Mechanism of action of antibodies

Mechanism of action of antibodies

Antibodies do not directly kill the pathogen or destroy the antigen but renders it able to be acted upon by other cells of defence system by  following process :

• Agglutination : Pathogens (or antigens) are agglutinated together to become effectless. Then neutrophils destroy them.
• Opsonisation  : Antibodies make a coat around pathogen so that Mcp or other cells get attracted to engulf (opsonin = to prepare for eating) it which is otherwise not possible or very difficult.
• Complement mediated lysis : Antibodies stimulate the enzyme cascade of the killer cells which hydrolyse the antigen or break the membrane system of the pathogen.
• Neutralization : Antibodies neutralize the effect of toxins released by bacteria.

Allergies

The allergens are weak antigens. Antibodies formed against it become associated with mast cells.
In case of the next encounter with same allergen, the antibodies immediately activate the mast cells which start producing histamine.
Most common allergies are – skin rashes, reddening and itching of skin, blisters, swelling, sneezing, coughing, fever, nausea, digginess etc.
Chemicals like penicillin, sulpha drugs, bee venom etc. cause severe reaction which could also be fatal. This is called as anaphylactic shock.
Other examples are : hay fever, asthma etc.
Antihistaminic drugs are used for the treatment.

Tissue/organ transplantation reaction

If MHC complex does not match, the host cell rejects the transplanted or grafted tissue or organ. Hence care is taken to make sure that the donor
and the host are of same genetic lineage.
To avoid the rejection in transplantation surgery immunosuppressive drugs are used, e.g., Steroids (cortisone).
Local immuno-suppression is made by cyclosporin A – obtained from fungus.