The immune response to oxidized ferredoxin. II. Cross reactivity of cells and antisera to modified ferredoxins and the nature of the cells responding in vitro

The cross reactivity of sera from rabbits sensitized to performic acid oxidized ferredoxin (O Fd) and of spleen cells from mice sensitized to O Fd was analysed using several chemically modified forms of ferredoxin in the complement fixation test and the in vitro lymphocyte stimulation assay. Only O Fd and native ferredoxin (native Fd) gave positive responses in both assays. Dinitrophenylated O Fd (DNP O Fd) and acid precipitated ferredoxin (TCA Fd) were able to fix complement (C') but did not simulate DNA synthesis in vitro. Ferredoxin alkylated with N ethylmaleimide (NEM Fd) induced cell transformation but fixed C' poorly. Carboxymethylated ferredoxin (CM Fd) was unable to stimulate DNA synthesis and was marginally able to fix C'. Methylated O Fd (meth O Fd) was not recognized in either assay. The various ferredoxin preparations were tested for their ability to sensitize mice for use in the in vitro lymphocyte stimulation assay. Only O Fd, NEM Fd and native Fd were capable of sensitizing lymphocytes for a proliferative response in vitro to the test antigens. This correlates with the observation that only these antigens were able to induce DNA synthesis in O Fd sensitized lymphocytes. The nature of the cells responding in vitro was examined by treating the cells with rabbit antimouse immunoglobulin and C' or rabbit anti mouse brain associated theta and C'. The 24 hr response was found to be sensitive to both sera while the 120 hr response was sensitive only to the anti theta sera.