An irrelevant human IgG1 mAb is included as an isotype control

An irrelevant human IgG1 mAb is included as an isotype control. reactive with different AM OS motifs, enhancedM.tuberculosisphagocytosis by macrophages and reduced intracellular growth in an FcR-dependent manner. P1AM25 in murine IgG2a, but neither murine IgG1 nor a nonFcR-binding IgG, given intraperitoneally prior to and after aerosolizedM.tuberculosisinfection, was protective in C57BL/6 mice. Moreover, we demonstrated the protective efficacy of human IgG1 P1AM25 in passive transfer withM.tuberculosisinfected FcR-humanized mice. These data enhance our knowledge of the important interplay between both antibody epitope specificity and Fc effector functions in the defense againstM.tuberculosisand could inform development of vaccines against TB. Keywords:Immunology, Infectious disease Keywords:Antigen, Immunoglobulins, Tuberculosis == Introduction == Active tuberculosis (TB) persists as one of the leading causes of death worldwide (1). In contrast to latent or cleared infection, the disease TB is caused by uncontrolled infection withMycobacterium tuberculosis(M.tuberculosis), a predominantly intracellular pathogen with many mechanisms to escape the hosts immune response (reviewed in refs.2,3). In 2020, fueled by the COVID-19 pandemic, TB-associated mortality increased for the first time in decades by around 100,000 to 1 1.5 million deaths globally (4). In 2021, mortality increased by an additional 100,000 to now 1.6 million TB-associated deaths (1), underscoring the urgency for a more effective vaccine against TB. Efforts to develop vaccines against TB focus on inducing cell-mediated immunity but, despite recent improvements, have thus far failed to lead to a highly effective vaccine (5). Antibodies (Abs) have shown protective efficacy againstM.tuberculosis, suggesting that inducing both cell-mediated and humoral immunity could be complementary (reviewed in refs.612). However, a better understanding of protective antigens, their epitopes, Citiolone and mechanisms of Ab-mediated protection remains a critical gap of knowledge in the TB field. Studies suggest that Abs against surface antigens ofM.tuberculosiscontribute to the protection against TB (reviewed in refs.612). While Citiolone most surface antigens do not appear to be relevant (13), Abs targeting the surface adhesion proteins 85B and PstS1 and surface glycan arabinomannan (AM) were shown to have protective efficacy in vivo (1421). Moreover, recent studies suggest that functions against intracellularM.tuberculosisare Fc receptor (FcR) mediated (14,15,22). The focus of our studies is AM, a highly immunogenic glycan of theM.tuberculosiscapsule and a component of the mycobacterial cell wall and membrane lipoarabinomannan (LAM) (2325). AM and LAM play important roles in host-microbe interaction and pathogenesis ofM.tuberculosisinfection (reviewed in ref.26). We and others have shown associations between human serum Abs against AM/LAM followingM.bovisbacilli Calmette-Gurin (BCG) vaccination and functions against BCG (21,27), and immunization with AM/LAM-conjugate vaccines reduced mycobacterial organ burden and/or prolonged survival ofM.tuberculosisinfected mice (1618). Passive transfer of some, but not all, murine monoclonal Abs (mAbs) against AM/LAM have shown protection against TB (19,20,28). Rabbit Polyclonal to ARHGEF5 However, the Ab features influencing their mechanisms and protective efficacy in vitro and in vivo are poorly understood (reviewed in ref.29). AM and LAM are composed of a mannan (Man) core, a highly branched arabinan (Ara) domain, and various ManLAM/AM capping motifs that can differ among mycobacterial strains (reviewed in refs.24,26,29). These motifs bind to different host cell receptors (30), but whether reactivity with certain glycan motifs impacts the functions of anti-AM/LAM mAbs againstM.tuberculosisis unknown. We have shown in vitro and in vivo protective efficacy of serum anti-AM IgG from asymptomaticM.tuberculosisexposed or latently infected individuals but have not seen that efficacy with polyclonal anti-AM IgG from patients with Citiolone TB (14). We further showed that polyclonal IgG reactivities to AM oligosaccharide (OS) motifs in humans with and without BCG vaccination and/orM.tuberculosisinfection are tremendously heterogeneous (14,21). Reactivity to certain capped ManAM/LAM motifs, including those with theM.tuberculosisunique Man cap 5-deoxy-5-methylthio-xylofuranose (MTX) (31,32), and a terminal Ara motif was associated with in vitro IgG functions with sera from asymptomatic BCG-vaccinated individuals and individuals with presumed Citiolone latentM.tuberculosisinfection (LTBI). However, establishing causation of the antigenic determinants within AM that are most relevant in eliciting protective Abs requires study with structurally defined mAbs. Based on our findings with polyclonal IgG, we hypothesized that Ab reactivity to certain AM OS structures, specifically terminal Ara motifs and those with Man capping, influences the functions of human mAbs againstM.tuberculosis. We previously reported 2 human mAbs.