Background: Milky spots in the human greater omentum are preformed spe
cific accumulations of primarily macrophages within the stroma of the
greater omentum, To obtain a better understanding of milky spots in th
e human greater omentum, the development and the earliest forms of mil
ky spots in the human greater omentum were studied, with special atten
tion to the macrophage population Methods: Specimens of human greater
omentum were obtained from fetuses of 20 to 40 weeks gestation and one
newborn three days old (n = 6), Using mature macrophages (RFD 7), act
ivated macrophages (RFD 1), B-lymphocytes (CD 22), and T-lymphocytes (
CD 2), and immunoperoxydase labeling, the percentage of these cells in
developing milky spots and the development of milky spots were studie
d by light microscopy, A time-dependent increase in the percentage of
positive staining cells and the size of clusters was analyzed using th
e non-parametric Spearman rank correlation test, Results: Small accumu
lations of cells with about 50% monocytes/macrophages were present at
20 weeks of gestation, With increasing gestational age the number of c
lusters of cells increased significantly (P < 0.01) as well as their s
ize (P < 0.01), Starting at 29 weeks, vascularized clusters of cells w
ere seen; true milky spots were present at 35 weeks, A significant (P
< 0.05) increase in the percentage of mature macrophages was found in
developing milky spots, whereas no activated macrophages were seen, Th
e percentage of B-lymphocytes and T-lymphocytes found in the clusters
of cells and milky spots increased significantly (P < 0.05) but did no
t exceed 10% of the total number of cells, Conclusions: From our data
it can be concluded that milky spots are specific structures in the gr
eater omentum formed between the 20th and 35th week of gestation, Furt
her, we concluded that immature cells (promonocytes) mature locally in
developing milky spots. (C) 1997 Wiley-Liss, Inc.