| Criteria | Transfection-Based Delivery of CagA | Infection with CagA-positive Helicobacter pylori | Remarks |
| Method Overview | Introduction of plasmid DNA encoding cagA directly into host cells | Co-culture of host cells with live H. pylori strains expressing the cagA gene | Represents mechanistic vs physiological delivery approaches. |
| CagA Entry Mechanism | Host cells express CagA after uptake and transcription/translation of plasmid | Bacteria use Type IV secretion system (T4SS) to inject CagA into host cells | Infection mimics natural CagA translocation via bacterial secretion system. |
| CagA Modification | May lack natural post-translational modifications like phosphorylation pattern | Undergoes phosphorylation on EPIYA motifs by host Src/Abl kinases post-injection | Natural infection better mimics native phosphorylation status. |
| Localization Dynamics | CagA is produced throughout the cell, depending on promoter and signal sequences | CagA is injected at the bacteria-host interface and targets the inner leaflet of the plasma membrane | Infection offers spatially restricted and regulated CagA delivery. |
| Control Over Expression | High control over timing, expression levels, and mutants via vectors | Expression is bacterial load-dependent and may vary between strains | Transfection offers flexibility for mechanistic studies using mutants or reporters. |
| Delivery Efficiency | High in transfection-competent cell lines but variable in primary cells | Depends on MOI, bacterial adherence, and T4SS activity | Both methods can vary in efficiency depending on host cell type and conditions. |
| Host Response Activation | Minimal innate immune response, mainly expression of protein | Triggers robust innate immune responses, inflammation, NF-κB signaling, etc. | Infection models host-pathogen interactions more comprehensively. |
| Experimental Simplicity | Technically simpler, no need for handling live bacteria | Requires live bacterial culture and biosafety precautions | Transfection is more accessible for basic molecular studies. |
| Reproducibility | High, depending on transfection protocol | Variable due to bacterial behavior, infection dynamics, and strain-specific differences | Transfection is more consistent across replicates; infection better simulates physiological variability. |
| Applicability in Screening | Suitable for mutational analysis, structure-function studies | Useful for studying bacterial virulence, host-pathogen interactions | Each model serves distinct research purposes. |
| Host Specificity & Tropism | Artificial; dependent on transfection reagent and promoter used | Natural preference for gastric epithelial cells, especially in polarized models | Infection better models tissue-specific colonization, e.g., in AGS or polarized MDCK cells. |
| Use in In Vivo Models | Limited; mostly in cell culture | Possible in animal infection models (e.g., mouse, Mongolian gerbil) | Infection allows in vivo relevance, but is more complex and variable. |
| Pathogenic Context Simulation | Does not replicate host cell interactions with bacteria or other virulence factors | Mimics natural context of pathogenesis, including co-delivery of other bacterial factors | Only infection captures the full pathogenic milieu of H. pylori. |
