Modulation of the biologic activities of IgE-binding factors. I. Identification of glycosylation-inhibiting factor as a fragment of lipomodulin

Splenic T lymphocytes of rats treated with complete Freund's adjuvant (CFA) spontaneously release a lymphokine that inhibits the glycosylation of IgE-binding factors during their biosynthesis and provides the factors with biologic activity: selective suppression of the IgE response. The lymphokine, which is called glycosylation-inhibiting factor, also prevents IgE-induced increases in FcεR+ cells. The glycosylation inhibiting factor is formed by stimulation of BCG-primed spleen cells with PPD and participates in the selective formation of IgE-suppressive factors. The lymphokine is derived from OX 8+ T cells in both the CFA and BCG systems. The glycosylation-inhibiting factor is a 16,000-dalton peptide, as estimated by gel filtration, and specifically binds to monoclonal antibody against lipomodulin, a phospholipase inhibitory protein. Furthermore, 'lipomodulin' was detected by radioimmunoassay in the 16,000-dalton fraction that contained glycosylation inhibiting factor. The fraction did not inhibit phospholipase A2 but after alkaline phosphatase treatment, the fraction did inhibit phospholipase A2. Furthermore, purified lipomodulin obtained from glucocorticoid-treated rabbit neutrophils had the same biologic activities as glycosylation inhibiting factors; i.e., it inhibited both protein glycosylation of IgE-binding factors and IgE-induced expression of FcεR. The results collectively indicate that glycosylation-inhibiting factor is a fragment of phosphorylated lipomodulin.