Contribution of stabilizing agents present in intravenous immunoglobulin preparations to modulation of mononuclear cell proliferation in vitro

Intravenous immunoglobulin (IVIG) preparations have been shown to suppress lymphocyte proliferation in vitro. This study aimed to investigate the effects of an IVIG produced by fractionation/DEAE-Sephadex adsorption on lymphocyte proliferation in vitro, with particular reference to contributions of the stabilizing agents present in the IVIG to the modulation of mononuclear cell proliferation. It was found that glycine significantly inhibited stimulation by the mitogenic lectin phytohaemagglutinin (PHA; 58% inhibition, P < 0.01). Glucose and human albumin also reduced the response to PHA but to a lesser extent (20% and 30%, respectively). In further experiments the effects of sucrose and maltose, two disaccharides used as stabilizing agents in IVIG preparations, were studied. Three doses were used (2.5 mM, 25 mM and 250 mM), representing levels likely to be found in vivo after infusion of IVIG at immunotherapeutic doses, on four different proliferative stimuli. Maltose was found to inhibit proliferation to PHA, anti-CD3 and PMA in a dose responsive manner. Sucrose also inhibited proliferation to these stimuli, but a dose response was not observed. For both sugars, only the highest dose (250 mM) inhibited the proliferative response of mononuclear cells to PMA and a calcium ionophore (ionomycin). The repurified IgG component of the IVIG preparation did not inhibit PBMC responses to PHA in this system. Kinetic analyses, in which the sugars were added 24 h after proliferative stimuli, indicated that both sugars still inhibited responses to PHA, and, to a lesser extent, PMA, but only maltose inhibited the anti-CD3 response. These findings show that stabilizing agents currently found in commercial IVIG preparations make a significant contribution to modulating mononuclear cell proliferation and need to be considered when assessing the immunomodulatory role of IVIG in vitro.