Multiple mechanisms mediate enhanced immunity generated by mAb‐inactivated F. tularensis immunogen

Abstract

We have previously demonstrated that immunization with inactivated Francisella tularensis, a Category A intracellular mucosal pathogen, combined with IgG2a anti-F. tularensis monoclonal antibody, enhances protection against subsequent F. tularensis challenge. To understand the mechanism(s) involved, we examined the binding, internalization, presentation, and in vivo trafficking of inactivated F. tularensis in the presence and absence of opsonizing monoclonal antibody. We found that when inactivated F. tularensis is combined with anti-F. tularensis monoclonal antibody, presentation to F. tularensis-specific T cells is enhanced, this enhancement is Fc receptor-dependent, and requires a physical linkage between the monoclonal antibody and the inactivated F. tularensis immunogen. This enhanced presentation is due, in part, to enhanced binding and internalization of inactivated F. tularensis by antigen presenting cells, and involves interactions with multiple Fc receptor types. Furthermore, targeting inactivated F. tularensis to Fc receptors enhances dendritic cell maturation and extends the time period over which antigen presenting cells stimulate T cells. In vivo trafficking studies reveal enhanced transport of inactivated F. tularensis immunogen to the Nasal Associated Lymphoid Tissue in the presence of monoclonal antibody, which is FcRn-dependent. In summary, these are the first comprehensive studies using a single vaccine protection model/immunogen to establish the array of mechanisms involved in enhanced immunity/protection mediated by an Fc receptor-targeted mucosal immunogen. These results demonstrate that multiple cellular/immune mechanisms contribute to Fc receptor-enhanced immunity.

B cell subsets are activated and produce cytokines during early phases of Francisella tularensis LVS infection

“…Models of F. tularensis infection have already demonstrated that polyclonal as well as monoclonal antibodies confer efficacious protection against otherwise lethal F. tularensis LVS challenge of passively protected hosts, but against virulent strains of subspecies tularensis have only marginal protective effect [10e13]. Monoclonal antibodies of IgG2a isotype combined with inactivated F. tularensis have been shown to enhance protection against subsequent F. tularensis challenge [14]. Moreover, serum antibodies have been seen to be capable of conferring protection against lethal respiratory LVS challenge when administered therapeutically up to 48 h post-exposure [15].…”

In VivoMechanisms Involved in Enhanced Protection Utilizing an Fc Receptor-Targeted Mucosal Vaccine Platform in a Bacterial Vaccine and Challenge Model

“…This is, in part, due to the increased binding and internalization of iFT by APCs (4). Furthermore, targeting iFT to Fc receptors enhances DC activation and maturation in vitro and also extends the period over which antigen-loaded APCs stimulate T cells (4,5). Lastly, we have also shown that targeting iFT to FcR i.n.…”

“…The antibody alone had no protective effect on mice against F. tularensis challenge (2). Furthermore, we have shown that targeting iFT to Fc␥Rs on APCs mediates internalization, processing, and presentation of the immunogen to an F. tularensis-specific T cell hybridoma in vitro (2,4). Since DCs play a key role in processing and presenting antigens to T lymphocytes, effectively bridging the innate and adaptive immune systems, we wanted to focus on the effect immunization with MAb-iFT ICs has on the number of activated DCs in the lungs of immunized mice during F. tularensis LVS challenge.…”

“…immunization with MAb-iFT ICs, we have recently demonstrated that iFT presentation to F. tularensis-specific T cells is significantly enhanced. This is, in part, due to the increased binding and internalization of iFT by APCs (4). Furthermore, targeting iFT to Fc receptors enhances DC activation and maturation in vitro and also extends the period over which antigen-loaded APCs stimulate T cells (4,5).…”

“…Lastly, we have also shown that targeting iFT to FcR i.n. also enhances trafficking of iFT Ag from the nasal passage to the nasal mucosa-associated lymphoid tissue (NALT) (4). Nevertheless, questions remain regarding the in vivo impact of MAb-iFT immunization and whether DC activation and T cell priming also occur in vivo when utilizing this FcR-targeted vaccine strategy.…”