Bacteriophages (phages) are viruses infecting bacteria. They are widely present in the environment, food, and normal microflora. The human microbiome is a mutually interdependent network of bacteria, bacteriophages, and human cells. The stability of these tri-kingdom interactions may be essential for maintaining immunologic and metabolic health. Phages, as with each other's antigens, may evoke an immune response during a human's lifetime and induce specific antibody generation. In this manuscript, we labeled these antibodies as naturally generated. Naturally generated antibodies may be one of the most important factors limiting the efficacy of phage therapy. Herein, we attempted to determine the physiological level of these antibodies specific to a population bacteriophage named I11mO19 in human sera, using an ELISA-based assay. First, we purified the phage particles and assessed the immunoreactivity of phage proteins. Then, affinity chromatography was performed on columns with immobilized phage proteins to obtain a fraction of human polyclonal anti-phage antibodies. These antibodies were used as a reference to elaborate an immunoenzymatic test that was used to determine the level of natural anti-phage antibodies. We estimated the average level of anti-I11mO19 phage antibodies at 190 µg per one milliliter of human serum. However, immunoblotting revealed that cross-reactivity occurs between some proteins of I11mO19 and two other coliphages: T4 and ΦK1E. The antigens probably share common epitopes, suggesting that the determined level of anti-I11mO19 phage might be overestimated and reflects a group of antibodies reactive to a broad range of other E. coli phages. Anti-I11mO19 antibodies did not react with Pseudomonas bacteriophage F8, confirming specificity to the coliphage group. In this work, we wanted to show whether it is possible to determine the presence and level of anti-phage antibodies in nontargeted-immunized sera, using an immunoenzymatic assay. The conclusion is that it is possible, and specific antibodies can be determined. However, the specificity refers to a broader coliphage group of phages, not only the single phage strain.
Keywords: anti-phage antibodies; bacteriophages; coliphages; cross-reactivity.