IgE synthesis by foals begins at about 9 to 11 months

of age, and at that time a pattern of relatively high or low IgE levels
is established. These levels are not correlated with the levels

resulting from suckling. Total levels of IgE in young horses (and
their susceptibility to allergies) are mainly determined by genetic
factors and the microbiota. IgE is also transferred in sheep
colostrum. Colostral IgE levels are significantly higher than in ewe's

serum. IgE is absent from pre-suckling lamb serum but can rise to
adult levels by 2 days after birth. It then declines steadily over
several weeks.
The IgG transferred through a mother's colostrum represents the

results of her history of antigen exposure, B cell responses, and
somatic mutation. This maternal IgG in effect represents the
immunological experiences of the mother. Maternal antibodies act
on the immune system of the newborn during a critical imprinting

period and exert a lifelong influence on the newborn's immune
development. This influence may be stronger than some genetic
predispositions! Thus maternal antibodies can enhance the
newborn immune responses to some antigens and suppress their

responses to others. They may also influence Th1/Th2 polarization
and the subsequent development of allergies.

MicroRNAs and Intestinal Development

MicroRNAs (miRNAs) are small single-stranded RNA molecules
about 22 nucleotides in length that regulate gene expression. They
bind to the 3'untranslated region or the coding regions of
messenger RNAs and promote their degradation. miRNAs regulate
many different biological processes including embryonic

development, cell differentiation, and apoptosis. Their expression
patterns and regulatory functions may be tissue specific. Some
miRNAs regulate gut development and mucosal immunity in

newborns. miRNAs are present in many body fluids including milk
and colostrum. They are shed into the colostrum in microvesicles
and exosomes. These colostral miRNAs are absorbed from the
intestine and enter the circulation of newborn mammals. These
miRNAs influence the development of the mucosal immune

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