B Lymphocytes & Humoral Immunity

A key part of the production of antibodies involves a T helper cell

If a pathogen enters the human body

• It is covered in antigen molecules

First the pathogen is engulfed by a macrophage during phagocytosis

Then the macrophage digests the pathogen and processes the antigen molecules.

The Macrophage now displays the nations on its surface attached to MHC molecules.

• Macrophages is acting as an antigen-presenting cell

Then the macrophage interacts with T helper cells.

• T helper cells are formed in the bone marrow and mature in thymus gland

• Each T helper cell has a unique T cell receptors on its surface.

• The T cell receptors on each T helper cell are specific for an individual antigen

• There are millions of unique T helper cells each targeting a differnet antigen

After some time the macrophage will encounter a T helper cell.

The T helper cell now binds it receptor to the antigen

Once the T cell receptor is bound to the correct antigen, the T helper cell is activated

The activated T helper cells produce chemicals called interleukins (type of cytokine)

The interleukins trigger the activated the T helper cell to undergo mitosis which forms idéntica clones of activated T helper cells.

The interleukins also template Macrophages to carry out phagocytosis

B lymphocytes are formed in the bone marrow which is where they mature before being released into the blood

B lymphocytes also have antigen receptors on their surface membrane

• The antigen receptors are membrane bound antibodies

All the antibodies on a particular B lymphocytes will bind to the same antigen

Since there are millions of unique B lymphocytes there will be at least one B lymphocytes for every possible antigen

Pathogen enter the body

Pathogen encounters a B lymphocyte with correct antibody to bind to the antigen on the pathogen’s surface

Now the B lymphocyte attaches to the pathogen and the pathogen is engulfed

The pathogen is digested and the antigens are presented on teh surface of the B lymphocyte

B lymphocytes is now acting as a antigen-presenting cell

Now the activated T helper cell uses its T cell receptor to attach to teh antigen on the B Lymphocyte surface

• Because the correct B lymphocyte has now been selected by the T helper cell this stage is called clonal selection.

Now the T helper cell produces inetrllrukinds which activate teh B lymphocyte

The activated B lymphocyte undergoes mitosis

• Forming clones of 2 types of cells:

  • Plasma cells

    • Release identical antibodies which bind to the antigens on teh pathogens surface

    • This disables the pathogen, marks it for phagocytosis or triggers agglutination

    • Ths process is called primary immune response

    • Can take days or weeks

  • B memory cells

    • Remain in blood ready for a second infection with the same pathogen

      • If a second infection happens then B memory cells rapidly turn into plasma cells and release antibodies

      • This second production of antibodies is called the secondary immune response

• Stage is called Clonal expansion

During primary immune response pathogens can reproduce causing the infected person to show symptoms

During secondary immune response the pathogen doesn't nt get time to reproduce and so no symptoms are developed