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

Abstract

T he limited success of immunization against mucosal pathogens and the lack of effective and safe adjuvants highlight the urgent need for mucosal vaccines. As a result, researchers have utilized novel strategies to target antigens (Ags) to receptors expressed on the surfaces of antigen-presenting cells (APCs), such as dendritic cells (DCs) and macrophages, in an effort to more effectively activate the mucosal immune system and elicit robust and protective immune responses (1). Importantly, in this regard, we have previously shown that targeting fixed (inactivated) Francisella tularensis (iFT) to FcR intranasally (i.n.), via the formation of monoclonal antibody (MAb)-iFT immune complexes (ICs), generated enhanced protection against lethal respiratory challenge with F. tularensis live vaccine strain (LVS) and the category A F. tularensis agent SchuS4 (2). This protection was dependent upon the expression of Fc␥R and the neonatal Fc receptor (FcRn), as immunization of Fc␥R-or FcRn-deficient mice, or i.n. administration of F(ab=) 2 MAb-iFT ICs, abrogated protection (2). Furthermore, protection was not mediated by the administration of the antilipopolysaccharide (anti-LPS) IgG2a antibody alone (2). In a different study using the same vaccine platform, targeting the pneumococcal protective Ag, PspA, to human Fc␥RI in a human Fc␥RI transgenic mouse model also elicited enhanced protection against Streptococcus pneumoniae challenge (3).In regard to the mechanisms involved in FcR-enhanced immune protection following i.n. 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.In this study, we have expanded on our previous work utilizing this vaccine platform by examining the effect of FcR-targeted mucosal vaccination on DC activation and memory CD4 ϩ T cell formation in vivo during lethal challenge with F. tularensis LVS. For the first time, we show that FcR targeting increases the frequency and activation status of DCs in the lungs of immunized mice and mediates the generation of F. tularensis-specific, gamma interferon (IFN-␥)-secreting, effector memory (EM) CD4 ϩ T cells during infection, thus further elucidating the immunological

B cells and antibodies in the defense against Mycobacterium tuberculosis infection

“…For example, intraperitoneal injection of monoclonal antibody targeting a lipopolysaccharide of the Q fever producing facultative intracellular organism Coxiella burnetii has shown to protect mice against aerosolized infection . Also in accordance with these notions, vaccines based on the induction of antibodies that promote phagocytosis of respiratory, intracellular pathogens such as Yersinia pestis and Francisella tularemia have recently been developed and shown protection against plague and tularemia . Furthermore, alveolar macrophages and epithelial cells produce several proteins of the classical and alternative pathways of complement , and complement proteins have been detected in the bronchoalveolar lavage fluid from various different mammalian species including humans .…”

Targeting of a Fixed Bacterial Immunogen to Fc Receptors Reverses the Anti-Inflammatory Properties of the Gram-Negative Bacterium, Francisella tularensis, during the Early Stages of Infection

“…Previous experiments have shown that co-culturing of Ft - specific T cell hybridoma with mouse PECs in the presence of mAb-i Ft noticeably increased Ft -specific T cell responses compared to using the i Ft immunogen alone [ 26 ]. In addition, in vivo administration of mAb-i Ft ICs intranasally increased the activation status of mucosal dendritic cells in the lungs of immunized mice [ 25 ]. Therefore, we hypothesized that targeting of immunogen to Fcγ receptors (FcγRs) increases systemically the activation status of antigen presenting cells following LVS challenge.…”

“…tularensis -specific cytokine and antibody responses, (4) generation of effector memory CD4 + T cells, and (5) increased protection against F . tularensis infection [ 19 , 25 , 26 ]. In the current study we hypothesized that F .…”

Role of B Cells and Antibodies in Acquired Immunity against Mycobacterium tuberculosis

“…For example, intraperitoneal injection of monoclonal antibody targeting a lipopolysaccharide of the Q fever producing facultative intracellular organism Coxiella burnetii has shown to protect mice against aerosolized infection (36). Also in accordance with these notions, vaccines based on the induction of antibodies that promote phagocytosis of respiratory, intracellular pathogens such as Yersinia pestis and Francisella tularemia have recently been developed and shown protection against plague and tularemia (28,29,122). Furthermore, alveolar macrophages and epithelial cells produce several proteins of the classical and alternative pathways of complement (123,124), and complement proteins have been detected in the bronchoalveolar lavage fluid from various different mammalian species including humans (125)(126)(127)(128).…”