Neuropathology and Applied Neurobiology 1993. zyxwvutsrqp 19,82-90 zyxwvuts Zn-binding globulin in human fetal brain and liver: a marker for passive blood/CSF transfer of protein z K. M. Dziegielewska', J. E. Bell?, N. Matthews", K. MsllgBrd$and zyxwv N. R. Saunders" *Clinical Neurological Sciences Group, University of Southampton, ?Department of Pathology, Western General Hospital, Edinburgh, and $Institute for Medical Anatomy, Department A, University of Copenhagen, Denmark zyxwvu K. M. Dziegielewska, J. E. Bell, N. Matthews, K. MollgArd and N. R. Saunders (1993) Neuropathology and Applied Neurobiology 19,82-90 Zn-binding globulin in human fetal brain and liver: a marker for passive blood/CSF transfer of protein The presence ofZn-binding globulin (ZnbG) during human fetal development was studied in cerebrospinal fluid (CSF) and plasma with immunodiffusion methods and in brain, CSF, plasma and liver using immunocytochemical methods. At the earliest stages examined with immuno- cytochemistry (5-6 weeks gestation) no staining for ZnbG was visible in liver, plasma, CSF or brain. However, the primitive mesenchyme exhibited a prominent staining reaction. In late embryonic and early fetal stages, staining for the protein was most prominent in the spinal cord, brain stem and diencephalon and in the choroid plexuses and marginal and subplate zones in the telencephalon. At the cellular level, synaptic strata and territories were most strongly stained. The distribution of ZnbG in the early developing central nervous system suggests that this protein may be involved in the initial establishment of CNS circuitry. Embryonic brain was positive for ZnbG well before the protein could be detected in CSF, plasma or liver. The early occurrence of ZnbG in brain tissue prior to its presence in liver or plasma also suggests that the protein is syn- thesized in early fetal brain. At the time when CSF first became positive ( 1 7 weeks gestation),the brain staining had largely disappeared. ZnbG in plasma increased throughout gestation to reach 2.6 zyxw f 0.4 mg/100 ml at term and subse- quentlyincreased toanadultvalueof6.8 f 1.5 mg/100 ml. The CSF to plasma ratio did not change significantly during development and was low (1-2%) at all fetal ages examined when compared with other plasma proteins: this is consistent with passive transfer between the two compartments both in the fetus and in the adult. Keywords: Zn-binding globulin, human fetus, neocortical development, blood-brain barrier Introduction It has been known for some years that several plasma proteins are present within cells in the developing brain [15,16]. Such proteins are generally thought of as being exclusively synthesized by the liver: it is therefore usually assumed that the source of plasma proteins in developing brain is uptake via, what has been incorrectly called, 'the immature' blood-brain barrier [20]. However, origins of plasma protein in fetal brain other than uptake from plasma, have also been considered [e.g. 41. There is increasing evidence that at least some of the immunocyto- Correspondence: Dr K. M. Dziegielewska. Department of Physiology. University of Tasmania, Hobart 7001, Australia. chemically detectable plasma proteins in the fetal brain are synthesized in situ [18,19,22]. Another route of access for protein into the brain is from the CSF. The level of protein in fetal CSF is much higher than can be accounted for by passive transfer from plasma [4] and a specific uptake mechanism that is developmen- tally regulated has been demonstrated to be present in the choroid plexus cells of the immature brain [6,8,11]. It has also become clear that choroid plexus cells can synthesize some plasma proteins [19] and that this may contribute to their high concentration in CSF [22]. In adult brain, the concentrations of individual proteins in CSF are directly related to their molecular radius and concentration in plasma [9], with a few exceptions, e.g.