IMMUNOACTIVATING POTENTIAL OF MULTILAMELLAR LIPOSOME VESICLES (MLV) IN MURINE POPLITEAL LYMPH-NODE (PLN) TEST

Immunoactivating properties of subcutaneously injected small unilamell ar vesicles (SUV) and multilamellar liposome vesicles (MLV) were studi ed in relation to different transition temperatures (Tc) of phospholip ids. Liposome-induced proliferative reaction in the popliteal lymph no de (PLN) was quantified by subsequent cytometric assay. Early cell act ivation during the onset of PLN reaction was monitored by immunophenot yping of lymphocyte subsets stained with a panel of monoclonal antibod ies (mAbs) and gating the subset-specific large/activated cells. Injec tion of MLV liposomes containing distearoyl phosphatidylcholine (DSPC) and dipalmityl phosphatidylcholine (DPPC), characterized by relativel y high Tc, resulted in a marked PLN reaction, increased numbers of CD4 (+), CD8(+), Ig(+) subsets and increased proportions of large/activate d EAM(+) (CD69(+)) and CD25(+) (IL-2 receptor(+)) cells. The reaction was dose and time dependent. In contrast, injection of MLV liposomes c ontaining lipids of low Tc, such as egg phosphatidylcholine (egg PC) a nd dimyristoyl phosphatidylcholine (DMPC), did not show any immunoacti vation. In addition, there was a highly reduced immunoactivating poten tial of small-size SUV liposomes over large-sized MLV of identical pho spholipid composition. Generally, both lipid composition and vesicle s ize appeared to be essential for the immunoactivating potential of lip osomes. The data suggest a possible correlation between the Tc of the phospholipid and the immunoactivating potential of the large-sized MLV liposomes.