Patients who have contracted COVID-19 are known to produce antibodies in response to the virus. Now, researchers are looking to isolate some of these antibodies for use as a preventative measure and treatment in the fight against the pandemic. But what are antibodies, and what are scientists considering as they move forward in antibody research?
Antibody’s and Antigens
When a person is infected by a foreign substance (often called an antigen), special blood cells called b-cells distinguish the invader from bodily tissue by binding to the proteins expressed on the surface of the substance. This triggers an immune response that causes the b-cell to divide into identical copies called clones. The clones then go on to create large numbers of a special protein called an antibody. By their nature, most antibodies have two binding sites that allow them to latch onto the specific section of the invader that each b-cell first recognized. Because antigens typically have many unique molecules on their surfaces, multiple types of clones and antibodies are produced in response to every foreign substance. These antibodies are thus referred to as being polyclonal.
The binding of an antibody to an antigen can have several effects. For example, multiple antibodies may incapacitate an invader, making it unable to move or penetrate any other cells in the body. Antibodies may also signal for a subsequent reaction to occur, such as the bursting of the invading cell or the ingestion of the antigen by immune cells called phagocytes. After the body has overcome an infection, the antibodies that were produced remain in the body for months, allowing for immunity against the same type of antigen.
In a natural immune response, multiple types of polyclonal antibodies are produced; each being equipped to recognize one of the specific sections of an antigen. Monoclonal antibodies, by contrast, are selected for and produced in a laboratory so that they all recognize the same section of protein on the antigen.
By utilizing blood samples from patients who have survived COVID-19, researchers have found two varieties of antibodies that can prevent the coronavirus from attaching to human cells. These varieties were isolated into monoclonal antibodies in the lab and were later injected into mice that had been infected by coronavirus. One study found that mice treated with the monoclonal antibodies showed a reduction in the amount of viral DNA in their lungs by up to 30%.
While monoclonal antibodies show promise in fighting COVID-19, scientists are also mindful of potential risks that could come from using antibodies as a treatment. For instance, a phenomenon called “antibody-dependent enhancement,” or ADE, has been observed to occur during viral infections such as dengue fever. In these cases, ADE develops when a patient has been exposed to two different strains of a virus. Antibodies that were created in response to the first strain bind to the new form of the virus; but are unable to properly neutralize the invader. These antibodies and the virus they have attached to can then bind to other immune cells and ultimately help the virus to infect them. While researchers are aware of ADE, there is no evidence that the phenomenon occurs in COVID-19 patients.