RESPONSE OF LEUKOCYTE POPULATIONS IN THE ILEAL PEYERS 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 e xamine the response of the ileal Peyer's patch of fetal lambs 7 days a fter treatment with ferritin per os. Consistent with previous studies in fetal lambs that have reported the ileal Peyer's patch to be indiff erent to antigen, the present study did not find any significant chang es in the size of the predominantly B-cell dome/follicle compartment o r the predominantly T-cell interfollicular area, nor were differences identified in the distribution of IgM-positive (+), CD4+, and CD8+ cel ls in these two compartments. However, both compartments showed a sign ificant 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 a rea 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 re present the transition of a purely primary lymphoid organ to an organ that has both primary and secondary lymphoid functions.