The immune response which is provided by the antibody molecule secreted from the plasma B-cells, activated by immunogenic encounter, is known as humoral or antibody mediated immunity. The mediator molecule or antibody is secreted by the activated plasma B-cell after the immunogenic interaction. Mediators: The major effector molecule of this immune response is antibody. For these reason humoral immunity is also known as antibody mediated immunity.
Mechanism: The extracellular antigen or other immunogenic material entered into the body activates the naive B-cells by binding of the B-cell receptors (BCR) to the specific signalling molecule (like cytokines) released by the activated T-cells. For this interaction, T-helper cell is required which collects the specific signal for the specific antigen, presented by the antigen presenting cells or APC (like macrophage, dendritic cells etc) through major histocompatibility complex (MHC-II) expressed on the surface of APCs. This interaction with the antigen, differentiate the naive B-cell into Effector B-cell and Memory B-cell.
- Effector B-cells: The effector B-cells which are also known as plasma B-cells start to secrete specific antibody for the specific antigenic material. Normally they do not contain any surface receptor and can survive only for a few days and die after their function is done by apoptosis or program cell death.
- Memory B-cell: The memory B-cells are those cells which are stored into the body with a knowledge about this specific antigen or immunogen for future use. It pays its function when this specific antigen or antigenic substance enters into our body for second time. These cells have longer life span and they expressed same membrane bound receptor or antibody as like their parent B-cells.
The antibody secreted from the plasma B-cell or effector B-cell plays different types of function – 1. They bind to the antigenic substance trough specific receptor which activates the complement system and ultimately results the formation pf membrane attack complex (MAC) and causes lysis of the antigen or other pathogenic substances. 2. They also act as opsonin and facilitate the opsonization which help the phagocytic cells to recognize the antigenic material and accelerates their digestion through this it plays vital role in phagocytosis.