The Binding of Plasma Proteins to Human Placental Cell Membranes

Abstract

1.To investigate the relative degree. to which human IgG and other plasma proteins bind to cell membranes of the full-term human placenta, suspensions of membranes mixed with radio-iodinated proteins were incubated at pH 6.5 and subjected to Sepharose 2B column chromatography. The amount of labelled protein associated with membrane protein in membrane-containing fractions of the eluate was then determined.2. Binding of IgG and each of the four subclasses of IgG was appreciable. Binding of IgG was markedly reduced if membranes were incubated at pH 8.0 rather than 6.5. Binding of labelled IgG was inhibited by excess of unlabelled IgG but not by excess of unlabelled albumin. Placental membranes bound much more IgG than did erythrocyte membranes. 3. Binding of insulin was relatively greater than that of IgG, whereas binding of IgE, IgM, IgA, albumin, transferrin and polyvinylpyrrolidone was much less than that of IgG and each of its subclasses.4. The relative binding of IgG and fragments of the IgG molecule was, in decreasing order of magnitude: light chains, IgG, Fc, heavy chains and F(ab')z. 5.The results are consistent with Brambell's hypothesis for the mechanism of the transmission of passive immunity from mother to young.

Expression of placental alkaline phosphatase does not correlate with IgG binding, internalization and transcytosis

“…This observation indicates that although in MDCK cells PLAP expression leads to an increase in IgG binding, PLAP is not primarily responsible for the IgG binding observed in BeWo cells. Because BeWo cells are trophoblastderived cells and various IgG-binding proteins had been localized in the syncytiotrophoblast plasma membrane [17,[27][28][29], several IgG-interacting proteins are expected to be also present on the surface of BeWo cells. Indeed, additional proteins not corresponding in size to PLAP were retained if lysates from BeWo cells that had been biotinylated to label plasma membrane proteins were incubated with IgG-agarose (results not shown).…”

“…Binding of the Fc portion of IgG to the brush border of villous syncytiotrophoblasts [26] led to the isolation of several IgG binding proteins with molecular masses of 60, 45, 37 and 40 kDa [17,[27][28][29]. Moreover, contradictory characteristics of the putative plasma membrane IgG receptor have been described suggesting that no single membrane receptor mediates IgG binding, internalization and transcytosis in syncytiotrophoblasts.…”

Vitamin A Transfer to the Fetus and to the Amniotic Fluid in Rhesus Monkey <i>(Macaca mulatto)</i>

“…Whereas the fetal concentrations of RBP and prealbumin were consistently below the maternal values (table I), the fetal values of IgG eventually exceeded the mater nal values [15]. Whether, as with IgG [20,21], specific receptors are involved in the pla cental transport of RBP and prealbumin, re mains to be established.…”

“…In lower species transmission of IgG occurs through other fetal membranes and via amniotic fluid [18,19]. IgG is actively transported across the placental membranes by a receptor-mediated mechanism which in volves pinocytosis [20,21]. The occurrence of membrane receptors for RBP in many tis sues [22][23][24] makes this an intriguing protein to study with regard to placental transmis sion.…”

Placental Transfer of Rh Antibody (Anti-D IgG) during Pregnancy

“…days. IgG3 has a shorter half-life, 7 days, with a turnover rate per day of 17% [34], The responsibility of regulating the cata bolic rate is largely a function of the Ig mol ecule; the Fc portion provides protection which prevents the molecule from being de stroyed [1], Transportation of IgG across the human placenta is also a function of the Fc region. IgG Fc receptor sites have been dem onstrated in human placenta, spleen, and liver [22], Brambell [6] suggested that both the cata bolism of immunoglobulins and the trans port of IgG from mother to young could be explained by the nonspecific uptake of pro tein by cells.…”