Friday, November 14, 2008

Adaptive/Acquired Immunity

Part 1: Adaptive/Acquired Immunity

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.

Innate immunity refers to non-specific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body.

Adaptive/Acquired immunity refers to antigen-specific immune response. The adaptive immune response is more complex than the innate. Adaptive immunity also includes a "memory" that makes future responses against a specific antigen more efficient. [This will be our main focus]

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.


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