lymphocytes and the Immune Response

lymphocytes and the Immune Response

lymphocytes and the Immune Response

The lymphocytes

Lymphocytes are a type of white blood cell that can respond to antigens as part of a specific host defense mechanism.

Under the microscope, all lymphocytes look the same, differing only in size and other physiologically variable features, but there is a hidden homogeneity beneath the surface of morphological homogeneity. To begin, lymphocytes are classified into three types: T cells, B cells, and natural killer (NK) cells. Because NK cells are a subset of T and B cells, we will ignore them.

The T and B sets are divided into subsets based on a variety of criteria. Finally, each subset is a mosaic of clones, with each clone expressing a specific receptor for a different antigenic eptiope.

B-lymphocytes

B-cells account for less than 15% of circulating lymphocytes and are derived from progenitor cells in the bone marrow and GALT via an antigen-independent maturation process.

These cells are the primary source of cells involved in the hurmonal (antibody) response, which is the primary host defense against microorganisms.

 

B-lymphocytes and the Immune response

B-cells participate in the humoral immune response by being stimulated into plasma cells, followed by the synthesis and secretion of immunogobulins in response to antigenic stimulation.

The humoral immune response requires the interaction of macrophages, T-cells, and B-cells to stimulate the production of antibodies. B-cells typically require the cooperation of antigen-presenting cells in order to recognize antigens.

Macrophages are the most important antigen-presenting cells, phagocytizing, processing, and presenting antigen to T-cells. T-cells with antigens on their surfaces bind with a specific antigen receptor of B-cells known as B-cell receptor, causing the B-cell to recognize its specific antigen and become activated.

When activated, the selected B-cell divides, producing a clone. It also causes B-cells to further differentiate into plasma cells, which produce the massive amounts of antibodies required to fight infection. Some members of this clone develop into effector cells that actively combat the virus.

Plasma cells are the final stage of B-cell differentiation and can synthesize and excrete antibodies. Plasma cells are not normally found in circulating blood.

 Primary and Secondary immune responses

In their resting state, B cells can be stimulated to enlarge, divide, mature, and secrete antibody. The appropriate signal for this sequence is determined by the type of antigen (foreign material), i.e. first or second antigen exposure.

The immune response varies depending on the type of advocate.

Primary immune response

When a person first encounters a specific antigen, antibody is produced during a primary immune response.

The first antibodies that appear are of the IgM class. The production of detectable serum IgM may take 1-2 weeks, and the produced antibody will decline quickly.

Secondary immune response

When exposed to the same antigen again, memory B-cells initiate a secondary immune response.

IgG is the most common antibody produced during a secondary immune response.

When compared to the primary response, the production of this antibody in detectable quantities may take a very short time.  IgG can last for months or years. Because of the memory B-cells. The secondary immune response has a higher affinity than the primary immune response.

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