Humoral vs Cell Mediated Immunity
Immunity is the ability of an organism to defend against pathogens and toxins and to avoid infections and diseases. This is basically provided by the immune system, which is composed primarily of individual cells spread throughout the body, rather than forming into organs. The immune system has two broad branches; innate and adaptive immunity. Adaptive immunity is also known as the specific immunity, which provides pathogen- specific immunity in vertebrates. Adaptive immune system is basically composed of T-lymphocyte and B-lymphocyte cells. According to the composition of the adaptive system, it can be further divided into two categories; humoral immunity and cell-mediated immunity. The adaptive immunity is very special as it is present only in vertebrates, and is able to recognize different foreign antigens in a very precise way.
What is Humoral Immunity?
Humoral immunity is also known as antibody-mediated immunity. It is mediated by antibody molecules secreted by the B- lymphocyte cells that can neutralize specific pathogens outside the cells. B-cells are bone marrow derived, and each cell makes only one kind of antibody which specifically reacts on a particular pathogen. Antibody diversity is generated by DNA rearrangement. These antibodies can directly neutralize viruses. For certain pathogens, the antibodies bind to target the cells and signal phagocytes or other white blood cells or other defense mechanisms to attack them.
What is Cell Mediated Immunity?
Cell mediated immunity is mediated by T-cell antigen receptors made by thymus-derived T-cells. As the name implies, T-cells themselves specifically bind with the antigens, instead of releasing the receptors from the cell body. Each T-cell makes only one kind of T-cell antigen receptor. T-cell receptor is composed of four proteins, namely, two large (α) and two small (β) chains. Each chain has constant and variable regions. The variable regions determine the specificity of the receptor toward a particular pathogen while the variable regions project outside helping to bind the T-cells to the antigen cell. The cell- mediated immune system is important as it eliminates tumor cells before they can grow and spread very much. This process is known as ‘immunological surveillance’. Also, when a tissue from an unrelated individual is introduced into another individual, this immune system will respond and kill the transplanted tissue immediately.
What is the difference between Humoral and Cell Mediated Immunity?
• Humoral immunity is mediated by B- cells while cell-mediated immunity is mediated by T-cells.
• In the humoral immunity, the B-cells secrete antibodies whereas in the cell-mediated immunity, the T-cells do not secrete receptors. T-cell receptors are bound to the T-cells and the cells themselves bind with antigens.
• The humoral immunity is more important to eliminate soluble antigens and to destroy extracellular microorganisms while the cell-mediated immunity is more important to eliminate intracellular organisms (such as viruses).
• The antibodies are used in the humoral immunity whereas the receptors are used in the cell-mediated immunity to defend against pathogens.
• Unlike in the cell-mediated immunity, the antigens are destroyed by B-cell antibodies outside the B-cells in the humoral immunity.