Immunohistochemical evidence for intracellular localization of plasma proteins in CNS and some neural crest derivatives in human embryos.

Recent work has provided immunohistochemical evidence for an intracellular localization of some plasma proteins in the central nervous system of chick embryos and of rat, mouse, sheep, monkey and human fetuses. A regional distribution of plasma proteins in human embryonic brain, spinal cord and some neural crest derivates is shown in this study. Alphafetoprotein was the most widespread and prominent of the plasma proteins examined in early embryos. It was observed intracellularly in the ventricular zone of the fore-, mid- and hindbrain whereas other CNS regions and neural crest derivates were negative in the earliest 9 mm crown rump length (CRL) embryo examined. The embryonic nervous system was markedly negative for all other plasma proteins tested at this stage. By 15 and 16 mm CRL, a few cells in the ventricular zone and in sensory cranial nerve ganglia were positive for albumin and transferrin whereas AFP exhibited a distribution similar to that of the 9 mm embryo. By 20 to 35 mm CRI, albumin and AFP had the same extensive distribution in the CNS. Many cells in sensory and autonomic ganglia showed positive staining for albumin in contrast to a few scattered cells which exhibited reactivity for AFP, transferrin and prealbumin. The staining pattern for albumin in the ganglia may reflect a rostral-caudal gradient in development. The possible origin of intracellular plasma proteins in the developing nervous system is discussed.