Two main strategies of immunity... Innate immunity Mechanisms always “on standby” Can respond rapidly Effective against a variety of different “enemies” Also called “nonspecific immunity”

Two main strategies of immunity... Adaptive immunity Mechanisms specialized to fight a particular “enemy” Often developed after first exposure, then “on standby” for further “attacks” First response is slow, to allow time to prepare Also called “specific immunity” or “acquired immunity”

Acquired immunity (Adaptive or Specific ) Cell-mediated immunity Humoral immunity

Two mechanisms 1) Humoral immune response: - Antibodies are produced by B-lymphocytes - These have the ability to recognize and bind specifically to antigen that induced their formation Functions: (Antibody Mediated Immunity ) Protection against bacteria through the following mechanisms:  Toxin neutralization  Inhibition of bacterial adherence to target cells.  Opsonization and enhancement of phagocytosis  Complement activation leading to bacterial lysis.  Bacterial agglutination and enhancement of phagocytosis

Functions: (Cell Mediated Immunity ) - Protection against bacteria through the following mechanisms:  Cytotoxic destruction of intracellular bacteria (e.g T.B).  Activation of macrophages.  Delayed hypersensitivity reactions. 2) The cell mediated immune response (CMI) - It is mediated by certain types of T-lymphocytes - T-lymphocytes recognize foreign material by means of surface receptors - T-lymphocytes attack and destroy foreign material directly or through release of soluble mediators i.e. cytokines Although T-cells do not produce antibody, they contain antibody-like receptors on their cell surfaces that specifically bind to foreign particles in exactly the same way that antibodies do.

Third Line of Defense - Is called specific immunity (Acquired or Adaptive immunity) - More virulent organisms that escape from the first line of defense will face the specific defense. 1 -Specificity for antigen. 2 -Memory: a rapid and response following subsequent with the same or a closely related antigen. 3 - Diversity: capacity to respond to millions of different antigens present in the environment. Adaptive response is characterized by:

Innate immunityAcquired immunity Response is antigen- independentResponse is antigen dependent There is immediate maximal response There is a lag time between exposure and maximal response Not antigen- specificAntigen- specific Exposure results in no immunological memory Exposure results in immunological memory Different ion between Innate and Acquired immunity

Is acquired over time Antigens trigger specific immune responses Various cells, tissues, and organs are part of specific immunity Includes B and T lymphocytes

Molecules that trigger a specific immune response Food and dust can also contain antigenic particles Enter the body by various methods Include components of bacterial cell walls, capsules, pili, and flagella, as well as proteins of viruses, fungi, and protozoa Through breaks in the skin and mucous membranes Direct injection, as with a bite or needle Through organ transplants and skin grafts

Foreigness : for a substance to be antigenic it must be foreign to the animal in which it is introduced. Antigens are recognized by the 3-dimensional shapes of their antigenic determinants ( epitopes ). Large molecular masses (5, ,000): monosaccharide &a`a` are not immunogenic. Chemical nature :proteins & some polysaccharides are good immunogens. Lipids alone are not immunogens unless they are combined with proteins or polysaccharides. E.g L.P.S Complexity : increase in the complexity of a compound is accompanied by increase in its immunogenicity. Not easily excreted from the body : e.g diphtheria toxoid is mixed with almm. Hydroxide to form alum- precipitated toxoid.

Types of antigens based on their relationship to the body: 1- Hetero-antigen: It is an antigen derived from one species and is capable of stimulating an immune response in another species 2- Iso- antigen ( allo-antigen): It is an antigen in an individual of one species which is capable of initiating an immune response in genetically different individual of the same species e.g fluids transfusion and tissue antigens.

Specific immunity Acquired immunity passive Artificial(immune serum) Natural (trans- placental) Active Artificial (vaccination) Natural(clinical infection)

 Active › reaction of your own system  Passive › borrow immune agents from another person WBC Pathogen Antibodies

a-Natural active acquired immunity : - Following clinical or subclinical infections - measles or mumps, in which immunity is long lasting b- Artificial active acquired immunity : - Following vaccination with live or killed infectious agents or their products

II- Passive acquired immunity a-Naturally passive acquired immunity Antibodies are passed through placenta to the fetus b- Artificially passive acquired immunity The injection of already prepared antibodies, such as gamma globulin (short-term immunization)

Active acquired immunity (Host make antibodies in response to antigen) Passive acquired immunity ( host receives performed antibodies) Takes timeimmediate Last for long durationLast for short duration Due to antigen administration Due to antibodies administration Used for prophylaxisFor treatment and prophylaxis Main differences between active and passive immunity

Characteristics of Types of Immunity

Immunization Artificial passive AntiseraAntitoxins Artificial active vaccination Immunization

A- Artificial passive immunization (Immediate but temporary protection):  Antisera : contain antibodies ( gamma globulin) against e.g hepatitis A induced I.M.  Antitoxins : some serious disease are caused not by the organism itself but by its toxin, e.g Prevention of diphtheria and tetanus. Antivenins for treatment of snake and spider bites. B- Artificial active immunization ( vaccination)

Vaccination: Producing immunity against pathogens (viruses and bacteria) by the introduction of live, killed, or altered antigens that stimulate the body to produce antibodies against more dangerous forms *

Immunization of young children : - Hepatitis B (HepB) and Hepatitis A (HepA) - Diphtheria, tetanus and pertussis given together as DTaP - Haemophilus influenzae b (Hib) - Poliomyelitis - Measles, Mumps, and Rubella, given together as MMR - Chickenpox - Neisseria meningitidis (meningococcal meningitis)

Types of vaccines( artificial active immunization)  Live attenuated vaccines: Prepared by culturing m.o in unfavorable condition to loss its virulence factors. Live vaccine should not given to immunodeficient patients. Example: BCG vaccine for T.B  Killed vaccine: Safer but weaker than live vaccine. Booster doses should be given. Example: cholera vaccine  Toxoids: Formed by treatment of exotoxin by formalin. Non toxic but antigenic. example: Diphtheria &tetanus toxoid

 Genetically engineered products: Example: hepatitis B vaccine  Bacterial components: e.g capsule of meningococci Types of vaccines ( continue )

Cells, Organs and Tissue Involved in the Immune Response. The immune system consists of a number of organs and different cells types which have the capability of responding to different immunologic stimuli. 1- Bone marrow 2- Lymphoid tissue

All the cells of the immune system arise from stem cells in the bone marrow, which differentiates into three main lines: Common lymphoid cells produce lymphocytes. Common myeloid cells produce phagocytes. Common erythroid cells produce RBC. 1) Bone marrow

2) Lymphoid tissue Lymphoid tissues Primary lymphoid tissues Bursa responsible for B- cell maturation Thymus responsible for T- cell maturation Secondary lymphoid tissues Lymph nodes tonsils spleen The 2ry lymphoid tissues have two functions: Responsible for trapping the antigens They are the main sites of production of antibodies.

The most important cells of the immune system B- lymphocytes ( Bursa derived lymphocytes)  Arise and mature in the red bone marrow  Found primarily in the spleen, lymph nodes, red bone marrow, and Peyer ’ s patches  Small percentage of B cells circulate in the blood (30%)  Major function is the secretion of antibodies.  Their life span is short(days or weeks)

Development of B and T Cells

T- lymphocytes ( Thymus- derived lymphocytes):  They constitute 65-80% of circulating blood lymphocytes.  Their life span is long (months or years).  Produced in the red bone marrow and mature in the thymus.  They have receptors called CD (clusters of differentiation) Which are identified by using monoclonal antibodies.  Mature T cells have either CD4 or CD8.

 T cells are subdivided into : 1) CD4 T –helper lymphocytes (TH), its functions are: -Activate B-lymphocytes. -Produce lymphokines. 2) CD8 lymphocytes: they include the following subpopulations a -Cytotoxic T cell (TC), its functions are: -Kill virus infected cell - Kill tumor and graft cells. b- Suppressor T cell (TS), its functions are: -suppress B- cell and T-cell activities. - They inhibit autoimmunity.

Types of T Cells

B-lymphocytesT- lymphocytes Bursa derivedThymus derived 30% of lymphocytes65-80% of lymphocytes Short life spanLong life span Responsible for acquired humoral immunity Responsible for acquired cellular immunity On stimulation give plasma cell then antibody 3 types: TH, TC&TS