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How Lymphocytes Produce Antibody

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The scanning electron micrograph above, shows a human
macrophage (gray) approaching a chain of Streptococcus pyogenes
(yellow). Riding atop the macrophage is a spherical lymphocyte.
Both macrophages and lymphocytes can be found near an
infection, and the interaction between these cells is important in
eliminating infection.

Here is an animation that illustrates the basic cell-cell interactions
that lead to antibody production.

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1. Antigen Processing. When the macrophage eats bacteria,
proteins (antigens) from the bacteria are broken down into short
peptide chains and those peptides are then "displayed" on the
macrophage surface attached to special molecules called MHC II
(for Major Histocompatibility Complex Class II). Bacterial
peptides are similarly processed and displayed on MHC II
molecules on the surface of B lymphocytes.

2. Helper T Cell Stimulating B Cell. When a T lymphocyte "sees"
the same peptide on the macrophage and on the B cell, the T cell
stimulates the B cell to turn on antibody production.

3. Antibody Production. The stimulated B cell undergoes repeated
cell divisions, enlargement and differentiation to form a clone of
antibody secreting plasma cells. Hence. through specific antigen
recognition of the invader, clonal expansion and B cell
differentiation you acquire an effective number of plasma cells all
secreting the same needed antibody. That antibody then binds to
the bacteria making them easier to ingest by white cells. Antibody
combined with a plasma component called "complement" may also
kill the bacteria directly.

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