Immune System II Acquired Immunity

Immunity There are four attributes characteristic of immunity: Specific: cells of the immune system recognize specific pathogens not others. (Inflammation is a nonspecific response) Memory: once the immune system has been exposed to a certain pathogen and has developed defenses against the organism, it can attack the pathogen over and over and more quickly when it reappears.

Immunity Diversity: the immune system is able to attack thousands of foreign microbes including bacteria, viruses, parasitic worms and fungi. Self - Nonself recognition; the immune system can distinguish between body cells and cells that have invaded the body.

Recognition How does the immune system recognize molecules? The immune system produces two distinct responses to invading organisms Production of antibodies (proteins that mark foreign molecules) Production of cells that recognize and attack infected body cells.

Specificity Antibodies are proteins that bind to nonself molecules which are called antigens Each antibody recognizes a specific shape and charge of an antigen.

Immune Cells Immune cells are a special class of white blood cells called lymphocytes and develop in the lymph tissue. The 3 main classes of lymphocytes are B lymphocytes (B cells) which make antibodies that recognize bacteria, fungi and protists marks them but does not kill them.

Immune Cells T lymphocytes (T cells), which recognize and destroy infected or damaged body cells. Natural Killer Cells (NK cells), attack tumor cells and cells infected by a pathogen

Antibodies Each line of B cells makes just one kind of antibody. Every antigen contains one or more epitopes ( a specific shape and charge)that the antibody recognizes All antibodies are globular proteins called immunoglobulins.

Antibodies Immunoglobulins are made of a collection of four amino acid chains, two heavy chains and two light chains. There are 5 classes of immunoglobulins. They all have the same light chains and differ by their heavy chains.

Antibodies Antibodies have at least two binding sites, allowing them to bind to more than one antigen. This allows them to link together bacteria, the clumped mass is a better target for phagocytes to attack.

5 Types of Antibodies

Antibodies IgG and IgM activate compliment proteins, which destroy marked cells IgM molecules are the first to appear after exposure to an antigen, while IgG are made in greater amounts in secondary responses.

Antibodies IgA molecules protect all of the body’s surfaces (intestinal respiratory and urogenital tracts) are in tears, saliva, and breast milk

Antibodies IgE antibodies probably evolved to defend the body against parasitic worms however many people produce IgE antibodies in response to harmless antigens. Allergy - a response to a harmless antigen like dust mites, pollen, shell fish

Antibodies When one of these antigens enters the respiratory tract, IgE molecules attach to mast cells, which release histamine. Inflammatory response is triggered, mucus secretions, contraction of airways Extreme response can end in death

B-Cells B cells are lymphocytes that are formed in bone marrow. Each B cell has B cell receptors (BCR) on its surface. These receptors recognize the same antigen sites as the antibodies it produces.

When an antigen binds to B cell receptors, the B cell begins to differentiate: Some become plasma cells, which make antibodies Some become memory cells, which make more B cells for when the antigen reappears

Differentiation of B cells Memory B cells Make more memory cells Antigen B cells Plasma Cells Make antibodies

Memory Second exposure to the antigen will cause a rapid and very strong response due to memory cells Multiplication of memory cells provides a lifelong immunity B cells cannot respond to body cells that have become infected with pathogens

B cells produce antibodies that can recognize bacteria and target them for destruction. But B cells do not respond to the body’s own cells that have become infected or are cancerous.

Vaccinations Because lymphocytes respond to epitopes (shape and charge of proteins on the surface of antigens) rather than the whole molecules antigens whose epitopes are identical can cause an immune response for each other.

T cells T cells recognize body cells that are infected or are growing out of control. A child born without a thymus, where T-cells mature, cannot fight viral, fungal and intracellular bacterial infections. The child may have plenty of B cells and can fight some bacterial infections.

T cells Two kinds of T cells T cytotoxic (killing cells by boring holes in the cell membrane) TC cells. Kill cancerous and infected T helper or TH cells alert B cells to make antibodies and stimulate TC cells. Produce cytokines

T Cells & MHC Proteins T cells recognize the cells of the body by proteins called major histocompatability complex or MHC. MHC proteins are on every cell of the body except sperm cells. Everyone’s set of MHC’s are unique Transplant surgeons make sure transplant organs have similar MHC’s to the patient.

MHC Proteins MHC Class 1 are on every cell with a nucleus except sperm. MHC Class 2 are on the surface of macrophages and dendritic cells.