Placental macrophages: ontogeny during bovine pregnancy

6. Placental macrophages: ontogeny during bovine pregnancy

Placentomes were collected at Taylor Packing Plant, Wyalusing, PA. Control tissues Ž included fetal gut, thymus, lymph node, and maternal mesenteric lymph node 6th month . Ž . gestation . Gestation age was estimated from fetal crownrrump length Harris, 1983 . Fig. 10. Change in numbers of fetal macrophages throughout gestation. This graph shows the number of fetal macrophages present in cotyledonary villi at 4, 6 and 8 months of gestation, in placentas collected at term by cesarean section, and in placentas shortly after natural vaginal delivery. Numbers of fetal macrophages, called Hofbauer Cells in human placentas, increase dramatically in the villi during the last trimester of bovine pregnancy. Ž . Ž . Ž . Placentas were sampled from cattle at approximately 4 n s 3 , 6 n s 2 , and 8 n s 3 months gestation. Periparturient placentomal samples were collected from seven first calf, holstein Ž heifers at C-section performed following a drop in progesterone - 2 ngrml ProgestAs- . say, Synbiotics, san Diego, CA . Placentomes were sampled from the mid-region of the uterine horn that contained the fetus. Post partum placentomes were collected from six cases, obtained per vagina within 30 min of normal vaginal delivery. During sampling, slabs 5 mm in thickness were carefully sectioned from the central area of each placentome perpendicular to the allantoic surface. Samples were frozen in chilled isopentane, cryosectioned at 8 mm, and fixed in cold acetone for 15 min. After blocking with normal serum, sections were incubated with primary monoclonal antibody Ž . Ž SBU-3 Ctr. An. Biotec., Melbourne, Australia or CD68 EBM 11 Dako, Carpenteria, . CA , an antibody that labels macrophages, for 2 h at 378C in a humid chamber. Sections Ž were then incubated with a biotinylated anti-mouse secondary antibody Vector Labora- . Ž tories, Burlingame, CA followed by streptavidin peroxidase conjugate Zymed Labora- . Ž . tories, San Francisco, CA and visualized with AEC Zymed and hematoxylin. Non-im- Ž . mune mouse ascites Zymed was used as a negative control. Analysis of the number of CD68 EBM 11 positive cells per unit area of tissue was Ž . determined using Image-Pro Pluse Media Cybernetics image processing software. A Ž . total of 15 fields per placentome two per case were digitized. For each field, fetal villi Ž . were traced and measured using a freeform ‘‘area of interest’’ AOI mechanism. For each AOI, macrophages were selected using the ‘‘color segmentation’’ function outlin- ing positively stained cells. Macrophage numbers were determined automatically, and calculated per unit area of AOI. Results of this study are presented in Fig. 10. Relatively few fetal macrophages were present in cotyledonary villi from fetuses younger than 6 months, but by 8 months, macrophages had increased by over 10-fold. Samples collected at cesarean section and from placentas sampled after vaginal delivery contained similar numbers. In cases of mycotic, yeast, and bacterial placentitis, fetal macrophages become prominent within the allantoic mesenchyme in areas of inflammation. The role these cells play in fetal placental defense and their likely role in transporting microbial agents from sites of inflammation within the placenta to the fetus via umbilical veins needs further elucida- tion.

7. Conclusion