Binding of Salmonella-specific antibody facilitates specific T cell responses via augmentation of bacterial uptake and induction of apoptosis in macrophages.
BACKGROUND
Most antigens from intracellular bacteria or vaccines induce both humoral and cell-mediated immune responses, but interactions between these responses are not fully understood. This study aims to resolve how specific antibodies participate in the activation of specific T cells in protecting hosts against Salmonella enterica serotype Typhimurium (S. typhimurium) infection.


METHODS
Mice were administered anti-Salmonella immunoglobulin G (IgG) 1 day before Salmonella infection, and survival rate was observed. For in vitro assay, Salmonella bacteria were treated with anti-Salmonella IgG or control IgG before infection of the RAW264.7 or HEp2 cells. After infection, cell-associated bacteria number, induction of apoptosis, and production of nitric oxide were examined. In addition, antigen presentation assays using Salmonella-primed T cells were performed.


RESULTS
Treatment of S. typhimurium with anti-Salmonella IgG enhanced the macrophages' uptake of bacteria and induced high-frequency apoptotic cell death. In vitro antigen presentation assay revealed that the extracellular vesicles isolated from apoptotic cells caused by infection with anti-Salmonella IgG-treated S. typhimurium facilitated the responses of Salmonella-specific T cells.


CONCLUSIONS
Our findings suggest that humoral immunity cooperates with cell-mediated immunity upon induction of apoptosis in host cells to establish protective immunity against Salmonella infection, even if it does not directly eliminate intracellular microorganisms.
Eguchi
Masahiro
M
Laboratory of Immunoregulation, Kitasato Institute for Life Sciences and Graduate School of Infection Control Sciences, Kitasato University, Tokyo, Japan. meguchi@lisci.kitasato-u.ac.jp
Kikuchi
Yuji
Y
D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002460:Cell Line; D005260:Female; D006801:Humans; D007111:Immunity, Cellular / Q000276:immunology*; D056724:Immunity, Humoral; D007116:Immunization, Passive; D007074:Immunoglobulin G / Q000627:therapeutic use; D008264:Macrophages / Q000276:immunology; D051379:Mice; D012481:Salmonella Infections, Animal / Q000276:immunology*; D012486:Salmonella typhimurium / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology
D007074:Immunoglobulin G