Page 729 - Veterinary Immunology, 10th Edition

mediated immune competence within the first week of life. IGHA
VetBooks.ir and IGHG expression reach adult levels by 14 to 28 days.

FIG. 23.1 The stages in the progressive development of the
immune system in the fetal calf.

Lamb

The gestation period of the ewe is about 145 days. Major
+
histocompatibility complex (MHC) class I cells can be detected by
+
day 19, and MHC class II cells can be found by day 25. The thymus
and lymph nodes are recognizable by 35 and 50 days post-
conception, respectively. Gut-associated follicles appear in the
colon at 60 days, jejunal Peyer's patches at about days 75 to 80, and

ileal Peyer's patches at days 110 to 115. Blood lymphocytes are seen
+
+
in fetal lambs by day 32, and CD4 and CD8 cells appear in the
thymus by 35 to 38 days. B cells are detectable at 48 days in the
spleen and by that time have already begun to rearrange their IGLV

genes. C3 receptors appear by day 120, but Fc receptors do not
appear until the animal is born. Fetal liver lymphocytes can
respond to phytohemagglutinin by 38 days. Lambs can produce
antibodies to phage ΦX174 at day 41 and reject skin allografts by

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