Response of Leucocyte Populations in the Ileal Peyer's Patch of Fetal Lambs Treated with Ferritin Per Os

A combination of immunohistochemical techniques, a panel of monoclonal antibodies, and computer-assisted morphometric analysis was used to examine the response of the ileal Peyerr's patch of fetal lambs 7 days after treatment with ferritin per os. Consistent with previous studies in fetal lambs that have reported the ileal Peyer's patch to be indifferent to antigen, the present study did not find any significant changes in the size of the predominantly B-cell dome/follicle compartment or the predominantly T-cell interfollicular area, nor were differences identified in the distribution of IgM-positive (+), CD4 +, and CD8+ cells in these two compartments. However, both compartments showed a significant increase (P < 0.05) in the percentage of area occupied by MHC II + cells and a significant decrease (P < 0.05) in the percentage of area occupied by CD44+ and B5+ cells. These changes show that the ileal Peyer’s patch of fetal lambs is not indifferent to antigen and may represent the transition of a purely primary lymphoid organ to an organ that has both primary and secondary lymphoid functions.