Antibodies in Virus Immunity

The coronavirus disease 2019 (COVID-19) pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic triggering people to explore virus immunity. Antibodies, as a part of humoral immunity, play an important role in protecting against antigenically variable viruses. Antibodies are made by our body after infection and after vaccination. Even after the infection has passed, antibodies remain in the body to help the body fight off future infections. How long these antibodies last in the body varies, ranging from days to a lifetime.

Function of Antibodies

The antibodies consist of pairs of light (L) and heavy (H) polypeptide chains. Variations in the constant portion of H-chains lead to production of Ig isotypes (IgM, IgA, IgD, IgE, and IgG (further subdivided into IgG1, IgG2, IgG3 and IgG4)), each having distinct effector functions. Among them, IgG is the most common antibody in protecting against bacterial and viral infections while IgM is the first antibody the body makes when it fights a new infection.

Antibodies serve as critical barriers to viral infection. The binding of antibodies and viruses serves many purposes in the eradication of the virus. The classic case is virus neutralization, the ability of an antibody to cause the loss of virus infectivity by blocking attachment to the host cell, preventing the penetration of the host cell membrane or interfering with uncoating of the virus within the cell. In addition, antibodies drive effector cells to lyse infected cells through activation of antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), or complement-dependent cytotoxicity (CDC).

Virus Escape

Immune responses against antigenically variable viruses and cellular pathogens are efficient in many cases. However, viruses have developed an impressive array of strategies to cope with the hosts' antiviral defense, in particular with the immune system. Some viruses are able to generate the escape variant to evade antibodies. For example, the influenza virus undergoes rapid antigenic evolution to escape antibodies. The virus is evolving, but the antibodies that fight it can change, too. In some instances, the presence of specific antibodies can be beneficial to the virus. This activity is known as antibody-dependent enhancement (ADE) of virus infection.

Co-evolution of virus and antibody response. Fig.1 Co-evolution of virus and antibody response. (Schmidt, 2015)

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  1. Schmidt, A.G.; et al. Immunogenic stimulus for germline precursors of antibodies that engage the influenza hemagglutinin receptor-binding site. Cell reports. 2015, 13(12): 2842-2850.

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