Liposomes in immunology: impairment of the adjuvant effect of liposomes by incorporation of the adjuvant lysolecithin and the role of macrophages.

The immune response against HSA (human serum albumin) was studied in rabbits after intravenous injection of various HSA preparations. When HSA was injected one day after, together with or coupled to lysolecithin, a late response was found in twelve out of thirteen rabbits, whereas a minority of the rabbits responded when lysolecithin was omitted. These results confirm the adjuvant activity of lysolecithin. A rapid response starting on day 6 was found in rabbits injected with HSA entrapped in liposomes which had been composed of lecithin, phosphatidic acid and cholesterol (PPC liposomes). The response against liposome entrapped HSA was delayed for about one day when the phospholipid adjuvant lysolecithin was incorporated in the liposomes (LPPC liposomes). Results lend support to the hypothesis that the adjuvant activity of lysolecithin and its opposite inhibition of the adjuvant activity of liposomes are mediated by the same mechanism, i.e. inhibition of enzymatic digestion in lysosomes of macrophages.