Human serum β2-microglobulin levels: correlation with total serum IgG and placental IgG transfer in HIV-infected and non-HIV infected individuals

The acquisition of maternal immunoglobulin G (IgG) is fundamental to the immune defence of the neonate. The receptor responsible for IgG transfer across the human placenta has also been implicated in the maintenance of IgG levels in the circulation. β2-microglobulin is part of the Fc receptor (FcR) that has recently been purified from the human placenta. In HIV infection, increasing serum levels of total IgG and β2-microglobulin are observed as the disease progresses. Herein, we have investigated the correlation between β2-microglobulin and total serum IgG levels in HIV-seropositive mothers and their term neonates (HIV group, n=37), as well as in HIV-seronegative mothers and their term neonates (control group, n=50). Serum maternal β2-microglobulin was directly correlated with total serum IgG levels in HIV-infected mothers (r=0.58; P=0.0002), but not in healthy HIV-seronegative mothers (r=−0.20; P=0.16). Maternal serum β2-microglobulin was also inversely correlated with placental antibody transfer of total IgG in mother-newborn pairs from the HIV group (r=0.38; P=0.02), but not from the control group (r=0.15, P=0.31). These results seem to indicate that, in HIV infection, elevated serum β2-microglobulin levels could be involved in maintenance of abnormally high total serum IgG concentrations; by interfering with the binding of IgG to Fc receptors at the maternal-fetal interface, they might also reduce IgG transfer. By contrast, in normal non-HIV infected individuals, serum β2-microglobulin levels do not appear implicated in regulation of these two phenomena.