bioRxiv2023
Ricin toxin (RT), a ribosome-inactivating protein derived from castor beans (Ricinus communis), is lethal in extremely small doses via inhalation, due in part to pulmonary inflammation triggeredby the toxin. While no licensed countermeasures for RT exists, a myriad of toxin-neutralizing monoclonal antibodies (mAbs) against RTs enzymatic (RTA) and binding (RTB) subunits have been described, including PB10 (anti-RTA) and SylH3 (anti-RTB). We recently demonstrated that a single administration of PB10 and SylH3 as an RT immune complex (RIC) to mice by the intranasal route functions as a potent immunogen, stimulating the rapid onset of high titer toxin-neutralizing antibodies that persist for months. In this report, we demonstrate that the de novo antibody response following RICs exposure is wholly dependent on CD4+ T cell help, as treatment of mice with an anti-CD4 monoclonal antibody abrogated the onset of RT-specific antibodies. To investigate other immunological factors associated with RICs, we examined the early local and systemic inflammatory cytokine and chemokine responses associated with intranasal RT and RIC administration. We report that RICs stimulate an inflammatory profile in the bronchoalveolar lavage fluids (BALF) and serum similar to that elicited by RT itself, but markedly reduced in magnitude. Of the 32 analytes examined, the most pronounced were IL-6, KC (CXCL1), G-CSF, and GM-CSF. To evaluate the role of IL-6 in driving the de novo onset of RT antibodies, groups of mice were treated (or not) with an IL-6 neutralizing monoclonal antibody prior to intranasal RICs challenge. While the monoclonal antibody treatment successfully depleted circulating IL-6 to levels below detection, it had no impact on the kinetics or magnitude of RICs-induced RT-specific antibody response. Thus, our results suggest that other cytokines/chemokines triggered by RICs are involved in influencing long lasting durable antibody responses to RT.