Activation of spleen lymphocytes by plasmid DNA

Plasmid pUC19 DNA was shown to stimulate in vitro proliferation of CBA mouse splenocytes in a dose-dependent manner. Simultaneous treatment of the cells with the plasmid DNA and Con A or LPS produced an additive effect, while PMA acted synergistically with DNA. Monovalent Fab fragments of rabbit anti-mouse Ig (RAMIg) antibodies significantly inhibited plasmid DNA-induced polyclonal lymphocyte activation suggesting the involvement of Ig receptors in this process. Affinity modification of lymphocytes membrane-cytosole proteins with a 32P-labeled alkylating oligonucleotide derivative resulted in labeling of 67-82 and 23 kDa polypeptides corresponding to IgD and IgM heavy and light chains respectively. The immunoglobulin nature of the 82 and 23 kDa oligonucleotide-binding polypeptides was confirmed by immunoprecipitation with RAMIg antibodies.