The negative effects of various mycotoxins on the immune system of poultry
It is often forgotten that protection of birds against infectious diseases is also imparted through special cells, the lymphocytes. The protection given through cells is known as cell-mediated immunity, which is equally important to that of antibody mediated (humoral) immunity.
In the chicken, lymphocytes are normally about 60 percent of the total number of white blood cells. In the incubating egg, lymphocytes are derived from the lymphoid stem cells (parent cells), which originate in the yolk sac membrane.
These stem cells travel into two different directions between 5 to 7 days of incubation. One set of stem cells goes to bursa of Fabricius - a round, sac like structure just above the cloaca - while the other set of stem cells enters the thymus.
Bursa and thymus reach their greatest size in the chick about 1-2 weeks after hatching and then gradually disappear. The stem cells which differentiate into lymphocytes in bursa are called B-lymphocytes ('B' for bursa) and those which differentiate into lymphocytes in thymus are called T-lymphoctye ('T' for thymus).
The B-lymphocytes on contact with pathogens are transformed into another type of cells known as 'plasma cells', instead of producing antibodies by themselves. The plasma cells are especially equipped to produce the antibodies (immunoglobulins, Ig).
These antibodies then inactivate the pathogens and thus protect the body. Each plasma cell can produce up to 300 molecules of antibody per second. Antibodies are continuosly replaced.
One type of plasma cells produces only antibodies against one infectious agent. This means that different types of B-lymphocytes must be activated to produce different sets of plasma cells, specific for each disease. It is now believed that B-lymphocytes carry tiny ready-made antibodies (immunoglobulin) on their surface against each infectious agent present in nature.
When any organism enters into the body, it identifies the particular antibody on the surface of a specific B-lymphocyte acting as a receptor for it. The organism then attaches to the specific antibody present on its surface, like a lock and key arrangement.
In other words, antibodies against one disease are derived from only one type of B-lymphocyte, which then multiplies and gives rise to a specific set of plasma cells.
This is immunologically expressed as "antibodies are monoclonal in origin", thus they are derived from a single cell (B-lymphocyte), which then proliferates and forms a colony of plasma cells.
The article further discusses effects of mycotoxins on antibody production, on non-specific humoral substances and on cell mediated immune response.
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Article made possible through the contribution of Biomin