The CD55 Knockout A-549 Polyclonal Cells are a CRISPR/Cas9-edited polyclonal cell population featuring targeted disruption of the CD55 gene in the A-549 human lung adenocarcinoma cell line. This loss-of-function model eliminates expression of decay-accelerating factor (DAF), a key complement regulatory protein. The polyclonal format, achieved through enrichment of edited cells without single-cell cloning, avoids clonal selection biases while providing a genetically diverse population suitable for a broad range of functional analyses.
The parental A-549 cell line, originally derived from a 58-year-old male with lung adenocarcinoma, is an adherent epithelial line with a hypotriploid karyotype and serves as a widely recognized model for non-small cell lung cancer (NSCLC). A-549 cells retain characteristics of alveolar type II pneumocytes and are extensively used in cancer biology, drug screening, and viral infection studies. This clinically relevant background is particularly appropriate for exploring immune evasion mechanisms, as NSCLC tumors frequently upregulate complement regulatory proteins such as CD55.
CD55 encodes a glycosylphosphatidylinositol (GPI)-anchored membrane protein that functions as a negative regulator of the complement cascade by accelerating the decay of C3 and C5 convertases (C4b2a and C3bBb). This activity limits C3b deposition and membrane attack complex (MAC) assembly, protecting cells from complement-mediated lysis. CD55 directly interacts with complement components C3b, C4b, and C2a, and it participates in a network involving factor B and factor D. Additionally, CD55 acts as a receptor for CD97??a member of the adhesion G protein-coupled receptor family??and for enteroviruses such as echovirus and Coxsackievirus. Its expression is transcriptionally regulated by pro-inflammatory cytokines (TNF-??, IL-1) and NF-??B, while its cell-surface localization depends on the GPI-anchor biosynthesis pathway, involving enzymes like PIGA and PIGF.
In the A-549 lung adenocarcinoma context, overexpression of CD55 is a common immune evasion tactic, shielding tumor cells from complement-mediated attack. Knockout of CD55 abrogates decay-accelerating activity, leading to increased C3b opsonization and MAC formation upon exposure to complement. This sensitizes the cells to complement-dependent cytotoxicity (CDC), enabling detailed investigation of NSCLC complement resistance. The loss of CD55 also disrupts CD97-mediated adhesive signaling, which may influence cell migration and proliferation. Thus, this polyclonal knockout model provides a valuable platform for studying the interplay between complement regulation and tumor biology, as well as for developing therapies aimed at overcoming immune evasion.
These polyclonal CD55 knockout cells support a diverse array of research applications, including complement-dependent cytotoxicity assays, screening of therapeutic antibodies that rely on CDC, and viral entry studies that compare CD55-dependent and -independent pathways. Researchers can employ C3b deposition assays, immunofluorescence for MAC components, flow cytometry for CD55 surface expression, Western blotting, and RT-qPCR. The model also facilitates investigations into paroxysmal nocturnal hemoglobinuria (PNH) and the evaluation of complement-targeted pharmacological interventions. For further technical assistance or to discuss custom requirements, please contact Ascent Research.
