N-3 POLYUNSATURATED FATTY-ACIDS MODULATE THE EXPRESSION OF FUNCTIONALLY ASSOCIATED MOLECULES ON HUMAN MONOCYTES AND INHIBIT ANTIGEN PRESENTATION IN-VITRO

N-3 polyunsaturated fatty acid (PUFA)-rich diets are associated with s uppression of cell-mediated immune responses, but the mechanisms are u nclear. Specific immune responses are initiated by antigen-presenting cells (APC). We have previously shown in vitro that the n-3 PUFA, eico sapentaenoic acid (EPA), inhibits the expression of HLA-DR, an MHC cla ss II molecule required for normal APC function on human blood monocyt es. In contrast, docosahexaenoic acid (DHA) enhanced the expression of this molecule on unstimulated monocytes, but both n-3 PUFA suppressed its expression on interferon-gamma (IFN-gamma)-activated monocytes. I n the present study we show that when EPA and DHA were combined at the same ratio as is commonly found in fish oil supplement capsules (3:2) there was no significant effect in vitro on the expression of HLA-DR on unstimulated monocytes, but the expression on IFN-gamma-activated m onocytes remained significantly inhibited. In the same in vitro system a significant reduction in the ability of IFN-gamma-activated monocyt es to present tetanus toroid antigen to autologous lymphocytes was obs erved following culture with the combined n-3 PUFA. These findings sup port previous animal studies which suggest that n-3 PUFA can inhibit t he antigen-presenting function of mononuclear phagocytes.