Differential endocytosis of T and B lymphocyte surface molecules evaluated with antibody-bearing fluorescent liposomes containing methotrexate.

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Abstract
Antibody-bearing fluorescent liposomes containing methotrexate became bound to [mouse] cells expressing determinants recognized by the antibody. The number of bound liposomes could be evaluated by fluorometry and the internalization of liposomes was evaluated by the methotrexate-mediated inhibition of radiolabeled deoxyuridine incorporation. The effect of methotrexate transferred from the liposomes into the cells was a function not of the number of liposomes bound but of the nature of the cells and of the target molecules. Liposomes bearing antibodies with specificity for the H-2K or MW 94,000 and 180,000 molecules were much more effective at drug delivery into T than B cells, even though these determinants were expressed by both cell types. B cells were more sensitive to the effect of methotrexate in anti-H-2 I-A and I-E liposomes than in anti-H-2K liposomes. Inhibition of the methotrexate effect by NH4Cl suggested that methotrexate entered the cell by endocytosis of the liposomes. The results are consistent with differential internalization of H-2K, I-A, I-E and MW 94,000 and 180,000 cell surface molecules by mitogen-stimulated T and B cells.

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