Cellular and Immunological Response of THP-1 Cells in Response to Lipopolysaccharides and Lipoteichoic Acid Exposure

Abstract

Introduction: Bacterial toxins are considered to be obscuring factors in multiple human diseases. Accidental contamination by bacterial lipopolysaccharides (LPS) and lipoteichoic acid (LTA) in biomedical and biotechnological products may lead to inflammation and associated pyrogenic reactions in humans. LPS are the most studied and clinically important pyrogen from gram-negative bacteria, while LTA is derived from the cell wall of gram-positive bacteria. Previous studies have identified that LPS and LTA induce a pyrogenic response in living systems. However, the detailed mechanisms of cellular toxicity have not yet been determined. The present study aimed to investigate LPS-induced and LTA-induced immune response activation and the ensuing effects on cellular integrity and organelle function in monocytes and monocyte-derived macrophages.

Methods: With monocytes and macrophages being the first lines of defense against pathogenic invasion, THP-1 cells were selected as an in vitro model for the present study. THP-1 is a cancerous monocyte cell line and can differentiate into macrophages via stimulation with phorbolmyristic acid. Intracellular responses of monocytes and monocyte-derived macrophages following exposure to LPS and LTA were analyzed through several assays, including MTT, Neutral red, DCFH-DA, NO release, DilCI (5), Annexin V-PI FACS, Rhodamine phalloidine, Acridine Orange, and JC1. The expression of the inflammation-related genes NFκB, COX2, IL-1β, and TNF-α, along with activation of inflammatory signaling, was also assessed in monocytes following toxic interaction.

Results & Conclusion: The results revealed that LPS and LTA can induce inflammatory signals at nanogram concentrations but are non-cytotoxic at low concentrations. LPS exposure had no significant toxic impacts on membrane integrity and organelle function. LPS induced neither apoptotic nor necrotic cell death of THP-1 cells at the selected concentration. However, LTA caused cell membrane damage and organelle dysfunction in a time and dose-dependent manner. LTA exposure led to oxidative stress and apoptotic cell death mediated by reactive oxygen species (ROS) and reactive nitrogen species (RNS). Both bacterial toxins augmented the expression of inflammatory genes and associated inflammatory signal transmission in THP-1 cells. The overall cellular effect was dependent on dose and time of exposure.