PROTECTION AGAINST INHALATION TOXICITY OF RICIN AND ABRIN BY IMMUNIZATION

1 Abrin and ricin are highly toxic plant proteins which are very simil ar in structure and function and inhibit protein synthesis in eukaryot es. 2 Rats have been immunised against either toxin using formaldehyde -toxoids by three subcutaneous injections at intervals of 3 weeks. For abrin, serum titres in 14 out of 15 rats were raised to between 1 : 1 2800 and 1 : 51200 after two injections, 6 weeks from the start of the experiment. Titres of between 1 : 256 and 1 : 1024 were also measured in lung washes after challenge with active abrin toxin. 3 The three m ajor antibody classes, IgG, IgM and IgA were present in the immune ser a but IgG and IgA only were detected in lung washes. The proportion of IgA to IgG was higher in the lung fluid than in sera. Rats immunised by abrin toroid were protected against 5 LCt(50)'s of abrin by inhalat ion but others exposed to ricin were not. 4 For ricin, serum titres ra nged from 1 : 800 to 1 : 25600 after two injections and after a third injection the titre range was the same but population samples were wei ghted towards the higher titres. All rats immunised with ricin toroid survived the challenge of 5 LCt(50)'s of ricin toxin by inhalation ove r the observation period of 28 days post-challenge. 5 Representative i mmunised rats (abrin toroid) were taken at various times post-exposure , humanely killed and tissues were examined for pathological changes. It was concluded that an apparently severe lung lesion occurred at a l ater time than in non-immunised, toxin challenged rats. This damage wa s not lethal over the experimental observation periods. 6 Immunisation by the sub-cutaneous route therefore protects against lethality from challenge by inhalation of ricin or abrin toxins but does not prevent significant lung damage.