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Humoral modulation of lymphokine‐activated killer (LAK)‐cell induction in humans: IgG‐related and non‐IgG inhibitors in sera from cancer patients

Soluble inhibitors of lymphokine‐activated killer (LAK) cell induction were characterized and purified from serous fluids from healthy donors or from patients with advanced cancer. Inhibitory activity in sera from cancer patients was partially absorbed with protein A agarose or anti‐human IgG agarose. Following absorption, residual inhibition varied with individ ual sera, suggesting the presence of IgG‐related and non‐IgG inhibitory factors, and the proportions varied in the patient population. IgG, purified by affinity chromatography from ascitic fluids, from plasma of cancer patients, and from plasma of healthy donors, significantly inhibited IL‐2 induction of LAK cells in a dose‐dependent manner. Irrespective of the sources, inhibitory activity resided in the high‐molecular‐weight IgG fraction composed of IgG aggregates and immune complexes, but not monomeric IgG Commercially prepared human IgG in aggregated form, but not in monomeric form, inhibited LAK cell induction in a dose‐dependent manner. In contrast, neither bovine IgG nor human albumin affected LAK cell induction, even at higher concentrations. Aggregated human IgG inhibited LAK cell induction in unfractionated peripheral blood mononuclear cells (PBMC) but not in monocytedepleted peripheral blood lymphocytes (PBL). Despite exten sive (>99%) depletion of IgG by protein‐G affinity chromatography, the serous fluid from cancer patients displayed significant inhibitory activity. Fractionation of the IgG‐depleted inhibitory materials by Sephacryl S‐300, high‐pressure ionexchange column (HPIEC) or gel‐permeation chromatography (HPGPC) demonstrated a 65‐kDa inhibitor, distinct from IgG. Affigel‐blue affinity chromatography of the 65‐kDa fraction depleted albumin but did not remove the inhibitory activity, suggesting that the 65‐kDa inhibitor is not serum albu min nor an albumin‐bound component. These results suggest that serous fluids from patients with advanced‐stage cancer contain 2 distinct regulators for LAK cell induction: (I) aggregated IgG and (2) a 65‐kDa inhibitor, distinct from albumin.