Humoral (Antibody-Mediated) Immunity Involves production of antibodies against foreign antigens. Antibodies are produced by a subset of lymphocytes called B cells. B cells that are stimulated will actively secrete antibodies and are called plasma cells. Antibodies are found in extracellular fluids (blood plasma, lymph, mucus, etc.) and the surface of B cells. Defense against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells. Also cause certain reactions against transplanted tissue.
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Humoral (Antibody-Mediated) Immunity Involves production of antibodies against
foreign antigens. Antibodies are produced by a subset of
lymphocytes called B cells. B cells that are stimulated will actively secrete
antibodies and are called plasma cells. Antibodies are found in extracellular fluids
(blood plasma, lymph, mucus, etc.) and the surface of B cells.
Defense against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells.
Also cause certain reactions against transplanted tissue.
Formation of antibodies by plasma cell
B cells develop from stem cells in the bone marrow
After maturation B cells migrate to lymphoid organs (lymph node).
Clonal Selection: When a B cell encounters an antigen it recognizes, it is stimulated and divides into many clones called plasma cells, which actively secrete antibodies.
Formation of “Memory” cells Few activated B lymphocyte do not go
on to form plasma cells, but instead form moderate numbers of new B lymphocyte similar to the cell population
They circulate in the body to populate all lymphoid tissue
They remain dormant until activated once again of the same antigen
These lymphocyte are called memory cells
Clonal Selection of B Cells is Caused by Antigenic Stimulation
B Lymphocytes
Production of antibodies
Stimulate production of memory cells
Transformed into plasma cells
Mechanism of activating clone of lymphocyte Activation of B lymphocyte is by
antigen attached to antibody in the cell membrane
Activation of T lymphocyte is by surface receptor proteins (T-cell marker) on the surface of the membrane
Role of macrophage in activation process
Most invading organism are first phagocytized by macrophages
Macrophages pass these antigens to the lymphocytes
This activates specific lymphocytic clones
In addition, Macrophages secrete special activating substance (interleukin-1) that promote growth and reproduction of specific lymphocyte
Role of macrophage in activation process
Most invading organism are first phagocytized by macrophages
Macrophages pass these antigens to the lymphocytes
This activates specific lymphocytic clones
In addition, Macrophages secrete special activating substance (interleukin-1) that promote growth and reproduction of specific lymphocyte
Role of the T cells in activation B lymphocyte
Some of the T cells called helper cells secret substance lymphokines activate B lymphocyte
Without the aid of T helper cells, the quantity of antibodies formed by B lymphocyte is usually low
Antibodies Immunoglobulins are a group of proteins (gamma
globulins) produced by the body from B lymphocytes and plasma cells in response to presence of foreign bodies (antigens).
They constitute 20% of all plasma proteins Antibody consist of two polypeptide building
blocks, a heavy chain and light chain Each antibody chain has a variable portion
and constant portion
Classes of antibodies
There are five classes of antibodiesIgM, IgG, IgA, IgD and IgE IgG consist of 75% of the antibodies
of the normal person. IgE involve in allergy IgM effective in protecting the body
against invader
Antibodies
Immunoglobulin Functions
lgG Main form of antibodies in circulation: production increased after immunization; secreted during secondary response
lgA Main antibody type in external secretions, such as saliva and mother’s milk
lgE Responsible for allergic symptoms in immediate hypersensitivity reactions
lgM Function as antigen receptors on lymphocyte surface prior to immunization; secreted during primary response
lgD Function as antigen receptors on lymphocyte surface prior to immunization; other functions unknown
Ig E Ig D I g M
Ig A Ig G
184 184 970 160 160 Mass (KD)
trace Less than 1
5-10 10-15 70-75 % of total Ig
NO NO NO NO yes Cross placenta
NO NO NO yes yes In breast milk
NO NO NO yes NO In secretions
yes NO NO NO NO Binding with mast cells
Mechanism of action of antibodies
1. Direct attack on the invader2. Activation of the complement
system
Direct action of antibodies on invading agent Agglutination: large particle with
antigen are bound together into clump
Precipitation: Molecular complex of soluble antigen and antibody become insoluble
Neutralization: Antibodies cover the toxin side of antigen
Lysis: Attacking membrane of cellular agent
Complement system for antibody action
Complement : describes system of about 20 proteins, many of which enzyme precursors
The principal actors in the system are 11 proteins designated C1 through C9, B and D
The enzyme precursors are inactive and they become activated by classic pathway
Classic pathway initiated by antigen-antibody reaction
Classic Pathway
Opsonization and phagocytosis: Activate phagocytosis by neutrophils and macrophages causing these cells to engulf the bacteria to which antigen-antibody complex are attached
Lysis: The effect is rupturing the bacteria cell membrane
Agglutination: invading organism adhere to one another
Classic Pathway
Neutralization of viruses: attach the structure of some viruses
Chemotaxis: Initiate chemotaxis of neutrophil and macrophages
Activation of mast cells and basophils: Release of histamine and other products
Inflammatory effects: increase blood flow, increase capillary leakage of proteins
Consequences of Antibody Binding
Related Documents
