An extremely high alkaline phosphatase (AP) concentration (3609 IU/litre) was found in a 20 year old primigravida at 37 week's gestation, prompting an examination of its histological and cellular origin. Immunohistochemistry and western blots using antibodies against AP, Ki-67, phosphoprotein kinase B (Akt), phospho-p44/42 mitogen activated protein kinase/extracellular signal regulated kinase 1/2 (MAPK/Erk1/2), phospho-glycogen synthase kinase-3b (GSK-3b), phospho-stress activated protein kinase/c-Jun Nterminal kinase, total-Akt, total-GSK-3b, and phospho-p38-MAPK were carried out on index and control placental samples of the same gestational age. Compared with controls, staining of the index placenta showed minimal AP labelling of the brush border and remarkable positivity of the intervillous space. Cytotrophoblastic proliferation was 8-10% in the index placenta compared with 1-2% in controls. The index placenta also had raised concentrations of protein kinases with important roles in cell differentiation. The proliferation and differentiation rates of the cytotrophoblasts were found to be five times higher in index samples than in controls. It is hypothesised that loss of syncytial membranes in immature villi led to increased AP concentrations in the maternal circulation and decreased AP staining of the placenta. Loss of the syncytium might also stimulate increased proliferation of villous cytotrophoblasts, which would then fuse and maintain the syncytium.A lkaline phosphatase (AP) is known to be produced by the liver, bones, small intestine, and kidneys, and different AP isoforms are also expressed by the placenta during pregnancy.1 The average amount of AP in one human term placenta amounts to 40 mg. 2 The placental isoforms are known as heat stable AP, because they are heat resistant at 60˚C, a property that is the main criterion for distinguishing them from the other isoenzymes. 3 In early pregnancy, the tissue non-specific AP isoenzyme is mainly expressed in the placenta, and reaches a peak value around 10 weeks of pregnancy. At the end of the second trimester, most of the AP activity comprises term placental AP isoenzymes 1 (90% of which are the P1 type, 10% the P2 type) produced by the syncytiotrophoblasts, and these isoenzymes appear in maternal serum between the 15th and 26th weeks of pregnancy.4 Their plasma concentrations increase exponentially during gestation-they are present at concentrations three times greater than those seen in nonpregnant women-and have a long half life (seven days) postpartum.

As previous sequential and structural analyses showed its conserved homology to members of the galectin superfamily, Placental Protein 13 (PP13) was designated galectin‐13. Similarly to eosinophil Charcot Leyden Crystal protein / galectin‐10, its weak lysophospholipase activity was proved. Sugar binding assays revealed that residues widely expressed in placenta had the strongest binding affinity to PP13, which expression was found to be restricted to placenta. With regard to its strong labeling of the syncythiotrophoblasts’ brush border membrane as well as its co‐localization and specific binding to annexin II, PP13 was assumed to be externalized to the cell surface like other galectins. In a comparative study we found, that in the 3rd trimester, expression of PP13 was significantly reduced in preeclamptic (n = 20) and HELLP syndrome (n = 5) placentas compared to gestational age matched healthy samples (n = 25). In the same pathologic cases, maternal PP13 serum levels were also lower than in controls. Recently, PP13 was also successfully tested as a new 1st and 2nd trimester placental marker for the prediction of preeclampsia and IUGR. With regard to these results, PP13 may have special immunobiological function at the lining of the common feto‐maternal blood‐paces. The possible clinical importance of PP13 in pathological pregnancies with immunological background have to be emphasized.