General and Local Immunity to Ricin

Summary and Conclusions

In tables 1a and 2 are given the histories of 14 animals immunized by intrarectal treatments of ricin and tested, respectively by intravenous, intradermal and intrarectal injections of the toxin. Only the 4 animals whose immunity was tested by intrarectal injections survived. The controls died in every instance.

This would appear to be a strictly local immunity of the intestines which is entirely cellular in nature, as no antibodies (precipitin or antitoxin) were demonstrable in the blood sera of the animals which survived.

Tables 3 and 4 give the histories of 14 rabbits treated by a single intradermal injection of ricin. The 2 rabbits tested by lethal intrarectal injections alone survived their final test dosage. The controls died in every instance. This appears to be a strictly local immunity of the intestines, since no antibodies were detectable in the blood sera of these rabbits, nor did the animals show any protection upon subsequent intradermal or intravenous injections of even 1 M.L.D. of the toxin.

No local protection of small areas of the skin of rabbits could be demonstrated by repeated intradermal injections of small doses of the toxin alone, as is shown in table 5.

There was an absolute failure in attempts to immunize small areas of the skin or the entire skin by the application of moist dressings of toxin on variously prepared skins.

Rabbits treated with toxin-antitoxin mixtures and subsequently tested by the same dose in the same spots gave reactions suggestive of the Arthus phenomenon.

Table 6 gives the histories of 10 rabbits treated respectively, 9 with intradermal injections of a toxin-antitoxin mixture, and 1 with antitoxin alone.

Three of the 4 rabbits tested in the treated spots with 2 intradermal M.L.D.'s survived. Two of the 4 tested in remote spots survived. The rabbit treated with antitoxin and then tested with toxin in the same spot did not survive its test dose. The controls receiving 1 M.L.D. of the toxin died. At no time did the sera of these rabbits show the presence of antibodies (precipitin or antitoxin) in their blood sera.

Table 7 gives the histories of 9 rabbits treated, respectively, in groups of 3 each with toxin-antitoxin plus aleuronat, toxin-normal rabbit serum plus aleuronat, toxin alone plus aleuronat. One control rabbit received normal rabbit serum plus aleuronat. All of the rabbits receiving intradermal injections of 1.25 M.L.D.'s in the original spot survived. None of the animals tested in areas remote from the original spot survived. The controls receiving 1 M.L.D. died.

Table 8 gives the histories of 6 rabbits treated as in experiment VII with the exception that aleuronat was not used. Only the rabbit tested in the spot treated with the toxin-antitoxin mixture survived its test injection. This survival would indicate again that there is a local protection in the small areas of skin treated by the toxin-antitoxin mixture which is brought about independently of circulating antibodies. The results would further indicate that the protection afforded the animals in experiment VII was either non-specific or mechanical.

A strictly local immunity appears to exist in a large percentage of the animals treated with the toxin-antitoxin mixture. This local regional immunity extends to an immunity of the entire skin in a small percentage of animals. Treatment with toxin alone or toxin-normal serum did not confer a local protection. The results obtained by the use of aleuronat suggest non-specific protection. The attempts to demonstrate a local production of antibodies by the tests on extracted immunized tissues were negative in every instance. That the antibodies were present, and by the technique used were not demonstrable, is a possibility.

In conclusion it may be said that:

1. 1. Rabbits immunized by intrarectal injections of ricin appear to be better protected against subsequent intoxication by that route than by the intravenous or intradermal routes.

2. 2. Rabbits immunized by intradermal injections of ricin appear to be protected against subsequent intoxication by the intrarectal route but not against intoxication through the intravenous or intradermal routes. This would appear to be due to the elimination of the toxin through the intestines.

3. 3. There is evidence of the production of a local immunity in small areas of skin injected with ricin toxin-antitoxin mixture. This local immunity is not constant.