Mouse H-2 histocompatibility antigen has been extracted, solubilized, and partly purified from the cells of an A strain spontaneous leukemia carrying TL (thymus-leukemia) antigens. H-2 and TL. 1, 2, 3 activities were measured by inhibition of the cytotoxic effect of the corresponding isoantibodies.

TL activity was associated with the H-2 active fraction obtained by solubilization and fractionation by gel filtration. TL specificity was largely separated from H-2 antigen by subsequent chromatography on DEAE Sephadex as an adjacent component in a series of fractions.

The soluble H-2 antigen prepared from the leukemia cells was tested for most of the specificities determined by H-2a with no exceptional results.

TL. 1, 2, 3 activities, measured as each component separately, were located in approximately the same position; there is no clear indication yet whether the three TL specificities are separable from one another.

It appears that in addition to the close genetic linkage between the H-2 and TL loci, and their reciprocal interaction in producing H-2 and TL antigens, these antigens exhibit some similarity at the chemical level.

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