# Inflammatory Profiles Induced by Intranasal Immunization with Ricin Toxin-immune Complexes

## TL;DR

This study explores how immune complexes formed with ricin toxin and antibodies trigger inflammation in mice when delivered intranasally.

## Contribution

The study reveals that ricin toxin-immune complexes induce a proinflammatory response dependent on CD4+ T cell help.

## Key findings

- RICs induce high-titer toxin-neutralizing antibodies that persist for months.
- RICs trigger inflammatory cytokines like IL-6, KC, G-CSF, GM-CSF, and MCP-1, albeit at lower levels than ricin toxin alone.
- The inflammatory response may influence antigen sampling and presentation in mucosal tissues.

## Abstract

The underlying contribution of immune complexes in modulating adaptive immunity in mucosal tissues remains poorly understood. In this report, we examined, in mice, the proinflammatory response elicited by intranasal delivery of the biothreat agent ricin toxin (RT) in association with two toxin-neutralizing mAbs, SylH3 and PB10. We previously demonstrated that ricin-immune complexes (RICs) induce the rapid onset of high-titer toxin-neutralizing Abs that persist for months. We now demonstrate that such responses are dependent on CD4+ T cell help, because treatment of mice with an anti-CD4 mAb abrogated the onset of RT-specific Abs following intranasal RICs exposure. To define the inflammatory environment associated with RIC exposure, we collected bronchoalveolar lavage fluid (BALF) and sera from mice 6, 12, and 18 h after they had received RT or RICs by the intranasal route. A 32-plex cytometric bead array revealed an inflammatory profile elicited by RT that was dominated by IL-6 (>1500-fold increase in BALF) and secondarily by KC (CXCL1), G-CSF, GM-CSF, and MCP-1. RICs induced inflammatory profiles in both BALF and serum response that were similar to RT, albeit at markedly reduced levels. These results demonstrate that RICs retain the capacity to induce local and systemic inflammatory cytokines/chemokines that, in turn, may influence Ag sampling and presentation in the lung mucosa and draining lymph nodes. A better understanding of the fate of immune complexes following intranasal delivery has implications for the development of mucosal vaccines for biothreats and emerging infectious diseases.