Journal of Lipid Research, Vol 38, 2003-2011, Copyright © 1997 by Lipid Research, Inc.

ARTICLES

Interactions between cationic liposomes and an antigenic protein: the physical chemistry of the immunoadjuvant action

LR Tsuruta, W Quintilio, MH Costa and AM Carmona-Ribeiro
Departamento de Bioquimica, Instituto de Quimica, S. Paulo, SP, Brazil.

The 18 kDa antigenic protein from Mycobacterium leprae (P) or its N- acyl derivative (AP) was incorporated in dioctadecyldimethylammonium bromide (DODAB) liposomes in water or in phosphate-buffered saline (PBS). In water, 100% P incorporation in liposomes contrasts with 65% in PBS. There is 75-80% AP incorporation to liposomes in water against 55-65% in PBS, showing that attachment of hydrophobic residues to the protein, instead of increasing, further decreases incorporation to the liposomes. From protein adsorption on latex, P affinity is larger than AP affinity for the latex surface whereas limiting adsorption for AP is much larger than that obtained for P, possibly due to AP aggregation in solution. P-induced rupture of liposomes containing [14C]sucrose was evaluated from dialysis of protein/liposomes mixtures. In water, P incorporation to the liposomes causes leakage of radioactive contents contrasting with the absence of leakage for P incorporation in PBS. Immunization tests for delayed type hypersensitivity indicate a enhancement of cell-mediated immunological response towards P/DODAB complexes that is not obtained for the isolated protein. Absence of leakage for P in PBS is associated with a P "lying-over" on the liposome and optimization of protein presentation to the immunological system.
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