Introduction/Terminology Immunology: the study of the body's defense against infection Immunity: Resistance to disease Immune system: The collection of cells, tissues and molecules that mediate the resistance Immune response: The coordinated work of the immune system to defend the host against foreign substances. Innate immunity: The native or natural immunity. Adaptive immunity: Acquired as an adaptation to infection

Antigen: Any molecule that can bind to an Ab (microbes, drugs, pollen …….) OR any molecule that can produce adaptive immunity Antigen determinant (epitope): a portion of an antigen that is bound to a given Ab or antigen receptor. Antigen presentation: Process of displaying the antigen as a peptide fragment on the surface of the cell. Adjuvant: Killed bacteria or bacterial extracts used to assess the non-immunogenic antigen to induce an immune response

Immunity The term immunity is derived from the Latin word immunitas, which referred to the protection from legal prosecution offered to the Roman senators during their tenures in office. Defined by: all mechanisms used by the body as protection against environmental agents that are foreign to the body.

Immunity These foreign agents may be microorganisms or their products, foods, chemicals, drugs, pollen, or animal hair and dander. Immunity may be innate or acquired. adaptive Innate

Features of Innate and Adaptive immunity Characteristics Innate Adaptive Specificity Microbes and products of damaged host cells Microbial and non microbial antigens Diversity Limited; germline encoded Very large; receptors are produced by somatic recombination of gene segments Memory None yes Non-reactivity to self Yes Components Cellular and chemical barriers Skin, mucosal epithelia; antimicrobial molecules Lymphocytes in epithelia; antibodies secreted at epithelial surfaces. Blood Proteins Complements, others Antibodies Cells Phagocytes, natural killer cells Lymphocytes

The Kinetics of the innate and adaptive immune responses are approximation and may vary in different infections.

Acquired immunity is induced by immunization, which can be achieved in several ways: Active immunization: It refers to immunization of an individual by administration of an antigen. 2. Passive: It refers to immunization through the transfer of specific antibody from an immunized individual to a nonimmunized individual. 3. Adoptive immunization: It refers to the transfer of immunity by the transfer of immune cells.

Cells Involved in the Acquired Immune Response: There are three major cell types involved in acquired immunity and that complex interactions among these cell types are required for the expression of the full range of immune responses. T cells B cells Both exhibit specificity toward an antigen. The major recognition and reaction functions of the immune response are contained within the lymphocytes.

3. Antigen – presenting cells “APCs” Such as Macrophages and dendritic cells. They do not have antigen – specific receptors as do the lymphocytes. Their function is to process and present antigen to the specific receptors “T cell receptors” on T lymphocytes. Two types of special molecules that function in antigen presentation are present on the surface of APCs: