Introduction To Immune Response Flashcards
What is immune response?
Definition of immunology?
The immune response is the recognition and defence of self against microorganisms and other substances that appear foreign or harmful to the body.
•Immunology is the study of host resistance to foreign substances
•Several immune mechanisms work in concert to ensure immunity and can be grouped into innate (nonadaptive) and adaptive (acquired) immune response.
What is INNATE IMMUNITY?
•Innate, or nonspecific, immunity is a defense system that is inherent in the individual.
•Innate immunity involves barriers that keep harmful materials from entering your body, forming the first line of defence in the immune response.
•They are nonspecific and include barriers to harmful agents. They include the skin, mucous membranes, phagocytic cells, inflammatory mediators and complement system.
CLASSES of innate immunity
- The surface & Physiologic barrier: such as skin and mucous membranes, Cough reflex
- Secretory component such as complement proteins, cytokines and interferons, enzymes in tears and skin oils, Stomach acid, Mucins, which traps bacteria and small particles (humoral immunity)
- Cellular components include neutrophils and macrophages for uptake and removal of particulate mater from the blood and lymphatic systems; and Natural Killer Cells which are non specific killer of infected and malignant cells (cellular immunity)
Acquired immunity and types
Unlike more primitive organisms, jawed vertebrates like we humans also have systems for adaptive immunity development following exposure to specific antigen e.g a microbe (acquired).
•This is usually a form of adaptation to the agent. Hence, adaptive immunity.
The immunity acquired is specific to the antigen and can be mediated by either antibody (B cell) or lymphocytes (T cells)
•The acquisition of this type of immunity can be passive (preformed from another host) or active (from the host).
Discuss PASSIVE IMMUNITY
•Acquisition of this immunity is from another host. It is preformed from another host
•It can be in form of lymphocytes or antibodies (e.g anti tetanus serum ATS, antirabied immunoglobulin)
•Large amounts of the antibody is usually delivered promptly before natural disease develops
•It is short-lived and can be associated with the risk of hypersensitivity to the foreign antibody
•
Discuss active immunity
This develops within the host after contact with foreign antigens e.g microbes
•Contact may be in the form of clinical or subclinical infection or after immunization or transplant of foreign materials
•The host is active in the production of specific antibody or lymphocytes clones to the antigen.
•The immunity development is slow in onset but long lasting. response is faster and stronger on subsequent exposure to the same antigen due to the activity of memory cells
ACQUIRED RESPONSE (MECHANISMS)
•Irrespective of the source, acquired or adaptive immunity can be antibody-mediated(Humoral), cell mediated (cell mediated) or both.
•The response is usually complex in form
•Contact of the host with potential antigen result in immediate or nonadaptive
response.
•This is followed by uptake of major antigen by the antigen presenting cells (APCs) e.g macrophages, monocytes, B lymphocytes, dendritic cells.
APCs process the antigen and present it, complexed with major histocompatibility complex (MHC) to clones of T- lymphocytes
•The clones of T lymphocytes is activated to release cytokines (proliferation inducing chemicals) by the processed antigen-MHC complex as it interacts with receptors on T lymphocytes
•Both the antibody and cell mediated immune responses develop concurrently
Antibody Mediated Response
• Helper (CD4) T cells recognises antigens complexed with MHC type II on APCs and produce cytokine that activate B lymphocytes to proliferate into actively dividing blasts cells
• The blast cells undergo clonal differentiation to become either effector B cells (plasma cells) or memory B cells.
• The plasma cells produce antibody/immuno-globulin specific for antigen that stimulate its proliferation and differentiation.
Functions of Antibody
•Neutralization of toxins and viruses (Ag-Ab complex)
•Enhancement of phagocytosis through Opsonization (coating) of pathogens
•Complement-mediated cytotoxicity- The membrane attack complex generated by complement through classical pathway is usually initiated/activated by antigen-antibody complex.
•Prevention of spread of intracellular organisms by intercellularly located antibodies
Functioning of Antibody
•Enhancement of the actions of (natural Killer cells NKC) in antibody dependent cytotoxicity (ADCC)
•During primary response, specific antibody initially present is majorly of the IgM class
•This primary antibody response is manifested by serum IgM antibodies as early as 3–5 days after the first exposure to an immunogen (immunizing antigen), peaks in 10 days, and persists for some weeks.
• As B cells also interact with helper T cells, they proliferate and switch the isotype (class) of immunoglobulin that is produced, while retaining the same antigen-binding specificity from IgM to IgG, IgA, or IgE isotypes.
•In secondary response, antibody formation takes 1-3 days (more rapidly) following secondary antigenic stimulation, are of longer duration, have higher affinity, and principally are IgG molecules.
Cell mediated immune response
•Antigen-MHC type I complex is recognized by cytotoxic (CD8) T lymphocytes.
•Each clone then produces cytokines, becomes activated and undergoes clonal proliferation and expansion to include helper T cell, suppressor T cells and Cytotoxic T cells
Functions Cell mediated immunity
•helper T cells: Stimulates B cells to produce antibodies, Promote development of delayed hypersensitivity targeted against intracellular pathogens through production of myriad of cytokines that attract and activate monocytes, macrophages, and other lymphocytes in the fight against mycobacteria, fungi, protozoa, viruses
•Cytotoxic T cell: Destruction of graft tissues, tumor and viral infected cells.
Suppressor T Cells: Involved in antigen-specific suppression and thus play an important role in maintenance of self-tolerance.
•T-suppressor lymphocytes are usually CD8+.
