The study of all aspects of immune system of all organisms is known as immunology. This study includes physiological functioning in both disease condition as well as healthy condition. The study of immune system includes but not limited to transplant acceptances and transplant rejections, malfunctions of the immune system, hypersensitivities, autoimmune diseases, chemical, physical and biochemical characteristics of immune system. These studies are done in vitro, in situ, or in vivo. There are many organs of body which are a part of our immune system. These includes bone marrow, secondary lymphatic tissue like tonsils, spleen, lymph vessels, lymph nodes, skin , liver and adenoids as well as , primary lymphoid organs like thymus and bone marrow.
It has been a fact that many components of immune system are actually cellular structures and not organs. But also are embedded in various group of cells known as tissue or circulating in our body.
Within immunology the study of diseases which are due to disorders in immune system it is known as clinical immunology. These include aberrant actions on such diseases, malignant growth of cellular elements of the immune structure. The diseases which are due to disorders in immune system are divided mainly into two types. The first one is immunodeficiency eg. Chronic granulomatous disease. In such disease, the part of immune system does not response to immunological triggers. The second type is autoimmunity in which there is a attack from immune system itself. The examples of such disease are lupus erythematosus, Hashimoto's disease, and rheumatoid arthritis. Few another immune system disorders are different hypersensitivities. In hypersensitivity the immune system respond in wrong manner to some harmless compound e.g. asthma, allergies.
AIDS, which is caused by HIV is the most well know disease that attacks immune system. HIV viruses destroy dendritic cells, T cells (CD4+ helper) and macrophages.
The most important part of immunology study is Developmental Immunology. Many factors are responsible for body's capability to reaction to antigens. It may be on type of antigen, person's age, maternal factors and environment in the antigen is present. One the child is born, its immune system starts responding to antigens. Study suggests that in such cases the responses are more to antigens with protein in nature as compared to that of polysaccharides and glycoproteins. The research has shown that the infection which occurs in neonates is by low virulence microorganisms like Pseudomonas and Staphylococcus. This may be because the capacity of immune system of neonates is less to activate the cascade. The reason is that the C3 levels in them are around 65 % of that of adults. This is called as lower opsonic activity. Phagocyte activity is also impaired in neonates. In the immunes responses the maternal factor play a very crucial role. IgG is the most present immunoglobulin at birth. There is a interesting fact for this. This is because IgM, IgE & IgD are unable to cross placenta. Even if found they are undetected and negligible. The immunoglobulin which is provided from mother's milk is IgA. These immunoglobulins which are passively provided protect the child for up to 18 months. By 6-9 months the Childs immune system starts responding more effectively to other antigens which are glycoprotein in nature. And thereafter from 12-24 months of age good immune responses are observed against many antigens. One of the reasons for vaccination schedule may be this developmental immunology.
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