HIV-AIDS

-AIDS is causd by Human Immunodeficiency Virus(HIV) which attacks helper T lymphocytes or macropahges.
-It causes reduction in number of lymphocytes and macrophage causing loss of immunity.
-HIV is a retrovirus which contains 2 molecules of RNA as carrier of genetic material, surrounded by 2 layers of globular proteins and outermost lipoprotein layer.
-HIV also contains reverse transcriptase enzyme which converts RNA to DNA in cytoplasm of infected cell and integrase which integrates HIV DNA into host cell DNA.
-HIV survives in body fluids such as blood and seminal fluid.

Mechanism of Transmission:
-Sexual intercouse-seminal fluid, vagina fluid, from person to person.
-Blood-passes HIV particles or infected lymphocytes
.sharing of contaminated needle-drug addicts.
.contaminatred blood-through blood received by blood transfusion.
.wound to wound.
-Mother to foetus-through placenta ad mother's milk.

Symptoms:
-First sign-attack of cold-revoer in few days.
-Next 6 years-no signs of disease, then rapid loss of weight.
-Fever and sweating at night.
-Diarrhoea, tiredness.
-Oppurtunistic disease-cough, infection in mouth and sexual organs and Kaposi Sarcoma infect patient-soon patient dies.

Prevention:
-Protection during sexual intercouse-condom
-Limiting 1 sexual partner.
-Avoid sharing injection needle.
-Donated blood-screening for HIV to ensure HIV Free.
-Educate public on mode of transmision.

Mechanism of HIV infection:
-HIV binds to cd4 receptors at the surface of Th lymphocyte.
-Endocytosis-lipoprotein of lymphocyte and HIV fuse.
-Viral RNA and reverse transcriptase enzyme enter lymphocyte.
-Reverse Transcription of RNA into single strand DNA by reverse transcriptase enzyme occurs.
-Reverse Transcription of the other RNA produces single strand DNA that is complementary the other single strand DNA produced.
-The 2 single strand DNA are bind to form viral DNA known as provirus.
-Provirus enters nuclues and incorporated into DNA of the host cell.
-Each time host DNA replicates, provirus replicates.
-Provirus stays dormant for about 6 years.
-Then transcription of provirus occurs forming mRNA.
-mRNA produced is then translated to synthesis viral proteins.
-Viral particles formed in the infected cells.
-Through lysis of T lymphocytes, HIV virus is liberated.
-Virus spreads to all Th cell, killing the T cells-lower amount of T cells then destroy infected persons immune system.
-Oppurtunistic disease such as Kaposi Sarcoma occurs.

Antibody Mediated Imminity Response-B cell

-B cells are formed in bone marrow and usually matures in lymph nodes or in blood circulation.
-The B cells matures by forming B cell receptors.
-B cells receptor are formed by attachment of antibodies to plasma membrane with the antigen binding sites facing outwards.
-The B cells migrate to blood circulation until it encounters pathogen that have complementary antigen with its B-cell receptor.
-Phagocytosis of the pathogen occurs.
-The pathogens are broken down into smaller pieces known as antigen by action of hydrolytic enzyme..
-The antigens are attached to MHC to form antigen-MHC complex on the outer surface of plasma membrane.

-The B cell then attaches to Th cell that has complementary TCR with its antigen-MHC complex.
-The attachment occurs between antigen-MHC complex of B cell with TCR of Th cell.
-In this process, B cell acts on antigen presenting cell (APC).

-The T cell secrete INterleukin 2 (IL2).
-The Th cell divides to form memory cells and large number of effector Th cells which secrete more IL2.
-IL2 stimulate the B cells to divide through mitosis to form memory cells and large number of plasma cells/effector B cells.
-Plasma cells secrete large quantity of antibodies into blood circulation.
-The antibodies are then used to attack and destroy specific type of antigen in body.

-Eg of antibody action are antitoxin, complement fixation, opsonisation, precipatation and agglutination.

Cell Mediated Immunity response-T cells

-T-cells are formed in bone marrow and mature in thymus gland by forming specific type of T cell receptor (TCR) on outer surface of plasma membrane.

-3 types of T cell with specific type are produced from thymus gland:
.T helper cell (Th)
.T cytotoxic cell (Tc)
.T suppressor cell (Ts)
-Macrophage that is involved in 2nd line of body defense mechanism does phagocytosis of pathogen.
-The pathogen are destroyed in cell through action of hydrolytic enzyme released by lysosome.
-Smaller pieces of pathogen known as antigen is bind to Major Histo-Compatibility Complex(MHC) to form antigen-MHC complex.
-The antigen-MHC complex is attached to outer surface of plasma membrane to enable the macrophage to function as antigen presenting cell (APC)
-When APC encounter Th cell that has complementary TCR to its antigen-MHC complex, the APC binds to the Th cell.

-Then, the APC secretes Interleukin 1 (IL1)
-IL1 stimulates Th cells to secrete Interleukin 2 (IL2)
-Secretion of IL2 stimulates the Th cell to divide through mitosis to form memory cells and large number of effector Th cells.
-Effector Th cell secretes more IL2.
-Increase in IL2 concentration stimulates mitosis cell division of Tc cell that have the same type of TCR with the Th cell.
-Tc cell divide to form memory cells and large number of effector Tc Cells.
-Effector Tc cells scouts for cells that are infected with the same type of pathogen.
-Cells that are infected are recognized by identification of antigen-MHC complex on plasma membrane of infected cells.

-The effector Tc cells binds complementarilary to the complex on plasma membrane of effector cell, it then secretes perforin.
-Perforin arranges on plasma membrane of infected cells, peforation of plasma membrane of infected cell occurs, lysis of the infected cells occurs.
-The effector Tc cells then scouts for other infected cells that have same type if antigen-MHC complex.

-Once immunity is achinved, Ts cell suppress action of Tc and Th cells.
-The binding occurs between MHC complex on APC with TCR on Th cell.

Immunity, Antibody, Antigen and Epitote

Immunity
-is the ability to produce lymphocytes or antibodies to destroy efficiently specific foreign substances such as antigens that has been detected by body.

Antibodies
-are specific proteins produced by B lymphocytes as as response to specific antigens detected in body.
-specific antibodies bind with specific antigens before the antigens are destroyed.
-Characteristics of antibodies:
.Each called Immunoglobulin-water soluble globular protein.
.Structure is 'Y' Shaped.
-Each molecule of antibody composes of:
.2 identical heavy chains (H chains) that are linked by disulphide bonds.
.2 identical light chains (L chains), each linked by disulphide bond to one H chains.
-Lower portion of the molecule is constant while 2 tips are variable.
-Both variable parts are antigen binding sites-each can bind specifically to same type of antigen like 'lock and key'.
-Immunoglobulin are divided into 5 groups: Immunoglobulin M, A, D, G, E.

Antigens
-foreign substances that stimulate the production of lymphocytes or antibodies in body specifically destroy them.
-Characteristics of antigens:
.Antigens are macromolecules-protein/polysaccharides/cojugated protein.
.Found on surface of micro-organisms, plasma membrane or as free molecules.
.Proteins produced in the same body cannot act as antigens but when it is transferred into another organism's body, they act as antigens.

Epitopes
-Small specific parts of a larger antigen which can bind with specific antibody.
-Characteristics of epitopes:
.Epitopes-antigenic determinant-may be more than one on an antigen.
.Each epitopes has specific configuration composed of certain side chains of amino acids or sugar.
-Bacteria-have more surface antigens-more epitopes-each epitopes capable of causing a specific antibody to bind with them.
-Viruses have fwer surface angtigens-fewer Epitopes.
-Macrophage that phagocytosise bacteria and viruses cuts its antigens into smaller epitopes which are then presented on the surface of the cell antigen-MHC complex for recognition by lymphocytes.

The lymphatic system

Lymphatic System functions are:
-Supplementary transport system to channel tissue fluid back to blood circulatory system.
-Major part of immune system-maturation of lymphocytes and in destroying pathogens.

3 main components:
-Lymphatic fluid(lymph)
-Lymphatic vessels
-Lymphatic tissues.

Lymphatic Fluid (Lymph)
-formed by diffusion of tissue fluid into lymphatic capillary.
-components alsmost similar as tissue fluid, but contains fewer plasma proteins and does not contain erythrocytes and platelets.
-Formation of lymphatic fluid:
.Ultrafiltration-fine molecules in blood diffuse out through partially permeable membrane (endothelium) of blood capillaries into extracellular space of body cells.
.Ultrafiltration is aided by difference in hydrostatic pressure and water potentials between blood in capillary and tissue fluid in extracellular space.
.Major portion of tissue fluid is reabsorbed into blood capillaries nearer to venule because water potential and hydrostatic pressure is lower in these areas compared to tissue fluid.
.A small portion of tissue fluid enters lymphatic capillaries through special pores with valves to form lymphatic fluid.
.Lymphatic fluid in lymphatic capillaries flows into lymphatic vessels.
.Fat soluble substances produced by digestion diffuses into lacteal in villi of small intestines before flowing into lymphatic vessels.

Lymphatic Vessels
-Consists of capillaries and ducts.

-Lymphatic Capillaries are:
.Smallest lymphatic vessels found in all tissue except spleen.
.Have closed ends that have pores with valves.
.Capillaries join to form venules which then join to form bigger lymphatic ducts.

-Lymphatic Ducts:
.Same structure as blood veins with valves for unidirectional flow of lymph.
.Flow is aided by contraction of skeletal muscle, peristalsis and pulse.
.Biggest lymphatic ducts are thoracic duct and right lymphatic duct which empties its content into subclavian veins.

Lymphatic Tissue
1.Spleen
-Largest lymphoid organ.
-Functions:
.Produces Red Blood Cells-foetal stage and few years after birth.
.Removes worn out white blood cells and platelets.
.Contain lymphocytes-filters blood to remove bacteria and antigens.
.Stores blood when required.

2.Thymus Gland
-Enlarages during childhood, shrinks after puberty.
-Functions:
.Activates T lymphocytes-lymphocytes originating from stem cells-matures, differentiates and functions after passing through thymus gland.
.Produces Hormones-causes T cells to mature by forming specific receptors. (TCR)
.T cells secretes lumphokine-helps in cell mediated response.

3.Lymph Nodes
-Bean Shaped and located at specific parts of body such as groins, armpits, beneath lower jaws.
-Functions:
.Location where antigens are presented to immune system.
.Location for activated B lymphocytes division to form plasma and memory cells.
.Lymphocytes and macropahges-filter pathogens and antigens.