A comparative study on the effect of gamma radiation and formaldehyde to detoxify diphtheria toxin

Corynebacterium diphtheriae is the main cause of diphtheria which still present in many countries. The most critical step in the production of diphtheria vaccines is the inactivation of the toxin by formaldehyde. This study evaluates the effect of different doses of gamma radiation (0.5, 2, 5, 10, 15, 25 and 40 kGy) on detoxifying the diphtheria toxin comparing to formaldehyde. Modified semi-synthetic Linggood medium was used to produce more purified diphtheria toxin. The purity of toxin and toxoid was evaluated by protein electrophoresis, cytotoxicity on Vero cells, and the immune response of diphtheria toxoid by measurement the level of total IgG, the level of some iso types (IgG1, IgG2a and IgE) and some biochemical parameters in the serum of Bulb/C mice. SDS showed that more purified diphtheria toxin and toxoid was obtained by using the modified semi-synthetic Linggood medium than classic medium. Also, there was no toxic effect of irradiated and formaldehyde diphtheria toxoid on Vero cells. The level of total IgG was increased gradually after each immunization dose. The level of IgE increased with increasing the dose of radiation and the maximum level was occurred at formaldehyde toxoid while the level of IgG2a showed the maximum value at dose of 10 kGy than the doses of 25 , 40 kGy and formaldehyde groups. On the other hand, the level of IgG1 increased at all toxoids, however the maximum elevation was at 10 kGy irradiated group. Aspartate aminotransferase and alanine aminotransferase (AST , ALT) levels were significantly different (P<0.05) at 25 kGy, 40 kGy and formaldehyde toxoid groups compared to control group. The level of urea and creatinine showed in all toxoid groups were stable compared to the control. The present study concluded that gamma radiation could replace the conventional methods for detoxification of diphtheria toxin to produce safe and effective toxoids