Immunity

Body Defenses First line - barriers Skin and mucous membranes Flushing action –Antimicrobial substances Lysozyme, acids, salts, normal microbiota Second line – inflammation & fever Both of these are non-specific

Third line – immune response 1.Specific 2.Memory 3.Inducibility

Antigens - substances recognized as “non- self” These can be: Infectious agents - bacteria, viruses, fungi or parasites Noninfectious substances – Environmental - pollen, foods, bee venoms Drugs, vaccines, transfusions and transplanted tissues

Antigen Antibody Generator The best antigens are: 1. large 2.recognized as foreign 3.complex

proteins and complex carbohydrates – good nucleic acids and lipids – not good Haptens – too small by themselves, piggy- back on larger molecules, us. Proteins Epitopes – regions of large molecules recognized by the immune system

Two cell types give us the immune response; both are lymphocytes, which are a type of leukocyte, or white blood cell. B lymphocytes or B cells T lymphocytes or T cells

The cells of the immune response differ from the cells of the inflammatory response in three ways: 1. They are SPECIFIC and each cell recognizes only one specific antigen. B cells produce antibodies T cells attack antigen directly

2. Both produce groups of cells called “memory cells” that act quickly the second time the antigen is encountered. 3. An antigen induces an immune response. Only small amounts of antibodies or T Cells are present before encountering an antigen.

Long lasting protection against a specific antigen is immunity. Natural immunity: Not produced by the immune response Species specific

Acquired immunity Active – person produces immunity natural artificial Passive – temporary immunity is given natural artificial

Lymphocytes Originate : in liver, spleen and bone marrow of fetus in bone marrow after birth From stem cells – hemocytoblasts – that produce all blood cells.

To become mature, immunocompetent cells, they must pass through lymphoid tissues in other parts of the body. As they do so, they become committed to becoming either T cells or B cells Cells that migrate through the bone marrow become B cells, and will produce antigens and participate in humoral immunity.

Cells that migrate through the thymus glands become T cells and participate in Cell-mediated immunity

Humoral Immunity Humoral immune response : B cells that produce antibodies. Antibodies are proteins that match the molecular structure of an antigen, and bind to that antigen. This leads to the destruction of the antigen.

Antibody

B cells mature in the human bursal equivalent – in bone marrow – and obtain the ability to bind antigens and produce antibodies. Clonal selection theory: During fetal development, B cells are produced which can bind with any potential antigen. Each B cell binds only one antigen.

When antigen binds to antibody receptors on the surface of the B cell, the B cell divides and differentiates into antibody producing plasma cells and also memory cells.

Immunoglobulins IgG - monomer IgA – dimer – 2 units - in secretions IgM – pentamer – 5 units IgD – monomer – on surface of B cells IgE – monomer – involved in hypersensitivities

Cell-mediated immunity Produced through Tcytoxic or Tc Cells (T 8 cell) DO NOT produce antibodies Attack invaders directly May produce toxic chemicals – such as perforins May stimulate cell’s self-destruct mechanism

Primary and Secondary Immune Responses Primary response –Latent period –IgM produced –IgG produced later

Secondary response Anamnestic response –much more rapid due to memory cells Primarily IgG

Cellular Interactions in the Immune Response Few antigens can activate B cells all by themselves For activation of B cells and Tc Cells need a second signal – cytokine ( “cell mover”)

Antigen-Presenting cells (macrophages) place antigen on their cell surface in combination with the MHC II complex Antigen is presented to a specific helper T cell that has receptors that match the antigen – MHC II complex

After binding, the APC produces Interleukin -1 (IL-1) which stimulates the T H Cell to produce IL-2 and/or IL-4 Interleukin-2 has an autocrine function, causes T H Cell to clone itself, and make more IL-2 and /or IL-4

Helper T cells T H1 cells produce IL -2 and influence cell- mediated immunity T H2 cells produce IL -4 (and other IL’s) and influence antibody-mediated (humoral) immunity

When B cell comes in contact with the antigen and IL-4, the B cell produces plasma cells and memory cells Tc Cells come in contact with the antigen on the surface of infected cells in combination with the MHC 1 complex. When also have binding with IL-2, cells produce activated Tc Cells and memory cells.