Down-regulation of cytokine production and interleukin-2 receptor expression by pooled human IgG

The influence of pooled human IgG preparations for intravenous use (i.v.Ig) on in vitro-induced cytokine production was studied at the single-cell level using cytokine-specific monoclonal antibodies (mAb) and indirect immunofluorescent technique. Cultured mononuclear cells from peripheral blood from healthy adult donors were polyclonally stimulated for 96 hr by either direct ligation of T-cell receptors using immobilized anti-CD3 mAb or by a combination of a protein kinase C activator [phorbol 12-myristate 13-acetate (PMA)] and a calcium ionophore (ionomycin) in the absence or presence of i.v.Ig. A marked inhibition of proliferation and blast transformation was noted in all i.v.Ig exposed cultures, despite good cell survival. The production of the T-cell lymphokines interleukin-2 (IL-2), IL-10,interferon-gamma (IFN-gamma) and tumour necrosis factor-beta (TNF-beta) was significantly down-regulated during the whole studied period in the i.v.Ig containing anti-CD3 stimulated cultures. The synthesis of the monokine IL-8 was not suppressed and that of TNF-alpha, which was made by both lymphocytes and monocytes, was only moderately inhibited. Somewhat different and more transient effects were observed in the i.v.Ig-exposed PMA/ionomycin-activated cultures. The production of IL-2, IL-3, IL-4, IL-5, IL-10, TNF-beta and granulocyte-macrophage colony-stimulating factor (GM-CSF) was down-regulated during the initial phase of the cultures up to 48 hr, but not at 48-96 hr. The synthesis of IFN-gamma and TNF-alpha was unaffected of the influence of i.v.Ig during the entire culture period. The expression of IL-2 receptors (IL-2R) was significantly suppressed in the i.v.Ig-treated anti-CD3-activated cells, but not in the PMA/ionomycin-stimulated cultures. Taken together our results indicate that pooled IgG may mediate immunomodulation by direct effects on cytokine production and on T-cell proliferation.