Solubilization of complexes between tumor‐associated and H‐2 antigens from a tumor cell plasma membrane

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Abstract
The tumor-associated cell surface antigens (TAA) gp71 and AgI cocap H-2, but are not associated with H-2 following solubilization of membranes with detergent. We have attempted to solubilize intact TAAIH-2 complexes from surface-labeled L cells using decreasing concentrations of the nonionic detergent Nonidet-P40 (NP40). Associations between gp71 and H-2 and between AgI and H-2 in solution were detected using sequential immunoprecipitation. gp7UH-2 and AgI/H-2 complexes were solubilized at the lowest detergent concentration used, 0.01% NP40. No co- precipitation of these antigen pairs was seen at any higher NP 40 concentration tested. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that precipitation of antigens solublized in 0.01% NP40 leads to co precipitation of a small number of other protein peaks and does not appear to involve wholesale inclusion of labeled membrane proteins. These results, together with previous observations of cocapping between TAA and H-2 antigens, suggest that the molecules are associated with one another in the membrane. Detergent solubilization of membranes with all but the most gentle conditions leads to disruption of these complexes.