Antibody mediated immunity refers to the destruction of antigens by producing antibodies, and as the antibodies are present in body fluids (humours), this type of immunity is also called humoral immunity.

B-cells cannot bring about humoral immune response but needs the cooperation of other cells such as macrophages (f), T-helper cells (T_H), and dendritic cells possessing high levels of surface MHC class II molecules that process and serum proteins) and are usually comprised of IgM, IgA, IgE, and IgG.

Immunoglobulins Participating in Humoral Immunity

The various immunoglobulins participating in humoral immunity are:

IgM: It is the first class antibody generated invariably in most humoral responses but normally gets switched over to the corresponding IgA, IgE, or IgG at a very early stage in the immune response.

IgG: It is the most versatile, important and abundantly available class of antibodies taking part in largest humoral immune reactions. It can cross the placenta, thereby providing a new born baby absolute temporary immunity against the immunogens the mother had earlier against IgG.

IgA: It is invariably found in a plethora of secretions like tears, saliva, and mucous membranes. This immunoglobulin is frequently termed as the first line-of-defence mechanism due to the fact that most bacteria, viruses and fungi that eventually gain entry into the body do cross a mucous membrane.

IgE: It is also important in the body’s defence against the parasitic worm infections. Prominently and predominantly several allergic manifestations give rise to the release of histamines (allergy due to pollens, house dust, dust mite, human hair, food allergens, etc.), which in turn afford the apparent discomforts resulting into extrinsic asthma, hay fever, hives, or excessive sneezing (during seasonal change and due to the presence of pollen grains in the air).

Immunoglobulins normally serve as surface receptors strategically located on certain immunologically active cells so as to enable them to bind immunogen.

Mechanism

Humoral immunity is also called B-cell mediated immunity since B-lymphocytes are involved in this response. This immune response defends the body against pathogens invading body fluids or humour. B-cells are antigen specific.

During the immune response, B-cells specific for specific antigens enlarge to become lymphoblasts that differentiate into plasma cells. These mature plasma cells rapidly produce γ-globulins or immunoglobulins or antibodies (at a rate of about 2000 molecules/second) for each plasma cell. These immunoglobulins are secreted into the lymph and they eventually enter the blood.

The different types of cells or entities that are held responsible for contributing to the humoral immunity are:

1. B-Lymphocytes (or B-cells),
2. Immunodominant Peptides (IDPs),
3. Antigen-Presenting Cells (APCss),
4. T-cell subsets, and
5. Class II MHC (Major Histocompatibility Complex) proteins.