Antibodies and Cellular Immunity

Subject: Science and tech

Context:

A study published in Nature Medicine suggests that antibodies in individuals who recovered from SARSCoV2 infection start to decrease within two three months after infection. Besides inducing neutralising antibodies, novel coronavirus has also been found to induce cellular immunity.

Concept:

The immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells.

Antibody:

Antibodies are proteins made by the immune system to fight antigens, such as bacteria, viruses, and toxins.The body makes different immunoglobulin to combat different antigens.

The five subclasses of antibodies are:

• Immunoglobulin A (IgA), which is found in high concentrations in the mucous membranes, particularly those lining the respiratory passages and gastrointestinal tract, as well as in saliva and tears.
• Immunoglobulin G (IgG), are involved in the secondary immune response (IgM is the main antibody involved in primary response). IgG can bind pathogens, like for example viruses, bacteria, and fungi, and thereby protects the body against infection and toxins. Comprising up to 80% of the antibodies found in the human body, IgG is the smallest, yet most abundant human antibody, and that of other mammals. IgG can be found in all bodily fluids, and is the only antibody that can protect a foetus by passing through the mother’s placenta.
• Immunoglobulin M (IgM), is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antigen. B-cells create IgM antibodies as a first line of defense. Their large size gives them excellent binding avidity, and can pick up trace amounts of infection to mark for recognition by phagocytes. IgM is primarily found in serum and due to its size, it cannot diffuse well, and is found in the interstitium only in very low quantities.
• Immunoglobulin E (IgE), which is associated mainly with allergic reactions (when the immune system overreacts to environmental antigens such as pollen or pet dander). It is found in the lungs, skin, and mucous membranes.
• Immunoglobulin D (IgD), which exists in small amounts in the blood, is the least understood antibody.

Cellular immunity

• Cell-mediated immunity is an immune response that does not involve antibodies.
• Cellular immunity is a protective immune process that involves the activation of phagocytes, antigen-sensitized cytotoxic T cells and the release of cytokines and chemokines in response to antigen.
• Cellular immunity is most effective against cells infected with viruses, intracellular bacteria, fungi and protozoans, and cancerous cells.