Active immunity induced by passive IgG post-exposure protection against ricin

Area of Science:

• Immunology
• Toxicology
• Biodefense

Background:

• Therapeutic antibodies offer immediate protection against biothreat agents like ricin.
• Understanding the protective mechanisms and duration of different antibody formats is crucial for effective antitoxin strategies.

Purpose of the Study:

• To compare the protective efficacy and immunogenicity of intact IgG and F(ab')2 antibodies derived from goat anti-ricin hyperimmune sera against ricin intoxication.
• To investigate the potential of passive antibody therapy to induce active immunity against ricin.

Main Methods:

• In vitro assessment of ricin-binding affinities and neutralizing activities of goat IgG and F(ab')2 at equimolar concentrations.
• Evaluation of protection in a murine model of ricin intoxication following a single dose of IgG or F(ab')2 administered post-exposure.
• Assessment of survival rates upon secondary ricin challenge in previously rescued mice to determine the induction of active immunity.

Main Results:

• Goat IgG and F(ab')2 exhibited similar in vitro ricin-binding affinities and neutralizing activities.
• Both antibody formats provided 100% protection against a lethal dose of ricin when administered one hour post-exposure.
• Only IgG-treated mice survived a secondary ricin challenge nine days later, indicating the induction of active immunity by IgG but not F(ab')2.

Conclusions:

• Passive administration of goat IgG post-ricin exposure not only provides immediate protection but also rapidly elicits active immunity in mice.
• This induced active immunity against ricin offers long-term protection, lasting at least five months.
• Intact IgG is superior to F(ab')2 for ricin antitoxin therapy due to its ability to induce sustained active immunity.