Commonly used antibody drugs are mostly monoclonal antibodies, which function like a "precision strike on a single target" by acting on a specific site of the pathogen. In contrast, neutralizing polyclonal antibodies resemble a "multi-directional coordinated defense," simultaneously targeting multiple sites on the pathogen. The core distinction lies in their coverage and resistance to variation: monoclonal antibodies are suitable for well-defined targets with low variability, while neutralizing polyclonal antibodies, due to their ability to cover multiple sites, are more effective against highly variable common pathogens such as influenza and SARS-CoV-2. This reduces the likelihood of viral "escape" leading to treatment failure.

Three core factors are prioritized: first, the research objective—if rapid acquisition of antibodies for basic research is needed, traditional animal immunization may be considered; if composition controllability and suitability for subsequent precise experiments (e.g., epitope analysis) are desired, recombinant antibody technology (such as B Cell Screening combined with Phage Display) is preferred. Second, sample size requirements—exploratory studies with small samples may simplify the process, while large-scale batch production requires emphasis on technical stability and reproducibility. Third, the intended application scenario—if for in vitro detection experiments, antibody purity is critical; if for cell-level experiments, it is also necessary to confirm the absence of cytotoxicity. The selection should align with the "objective-sample-application" framework.

Three fundamental validations are required: first, antibody labeling compatibility—confirming whether the antibody can be labeled with fluorophores used in flow cytometry (e.g., FITC, PE) or ensuring that pre-labeled antibodies do not have overlapping fluorescence channels with flow cytometry antibodies. Second, concentration optimization—incubating target cells with antibodies at varying concentrations and using flow cytometry to determine the optimal concentration that produces a clear positive signal with low nonspecific binding. Third, negative control validation—including target cells without antibodies and control groups with irrelevant antibodies to exclude interference from nonspecific binding.

The principle leverages the characteristics of "pseudoviruses": pseudoviruses retain the envelope protein of the target virus (which can bind to host cells) but lack key genes required for viral replication, preventing extensive replication within cells and ensuring high safety. In the experiment, antibodies are mixed with pseudoviruses. If the antibodies can neutralize the virus, they will bind to the pseudovirus envelope protein, preventing its adhesion and entry into host cells. The neutralizing capacity of the antibodies is then assessed by detecting the signal intensity of a reporter gene (e.g., a fluorescent gene) carried by the pseudovirus in cells—the weaker the signal, the more effective the antibody is at preventing pseudovirus infection. This method is widely used because it avoids the biosafety risks associated with live viruses while simulating the infection process of real viruses, yielding results that closely reflect actual neutralizing effects.