A crude lipid fraction obtained from (Ml whole lipids) suppressed concanavalin A (Con A)-induced blastogenesis of murine spleen cells (SPCs). Among three lipid fractions, the phospholipid fraction possessed the highest inhibitory activity, followed by the polar mycoside fraction, but the apolar mycoside fraction showed no activity. Since MI whole lipid and phospholipid fractions inhibited the Con A-induced proliferative response of SPCs which had been treated with Con A before the addition of the lipid fractions, their action is not due to hindrance of Con A binding to T cells. These two MI lipid fractions reduced IL-2-producing ability, acquisition of IL-2 reactivity, and expression of IL-2 receptors in Con A-stimulated T cells. However, they did not affect IL-2-induced proliferation of an IL-2-dependent cytotoxic T cell line, CTLL-2. When SPCs were pretreated with either MI whole lipid or phospholipid fraction for 24 h, an irreversible reduction in Con A responsiveness was seen only in the phospholipid-treated SPCs. The action of these MI lipid fractions was phase-dependent and they exhibited considerably decreased but still significant inhibitory activity against Con A blastogenesis of SPCs, even when they were added at 24 h after the initiation of SPC culture with Con A. MI whole lipids and the three lipid fractions (polar mycoside, apolar mycoside, and phospholipid fractions) did not exhibit suppressor cellinducing activity, while MI whole lipid fraction antagonized the Con A-mediated generation of suppressor cells. Silica gel thin layer chromatography of the phospholipid fraction showed four spots containing phosphate and one spot without. SPC Con A blastogenesis-inhibitory activity was shared by the two least polar phosphate-containing substances. One of those apparently contained amino groups and carbohydrate moieties. The second component contained no such moieties.


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