Monoclonal antibodies to a nitroxide lipid hapten

The isolation and characterization of a hybridoma cell line producing a monoclonal IgG1 antibody against a spin-label nitroxide group is described. The antibody recognizes a synthetic hapten containing linked dinitrophenyl and 2,2,6,6-tetramethylpiperidinyl-1-oxy groups, having an affinity of 3.6 +/- 1.0 . 10(6) M-1 for the soluble hapten at 25 degrees. The antibody binds to phospholipid vesicles containing 2 mol% of spin label-derivitized lipid (lipid hapten) with an affinity of 1.5 +/- 0.2 . 10(8) M-1. This monoclonal IgG1 mediates the binding of hapten-bearing lipid vesicles to mouse macrophage RAW264 cells bearing Fc receptors. The cellular responses to this binding are similar to those observed previously using polyclonal rabbit anti-hapten IgG. As with the heterogeneous antibodies, the monoclonal IgG1 is more efficient in mediating cellular uptake when the vesicles are in the "fluid' physical state (dimyristoylphosphatidylcholine at 37 degrees C) compared to "solid' (dipalmitoylphosphatidylcholine at 37 degrees C). Despite the enhanced binding of "fluid' phospholipid vesicles to cells, only the "solid' vesicles triggered a significant respiratory burst in Raw264 macrophages.