Anti-beta-2 glycoprotein I antibodies affect Bcl-2 and Bax trophoblast expression without evidence of apoptosis

Antiphospholipid antibodies (aPLs) reacting with beta-2 glycoprotein I (β2GPI) have been associated with recurrent fetal loss and pregnancy complications. The aim of the study was to investigate whether aPLs with anti-β2GPI specificity induce apoptosis of human trophoblasts in vitro. To this end, human anti-β2GPI monoclonal IgM derived from a patient with antiphospholipid syndrome and a human irrelevant monoclonal IgM were incubated with human trophoblast cell cultures for 24, 48, and 72 h. In all the cultures we evaluated: (i) Bcl-2 and Bax mRNA and protein expression by Western blot and reverse transcription polymerase chain reaction (RT-PCR), respectively; (ii) DNA fragmentation by a commercial ELISA kit and by agarose gel electrophoresis; and (iii) the percentage of cells reactive with the monoclonal antibody (MAb) M30 by indirect immunofluorescence. The results were: Bcl-2/Bax ratio increased in untreated trophoblast cells during the time of culture, showing the highest values detectable after 72 h (2.68 and 2.28 at protein and mRNA levels, respectively). Cell incubation with anti-β2GPI MAbs induced a significant Bcl-2/Bax ratio reduction in comparison with untreated cells (1.22 and 1.28 at protein and mRNA levels, respectively, after 72 h incubation). No significant difference was detected after cell exposure to irrelevant MAbs. However, neither DNA fragmentation nor increase in cells positive for the caspase-cleaved epitope of cytokeratin 18 cytoskeletal protein (M30) was found. In Conclusion, anti-β2GPI antibodies react with trophoblast cells and reduce the Bcl-2/Bax ratio, but without any clear apoptotic effect.