As shown in the above flowchart, our immunity can be divided into two categories, namely, innate and adaptive/acquired. So what exactly is immunity? Simply put, it is a body's ability to resist a disease.
Differences between innate and adaptive immunity [click to enlarge]
More about adaptive immunity
Adaptive immunity is carried out by B cells and T cells.
Both B cells and T cells are lymphocytes. A lymphocyte is a type of white blood cell [White blood cells, or leukocytes, are cells of the immune system defending the body against both infectious disease and foreign materials] in the vertebrate immune system. T cell can be further divided into helper T cells and cytotoxic T cells. Helper T cells activate other immune cells while cytotoxic T cells kill infected or mutated cells. B cells produce antobodies.
Adaptive immunity can be distinguished by its specificity and memory.
Specificity is provided by antigen receptors on B and T cells. Memory is provided by long-lived memory cells that are formed during the infection and persist for a long time.
Recognition by the adaptive immune system
There are antigen receptors on B cells and T cells that recognise epitopes on antigens. Each B and T cell has a unique receptor that will bind very specifically to a particular antigen.
- B cells - B cell receptors and antibodies
- T cells - T cell receptors
Receptor - A nerve ending that is sensitive to stimuli and can convert them into nerve impulses. Like a "receiving device". The diagram below simply illustrates how a receptor generally works.Epitope - An immunologically active binding site on an antigen to which an antibody or a B or T cell receptor becomes attached.
Primary and Secondary immune responses
Primary immune response - The immune response occurring on the first exposure to an antigen, with specific antibodies appearing in the blood after a multiple day latent period.
Secondary immune response - The immune response occurring on second and subsequent exposures to an antigen, with a stronger response to a lesser amount of antigen, and a shorter lag time compared to the primary immune response.