Toll-Like Receptor 2 Agonists Exacerbate Accelerated Nephrotoxic Nephritis(1)
Glomerulonephritis in humans can be exacerbated by infection. For example, in IgA nephropathy, an upper respiratory tract infection commonly precedes episodes of hematuria. In addition, relapses of anti-neutrophil cytoplasmic antibody–associated vasculitis are associated with the nasal carriage of Staphylococcus aureus, and exacerbations of anti–glomerular basement membrane disease can be attributed to infective episodes. A variety of infectious organisms, including both bacteria and viruses, may contribute to the exacerbation of disease in glomerulonephritis. Toll-like receptor 2 (TLR2). TLR2, in particular, recognizes constituents of Gram-positive and Gram-negative bacteria and not only affects the initial innate immune response but also has a role in the control of adaptive immunity.
TLR2 recognizes pathogen-associated molecular patterns that are associated with both Gram-negative and Gram-positive bacteria, including lipopeptide, peptidoglycan, and lipoteichoic acid. The synthetic compound N-palmitoyl-S-(2,3-bis(palmitoyloxy)-(2R,S)-propyl)-(R)-cysteinyl-seryl-(lysyl)3-lysine (Pam3CysSK4) is a triacylated lipopeptide that mimics the activity of naturally occurring triacylated lipopeptides.
Mice were immunized intraperitoneally with 200 μg of normal sheep IgG that was given with 80 μl of aluminum hydroxide gel in 310 μl of PBS, with 100 μg of Pam3CysSK4 in 10 μl of DMSO or with 10 μl of DMSO alone. All of these components were given as a single intraperitoneal injection. Five days later, mice received an injection of 160 μl of NTS via the tail vein to induce disease.
Wild-type mice that were immunized with lipopeptide had a significantly worse survival when compared with the wild-type animals that were not immunized with lipopeptide. The TLR2-deficient mice that were immunized with lipopeptide showed a survival advantage when compared with the wild-type mice that were immunized with lipopeptide, although this did not reach statistical significance.
Wild-type mice that were immunized with lipopeptide developed severe glomerular injury, characterized by glomerular thrombosis, crescent formation, and glomerular macrophage infiltration, at 14 d after disease induction. When compared with wild-type mice that were not immunized with lipopeptide, there was significantly greater disease as measured by glomerular thrombosis score, glomerular crescents, and glomerular macrophage infiltration. In the same experiment, TLR2-deficient mice that were immunized with lipopeptide were significantly protected from disease: TLR2-deficient mice had less glomerular thrombosis, fewer glomerular crescents.
The wild-type mice that were immunized with lipopeptide also had more severe renal impairment when compared with the wild-type mice that were not immunized with lipopeptide, as shown by a higher serum creatinine level at day 14. Despite the marked differences in glomerular histology, there were no differences in the 24-h albuminuria measured at day 14 in these groups. TLR2-deficient mice also had less functional impairment with lower serum creatinine levels. The albuminuria also was measured at 14 d; however, there was no difference between these two groups.
In wild-type animals; serum was collected for analysis at 5, 9, and 14 d after disease induction with NTS. At 5 d, there was a significantly greater titer of antigen-specific IgG1, IgG2b, and IgG3 in the serum in the wild-type mice that were immunized with lipopeptide. There was no difference in the titers of antigen-specific IgG2a in the serum at 5 d. The glomerular CD4 T cell numbers were significantly greater in the mice that were immunized with lipopeptide.
There was a significantly greater deposition of IgG3 in the glomeruli of wild-type mice that were immunized with lipopeptide when compared with wild-type mice that were not immunized with lipopeptide and TLR2-deficient mice that were immunized with lipopeptide.
More severe disease in the wild-type mice that were immunized with lipopeptide was associated with higher antigen-specific IgG1, IgG2b, and IgG3 at day 5 after disease induction, which was 10 d after immunization. In models of chronic glomerular disease, viral double-stranded RNA, a known TLR3 ligand, and bacterial DNA, a TLR9 ligand, have been shown to aggravate lupus nephritis. The low doses of LPS encouraged a predominant Th2-type response and tissue infiltration with eosinophils, whereas those that were given the higher dose produced a Th1 response and lung infiltration with neutrophils.
NOTE: B6 mice have IgG2c instead of IgG2a. Therefore, IgG2a might be found in this study.