# Phage Display Preparation of Specific Polypeptides in Atherosclerotic Foam Cells
## 4 Discussion
In contrast, the efflux of intracellular cholesterol in macrophages is mediated by reverse cholesterol transporters ABCA1 and ABCG1 [26]. qRT-PCR (Figure 4) showed that the genetic expressions of LDLR, CD36, ABCA1, and ABCG1 in foam cells we induced were all higher than THP-1. It is worth noting that foam cells accumulate lipids and also produce various chemokines and cytokines to induce inflammation in atherosclerotic lesions. Tumor necrosis factor alpha (TNF-\(\upalpha\)) is the crucial pro-atherosclerotic cytokines secreted by ox-LDL-activated foam cells. In this experiment, the expression of TNF-\(\upalpha\) in foam cell was the highest. The aboveresults effectively proved, on the basis of molecular biology, that the foam cell model was successfully established. In 1985, [PERSON] discovered that foreign DNA sequences could be cloned into filamentous bacteriophages such that the cloned sequences were expressed on the surface of the phage particles as fusion proteins. These phage particles could then be enriched for specific sequences based on the binding properties of the displayed fusion proteins [27; 28]. The peptides in a phage display library have two critical characteristics required for chemical evolution, i.e., replicability and mutability. If the phage's DNA suffers a mutation in the peptide coding sequence, that mutation is passed on to the phage's progeny and can affect the structure of the peptide. Because of its solvent accessibility, a displayed peptide often behaves essentially as it would if it were not attached to the virion surface. Affinity purification has been used to precisely capture phage-displayed peptides from a complex mixture of compounds [29]. Specific binding between polypeptide and foam cells was realized by forming the non-covalent and mediated hydrophobic and Van-der-Waals interactions [30]. This reversible process without bond formation could be disbanded in surfactant solution. In this work, as the pretreatment, the Ph.D.-12 phages experienced negative screening by THP-1, and positive screening by foam cells, to eliminate interference from nonspecific binding and ensure the purity of the target phages; only the unbound phages in negative screening were qualified for the next positive screening, and only the eluted phages from foam cells in positive screening could be used for amplified each cycle. Theoretically speaking, negative screening could ensure that there were no proteins or peptides on the phages' surfaces that could bind to the THP-1, and positive screening could ensure that the phages displayed enough target polypeptides for the following amplification. The principles and process are shown in Figure 5.  
molecules and reflected the different affinities. For this reason, we selected ELISA and immunofluorescence labeled to characterize the affinity of the peptides in parallel, to ensure that the conformation change did not seriously affect the specific affinities between peptides and foam cells. The different affinities between T5 and T6 in Figures 7 and 8 may be derived from the above reason. Moreover, although we tried to use the same parameter settings in the process of collecting fluorescence images, certain errors could have inevitably occurred due to experimental operation and equipment accuracy.