Cm. Diazaraya et al., IMMUNOHISTOCHEMICAL AND TOPOGRAPHIC STUDIES OF DENDRITIC CELLS AND MACROPHAGES IN HUMAN FETAL CORNEA, Investigative ophthalmology & visual science, 36(3), 1995, pp. 644-656
Purpose. To investigate the distribution and phenotype of major histoc
ompatibility complex (MHC) class II-positive dendritic cells and macro
phages in normal human fetal cornea in the age range 10 to 25 weeks ge
station. Methods. Peroxidase and gold immunohistochemistry were used t
o visualize MHC class II and macrophage antigen (S22) immunoreactive c
ells. Cell distributions were analyzed quantitatively, and topographic
maps were produced. Results. Immunoreactive cells, concentrated centr
ally, were present at 10 weeks gestation in the corneal epithelium and
stroma. Average densities increased steadily up to 25 weeks gestation
. Two morphologic forms of MHC class II and S22 immunoreactive cells w
ere observed-large, dendritiform cells and small, rounded cells with s
hort processes. Electron microscopy revealed that most MHC class II-po
sitive cells were morphologically consistent with previous ultrastruct
ural descriptions of corneal Langerhans cells. Immunoreactive cells we
re more numerous in immunogold-labeled specimens than in peroxidase-la
beled specimens of similar ages. However, quantitative analysis of bot
h techniques revealed that S22-positive cells comprised 30% to 50% of
MHC class II-positive cells. Conclusions. This study provides a detail
ed description of heterogeneous populations of MHC class II and S22 im
munoreactive cells in the human fetal cornea. In contrast to the adult
cornea, which is typically devoid of MHC class II-positive cells, imm
unoreactive cells in the fetal cornea are concentrated centrally and i
ncrease in density up to at least 25 weeks gestation. These results in
dicate that reduction in Langerhans cell numbers to adult levels must
occur after 25 weeks gestation. The presence of dendritic cells and ma
crophages in the fetal cornea has important implications for the under
standing of corneal immunology.