The part of the alarm system that we tested is called the human leukocyte antigen system, or HLA. Each person has multiple alleles of the genes that make up their HLA type. Each allele codes for a different HLA protein. These proteins are the sensors of the alarm system and find intruders by binding to various peptides—chains of amino acids that make up parts of the coronavirus—that are foreign to the body.
Once an HLA protein binds to a virus or piece of a virus, it transports the intruder to the cell surface. This "marks" the cell as infected and from there the immune system will kill the cell.
In general, the more peptides of a virus that a person's HLAs can detect, the stronger the immune response. Think of it like a more sensitive sensor of the alarm system.
The results of our modeling predict that some HLA types bind to a large number of the SARS-CoV-2 peptides while others bind to very few. That is to say, some sensors may be better tailored to SARS-CoV-2 than others. If true, the specific HLA alleles a person has would likely be a factor in how effective their immune response is to COVID-19.
