Immunity – Refers to the general ability of a host to resist a particular infection or disease
Immunology – Science that is concerned with immune responses to foreign challenge and how these responses are used to resist infection
Immune Response is of 2 Types –
- Non-specific / Innate / Natural Immunity
- Specific / Acquired / Adaptive
Antigens (Antibody + generators = Antigens) – Substances that are recognized as foreign and provoke immune responses
Effector response – The kind of immune response mounted, once a foreign organism has been recognized by the immune system that recruits various types of cells and molecules to neutralize or eliminate the organism
Memory response – Immune response that is mounted in case of subsequent encounters to the same foreign organism which is more rapid and intense in order to eliminate the pathogen an prevent disease
Clonal Selection theory – A lymphocyte expresses membrane receptors specific to a particular antigen and this unique receptor specificity is determined long before the lymphocyte is exposed to the antigen. Binding of the antigen causes the cell to proliferate giving rise to a clone of cells that have the same immunologic memory as the parent cell
Innate Immune System – Macrophages and Dendritic cells – Mature in the Bone Marrow prior to leaving and provide the same physiological response regardless of Antigens (Ags)
Adaptive Immune System – T & B Cells – Are not functional after leaving the bone marrow and hence migrate to specific organs or tissues where they differentiate in response to various types of Ags presented
Some leukocytes (WBC) are restricted to certain tissues e.g. macrophages, dendritic cells while some migrate in tissue e.g. neutrophils in blood
Overview of Immune Cells
-
Agranulocytes
– Do not have granules or less granular cytoplasm
- Monocytes – Mononuclear leukocytes with a kidney-shaped nucleus and granules in cytoplasm that stain grey-blue with basic dyes. Produced in the bone marrow, enter the blood, circulate there for about 8 hours and then enter host tissue to mature into either macrophages or dendritic cells
- Macrophages – Phagocytic mononuclear leukocytes that are larger than monocytes and contain more organelles (phagocytes) such as lysosomes and have a plasma membrane covered with microvilli. Have surface receptors that non-specifically recognize foreign bodies. Made up of mannose and fucose and bind to LPS, glycoproteion, zymosan or viral NA. Also possess scavenger receptors – CD14 – bind to LPS. Also have receptors to bind to Abs and complement proteins that enhance phagocytosis – Opsonization
- Lymphocytes – Major cells of specific immune system. 3 types – T-cells, B-cells. Exit bone marrow in a kind of cellular stasis i.e. do not actively divide. This is to ensure that the gene products are produced only when needed. Blocked from entering phase G0. Require specific Ags to bind to a surface receptor for lymphocyte activation. This stimulates the cell to enter mitosis. Once activated, the lymphocytes actively divide to form several clones circulating in the body to populate other several lymphoid tissue. Some lymphocytes are inhibited from further replication so that they can counteract the attack by the same Ag later on.
- T-cells – Lymphocytes leave the bone marrow and migrate to thymus for maturation into T-lymphocytes. Remain in thymus, circulation in blood, migrate to lymphoid tissues – spleen, lymph node. Require antigens to bind to their surface receptors for activation. Unlike B-cells, they do not produce Abs, instead produce and secrete cytokine that have various effects on other T, B-Cells, granulocytes and other somatic cells. Cytokines stimulate cells to mature and differentiate, produce new effector products or cause cells to die
- B-Cells – After they attain maturity, they circulate in blood and then migrate to various lymphoid tissues. On maturation, B-cells become elongated and visible called Plasma cells that secrete large quantities of Abs some of which can neutralize toxins and viruses and are effective in stimulating an effective immune response