The humoral antibody response of rats immunized with chemically modified syngeneic brain cells and glioma cells

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Abstract
Six‐month‐old Fischer rats (F344) were given the carcinogen methylnitrosourea in their drinking water. Of the induced brain tumors, four were established in culture and propagated as 78FR‐G‐219 (pleomorphic glioma), 78FR‐G‐299 (astrocytoma), 78FR‐G‐284 and 78FR‐G‐344 (mixed glioma) permanent lines. All cell lines produced S‐100 protein and grew as tumors when inoculated s.c. or i.c. in syngeneic hosts. A comparative study of the antigenicity of these lines at different passage levels was carried out using native and chemically modified cells. Syngeneic rats were immunized with cells conjugated with dimethylsulfate and trinitrobenzene sulfonic acid. The immune response was characterized and quantified by an indirect immunofluorescence method and by a complement‐dependent microcy‐totoxicity test. Chemical modification of the tumor cells enhanced antigenicity of the treated cells. The best results were attained with trinitrobenzene sulfonic‐acidtreated cells and constituted a two‐fold increase in the cytotoxicity index. Cytotoxicity values varied in the different cell lines. Antisera raised with trinitrobenzene sulfonic‐acid‐modified cells of all lines cross‐reacted with cells of all lines. Cytotoxicity values were insignificantly reduced by absorbing the antisera with a variety of syngeneic tissues. Antisera raised against native syngeneic brain cells showed virtually no cytotoxicity for glioma cells. Antisera raised against syngeneic brain cells treated with trinitrobenzene sulfonic acid, however, were slightly cytotoxic for normal brain cells and glioma cells as well. The results of the present studies show that antigenicity of glioma cells can be definitely raised with trinitrobenzene sulfonic acid treatment. Furthermore, it would seem that haptenization of glioma‐associated antigens may be a promising approach to the study of glioma—host interactions.