Immunity and Immunodeficiency Disease
This explains in details how group of cells, molecules and organs resist almost all forms of invasion by organisms, tumour cells and foreign substances.
• Immune system consists of group of cells, molecules and organs that collectively defend the body against invasion by organisms, tumour cells and foreign substances.
• The health of the body is dependent on the immune system’s ability to recognize, neutralise or destroy the invaders.
• The ability of the body to resist almost all forms of invasion is known as immunity.
Components of Immune System
• Organs: thymus, bone marrow, lymph nodes and spleen
• Cells: White blood cells, antigen-presenting cells
• Molecules: immune modulators; cytokines,
• Antibodies/immunoglobulins: IgA, IgE,IgG,IgD & IgM
• Complement system
Classification of Immunity
• Body immunity is classified into two;
1. Innate /natural immunity: a non-specific type of immunity; in-born ability of the body to resist invasion by organisms or foreign substances.
2. Acquired/adaptive immunity- as specific type of immunity developed in response to a specific antigenic challenge
LINES OF DEFENSE:
1) In the first line of Defense: the elements of Immunity found includes; Surface Barriers; skin and mucosa, secretions of GIT, respiratory and genitourinary tracts Normal flora-microbes that live in or on the body that mutually coexist with the body preventing occupation of such areas by pathogenic organisms. This immunity is classified as innate immunity.
2) In the second line of Defense: the element of immunity includes Internal defensive mechanisms; phagocytosis, inflammation, fever, natural killer(NK) cells, antimicrobial substances, complement system. This immunity is also classified as innate immunity.
3) In the third line of Defense: Elements of immunity includes Specialized B and T lymphocytes this immunity is classified as Specific immunity
DEFINITIONS/TERMS IN IMMUNITY
• Antigen-substance that elicits an immune response. Most potent antigens are complex proteins or polypeptides but occasionally can also be carbohydrate moieties.
• Antibody(immunoglobulins): γ-globulins produced by plasma cells(differentiated B cells) in response to antigenic challenge
• Memory: ability of the immune system to remember a previous encounter with antigen so that a second exposure to same antigen produces a more rapid and powerful response.
• Lymphocytes constitute 25-40% of white blood cells.
• Depending on the modes of development, lymphocytes are classified into B or T lymphocytes.
• In utero, lymphocytes develop from their precursors in bone marrow and when released into circulation differentiate into two categories;
• The lymphocytes that are destined for cellular immunity- migrate to thymus and are transformed to T lymphocytes.
• The lymphocytes that are destined for humoral immunity are transformed in bursal equivalents(fetal liver in utero and bone marrow after birth) to B lymphocytes.
• N.B. B lymphocytes are first discovered in bursa of Fabricius, a lymphoid organ located close to cloaca of birds; in mammals, there is no bursa but the B lymphocytes are processed in the bursa equivalents.
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