IgA monoclonal and polyclonal proteins as regulatory factors of the NK cytotoxic activity

The presence of receptors for IgA (IgAR) on natural killer (NK) cells was only indirectly suggested yet. To elucidate the presence of IgAR on NK cells and its possible role in modulation of the NK activity, was initiated a preliminary study carried out in a homologous system, using human non adherent lymphocytes (NAL) and human seric or secretory IgA. A proportion of over 20% NK cells (CD16+ CD56+) was determined by flow-cytometry in the NAL-cells population. Dose-dependent IgA-binding to NAL cells was determined, showing a limitation of the IgA+ NAL proportion for a cell population of 32% and a ligand concentration of 4 mg/ml/10(7) cells. The binding parameters of the IgA/IgAR system, calculated by Scatchard procedure, revealed values of the affinity constant (K) and of the maximum number of ligand molecules bound/cell (n) depending on the aggregation degree of the ligands: K-values of 1.0 and 0.4 x 10(7) M-1 for dimeric and respectively, monomeric IgA, and n-values of 0.8 and 1.7 molecules/cell, respectively. A proportion of 3% IgA molecules endowed with cytophilic property was also calculated. The turnover rate of secretory IgA (sIgA) on the NAL cells surface showed values of the ligand half time (T 1/2) of 1 h. The effect of polyclonal IgA, (sIgA and normal seric IgA) and of monoclonal IgA myeloma (monomeric and dimeric IgA) on the NK cytotoxicity target K562 cell line was of inhibition, depended on the ligand doses and varied with the IgA type. The possible relevance of immunoglobulins A and of the activity of natural killer cells in processing of some mechanisms of the antiviral protection was discussed.