1. Immunity Innate and Adaptive Immunity Cells of the Immune System
Physical & Chemical Barriers

2. Innate and Adaptive Immunity
Innate Defenses
Nonspecific physical and chemical barriers that contribute to resistance against infection
Does not exhibit immunological memory
Mediated several classes of cells and tissues, with close interactions with the adaptive response

3. Innate and Adaptive Immunity
Response to specific biochemical groups that distinguishes between “self” and “nonself”
Antigen: Any substance that the adaptive immune system responds to
Exhibits “immunological memory:” Once the immune system has been exposed to an antigen, the response in subsequent exposures is much faster and stronger
Mediated by lymphocytes

4. Cells of the Immune System
Monocytes and macrophages
Function as phagocytic cells
Typically have round or horseshoe-shaped nuclei
Monocytes circulate in the blood & lymph; macrophages are derived from monocytes that have moved from the blood & lymph into surrounding tissue
Both are active as phagocytes

5. Cells of the Immune System
Polymorphonuclear granulocytes
Irregular-shaped nuclei and cytoplasm with vesicles (granules) filled with hydrolytic enzymes
Neutrophils: Function primarily as phagocytes
Eosinophils: Function by degranulation in response to larger parasites
Basophils: Also function predominantly by degranulation; similar to mast cells and releases histamine

6. Cells of the Immune System
Dendritic Cells
A class of phagocytes associated with tissues in contact with the external environment, such as skin, mucous membranes, & the intestinal lining
Dendritic cells act as “antigen-presenting cells” - they phagocytize targets such as bacteria, process the bacterial antigens and “present” them to lymphocytes

7. Cells of the Immune System
Lymphocytes
Responsible for the adaptive immune response
Each lymphocyte cell possesses a receptor that can bind to a specific molecular group on an antigen
There are believed to be millions of different receptor specificities, but each lymphocyte only expresses a single type of receptor on its surface

8. Cells of the Immune System
Lymphocytes
Primary lymphocytes are lymphocytes that have never responded to antigen
Primary lymphocytes respond to antigen by clonal selection, clonal expansion, and differentiation into effector cells and secondary (memory) lymphocytes
Secondary lymphocytes are able to respond more rapidly and effectively to subsequent exposures to the antigen

9. Cells of the Immune System
Lymphocytes
Two classes of lymphocytes: T lymphocytes and B lymphocytes
B lymphocytes
formed in the bone marrow of mammals or the Bursa of Fabricus in birds
during an immune response, B lymphocyes differentiate into plasma cells that secrete antibody protein specific for the antigen(s) encountered

10. Cells of the Immune System
Lymphocytes
T lymphocytes
formed in the thymus gland
during an immune response, T lymphocyes may differentiate into several different classes of effector cells
Helper T lymphocytes (TH or CD4+ T cells) secrete cytokines that stimulate the activity of other immune cells, including B lymphocytes and other T cells
Cytotoxic T lymphocytes (TC or CD8+ T cells) destroy virally-infected cells and tumor cells, and are responsible for transplant rejection
Regulatory T lymphocytes (Treg cells) help to mediate immunotolerance

11. Physical & Chemical Barriers
Skin Barrier
Mucous membranes
Lysozyme
Antibacterial enzyme found in tears
Complement
A series of proteins in the blood and tissue fluid that can mediate cytolytic processes
Inflammation
Activation of immune cells in a damaged or infected region causes vasodilation, chemotaxis of leukocytes into the region, and diapedesis (movement of leukocytes from the capillaries into the surrounding tissue)

12. Physical & Chemical Barriers
Antibodies (Immunoglobulins)
Proteins secreted from plasma cells (which have differentiated from B lymphocytes)
5 different classes of immunoglobulins:
IgM: Represents the cell-surface receptor on B lymphocytes; also is the first Ig to be secreted in a primary immune response
IgD: A minor Ig
IgG: The major immunoglobulin found in blood & tissue fluid
IgA: Found in secretions such as saliva and breast milk
IgE: Stimulates mast cells & causes them to release histamine

13. Physical & Chemical Barriers
Antibodies (Immunoglobulins)
Antibody structure
Two light chains
Two types, κ and λ
Two heavy chains
Five different types: μ, δ, γ, α, and ε
Class specific
Each heavy and light chain has two regions
Variable region
Constant region

14. Physical & Chemical Barriers
Antibodies (Immunoglobulins)
Antibody molecules bind with great specificity and affinity to the antigen that originally activated the B lymphocyte
Each antibody molecule has two or more sites for binding antigen, so antigen molecules can be cross-linked, as in precipitation or aggluttination reactions
Antibodies play a number of essential roles in an effective immune response

15. Physical & Chemical Barriers
Antibodies (Immunoglobulins)
Roles of Antibodies
Precipitation: Clumping and precipitation of soluble antigens
Agglutination: Clumping together of cellular antigens
Virus neutralization
Toxin neutralization
Complement fixation: Antibody molecules can trigger a complement pathway leading to the lysis of a cellular antigen
Opsonization: Antibody molecules can coat a cellular antigen, making it much easier for a phagocyte to recognize and engulf