Disorder of Immune System
Allergy or Hypersensitivity
It is the hypersensitiveness of a person to some foreign substances called allergens coming in contact with or entering the body. It is the exaggerated response of the immune system to certain antigens present in the environment. The substances to which such an immune response is produced are called allergens. It may be mites, dust, pollens, animals dander’s fabrics, feather, mould, heat, cold and sunlight etc.
Cause- The antibodies produced against these allergens are of lgE type. Allergic reaction is due to the release of chemicals like histamine and serotonin from the mast cells. During allergic reaction there is an increased release of histamine from the mast cells
Disorder of Immune System
It causes marked dilation of all the peripheral blood vessels and the capillaries become highly permeable so that large amounts of fluid leak out from the blood into the tissues. The blood pressure decreases drastically often resulting in the death of the individual within a short time. The exact nature of the substance to which a person is hypersensitive must be known before he can be properly treated.
Types of allergy:-
(i) Hay fever:– In the allergic form, there is swollen, reddened, runny eyes and nose. The drugs called antihistamines are of major importance in the treatment of this allergic disorder
(ii) Asthma:– It is the sudden reaction involving all the tissues of the body and occurs within a few minutes after the injection of an antigen such as penicillin.
Such a reaction is very serious. Histamine released from ruptured mast cells causes marked dilation of all the arteries so that a large amount of fluid is passed from the blood to the tissues and there is a drastic fall in blood pressure. The affected person may become unconscious and the individual may die within a short time.
(iv) Eczema :– In eczema the skin becomes red, followed by the appearance of minute blisters.
Treatment:- For determining the cause of allergy, patient is exposed to or injected with a very small doses of possible allergen and after that the reactions on the body are studied. The use of drugs like antihistamines, adrenaline and steroids quickly reduce the symptoms of allergy.
Autoimmunity:– Higher vertebrates have memory – based acquired immunity. The uniqueness of the immune system is that it always destroys the foreign particles/proteins but never attacks the body’s own protein as it has the ability to differentiate foreign organisms (e.g pathogens) from self cells. But sometimes, due to genetic and other unknown reasons, the body attacks self cells. This results in damage to the body and is called as Autoimmune Disease.
So autoimmune disease occur if the body’s immune system fails to recognize ‘self’ from ‘non-self’ and starts destroying the body’s own cells.
For example, if the autoantigens are RBCs then the body destroys its own RBCs resulting in chronic anaemia, if the autoantigens are muscle cells then it results in destruction of its own muscles resulting is severe weakness: (Myasthenia gravis); if the autoantigens are liver cells, then it results in chronic hepatitis. Other autoimmune diseases are insulin-dependent diabetes, Addison’s disease, ulcerative colitis and rheumatoid arthritis.
Immune System in the Body
The human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies. Immune system recognizes, respond to foreign antigens and remembers them (memory). Human immune system also plays an important role in allergic reactions, auto immune diseases and organ transplantation.
Lymphoid Organs:-
These are the organs where origin, maturation and proliferation of lymphocytes occur
There are two types of lymphoid organs:-
(i) Primary lymphoid organs:– Primary lymphoid are those where immature lymphocytes differentiate into antigen specific lymphocytes, e.g bone marrow and thymus.
Bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced and is considered equivalent to Avian Bursa of Fabricius. It is the site where B-lymphocytes mature
Thymus is a lobed organ located near the heart and beneath the breast bone (sternum). It is quite large at the time of birth but keeps on reducing in size with age and by the time puberty is attained it reduces to a very small size. It is is the site where T-lymphocytes mature.
(ii) Secondary lymphoid organs:- After maturation, B-lymphocytes and T-lymphocytes migrate through blood vascular and lymphatic system to secondary lymphoid organs which provide the site for interaction of lymphocytes with the antigens, here they proliferate and differentiate to become effector cells e.g spleen, lymph nodes, tonsils, peyer’s patches of small intestine and appendix.
Spleen:- It is a large bean shaped organ which mainly contains lymphocytes, phagocytes and large number of erythrocytes. It acts as a filter of blood by trapping blood borne micro-organisms. Spleen also has a large reservoir of RBCs and is commonly called as “Graveyard of RBCs.
Lymph nodes:– These are the small solid structures located at different points along the lymphatic system. Lymph nodes serve to trap the micro-organisms or other antigens which are present in lymph and tissue fluid. Antigens trapped in lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response.
MALT:- Mucosa associated lymphoid tissue constitutes about 50% of lymphoid tissue in human body.
