Are DNA-based vaccines useful for protection against secreted bacterial toxins? Tetanus toxin test case.

Polypeptide and DNA vaccine alternatives to the conventional tetanus toxoid were compared. Mouse immunizations with plasmid DNA that encoded the tetanus toxin C fragment polypeptide induced consistently lower antibody responses than direct immunization with the C fragment polypeptide or toxoid, yet provided some degree of protection from a lethal toxin challenge. Cytotoxic T-cell responses dominated DNA immunizations, while specific T-cell proliferation resulted from all vaccines tested. Immune responses to the DNA vaccine exhibited a T-helper type-1 propensity, while polypeptides elicited T-helper type-2 responses. The lower antibody response to the plasmid vaccine was not due to insufficient quantity of C fragment in vivo but was likely the result of a mode of antigen presentation that was less efficient for supporting antibody production. Collectively, these results suggest that polypeptide or toxoid vaccines are preferable to plasmid-based vaccination for control of diseases caused by tetanus toxin.

The hepatocyte protein synthesis defect induced by galactosamine involves hypomethylation of ribosomal RNA.

D-galactosamine produces an early defect in protein synthesis, independent of its effects on RNA synthesis. Here we show that the defect in protein synthesis is inherent in purified ribosomal subunits in vitro. Further, galactosamine treatment is associated with an 85% decrease in methylation of ribosomal RNA, involving all sites (2'-0-ribose and base positions), intact ribosomes from galactosamine-treated animals can be methylated to a greater extent than control ribosomes and in vitro methylation restores their functional capacity. Statistical analyses of these data, along with those with a number of other hepatotoxins, reveal a correlation coefficient of r = 0.95 (p less than 0.003) between protein synthetic capacity and ribosomal RNA methylation, and linear regression accounts for more than 90% of the observed variation. In contrast, no relationship was found between nucleolar RNA methylation and protein synthetic capacity. A relationship of borderline statistical significance was found between messenger RNA methylation and protein synthetic capacity, but it does not appear consistent with results obtained after CCl4 intoxication. These results lend strong support to the notion that methylation status of ribosomal RNA is an important control for protein synthesis in quiescent hepatocytes and that net hypomethylation is a common response to such divergent hepatotoxins as CCl4, ethionine and D-galactosamine.