Critical Negative Regulation of Type 1 T Cell Immunity and Immunopathology by Signaling Adaptor DAP12 during Intracellular Infection

Abstract

Transmembrane signaling adaptor DAP12 has increasingly been recognized for its important role in innate responses. However, its role in the regulation of antimicrobial T cell responses has remained unknown. In our current study, we have examined host defense, T cell responses, and tissue immunopathology in models of intracellular infection established in wild-type and DAP12-deficient mice. During mycobacterial infection, lack of DAP12 leads to pronounced proinflammatory and Th1 cytokine responses, overactivation of Ag-specific CD4 and CD8 T cells of type 1 phenotype, and heightened immunopathology both in the lung and lymphoid organs. DAP12-deficient airway APC display enhanced NF-κB activation and cytokine responses upon TLR stimulation or mycobacterial infection in vitro. Of importance, adoptive transfer of Ag-loaded DAP12-deficient APC alone could lead to overactivation of transferred transgenic or endogenous wild-type T cells in vivo. We have further found that the immune regulatory role by DAP12 is not restricted only to intracellular bacterial infection, since lack of this molecule also leads to uncontrolled type 1 T cell activation and severe immunopathology and tissue injury during intracellular viral infection. Our study thus identifies DAP12 as an important novel immune regulatory molecule that acts, via APC, to control the level of antimicrobial type 1 T cell activation and immunopathology.

Negative Regulation of Lung Inflammation and Immunopathology by TNF-α during Acute Influenza Infection

“…Serial dilutions of the supernatants were applied to a confluent monolayer of Madin-Darby canine kidney (MDCK) cells, as previously described. 46 Briefly, an enriched agarose medium (1% agarose, 2ϫ F-11 minimal essential medium, 2% L-glutamine, 2% penicillin-streptomycin, and 5 mg/mL trypsin) was added to the infected cells after 30 minutes at 37°C, and then incubated at 37°C for 2 days. The cells were fixed with Carnoy's fixative (25% acetic acid and 75% methanol), and plaques counted.…”

Control of Pathogenic CD4 T Cells and Lethal Immunopathology by Signaling Immunoadaptor DAP12 during Influenza Infection

“…A number of innate immune receptors including the triggering receptor expressed on myeloid cells, MDL-1 and NKG2D, are associated with and signal though DAP12 (24)(25)(26)(27)(28)(29). Although initially identified to be a proinflammatory or immune-activating molecule, recent emerging evidence suggests a dual role of DAP12 signaling pathway, depending on the target immune cell type, the nature of Ags or infectious agents or the variation in different animal models (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40). However, the precise role of DAP12 pathway in the regulation of immunopathogenic T cell subsets and immunopathology in acute influenza infection remains unclear.…”

Influenza Infection Leads to Increased Susceptibility to Subsequent Bacterial Superinfection by Impairing NK Cell Responses in the Lung

“…Levels of virus in the lung were quantified 3, 7, and 10 d postflu infection by plaque forming assay as previously described (25). Briefly, Madin-Darby canine kidney cells were grown to 100% confluence in 6-well plates and washed twice with PBS.…”

“…A mouse-adapted strain of influenza A/FM/1/47 (H1N1) virus was prepared and used as previously described (25). A clinical isolate of S. aureus B33349 strain was prepared as previously described (16).…”