DOWN-REGULATION OF LYMPHOKINE SYNTHESIS BY INTRAVENOUS GAMMA-GLOBULINIS DEPENDENT UPON ACCESSORY CELLS

We have investigated one mechanism by which pooled human IgG preparati ons for intravenous use (IVIg) selectively down-regulates lymphokine s ynthesis. Effects of IVIg on cytokine production were quantified at a cellular level by using an immunocytochemical staining technique. Pure T-lymphocyte preparations (from the peripheral blood of healthy adult s) were separated by the use of magnetic beads and were then used in p arallel experiments with unfractionated mononuclear cells (MNC). Cell activation was induced either by a combination of the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), and the calcium ion ophore, ionomycin, or by direct ligation of the T-cell receptor, using immobilized anti-CD3 monoclonal antibody (MoAb). Cells were cultured in the presence or absence of IVIg and subsequently harvested and stai ned for the following cytokines: interleukin-2 (IL-2), interferon-gamm a (IFN-gamma), tumour necrosis factor-beta (TNF-beta) and granulocyte- macrophage colony-stimulating factor (GM-CSF). Assessment of the frequ encies of positively stained cells was performed by manual microscopy and by computerized image analysis. Activation by PMA/ionomycin or by immobilized anti-CD3 MoAb induced substantial lymphokine production in both MNC and in purified T cells. Addition of IVIg led to a diminishe d synthesis of all of the T-cell products studied in unfractionated MN C preparations, whereas production was maintained or occasionally incr eased in the purified T-cell preparations. These findings indicate tha t the immunomodulatory effect by IVIg on T-cell activation and lymphok ine production was dependent on accessory cells.