Development and characterization of rat monoclonal antibodies for N-acylated homoserine lactones

Quorum sensing (QS) is a communication mechanism between bacteria using diffusible chemical signaling molecules, which are called autoinducers (AI). By detecting the concentration of quorum sensing molecules through binding to a specific receptor protein, bacteria regulate their gene expressions when the concentration of autoinducers and thus the cell density reaches a threshold level. Many Gram-negative bacteria use acylated homoserine lactones (HSLs) as autoinducers. Because of the broad biological functions of HSLs, interest in detection and analysis of HSLs is increasing with a view to their medical, biotechnological, and agricultural applications. In this study, an anti-HSL antibody-based immunochemical detection method has been developed. Four structurally distinct HSL haptens, named HSL1, HSL2, HSL3, and HSL4, have been designed for antibody and assay development. New rat anti-HSL monoclonal antibodies (mAbs) have been produced in-house and characterized with enzyme-linked immunosorbent assays (ELISA), both in the coating antigen and in the enzyme tracer format. Eight mAbs (HSL1-1A5, HSL1-8E1, HSL1/2-2C10, HSL1/2-4H5, HSL4-4C9, HSL4-5E12, HSL4-5H3, and HSL4-6D3) will be presented in this paper. We demonstrate that the anti-HSL mAbs have distinguished sensitivity and selectivity toward HSLs depending upon their chemical structures. The optimized assays are capable of detecting HSLs in the microgram per liter (low micromolar to nanomolar) range. The best IC₅₀ (test midpoint) was 134 ± 30 μg L⁻¹ (n = 54) for N-(3-oxodecanoyl)-l-homoserine lactone (3-oxo-C10-HSL) using mAb HSL1/2-2C10 and HSL1–HRP in the enzyme tracer format. In the coating antigen format, the most selective mAb for N-octanoyl-l-homoserine lactone (C8-HSL) was mAb HSL4-4C9. Additionally, anti-HSL mAbs showed higher sensitivity against hydrolyzed HSLs, namely homoserines. These compounds might also occur under certain biological conditions. This study marks the beginning of new ways for quick and cost-effective HSL detection, requiring small sample amounts (less than 1 mL) and little to no sample preparation.