We have previously produced a MoAb, B1D6, against a plaeental FcR. The antigen isolated using F(ab')2-fragments of B1D6 exhibits Fc-binding properties with low affinity for IgG. The antigen is a single-chained glycoprotein with a molecular weight of approximately 37 kDa and a pi of about 7.0-8.5. Amino acid sequences from enzymatic digests of the antigen indicated that it is annexin II. Immunoreactivity using anti-annexin antisera and purified placental annexin II have further established the specificity of BID6 to annexin II. The B1D6 epitope appears to be intramembraneous and intracellular on placental syncytiotrophoblasts, monoeytes and other cells investigated.
"Annexin II has long been shown to have anti-inflammatory and anticoagulant activities as a consequence of its capacity to sequester phospholipids (reviewed in ). Low-affinity Fcg receptor activity in the human placenta has also been reported for extracellular annexin II ; it is conceivable that part of the IgG found associated with the HCW may be bound to annexin II. Particularly interesting in the context of hydatid disease is the precedent that extracellular annexin II plays an important role in the calcification of cartilage , by virtue of its Ca 2 + -binding properties . "
[Show abstract][Hide abstract] ABSTRACT: Annexin II, a member of the annexin family of Ca2+ and phospholipid binding proteins, is present in human placenta. Placental annexin II has low affinity FcR activity, and is present as a heterotetramere on syncytiotrophoblast apical cell membrane extracellular surface. In addition to annexin II, transmembraneous leukocyte FcRIII is present on syncytiotrophoblast apical membrane. Either one, or both molecules may mediate the binding of IgG and thereby facilitate its transport through the syncytiotrophoblast layer. However, the presence of other maternal plasma proteins in syncytiotrophoblasts that are not transported to the human fetus is suggestive of nonspecific fluid phase endocytosis. The MHC class I like FcR, similar to the receptor found in neonatal rodent intestine, FcRn, is present intracellularly in human syncytiotrophoblasts, as is its light chain beta 2-microglobulin. The hFcRn is not detected on the apical plasma membrane. The placental hFcRn co-localizes with IgG in syncytiotrophoblast granules. It is likely that hFcRn binds and transcytoses IgG through the syncytiotrophoblast. Protected transfer of IgG may occur within syncytiotrophoblast endocytotic vesicles prior to release in the villous stroma and subsequent translocation into the lumen of fetal stem vessels by uptake and transport in endothelial caveolae.
[Show abstract][Hide abstract] ABSTRACT: Annexin II (AXII) was reported to suppress lymphoproliferation and immunoglobulin production. To investigate this further, the AXII-negative human B-lymphoma cell line Raji was transfected with AXII followed by transfection with p11. Stable transfectants were generated. In vitro immunological effects of Raji, Raji-AXII and Raji-AXII-p11 were compared by using irradiated cells as stimulators for PBM in mixed lymphocyte reactions or by adding the supernatants to lymphoproliferation or ELISPOT cultures. None of the assays provided evidence of significant immunosuppression by AXII. Thus, expression of AXII or AXII plus p11 does not by itself give a cell immunosuppressive ability.
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