LLO (91-99), Listeria monocytogenes Listeriolysin O

Product Name: LLO (91-99), Listeria monocytogenes Listeriolysin O

Sequence One Letter Code: GYKDGNEYI

Sequence Three Letter Code: H-Gly-Tyr-Lys-Asp-Gly-Asn-Glu-Tyr-Ile-OH

Chemical Formula:C47H67N11O17

Molecular Weight: 1058.2

Purity: 95%

Form: Lyophilized

Storage Conditions: - 20 °C

Research Area: Bacterial

Source / Species: Listeria

Conjugation: Unconjugated

Code Nacres: NA.26

Application: LLO (91–99) is a synthetic peptide corresponding to residues 91–99 of listeriolysin O, a virulence factor of Listeria monocytogenes. This fragment represents an H-2Kᵈ-restricted cytotoxic T lymphocyte (CTL) epitope essential for immune recognition of infected cells. Immunization with this peptide elicits strong CD8⁺ T cell responses and has been explored in vaccine development against intracellular bacterial infection. The peptide is widely used in immunology research to study antigen processing and presentation, CTL activation, and host–pathogen interactions. It provides a defined epitope for evaluating cellular immunity and vaccine-induced protective responses.

Current Research: Listeria monocytogenes is an intracellular bacterial pathogen widely used as a model organism for studying cell-mediated immunity against intracellular infections. A key virulence factor produced by this bacterium is listeriolysin O (LLO), a pore-forming toxin that enables the bacterium to escape from phagosomes and replicate within the host cell cytoplasm. During infection, fragments of LLO are processed and presented by major histocompatibility complex (MHC) class I molecules, allowing cytotoxic CD8⁺ T lymphocytes (CTLs) to recognize and eliminate infected cells. Among the immunodominant epitopes derived from LLO, the LLO (91–99) peptide has become one of the most widely studied antigenic fragments. This peptide represents an H-2Kᵈ–restricted CTL epitope, making it particularly useful in mouse models for investigating T cell–mediated immune responses. Current research frequently uses the LLO (91–99) peptide to study the mechanisms of antigen processing and presentation in MHC class I pathways. During intracellular infection, bacterial proteins are degraded into peptide fragments that are transported into the endoplasmic reticulum and loaded onto MHC class I molecules. These peptide–MHC complexes are then presented on the surface of infected cells, where they are recognized by antigen-specific CD8⁺ T cells. Because LLO (91–99) is a well-characterized immunodominant epitope, it provides a controlled system for investigating how intracellular antigens are processed, transported, and presented to T cells. Another major area of research involves examining cytotoxic T lymphocyte activation and effector functions. When CD8⁺ T cells recognize LLO (91–99) presented on H-2Kᵈ molecules, they become activated and differentiate into effector CTLs capable of eliminating infected cells. Experimental studies frequently use this peptide to stimulate T cells in vitro, allowing researchers to measure immune responses such as cytokine secretion, proliferation, and cytotoxic activity. Techniques including ELISPOT assays, intracellular cytokine staining, and tetramer-based flow cytometry are commonly used to quantify LLO-specific T cell responses. The peptide is also extensively used in vaccine development research targeting intracellular pathogens. Effective vaccines against intracellular bacteria require strong cellular immune responses, particularly the activation of antigen-specific CD8⁺ T cells. Immunization with defined epitopes such as LLO (91–99) has been explored as a strategy to induce protective CTL responses in experimental models. In some studies, the peptide is delivered using adjuvants, nanoparticle carriers, or viral vectors to enhance immunogenicity and improve immune memory formation. These approaches help evaluate how antigen presentation and immune priming can be optimized for vaccine design. Another important research focus involves host–pathogen interaction studies. Listeria monocytogenes has become a valuable model for examining how the immune system detects and eliminates intracellular microbes. By tracking CD8⁺ T cell responses against the LLO (91–99) epitope, researchers can monitor how immune responses develop during infection and how memory T cells contribute to long-term protection. Such studies provide insights into the mechanisms underlying protective immunity against intracellular pathogens. The LLO (91–99) peptide is also frequently used to investigate T cell receptor (TCR) specificity and antigen recognition. Because the peptide–MHC complex is well defined, it can be used to analyze how different TCRs recognize antigenic peptides and how subtle sequence variations influence immune recognition. These investigations are important for understanding the structural basis of T cell antigen recognition and the factors that determine immunodominance. In addition, the peptide serves as a valuable reagent for immune monitoring in experimental infection models. Researchers studying Listeria infection often use LLO (91–99)–specific tetramers to detect antigen-specific CD8⁺ T cells in infected animals. This approach allows precise measurement of immune responses over the course of infection and during the establishment of immune memory. In summary, LLO (91–99) is a well-characterized CTL epitope derived from the listeriolysin O protein of Listeria monocytogenes. Its defined MHC restriction and strong immunogenicity make it an essential tool for studying antigen presentation, cytotoxic T cell activation, and host–pathogen interactions. Through applications in vaccine research, immune monitoring, and mechanistic studies of cellular immunity, this peptide continues to contribute to a deeper understanding of how the immune system responds to intracellular bacterial infections.